Physical, Earth, and Space Science [First ed.] 9781604310979

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Author Thomas C. Hsu, Ph.D., Applied Plasma Physics, Massachusetts Institute of Technology Co-Authors Scott Eddleman, M.Ed., Harvard University; Mary Beth Abel, M.S., Biological Sciences, University of Rhode Island; Patsy Eldridge, M.Ed., Tufts University; Erik Benton; Sonja L. Taylor, M.Ed., Divergent Learning, Columbia College

Editorial Team

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Lynda Pennell – Senior Editor Polly Crisman – Graphics Manager/Illustrator Bruce Holloway – Senior Designer/Illustrator Jesse Van Valkenburgh – Designer/Illustrator Susan Gioia – Administrator Lynn L’Heureux – Technical Consultant

Thomas Narro – Senior Vice President Danielle Dzurik – Mechanical Engineer Kathryn Gavin – Purchasing and Quality Control Manager

Contributing Writers and Editors

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Laine Ives, Stacy Kissel, James Sammons, Mary Ann Erickson, David H. Bliss, Lawrence Sabbath, Pamela J. W. Gore, Ph.D. Editorial Consultant: Christine Golden

Ancillary Materials Laine Ives – Skill and Practice Worksheets, Projects, Connections Mary Ann Erikson – ExamView®Assessment Suite Laura Preston – Guided Readings, Connections Leslie Sheen – Graphic Organizers, Connections Cory Ort and Laura Ort – Lesson Organizer

Reviewers Mark Baker – Diamond, OH Dr. Nicholas Benfaremo – South Portland, ME Kip Bollinger – Carlisle, PA Daryl Campbell – Needham, MA Nancy Baker Cazan – Massillon, OH Ann Cleary – Medina, OH Jean A. Cyders – Canton, OH Lou Fellner – Bayville, NJ Dr. Gregorio Garcia – Brownsville, TX Cort Gillen – Cypress, TX Alan P. Gnospelius – San Antonio, TX Lisa Q, Gothard – East Canton, OH Liz Gregory – Austin, TX Tracy Hollars – Cleveland, OH William C. Huckeba – Irving, TX Chrystal Brooke Johnson – Irving, TX Marty Kilroy – White, GA Daniel Klein – Navarre, OH Kathleen Kuhn – Uniontown, OH

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Physical, Earth, and Space Science, An Integrated Approach – First Edition

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Jeff Pickle – North Canton, OH Lisa M. Polar – Corapolis, PA Emily O. Price – Waxahachie, TX Julie Randolph – Beaumont, TX Steve Remenaric – Massillon, OH Michael Vela – Concord, MA Melissa Vela – Concord, MA Scott Vetter – Shreveport, LA Elizabeth Volt – Cleveland, OH David Warner – Massillon, OH Larry Weathers – Arlington, MA Dan Williamson – Irving, TX Kathleen Woodring – Edna, TX Jaclyn L. Ziders – Uniontown, OH Special Thanks Brookline High School Science Students Brookline High School, MA

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Chapter 6: Newton’s Laws of Motion ��������������������� 125 6.1

Newton’s First Law ������������������������������������������ 126

6.2

Newton’s Second Law ������������������������������������ 130

1.1 Measurements ����������������������������������������������������� 6

6.3

Newton’s Third Law and Momentum �������������� 136

1.2

Time and Distance ���������������������������������������������12

Chapter 6 Assessment ���������������������������������������������� 144

1.3

Converting Units �������������������������������������������������17

Chapter 7: Work and Energy ����������������������������������� 147

1.4

Measurement and Graphing ����������������������������� 24

7.1

Force, Work, and Machines ���������������������������� 148

Chapter 1 Assessment ������������������������������������������������ 30

7.2

Energy and the Conservation of Energy ����������� 155

Chapter 2: The Scientific Process ���������������������������� 33

7.3

Efficiency and Power ��������������������������������������� 167

Chapter 1: Measurement ��������������������������������������������� 5

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2.1

Inquiry and the Scientific Method ��������������������� 34

2.2

Experiments and Variables �������������������������������� 40

2.3

The Nature of Science and Technology ������������ 44

Chapter 2 Assessment ������������������������������������������������ 48

Chapter 3: Mapping Earth ����������������������������������������� 51

Chapter 7 Assessment ���������������������������������������������� 172

Unit 3 Matter, Energy, and Earth

176

Chapter 8: Matter and Temperature ����������������������� 177

3.1

Position, Coordinates, and Maps ���������������������� 52

8.1

3.2

Topographic Maps �������������������������������������������� 61

8.2 Temperature ���������������������������������������������������� 184

3.3

Bathymetric Maps ��������������������������������������������� 66

8.3

Chapter 3 Assessment ������������������������������������������������ 70

Table of Contents

Unit 1 Science Skills

The Nature of Matter ��������������������������������������� 178 The Phases of Matter �������������������������������������� 190

Chapter 8 Assessment ���������������������������������������������� 196

Chapter 9: Heat ��������������������������������������������������������� 199

Unit 2 Motion, Force, and Energy

74

Chapter 4: Motion ������������������������������������������������������� 75

9.1

Heat and Thermal Energy �������������������������������� 200

9.2

Heat Transfer ��������������������������������������������������� 206

Chapter 9 Assessment ���������������������������������������������� 212

4.1

Speed and Velocity ������������������������������������������� 76

Chapter 10: Properties of Matter ������������������������������ 215

4.2

Graphs of Motion ���������������������������������������������� 81

10.1 Density ������������������������������������������������������������ 216

4.3 Acceleration ������������������������������������������������������ 86

10.2 Properties of Solids ����������������������������������������� 222

Chapter 4 Assessment ������������������������������������������������ 94

10.3 Properties of Fluids ����������������������������������������� 227

Chapter 5: Force ��������������������������������������������������������� 97

10.4 Buoyancy �������������������������������������������������������� 234

5.1 Forces ��������������������������������������������������������������� 98

Chapter 10 Assessment �������������������������������������������� 242

5.2 Friction ������������������������������������������������������������ 107

Chapter 11: Earth’s Atmosphere and Weather ��������� 245

5.3

Forces and Equilibrium������������������������������������ 114

11.1 Earth’s Atmosphere ����������������������������������������� 246

Chapter 5 Assessment ���������������������������������������������� 120

11.2 Weather Variables �������������������������������������������� 253 11.3 Weather Patterns ��������������������������������������������� 263 Chapter 11 Assessment �������������������������������������������� 272

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Table of Contents

Unit 4 Matter and Its Changes

276

Unit 5 Electricity and Magnetism

382

Chapter 12: Atoms and the Periodic Table �������������� 277

Chapter 16: Electricity ����������������������������������������������� 383

12.1 The Structure of the Atom ������������������������������� 278

16.1 Charge and Electric Circuits ���������������������������� 384

12.2 Electrons ��������������������������������������������������������� 285

16.2 Current and Voltage ���������������������������������������� 389

12.3 The Periodic Table of the Elements ����������������� 291

16.3 Resistance and Ohm’s Law ����������������������������� 393

12.4 Properties of the Elements ������������������������������ 297

16.4 Types of Circuits ���������������������������������������������� 401

Chapter 12 Assessment �������������������������������������������� 304

Chapter 16 Assessment �������������������������������������������� 412

Chapter 13: Compounds �������������������������������������������� 307

Chapter 17: Magnetism ��������������������������������������������� 417

13.1 Chemical Bonds and Electrons ����������������������� 308

17.1 Properties of Magnets�������������������������������������� 418

13.2 Chemical Formulas ����������������������������������������� 315

17.2 Electromagnets ����������������������������������������������� 425

13.3 Molecules and Carbon Compounds���������������� 323

17.3 Electric Motors and Generators����������������������� 430

Chapter 13 Assessment �������������������������������������������� 330

17.4 Generating Electricity �������������������������������������� 436

Chapter 14: Changes in Matter ��������������������������������� 333

Chapter 17 Assessment �������������������������������������������� 444

14.1 Chemical Reactions ���������������������������������������� 334 14.2 Types of Reactions ������������������������������������������ 343 14.3 Energy and Chemical Reactions ��������������������� 348

Unit 6 Earth’s Structure

448

14.4 Nuclear Reactions ������������������������������������������� 354

Chapter 18: Earth’s History and Rocks �������������������� 449

Chapter 14 Assessment �������������������������������������������� 360

18.1 Geologic Time ������������������������������������������������� 450

Chapter 15: Chemical Cycles and Climate Change  363

18.2 Relative Dating ������������������������������������������������ 456

15.1 Chemical Cycles ���������������������������������������������� 364

18.3 The Rock Cycle ����������������������������������������������� 462

15.2 Global Climate Change ����������������������������������� 373

Chapter 18 Assessment �������������������������������������������� 468

Chapter 15 Assessment �������������������������������������������� 380

Chapter 19: Changing Earth �������������������������������������� 471 19.1 Inside Earth������������������������������������������������������ 472 19.2 Plate Tectonics ������������������������������������������������ 478 19.3 Plate Boundaries���������������������������������������������� 485 19.4 Metamorphic Rocks����������������������������������������� 492 Chapter 19 Assessment �������������������������������������������� 496

Chapter 20: Earthquakes and Volcanoes ����������������� 499 20.1 Earthquakes ���������������������������������������������������� 500 20.2 Volcanoes �������������������������������������������������������� 508 20.3 Igneous Rocks ������������������������������������������������ 518

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Chapter 20 Assessment �������������������������������������������� 524

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528

Unit 9 Matter and Motion in the Universe 656

Chapter 21: Water and Solutions������������������������������� 529

Chapter 26: The Solar System ����������������������������������� 657

21.1 Water ��������������������������������������������������������������� 530

26.1 Motion and the Solar System �������������������������� 658

21.2 Solutions ��������������������������������������������������������� 536

26.2 Motion and Astronomical Cycles �������������������� 666

21.3 Acids, Bases, and pH �������������������������������������� 546

26.3 Objects in the Solar System����������������������������� 674

Chapter 21 Assessment �������������������������������������������� 554

Chapter 26 Assessment �������������������������������������������� 684

Chapter 22: Water Systems���������������������������������������� 557

Chapter 27: Stars �������������������������������������������������������� 687

22.1 Water on Earth’s Surface���������������������������������� 558

27.1 The Sun ����������������������������������������������������������� 688

22.2 The Water Cycle ���������������������������������������������� 563

27.2 Stars ���������������������������������������������������������������� 694

22.3 Oceans������������������������������������������������������������� 570

27.3 The Life Cycles of Stars ���������������������������������� 699

Chapter 22 Assessment �������������������������������������������� 578

Chapter 27 Assessment �������������������������������������������� 704

Chapter 23 How Water Shapes the Land����������������� 581

Chapter 28: Exploring the Universe �������������������������� 707

23.1 Weathering and Erosion ���������������������������������� 582

28.1 Tools of Astronomers �������������������������������������� 708

23.2 Shaping the Land �������������������������������������������� 591

28.2 Galaxies ����������������������������������������������������������� 718

23.3 Sedimentary Rocks ����������������������������������������� 598

28.3 Theories about the Universe ��������������������������� 725

Chapter 23 Assessment ������������������������������������������ 602

Chapter 28 Assessment �������������������������������������������� 732

Unit 8 Waves

604

Table of Contents

Unit 7 Earth’s Water

Glossary ����������������������������������������������������������������������� 735 Index ����������������������������������������������������������������������������� 748

Chapter 24: Waves and Sound ���������������������������������� 605 24.1 Harmonic Motion ��������������������������������������������� 606 24.2 Properties of Waves ���������������������������������������� 613 24.3 Sound��������������������������������������������������������������� 620 Chapter 24 Assessment �������������������������������������������� 628

Chapter 25: Light and Optics ������������������������������������ 631 25.1 Properties of Light ������������������������������������������� 632 25.2 Color and Vision ���������������������������������������������� 638 25.3 Optics �������������������������������������������������������������� 645 Chapter 25 Assessment �������������������������������������������� 652

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Unit 1 Science Skills CHAPTER 1 Measurement

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

CHAPTER 2  The Scientific

Process

CHAPTER 3 Mapping Earth

‹ Try this at home Does a 1-cup dry measuring cup hold the same amount as a 1-cup liquid measuring cup? Fill a 1-cup measuring cup that is meant to be used for dry cooking ingredients with water. Pour the water into a plastic cup and mark the water level, then discard the water (use it to water a plant!). Now measure out 1 cup of water in a liquid measuring cup. Pour this into the plastic cup and mark the level. How do the amounts compare? Why should scientists use a standardized system of measurement?

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CHAPTER

1

CHAPTER 1

Measurement FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

Measurement is to physical science what power tools are to a house builder, what clues are to a detective, and what musical notes are to a musician. Scientists measure dimensions, distances, temperature, mass, force, electrical current—the list could go on for pages. Scientists want to discover the natural laws of the universe. Measurements give them information about the world around them—reliable facts that form the basis of scientific theories that explain how the world works. In this chapter, you will make measurements and learn how to convert from one unit of measurement to another. You will also learn how to decide if one measurement is significantly different from another, or if they are essentially the same. These skills will be used many times throughout this physical science course as you collect data to learn how things work.

4 What is the SI system of measurement and how does it compare to the English system?

4 What are two of the most important physical science quantities to measure?

4 How do you decide how many digits to include in a measurement value?

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CHAPTER 1

MEASUREMENT

1.1 Measurements

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

If you were to walk around Earth at the equator, you would have to walk approximately 40,075 kilometers, or almost 24,902 miles. How do kilometers and miles compare? Which is a longer distance: 1 kilometer or 1 mile? Why do we talk about distance using two different units? Kilometers and miles are two common ways to describe distance, but scientists prefer to use kilometers. Read on to find out why.

Measurement and units

measurement - a determination of the amount of something. A measurement has two parts: a value and a unit.

unit - a fixed amount of something, like a centimeter (cm) of distance.

Measurements When studying physical science, you will make many measurements.

Distance, time, mass, volume, weight, and temperature are just some of the quantities you will measure. A measurement is a determination of the amount of something. A measurement has two parts: a number value and a unit (Figure 1.1). For example, 2 meters (2 m) is a measurement because it has a number value, 2, and a unit, meters. Units A unit is a standard amount that everyone agrees on. Without units, the

numbers in a measurement don’t make any sense. For example, if you asked someone to “walk 22,” she would not know how far to go. Do you want her to walk 22 meters, 22 miles, or 22 centimeters (the height of this textbook)? If you say “walk 22 meters,” then you have given her enough information because the unit “meters” tells her how to understand the quantity “22.” An important rule of science is to always include the correct units with number values.

Figure 1.1: A measurement includes a number value and a unit. Two meters is much taller than two feet!

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MEASUREMENT

CHAPTER 1

Two common measurement systems English System The English System is used for everyday measurements in the United of measurement States. Miles, yards, feet, inches, pounds, pints, quarts, gallons, cups, and

teaspoons are all English System units. However, only one or two countries other than the United States still use this old system of measurement.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

Measuring During the 1800s, a new system of measurement—the Metric System—was with SI units developed in France and was quickly adopted by other European and South

American countries. The goal of this system was for all units of measurement to be related, and for the units to form a base-10, or decimal, system. In 1960, the Metric System was revised and simplified, and a new name was adopted—International System of Units, or SI for short. The acronym SI comes from the French name Le Système International d’Unités. Today, the United States is the only industrialized nation that has not switched completely to SI. Scientists use SI Almost all fields of science worldwide use SI units because they are so much

easier to work with. In the English system, there are 12 inches in a foot, 3 feet in a yard, and 5,280 feet in a mile. The relationship between these units is not easy to remember. In the metric system, there are 10 millimeters in a centimeter, 100 centimeters in a meter, and 1,000 meters in a kilometer. These factors of 10 are easier to remember and work with mathematically (Figure 1.2). United States In the United States, we use both English and SI units in our daily lives uses both (Table 1.1). In many other countries, though, people use SI units for all systems measurements. Do you think the United States will ever use SI units for

all measurements? Table 1.1: Everyday SI Measurements Used in the United States Measurement

Unit

Symbol

Usage

length length volume mass power

millimeter meter liter milligram kilowatt

mm m L mg kW

film, nails and screws, tools, pencil lead track and field sports, Olympic swimming pools 1- and 2-liter soda bottles medication, nutrition labels electricity

English System - measurement system used for everyday measurements in the United States.

SI - International System of Units, used by most countries for everyday measurement and used by the scientific community worldwide.

Prefix

Meaning

Value

giga (G)

1 billion

1,000,000,000

mega (M)

1 million

1,000,000

kilo (k)

1 thousand

1,000

centi (c)

onehundredth

0.01

milli (m)

onethousandth

0.001

micro (μ)

onemillionth

0.000001

Figure 1.2: SI prefixes and

their values.

1.1 MEASUREMENTS

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CHAPTER 1

MEASUREMENT

The International System of Units (SI) Units allow people to communicate amounts. To make sure their measurements are accurate, scientists use a set of standard units that have been agreed upon around the world. Table 1.2 shows the units in the International System of Units, or SI. Table 1.2: The International System of Units (SI)

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

Measurement approximations

LENGTH width of little finger = 1 cm

VOLUME 10 drops of water = 1 mL

MASS 1 large paperclip = 1 gram

TEMPERATURE 21ºC = room temperature

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Unit

Comparison with standard

meter (m) kilometer (km) decimeter (dm) centimeter (cm) millimeter (mm) micrometer (µm) nanometer (nm)

1 km = 1,000 m 1 dm = 0.1 m 1 cm = 0.01 m 1 mm = 0.001 m 1 µm = 0.000001 m 1 nm = 0.000000001 m

cubic meter (m3) cubic centimeter (cm3) liter (L) milliliter (mL)

1 cm3 = 0.000001 m3 1 L = 0.001 m3 1 mL = 0.000001 m3

kilogram (kg) gram (g) milligram (mg)

1 g = 0.001 kg 1 mg = 0.000001 kg

Kelvin (K) Celsius (°C)

0°C = 273 K 100°C = 373 K

STUDY SKILLS Learn to Think SI How long is a centimeter? How heavy is a gram? How much is a milliliter? The easy way to “think SI” is to remember some simple measurements. Take a look at the pictures in the table at the left, and see if you can remember them. 1. 1 cm is about the width of your little finger. 2. 1 mL is about the same volume as 10 drops of water. 3. 1 g is about the mass of one large paperclip. 4. 21°C is a comfortable room temperature. Learning to think SI is like learning a new language; the more practice you have, the easier it is to understand.

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MEASUREMENT

CHAPTER 1

Bytes and SI prefixes A byte is a unit of computer data storage. When you add SI prefixes to any unit, you change the size of the unit, as you can see in the chart below and in Figure 1.3. It’s difficult to imagine a quantity as large as one quadrillion! One quadrillion bytes equals 1,000 trillion—that’s a petabyte.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

BYTE One unit of computer storage

KILOBYTE One thousand bytes

MEGABYTE One million bytes

GIGABYTE One billion bytes

TERABYTE One trillion bytes

PETABYTE One quadrillion bytes

8 bits

1/2 page of text

1 character = anything you type on a keyboard One computer onboard Apollo (1969)

= 74 KB of memory

One minute of music

500 pages of text

18 hours of mp3 music

12 hours of flash video

Library of Congress has about 10 TB of print collections

Superstore data warehouse has about 9,000 TB of data

Internet search engine processes over 20 PB per day

About 700 years of full HD-quality movies = 100 PB

Figure 1.3: Use these prefixes on any SI unit to change its size. A nanometer is one billion times smaller than a meter!

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Accuracy, precision, and resolution Accuracy The words accuracy and precision have special meanings in science that are

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a little different from how people use these words in daily conversation (Figure 1.4). Accuracy is how close a measurement is to the true value. An accurate clock or watch will give a time reading that is the same as or extremely close to the official time from a government standard. An accurate golf putt is one that falls in the hole. A very accurate golf drive would be a hole-in-one. Precision Precision does not have the same meaning as accuracy. Precision describes

accuracy - how close a measurement is to an accepted or true value.

precision - describes how close together or reproducible repeated measurements are.

resolution - refers to the smallest interval that can be measured.

how close together repeated measurements or events are to one another. Precise clocks throughout a school would all read the same time at any given moment. School clocks can be precise without being accurate. Can you explain how this could be true? If I hit three different golf balls off the same tee, and each one of them goes into the same sand trap, I have good precision but poor accuracy. Resolution Resolution is another important term to understand when you are working

with measured quantities. Resolution refers to the smallest interval that can be measured (Figure 1.4). The resolution of a centimeter ruler is 0.5 mm. This is because, if you look closely, you can tell if a measurement falls right on a millimeter mark, or between millimeter marks. The resolution on most classroom clocks is 0.5 seconds. Without a second hand, the resolution of a clock would be only 0.5 minutes. Resolution in The word resolution often appears in connection with digital cameras or high images definition (HD) TV. A high-resolution image is very sharp and high quality.

For example, an HDTV image has 1,980 dots in the horizontal direction. A standard TV image has only 640 dots. A feature that is two dots wide in an HDTV image is just a blur on a standard TV. You can think of resolution as the “sharpness” of a measurement. A measurement with lots of resolution is a very “sharp” measurement. A timer that measures seconds to four decimal places has a resolution of one ten-thousandth of a second. A stopwatch that measures seconds to two decimal places has a lower resolution of onehundredth of a second.

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Figure 1.4: Accuracy, precision, and

resolution.

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Section 1.1 Review 1. Explain, using your own example, why you must always give a unit when reporting a measurement. 2. Tell two reasons why SI is easier to use than the English System.

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3. An external computer flash drive can hold 1 gigabyte of data. How many bytes is this? 4. Which is larger: a megawatt or a kilowatt? How many times larger is it? 5. Put these units in order from smallest to largest: decimeter, meter, kilometer, millimeter, centimeter, nanometer, micrometer. 6. Your friend asks you for a glass of water and you bring her 5 milliliters of water. Is this more or less than what she was probably expecting? Explain your reasoning. 7. The length of a sheet of U.S. standard (letter size) paper is closest to: a. 8 centimeters b. 11 centimeters c. 29 centimeters d. 300 centimeters 8. A nickel has a mass of about: a. 0.1 gram b. 5 grams c. 50 grams d. 100 grams 9. Why do you suppose the United States still uses the English System for everyday measurements, while almost every other country uses SI? Give several possible reasons.

Everyday English and SI Units How many different ways are English and SI units used to measure everyday things in the United States? Speed is measured in miles per hour (mph). Is that an English or SI unit? Is gasoline sold in English or SI units? What is that unit? Following is a list of things that are commonly measured. Make a chart that shows what unit is most commonly used to measure each thing in the United States, and show whether that unit belongs to the English System or SI. You might be surprised at how much we use both systems! • • • • • • • • • • •

gasoline road map distances aspirin/pain reliever tablets mechanical pencil lead skis milk large soda bottles electricity body weight mountain bike size racing bike size

10. Refer to Figure 1.5 to answer these questions: a. What is the resolution of the stopwatch? b. Time measurements from a stopwatch are not very precise. Why not? Figure 1.5: Question 10. 1.1 MEASUREMENTS

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1.2 Time and Distance Measurement is a key skill and concept in physical science. In this section, you will learn about measuring two fundamental properties of the universe: time and distance.

Time FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

Time in science We often want to know how things change over time. For example, a car

rolls down a hill over time. A hot cup of coffee cools down over time. The laws of physical science tell us how things change over time. What time is it? Time is used two ways (Figure 1.6). One way is to identify a particular

moment in the past or in the future. For example, saying your 18th birthday party will be on January 1, 2017, at 2:00 p.m. identifies a particular moment in the future for your party to start. This is the way “time” is usually used in everyday conversation.

How much time? The second way is to describe a quantity of time. The question “How much

time?” is asking for a quantity of time. A quantity of time is also called a time interval. Any calculation involving time that you do in physical science will always use time intervals, not time of day. Many problems in science use time in seconds. For calculations, you might need to convert hours and minutes into seconds. For example, the timer (left) shows 2 hours, 30 minutes, and 45 seconds.

Time in seconds

Hours

Minutes

Seconds

How many total seconds does this time interval represent? There are 60 seconds in a minute, so multiply 30 minutes by 60 to get 1,800 seconds. There are 3,600 seconds in an hour, so multiply 2 hours by 3,600 to get 7,200 seconds. Add up all the seconds to get your answer: 45 + 1,800 + 7,200 = 9,045 seconds.

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Figure 1.6: There are two different ways to understand time. What is your reaction time? Sit at a table and rest your arm on the table, with your hand hanging off the edge. Have a friend dangle a metric ruler just above your thumb and index finger. When your friend drops the ruler, catch it quickly between your thumb and finger. Record the centimeter mark where you caught the ruler. Approximate reaction times are: 0.10 seconds for 5 cm, 0.14 s for 10 cm, 0.18 s for 15 cm, 0.20 s for 20 cm, 0.23 s for 25 cm, and 0.25 s for 30 cm. Do several trials and discuss.

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Distance What is Distance is the amount of space between two points (Figure 1.7). You can also distance? think of distance as how far apart two objects are. You probably have a good

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understanding of distance from everyday experiences, like the distance from your house to school, or the distance between your city and the next town. The concept of distance in physics is the same, but the actual distances might be much larger or much smaller than anything you measure in everyday life.

distance - the amount of space between two points. length - a measured distance. meter - a basic SI unit of length.

Distance is Distance is measured in units of length. The English System uses inches, measured in feet, yards, and miles for length units. One foot equals 12 inches. Do you units of length know how many feet are in a yard? There are three feet in a yard. How many

yards are in a mile? There are 1,760 yards in a mile. These numbers are not easy to remember. The SI units of length are much easier to use, because they are based on powers of 10, and the prefixes tell you something about the unit value. For example, the prefix centi- means one hundredth, so you know that a centimeter is 100 times smaller than a meter. There are 100 centimeters in a meter. The word inch does not tell you anything about how it is related to a foot. There are 12 inches in a foot, but you wouldn’t know that from the unit name!

Figure 1.7: Distance is the amount of space between two points.

SI distance unit The meter is a basic SI distance unit. In 1791, a meter was defined as one

10-millionth of the distance from the North Pole to the equator (Figure 1.8). Today a meter is defined more accurately using the speed of light. The meter was used as a starting point for developing the other SI units. Useful prefixes Prefixes are added to the names of basic SI units. Prefixes describe very small

or very large measurements. There are many SI unit prefixes, but the following three (Table 1.3) are commonly used with meters to measure distance. Table 1.3: Common Distance Prefixes Prefix

Prefix + meter

Compared to 1 meter

kilo-

kilometer

1,000 times bigger

centi-

centimeter

100 times smaller

milli-

millimeter

1,000 times smaller

Figure 1.8: In 1791, a meter was defined as 1/10,000,000 of the distance from Earth’s North Pole to the equator. Today, a meter is defined more accurately as the distance that light travels in a fraction of a second. 1.2 TIME AND DISTANCE

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The meter stick A meter stick is a good tool for measuring ordinary lengths in the laboratory.

A meter stick is 1 meter long and is divided into millimeters and centimeters. Figure 1.9 shows a meter stick next to objects of different lengths. Can you see how the meter stick is used to measure the length shown for each object? Using a Using a meter stick or a centimeter ruler to make distance or length centimeter ruler measurements is easy. Each centimeter is divided into 10 smaller units,

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called millimeters. Try using the centimeter rulers below to find the measurement of the length of each object. Check your answers in the sidebar answer box.

Figure 1.9: Reading a meter stick.

The measurements are: bolt: 4.70 cm pencil: 7.90 cm pushpin: 2.60 cm

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Units of distance in space What is a light Astronomers have developed units other than kilometers and meters to year? measure the vast distances in space. You may have heard of light years (ly),

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an astronomical term. Even though the name might sound like it, this unit does not measure time. One light year is equal to the distance that light travels through space in one year.

light year - the distance that light travels through space in one year. One light year is equal to 9.46 × 1012 km.

parsec - An astronomical distance equal to about 3.26 light years.

Calculating a In space, light travels at the amazing speed of about 300,000 km/s. How far light year will light travel in 1 year? We can calculate the distance light travels in 1 year

by multiplying the speed of light (300,000 km/s) by time (1 year). To get the correct answer, we must convert years into seconds since the value for the speed of light contains seconds. There are 31,536,000 seconds in 1 year! Here’s how to find the distance of 1 light year in kilometers: 1 light year = speed of light × time = 300,000 km/s × 31,536,000 s = 9,460,000,000,000 km = 9.46 × 1012 km Light years are Light years are more useful to astronomers than kilometers. For example, useful to the distance from the brightest star in the sky, Sirius, to Earth is about astronomers 83,200,000,000,000 or 8.32 × 1013 km. That distance is equal to about

8.8 light years. You can see that it is much easier to express the distance from Earth to Sirius in light years than it is to describe the distance in kilometers (Figure 1.10).

What is a A parsec (parallax of one arcsecond) is another unit of length used by parsec? astronomers. A parsec (pc) is about 3.26 light years. If you read a popular

science magazine or watch a science show about astronomy, you will see astronomical distances expressed in light years. If you read a technical, scholarly journal article on astronomy, you will see the unit parsec used instead of light years. For example, a star’s absolute brightness is defined as the brightness that star would have if it were 10 parsecs from Earth. Ten parsecs is about 32.6 light years. A parsec is a unit derived by using geometry and trigonometry to describe the position and distance of objects in space, relative to Earth.

Object

Distance from Earth (ly)

Sirius (brightest star in the sky)

8.8

Betelgeuse (appears as a red star in the sky)

700

Crab Nebula (remnant of an exploded star)

4,000

Andromeda galaxy (a huge group of billions of stars)

2.5 million

Figure 1.10: Distance of some space objects from Earth in light years.

1.2 TIME AND DISTANCE

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Section 1.2 Review 1. What are two different ways to understand time? Explain and give examples. 2. How many minutes are there in 1.5 hours? Don’t forget to show your work!

Movie

Running time (min)

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3. Convert 330 minutes to hours. Show your work.

Casablanca

102

4. Men in the age group of 18–34 years need to be able to run a marathon in 3 hours and 10 minutes to qualify for the Boston Marathon. How many seconds is this? Show your work.

Citizen Kane

119

Gone with the Wind

222

E.T. the Extraterrestrial

115

Jaws

124

King Kong (2005)

188

Titanic (1997)

194

Back to the Future

116

5. Study the table in Figure 1.11 to answer the following questions. a. Which movies are longer than 2 hours? b. Which (if any) movies are longer than 3 hours? c. Convert the running time of Gone with the Wind to hours and minutes. d. Does any movie have a running time of less than 1.5 hours? If so, which one(s)? 6. Your teacher says, “There are 100 centimeters in a meter, and this fact is revealed in the unit’s name (centimeter). There are 3 feet in 1 yard, but this fact is not revealed in the unit’s name (yard).” Explain what your teacher means by this.

Figure 1.11: Question 5.

7. Which is larger? Copy each pair of measurements and circle the length that is the longest for each pair. a. 42 mm or 10 cm b. 15 mm or 0.15 cm c. 10 mm or 2 cm 8. Regulus, the brightest star in the constellation Leo, is approximately 77 light years from Earth. Which year did Regulus give off the light you see when you look at the star today?

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1.3 Converting Units When describing the length of a ski, you could say that it is 150 centimeters or 1.5 meters. The ski length is the same—the only thing that is different is the measurement unit. Unit conversion is an important skill in measurement.

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Why convert? What does it Suppose you empty your coin bank and count out 1,565 pennies. How do you mean to figure out how many dollars you have? You have to convert the 1,565 cents to “convert”? a dollar amount. Since there are 100 pennies in a dollar, you divide 1,565 by

100. This is the same as moving the decimal point two places to the left. 1,565 pennies and 15.65 dollars represent the same amount of money.

SI Estimation Challenge For each item below, only one measurement in the list is realistic. The other two measurements are wildly wrong. Can you choose the realistic measurement for each item? 1. width of a postage stamp 1 m, 15 cm, or 20 mm 2. thickness of a CD 0.1 m, 0.01 m, or 0.001 m 3. height of a bus 152.4 mm, 20 m, or 250 cm 4. length of an inchworm 25.4 mm, 25.4 cm, or 0.254 m 5. length of a football field 91.44 m, 200 m, or 1 km

Converting SI Converting SI units is just as easy as converting pennies to dollars. Suppose a units snail can travel about 65 millimeters in one minute. In 10 minutes it can go

10 times as far (65 × 10) or 650 mm. It’s hard to visualize 650 mm. You know that a meter stick is relatively close in size to a yard stick, which you are familiar with. If you convert millimeters to meters, you might be able to better visualize how far the snail can travel in 10 minutes.

1.3 CONVERTING UNITS

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Solving Problems: Converting SI Units When you convert from one SI unit to another, you multiply or divide by a series of 10s. This conversion tool will help you move the decimal point.

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meter gram liter Convert 650 millimeters to meters.

kilo 1000

hecto 100

deca 10

deci 0.1

1. Looking for:

You are asked for the distance in meters.

2. Given:

You are given the distance in millimeters.

3. Relationships:

There are 1,000 millimeters in 1 meter.

4. Solution:

1.

milli 0.001

SI Conversion Tool Copy this SI place value table on an index card so you can refer to it whenever you have to convert SI units. The table will tell you how many places to move the decimal point, and in what direction to move it.

Find the millimeter place, and put your pencil on that space. kilo

2.

centi 0.01

STUDY SKILLS

hecto

deca

meter

deci

centi

milli

Move your pencil to the meters place, and count how many spaces you move your pencil, including the last landing space. a. 142,000 m

3.

Now move the decimal point in 650 to the left three places.

6 5 0.

becomes

b. 7.54 km

.6 5 0

650 mm = 0.650 m Your turn...

a. Convert 142 kilometers to meters. b. Convert 754,000 centimeters to kilometers.

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Converting between English and SI units The problem of It would be easier if everyone always used the same unit, such as the meter, multiple units for length. Unfortunately, many different units of length are used depending

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on what’s being measured and where the measurer lives. In the United States, inches, feet, and miles are used more commonly than centimeters, meters, and kilometers, but sometimes you will need to convert from English to SI units. Comparing Downhill skis come in many different lengths, measured in centimeters. If English and SI you stand a ski up next to you, the ski should come up as high as your chin. units Suppose the distance from your toes to your chin is 4.5 feet. What length skis,

in centimeters, should you buy? To answer the question, you need to convert from feet to centimeters. To do the conversion, you have to multiply 4.5 feet by a conversion factor. A conversion factor is a ratio that has the value of one. Study the problem solving steps on the next page to learn how to set up a conversion using conversion factors. This method of converting units is called dimensional analysis.

conversion factor - a ratio that has a value of one and is used when setting up a unit conversion problem. dimensional analysis - a method of using conversion factors and unit canceling to solve a unit conversion problem.

English and SI Units Suppose you are working on your bicycle and the wrench you select is one size too small. The illustration below shows that it is easier to choose the next bigger size if you use SI units. Wrenches in inches (English Units)

3/8" 7/16" Wrenches in millimeters (SI Units)

11 10 Which is the bigger wrench in each pair?

1.3 CONVERTING UNITS

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Solving Problems: Converting Units Convert 4.5 feet to centimeters.

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1. Looking for:

You are asked for a length in centimeters.

2. Given:

You are given the length in feet.

3. Relationships:

There are 30.48 cm in 1 foot (you can look this up in a conversion table).

4. Solution:

1.

Write down the given measurement and a multiplication symbol.

2.

Create a conversion factor by drawing a fraction bar and copying the given unit (feet) into the bottom of the fraction. Next, put the unit you are looking for in the numerator (cm). Put the number “1” next to the larger unit (foot) and for the smaller unit, write down how many of them equal one of the larger unit (30.48).

3.

Cancel like units in the problem setup. This is how you keep track of how well your dimensional analysis setup is working. Your goal is to cancel all units except the one you are solving for (cm).

STUDY SKILLS Handy Conversion Factors Use these handy conversion factors anytime you need to set up a unit canceling problem like the one on this page. Note: You can flip these fractions around as needed; the 1 (larger unit) isn’t always in the denominator.

a. 160 m 4.

Now you are ready to do the math! This problem setup tells you to multiply 4.5 by 30.48. The answer is 137 cm (rounded).

b. 63.5 mm

Your turn...

a. Convert 175 yards to meters. (You might need more than one fraction!) b. Convert 2.50 inches to millimeters. (More than one fraction is needed!)

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Working with measurements Significant All measurements involve a degree of uncertainty. The object in Figure 1.12 Digits is definitely longer than 2.6 cm. But how much longer? Not everyone would

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agree on the third digit of the measurement. One person might read the measurement as 2.63 cm, and another might argue it is closer to 2.65 cm. In the real world it is impossible to make a measurement of the exact true value of anything (except when counting). Using the ruler pictured in Figure 1.12, the best answer for the length of the paper clip is 2.65 cm. To a scientist this number means “between 2.60 and 2.70 cm.” The last digit, 5, representing the smallest amount, is uncertain. Significant digits are the meaningful digits in a measured quantity. For the paper clip, the third digit is meaningful even though it is uncertain. The third digit tells someone the object is about halfway between 2.60 and 2.70 cm long. Therefore, we say there are three useful or significant digits in this length measurement. It is important to be honest when reporting a measurement, so readers know how much resolution it has. We do this by using significant digits to report the measurement.

significant digits - meaningful digits in a measured quantity.

Using What happens when you use measured quantities with different numbers of significant digits significant digits in a math problem? For example, a shoe is 38 cm long and in math you want to convert the length to inches. problems

To find the answer, divide 38 by 2.54 and you get 14.960629. This answer has an artificially large number of significant digits (eight)! An answer involving measured quantities should have no more significant digits than the starting measurement with the least number of significant digits. The correct answer to this conversion problem is rounded up to 15 inches, since 38 centimeters has two significant digits. Study the next page for more help with using significant digits in math problems.

Figure 1.12: Find the length of the

object in centimeters. How many digits does your answer have?

1.3 CONVERTING UNITS

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Solving Problems: Significant Digits

STUDY SKILLS Which digits are significant? Digits that are always significant:

What is the area of an 8.5-inch by 11.0-inch piece of paper?

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

1. Looking for:

You are asked for an area.

2. Given:

You are given the width, 8.5 inches, and the height, 11.0 inches.

3. Relationships:

Area = width × length

4. Solution:

Area = 8.5 inch × 11.0 inch Area = 93.5 square inches (too many significant digits—see below) The number 93.5 has three significant digits. The width measurement had only two significant digits (8.5), and the length measurement had three significant digits (11.0). So how many significant digits should your answer have? The answer can have no more significant digits than the measurement with the least number. In this case, since the width measurement only had two significant digits, your answer can only have two. You must round 93.5 square inches to 94 square inches. The correct answer is 94 square inches. Your turn...

a. How many significant digits does each of these numbers have? 40 cm, 4 cm, 4.0 cm, 40. cm, 45 cm, 450 cm, 450. cm

1. Non-zero digits. 2. Zeros between two significant digits. 3. All final zeros to the right of a decimal point. Digits that are never significant: 1. Leading zeros to the right of a decimal point. (0.002 cm has only one significant digit.) 2. Final zeros in a number that does not have a decimal point. Note: A decimal point is used after a whole number ending in zero to indicate that a final zero is significant. Thus, 50. cm has two significant digits, not one.

a. 40 cm: 1; 4 cm: 1; 4.0 cm: 2; 40. cm: 2; 45 cm: 2; 450 cm: 2; 450. cm: 3 b. 1.8 km

b. Convert 1.10 miles to kilometers and report your answer with the correct number of significant digits. Use the relationship 1 mi = 1.6 km.

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Section 1.3 Review 1. What does it mean to “convert” from one unit to another? Give an example. 2. How many meters do you cover in a 10-kilometer (10-K) race?

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3. An Olympic swimming pool is 50 meters long. You swam from one end to the other four times. a. How many meters did you swim? b. How many kilometers did you swim? c. How many centimeters did you swim? 4. In the United States, a standard letter-sized piece of paper is 8.5 inches wide by 11.0 inches long. The international standard for a letter-sized piece of paper is different. The international standard is based on SI units: 21.0 cm wide by 29.7 cm long. a. Convert 21.0 cm to inches. Show your dimensional analysis setup. b. Convert 29.7 cm to inches. Show your dimensional analysis setup. c. State the dimensions, in inches, of the international standard for a letter-sized piece of paper. d. Which piece of paper is longer: a U.S. letter-sized piece of paper, or an international letter-sized piece of paper? e. Suppose the United States adopted the international standard for letter-sized paper. Explain at least two things that might result from this change. 5. Which of these measurements has three significant digits? (There might be more than one correct answer choice.) a. 29.3 cm b. 290 cm c. 0.029 cm d. 290. cm

Find Out! What are the official measurements for an Olympic swimming pool? Create a table in your journal with the answers: • • • • • •

length of pool width of pool number of lanes lane width water temperature depth

Do an Internet search using the key words international paper size. Write a report of your findings about the standards for paper sizes. Do all countries use the same size paper for letters? How was the international standard paper size defined? What are some interesting outcomes of having different standard paper sizes in different countries? What surprised you the most about what you learned from your research?

6. Convert 345 cm to inches. Show your dimensional analysis setup and report your answer with the correct number of significant digits. (1 in = 2.54 cm).

1.3 CONVERTING UNITS

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1.4 Measurement and Graphing

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We have been practicing measurement skills in this chapter. Once we have measured and collected data, it is often necessary to organize it visually in order to look for relationships. A graph is a visual way to organize data. In this section, we will focus on creating and interpreting scatterplots (XY graphs). There are other types of graphs, but scatterplots are the most useful for organizing and presenting physical science data.

graph - a visual representation of data.

scatterplot (or XY graph) - a graph of two variables thought to be related.

Types of graphs Scatterplots, bar graphs, pie graphs, and line graphs

Most graphs are either scatterplots, bar, pie, or line graphs. A scatterplot or XY graph is used to determine if two variables are related. For example, the more hex nuts you have, the more space they take up (Graph A). Scatterplots are commonly used in science and you will create many of them from the data you collect in your investigations. A bar graph compares groups of information (Graph B). A pie graph is a circular graph that shows how a whole is divided up into percentages. (Graph C). A “connect-the-dots” line graph is often used to show trends in data over time (Graph D). Strictly speaking, a line graph does not usually show cause and effect. For example, a line graph of a stock price might change over time, but it is not the time that causes the change to happen.

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Making a scatterplot or XY graph Independent and Scatterplots show how a change in one variable influences another variable. dependent The independent variable is the variable you believe might influence variables another variable. It is often controlled by the experimenter, and is sometimes called the manipulated variable. The dependent variable is the variable

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that might be influenced by the independent variable, and can also be called the responding variable.

independent variable - a variable that you believe might influence another variable.

dependent variable - the variable that you believe is influenced by the independent variable.

An example Pressure is measured in units of atmospheres. You live at Earth’s surface

under a pressure of 1 atmosphere. Pressure is critical to safe scuba diving. As a diver goes deeper under water, she has to think about pressure. How does an increase in depth affect the pressure? What sort of graph would best show the relationship between pressure and depth? Figure 1.13 shows depth and pressure data for the ocean.

Depth (m) (x-axis)

Step 1: Assign In this example, depth is the independent or manipulated variable. The diver the x- and y- can choose her depth in the water. The independent variable always goes on axes the horizontal, or x-axis of a graph. The dependent variable always goes on

the vertical or y-axis. In this example, pressure is the dependent variable. Pressure depends on the diver’s depth in the water. Step 2: Make a To create a pressure versus depth graph, you first make a scale. When talking scale about a graph, scale refers to how each axis is divided up to fit the range of

data values. Use the formula below to make a scale for any graph. value per box on graph =

data range number of boxes on axis

A quick rule of thumb to use for creating scales is to try counting first by ones, then twos, then fives, then 10s. One of these should work most of the time. For example, if the data range for the x-axis is 0 to 40 units and the x-axis on your graph covers 8 boxes, each box would be worth 5 units.

0

1.0

5

1.5

10

2.0

15

2.5

20

3.0

25

3.5

30

4.0

35

4.5

40

5.0

Figure 1.13: Depth of the ocean and pressure data.

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Pressure (atm) (y-axis)

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Step 3: Plot your Using the data in Figure 1.13, plot each point by finding the x-value and data tracing the graph upward until you get to the correct y-value. Make a dot for

each point. Draw a smooth curve that shows the pattern of the points.

STUDY SKILLS Key Elements of a Scatterplot

MIXES TUCS Pressure vs. depth

y-value range

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

M: maximize your graph (use all of the graph paper!)

Title

IX: Independent variable on x-axis (dependent variable on y-axis)

5.5

units for the y-values

5

ES: Equally spaced scale increments

Pressure (atm)

4.5

(start at 0)

4

T: Title (y-variable vs. x-variable) U: Units and labels on both axes CS: Continuous smooth curve to

3.5 3 2.5 2

connect the data points

1.5

y-axis label

1

x-value range

0.5

Old Faithful eruptions

25

30

35

Depth (m)

40

45

50

55

60

units for the x-values

Step 4: Create a Create a title for your graph. Also, be sure to label each axis including units title (shown above). If time is a Like many rules, there are important exceptions. Time is an exception to the variable rule about which variable goes on which axis. When time is one of the

variables on a graph, it usually goes on the x-axis. This is true even though you might not think of time as an independent variable. Using When scientists create scatterplots they are usually working with large scatterplots in amounts of data. Figure 1.14 shows a scatterplot of data for the Old Faithful science geyser in Yellowstone National Park, Wyoming. The graph shows there

are generally two types of eruptions: short-wait-short-duration and long-wait-long-duration. This discovery about the geyser activity would be hard to demonstrate without the visual aid of the scatterplot!

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90

20

80

15

70

10

60

x-axis label

5

50

0

Waiting time bewteen eruptions (min)

0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

Eruption duration (min)

Figure 1.14: Waiting time versus eruption duration for Old Faithful.

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CHAPTER 1

Identifying relationships between variables on a graph Patterns When there is a relationship between the variables, the graph shows a clear indicate pattern. The speed and distance variables (below left) show a direct relationships relationship. In a direct relationship, when one variable increases, so does

the other.

10 20 30 40 50 60 70 80 90

99 140 171 198 221 242 262 280 297

200

100

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# of groups

Last 2 digits

10 15 19 6 22 9 26 12 11

06 05 15 22 09 11 13 14 19

Last 2 digits of phone number

Inverse Some relationships are inverse. In an inverse relationship, when one relationships variable increases, the other decreases. If you graph how much money you

spend against how much you have left, you see an inverse linear relationship. The more you spend, the less you have. Graphs of inverse relationships always slope down and to the right (Figure 1.15).

Inverse relationship between variables How much money you have

300

Distance Speed (cm/s) (cm)

inverse relationship - a relationship in which one variable decreases when another variable increases.

No relationship between variables Number of musical groups

Strong relationship between variables

Speed (cm/s)

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

When there is no relationship, the graph looks like a collection of dots. No pattern appears. The number of musical groups a student listed in one minute and the last two digits of his phone number are an example of two variables that are not related.

direct relationship - a relationship in which one variable increases with an increase in another variable.

$100 $80 $60 $40 $20 0

0

$20

$40

$60

$80

$100

How much money you spend

Figure 1.15: Graphs of inverse relationships slope down and to the right.

What type of relationship does the depth versus pressure graph on the previous page show? The depth versus pressure scatterplot shows a strong direct relationship. That makes sense. The deeper you go, the more water is on top of you, pushing down and creating more pressure.

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Reading a graph Using a graph to Suppose you measure the speed of a car at four places on a ramp. Can you make a figure out the speed at other places without having to actually measure it? prediction As long as the ramp and car are set up the same way, the answer is yes! A

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

graph can give you an accurate answer even without doing the experiment. Look at the example below to see how. The students doing the experiment measured and graphed the speed of the car at 20, 40, 60, and 80 cm. They want to know the speed at 50 cm. 1)

Start by finding 50 centimeters on the x-axis.

2)

Draw a line vertically upward from 50 centimeters until it hits the curve that fits the points that were measured.

3)

Draw a line across horizontally to the y-axis.

4)

Use the scale on the y-axis to read the predicted speed.

A student measures the mass of water collected every five minutes on a rainy day. Design a graph to show the student’s data. Estimate how many minutes it took for 20 grams of water to be collected. Time is the independent variable, therefore mass is the dependent variable. The mass axis should go from 0 to at least 50 grams. The time axis should go from 0 to at least 20 minutes. The graph shows that 20 grams of rainwater fell in the first 7.5 minutes. Mass of rainwater vs. time 60

Mass (g)

50 40 30 20

Large graphs For this example, the graph predicts the speed to be 76 cm/s. You will get the are more precise best predictions when the graph is big enough to show precise measurements.

That’s why you should draw your graphs so they fill as much of the graph paper as possible.

10 0 0

5

10

7.5 minutes

15

20

25

Time (min)

A graph is a A graph is a simple form of a model. Remember, a model is a relationship form of a model that connects two or more variables. Scientists use models to make and test

predictions.

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Section 1.4 Review

CHAPTER 1

STUDY SKILLS

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

1. Scatterplots, bar graphs, pie graphs, and line graphs all have different purposes. Which type of graph best fits each purpose? a. Grouping data for comparison b. Comparing parts of a whole c. Seeing if two variables are related, such as in cause and effect 2. For each pair of variables, identify which is the independent variable and which is the dependent variable. a. How much gas is in the car versus how far the car has traveled b. How much money you’ve spent versus how much money is in your wallet c. How far a wind-up toy car traveled versus how much time went by 3. You have a small tank of water. Suppose you make waves in the tank and measure their speed in different depths of water. Which is the independent variable and which is the dependent variable? (Look in the sidebar for helpful reminders.) 4. Make a scatterplot using the data below. Water depth (cm)

Wave speed (cm/s)

0 1 2 3 4 5 6

0 29.8 43.3 52.1 59.2 64.4 69.3

Four Steps for Making a Graph Step 1: Choose which will be the dependent and independent variables. The dependent variable (responding variable) goes on the y-axis and the independent variable (manipulated variable) goes on the x-axis. If time is one of the variables, it goes on the x-axis. Step 2: Make a scale for each axis by counting boxes to fit your largest value. Count by multiples of 1, 2, 5, or 10. Step 3: Plot each point by finding the x-value and tracing upward until you get to the corresponding y-value. Step 4: Draw a smooth curve that shows the trend of the points. Do not just connect the dots with straight lines.

5. Use your scatterplot of wave speed versus water depth to answer the following questions. a. What happens to wave speed as the depth of the water increases? b. What would the estimated wave speed be at 4.5 cm?

1.4 MEASUREMENT AND GRAPHING

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Chapter 1 Assessment Vocabulary

11. A(n) ____ is a unit of length in SI that equals 100 cm.

Select the correct term to complete the sentences.

12. A(n) ____ is equal to about 3.26 light years.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

accuracy

graph

parsec

Section 1.3

conversion factor

independent variable

precision

13. ____ are meaningful digits in a measured quantity.

dependent variable

inverse relationship

resolution

dimensional analysis

length

scatterplot

14. A ratio that has a value of one and is used when setting up unit conversion problems is called a(n) ____.

direct relationship

light year

SI

distance

measurement

significant digits

English System

meter

unit

Section 1.1

1.

A(n) ____ is a standard amount, like a kilometer or a gallon, which is used to communicate various quantities.

2.

The ____ is a measurement system used for everyday measurements in the United States.

3.

____ is the international system of units used by scientists.

4.

When someone determines the amount of something using a value and a unit, they are making a(n) ____.

5.

When you describe how close a measured quantity is to a true or accepted value, you are describing its ____.

6.

____ describes how close together repeated measurements are.

7.

____ refers to the smallest interval that can be measured.

15. A method of using conversion factors and unit canceling to solve a unit conversion problem is called ____. Section 1.4

16. A(n) ____ is shown by a continuous smooth curve rising from left to right on a scatterplot. 17. The ____ can also be called the manipulated variable. 18. A(n) ____ is also called an XY graph, and it is often used to determine if one variable causes an effect in another variable. 19. The ____ is always plotted on the y-axis of a scatterplot. 20. A(n) ____ is a visual representation of data; there are four major types. 21. When one variable decreases as another increases, you have a(n) ____.

Concepts

Section 1.2

Section 1.1

8.

____ describes how far it is from one place to any other place.

1.

9.

The amount of space between two points is measured in units of ____.

Explain, using examples, how SI and English systems of measurement are both used in daily life in the United States.

2.

Define the terms accuracy, precision, and resolution. Give an example of each.

10. A(n) ____ is the distance light can travel in one year.

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Section 1.2

Problems

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

3.

What are the two different ways to understand time? Give examples to support your explanation.

Section 1.1

4.

In the following list of units, which are SI units of length: mm, yd, cm, mi, m, g, mg, lb, oz, km, ml?

a.

the width of your pinky finger

5.

Why are light years used to measure distances to stars instead of kilometers?

b.

the length of a dollar bill

c.

the length of a small paperclip

6.

Which is a larger unit of distance: a light year or a parsec? Justify your answer.

CHAPTER 1

1.

2.

Which of the following is closest to 2 cm?

Rank these units from smallest to largest: micrometer, nanometer, kilometer, centimeter, meter.

Section 1.3

Section 1.2

7.

How do you use the SI conversion tool to perform unit conversions? Explain the process step by step.

3.

Arrange the following intervals of time from shortest to longest: 160 seconds, 2 minutes, 2 minutes 50 seconds.

8.

Why can’t you use the SI conversion tool to convert from SI to English units?

4.

Write 3,800 seconds in hours, minutes, and seconds.

9.

The dimensional analysis method of unit conversion is sometimes called “unit canceling.” Explain why this is a good name for the method.

5.

What is the length of the object shown below?

10. Why do you often have to round off answers to math problems that involve measured quantities? Section 1.4

Section 1.3

11. A blank graph grid is 20 boxes by 20 boxes. You want to plot a data set on this graph. The range of x-axis values is 0–60. The range of y-axis values is 0–15. Sketch the best scale to use that would maximize the graph size.

6.

Convert 54 grams to kilograms.

7.

Convert 26 decimeters to meters.

8.

Convert 1,200 meters to millimeters.

12. You wish to make a graph of the height of the Moon above the horizon every 15 minutes between 9:00 p.m. and 3:00 a.m. during one night.

9.

Convert 525 pounds to kilograms. Show your dimensional analysis setup. 1 kilogram = 2.2 pounds.

a. b. c.

What is the independent variable? What is the dependent variable? On which axis should you graph each variable?

10. A runner completes a 4,000.-meter race. How many yards did she run? Show your dimensional analysis setup. 11. A star is 15 parsecs from Earth. How far is this distance in light years? How far in kilometers? CHAPTER 1 ASSESSMENT

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Section 1.4

Use the graph of mass versus volume to answer the questions in this section of problems. The graph was created by a student who measured the mass and volume of a collection of hex nuts from a hardware package. Each hex nut was made of the same material, and each was the same size and shape.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

40

1.

Do some research to find out what influenced the development of the International System of Units. Where did the system originate? When did other countries decide to adopt the system? Did the United States adopt the system? (You might be surprised at what your research will reveal!)

2.

Do you think the United States will ever switch completely to SI? Why or why not?

(3.75, 30)

30 Mass (g)

Applying Your Knowledge Section 1.1

Mass and volume of hex nuts

35

14. Make a quick sketch of what you think the scatterplot would look like if you used random hex nuts of different materials and sizes, rather than a collection that is all the same.

(3.00, 24)

25 (2.25, 18)

20 (1.50, 12)

15 10

Section 1.2

(0.75, 6)

3.

5 0

0

1

2

3

4

Volume (mL)

12. Each data point in the mass versus volume graph represents adding another hex nut to the group. The first data point shows the mass and volume of one hex nut, and the second data point shows the mass and volume of two hex nuts together, and so on up to five hex nuts. a. b. c.

What is the mass and volume of one hex nut? What is the mass and volume of five hex nuts together? What do you predict the mass and volume of six hex nuts would be?

What is the distance from Earth to the Moon? Is that distance changing? Do some research to find out.

Section 1.3

4.

Why do you think it is necessary to know how to convert from English to SI units and vice versa? Give your own example.

Section 1.4

5.

Look through recent newspapers and/or magazines to find at least one example of a scatterplot, bar graph, pie graph, and line graph. Photocopy or cut out the graph examples and create a small poster that illustrates the differences between these types of graphs.

13. What type of relationship exists between mass and volume on the mass versus volume graph?

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CHAPTER

2

CHAPTER 2

The Scientific Process FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

On August 21, 2003, on a specially built hill in Irvine, California, six adults climbed into cars with no motors and rolled downhill. In the Extreme Gravity Race, the cars reached speeds of up to 60 miles per hour as they raced down the hill using nothing but gravity for energy. The six cars represented six fiercely-competitive design and engineering teams. The race featured teams from five different automakers. Each team had created the slipperiest low-friction car they could, using carbon fiber, titanium, and many other high-tech materials. How did the cars reach such high speeds using nothing but gravity? How did each team design its car so that it would be as fast as possible? Answers to these questions involve experiments and variables. Read on, and you will find out how engineers learn to make things better, faster, and more efficient!

4 What does “learning by inquiry” mean? 4 How do you design a good scientific experiment?

4 How are science and engineering similar and how are they different?

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2.1 Inquiry and the Scientific Method Scientists believe the universe follows a set of rules called natural laws. Everything that happens obeys the same natural laws. Unfortunately, the natural laws are not written down, nor are we born knowing them. The primary goal of science is to discover what the natural laws are. Over time, we have found the most reliable way to discover natural laws is through scientific inquiry.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

What inquiry means Learning by asking questions is called inquiry (Figure 2.1). Inquiry resembles a crime investigation with a mystery to solve. Something illegal happened and the detective must figure out who did it. Solving the mystery means accurately describing who did what, when they did it, and how. The problem is that the detective never actually saw what happened. The detective must deduce what happened in the past from information collected in the present.

Inquiry is learning through questions

natural law - a theory that has been tested many times without any contradictions.

inquiry - a process of learning that starts with asking questions and proceeds by seeking the answers to the questions.

deduce - to figure something out from known facts using logical thinking.

Searching for In the process of inquiry, the detective asks lots of questions related to the evidence mystery. The detective searches for evidence and clues that help answer the

questions. Eventually, the detective comes up with a theory about what happened. The theory is a description of what must have occurred in the crime, down to the smallest details. How do you know you have learned the truth?

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At first, the detective’s theory is only one possible explanation among several of what might have happened. The detective must have evidence to back up the theory. To be accepted, a theory must pass three demanding tests. First, it must be supported by enough evidence. Second, there cannot be even a single piece of evidence that contradicts the theory. Third, the theory must be unique, because if two theories both fit the facts equally well, you cannot tell which is correct. When the detective arrives at a theory that passes all three tests, he believes he has “solved” the mystery by using the process of inquiry.

Figure 2.1: The steps in learning through inquiry.

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THE SCIENTIFIC PROCESS

CHAPTER 2

Scientific evidence What counts as In science, the only way to know if you are right is to test your idea against scientific real evidence. But, what types of evidence qualify as scientific evidence? Do evidence? feelings or opinions count as scientific evidence? Does what other people

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

think qualify as scientific evidence? The answer to both questions is no. Because evidence is so important in science, there are exacting rules defining what counts as scientific evidence. An example of Scientific evidence might include numbers, tables, graphs, words, pictures, scientific sound recordings, or other information. The important thing is that the evidence evidence accurately describes what happens in the real world (Figure 2.2).

objective - describes evidence that documents only what actually happened as exactly as possible.

repeatable - describes evidence that can be seen independently by others if they repeat the same experiment or observation in the same way.

Scientific evidence might be collected without doing experiments in a laboratory. For example, Galileo used his telescope to look at the Moon. He recorded what he saw by sketching in his notebook. Galileo’s sketches are considered scientific evidence. When is evidence considered scientific?

Scientific evidence must be objective and repeatable. Objective means the evidence should describe only what actually happened as exactly as possible. Repeatable means that others who look the same way at the same thing will observe the same results. Galileo’s sketches describe in detail what he actually saw through the telescope. That means the sketches are objective. Others who looked through his telescope saw the same thing. That makes the sketches repeatable. Galileo’s sketches are good scientific evidence because they are both objective and repeatable. Galileo’s sketches helped convince people that the Moon was actually a world like Earth with mountains and valleys. This was not what people believed in Galileo’s time.

Communicating scientific evidence with exact definitions

It is important that scientific evidence be clear, with no room for confusion or misunderstanding. For this reason, scientists define concepts like force and weight very clearly. Usually, the scientific definition is similar to the everyday meaning of the word, but more exact. For example, when you talk about your weight in everyday terms, you’re talking about the number of pounds that your body weighs. In science, your weight is the force of gravity pulling on the mass of your body.

Figure 2.2: Some examples of scientific evidence.

2.1 INQUIRY AND THE SCIENTIFIC METHOD

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Scientific theories How theories A scientific theory is a human attempt to describe a natural law. For are related to example, if you leave a hot cup of coffee on the table, eventually it will cool natural laws down. Why? There must be some natural law that explains what causes the

theory - a scientific explanation supported by a lot of evidence collected over a long period of time.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

coffee to cool. A good place to start looking for the law is by asking what it is about the coffee that makes it hot. Whatever quality that creates “hot” must go away or weaken as the coffee gets cold (Figure 2.3). The question of what causes hot and cold puzzled people for a long time. The theory of Before 1843, scientists believed (a theory) that heat was a kind of fluid (like caloric water) that flowed from hotter objects to colder objects. They called this

fluid caloric. People thought hot objects had more caloric than cold objects. When a hot object touched a cold object, they believed the caloric flowed between the objects until the temperatures were the same. Testing the The caloric theory explained what people knew at the time. However, a big theory problem arose when people learned to measure weight accurately. Suppose

caloric really does flow from a hot object to a cold object. That means an object should weigh more when it’s hot than it does when it’s cold. Experiments showed this was not true. Precise measurements showed that objects have the same weight, whether hot or cold. The caloric theory was soon abandoned because it could not explain this new evidence. How theories Scientists are always testing theories against new experiments and new are tested evidence. One of two things can happen when new evidence is found. against evidence 1. The current theory correctly explains the new evidence. This gives us

confidence that the current theory is the correct one. OR

2.

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The current theory does not explain the new evidence. This means there is a new (or improved) theory waiting to be discovered that can explain the new evidence (while continuing to validate the existing evidence).

Figure 2.3: A question that might begin inquiry into what “heat” really is.

Humans understood much less about science 1,000 years ago. That doesn’t mean that people didn’t know about things like temperature. They knew the difference between hot and cold, but they didn’t know the scientific reason for why things were hot or cold. In Aristotle’s time, scientific thinkers were convinced that Earth was the center of the universe. How did Copernicus and Kepler convince people to change their minds? Do some research on how Copernicus and Kepler contributed to our scientific understanding of Earth’s place in the universe.

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THE SCIENTIFIC PROCESS

CHAPTER 2

Hypotheses The hypothesis Based on observations and evidence, a good detective evaluates many

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

different theories for what might have happened. Each different theory is then compared with the evidence. The same is true in science, except that the word theory is reserved for a single explanation supported by lots of evidence collected over a long period of time. Instead of theory, scientists use the word hypothesis to describe a possible explanation for a scientific mystery.

Theories start Theories in science start out as hypotheses. The old explanation that heat was out as the fluid caloric was an incorrect hypothesis, one of many leading up to the hypotheses modern theory of heat. The first hypothesis that heat is a form of energy was

made by a German doctor, Julius Mayer, in 1842, and confirmed by experiments done by James Joule in 1843. Energy has no weight, so Mayer’s hypothesis explained why an object’s weight remained unchanged whether it was hot or cold. After many experiments, Mayer’s hypothesis (that heat was a form of energy) became the theory of heat that we accept today (Figure 2.4).

hypothesis - a possible explanation that can be tested by comparison with scientific evidence.

Figure 2.4: A hot cup of coffee has more heat energy than a cold cup of coffee. As coffee cools, its heat energy is transferred to the air in the room. As a result, the air is warmed.

Hypotheses A scientific hypothesis must be testable. That means it must be possible to must be testable collect evidence that proves whether the hypothesis is true or false. This to be scientific requirement means not all hypotheses can be considered by science. For

instance, it has been believed at times that creatures are alive because of an undetectable “life force.” This is not a scientific hypothesis because there is no way to test it. If the “life force” is undetectable, that means no evidence can be collected that would prove whether it exists or not. Science restricts itself to only those ideas that may be proved or disproved by actual evidence.

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The scientific method Learning by In their early years, children learn about the world by trial and error. Imagine chance a small child trying to open a jar. She will try what she knows—biting the

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

lid, pulling on it, shaking the jar, dropping it—until, by chance, she twists the lid. It comes off. She puts it back and tries twisting it again, and the lid comes off again. The child learns by trying many different things and then remembering what works.

scientific method - a process of learning that begins with a hypothesis and proceeds to prove or change the hypothesis by comparing it with scientific evidence.

Learning by the It takes a long time to learn by randomly trying everything. What’s worse, scientific you can never be sure you tried everything. The scientific method is a method much more dependable way to learn.

The Scientific Method 1.

Scientists observe nature, then develop or revise hypotheses about how things work.

2.

The hypotheses are tested against evidence collected from observations and experiments.

3.

Any hypothesis that correctly accounts for all of the evidence from the observations and experiments is a potentially correct theory.

4.

A theory is continually tested by collecting new and different evidence. Even one single piece of evidence that does not agree with a theory will force scientists to return to step one. Why the The scientific method is the underlying logic of science. It is a careful and scientific cautious way to build an evidence-based understanding of our natural world. method works Each theory is continually tested against the results of observations and experiments. Such testing leads to continued development and refinement of theories to explain more and more different things. The way people came to understand the solar system is a good example of how new evidence leads to new and better theories (Figure 2.5).

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Figure 2.5: Three different models for Earth and the solar system that were believed at different times in history.

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THE SCIENTIFIC PROCESS

Section 2.1 Review

CHAPTER 2

STUDY SKILLS

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

1. Which of the following is an example of deduction? a. Hector calls the weather service to find out if the temperature outside is below freezing. b. Caroline looks out the window and concludes that the temperature is below freezing because she sees that the puddles in her neighbor’s driveway are frozen. 2. Describe the relationship between a hypothesis, a theory, and a natural law. 3. To be correct, a scientific theory must be everything except a. supported by every part of a large collection of evidence. b. considered to be unchangeable even if new scientific evidence disproves it. c. testable by comparison with scientific evidence. d. an explanation of something that actually occurs within the natural world or within technology. 4. Julie, a third-grade student, believes that the Moon disappears on certain days every month. Explain why the following information is or is not scientific evidence that can be used to evaluate Julie’s hypothesis. a. Julie sometimes cannot see the Moon all night even though the sky is clear. b. Anne, Julie’s older sister, thinks the phases of the Moon are caused by the Moon’s position in its orbit around Earth. 5. When describing scientific evidence, what is the meaning of the word repeatable? 6. Which of the following is an example of learning through inquiry? a. Miguel is told that hot objects, like a cup of coffee, cool off when left on the table in a cooler room. b. Erik wonders what happens to hot objects if you remove them from the stove. He puts a thermometer in a pot of boiling water and observes that the water cools off once it’s removed from the heat source.

Keep Your Eyes and Ears Open A great many discoveries were made almost by accident! For example, paper used to be made of cotton or linen, which are costly plant fibers. Inventors searched for a less expensive way to make paper. In 1719, French scientist and inventor Rene de Reaumer was walking in the woods when he noticed that wasp nests were made from something a lot like paper! How did the wasps do it? In 1840, Friedrich Keller made the first all-wood paper and today nearly all paper is made from wood. Reaumer’s curiosity and alert eyes lead directly to the paper we use today.

2.1 INQUIRY AND THE SCIENTIFIC METHOD

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CHAPTER 2

THE SCIENTIFIC PROCESS

2.2 Experiments and Variables

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An experiment is a situation specifically set up to investigate something. For example, you could do an experiment in your class to investigate how fast a car moves as it travels down a ramp (Figure 2.6). An experiment is designed around a system, or a group of variables that are related in some way.

experiment - a situation specifically set up to investigate relationships between variables.

Experiments

variable - a factor that affects how

Experiments tell us how variables are related

The goal of any experiment is to understand the relationship between variables. For example, what is the relationship between the speed of the car and the angle of the ramp? To answer the question, you set up the experiment with the ramp attached to different holes in the stand. Each hole sets the ramp at a different angle. You measure all the variables that affect the speed of the car and see how (and if) they change when the angle is changed. A variable is a factor that affects how an experiment works.

system - a group of variables that are related. an experiment works.

experimental variable - the variable you change in an experiment.

control variable - a variable that is kept constant (the same) in an experiment.

Changing one In a simple, ideal experiment only one variable is changed at a time. You can variable at a assume that any changes you see in other variables were caused by the one time variable you changed. If you change more than one variable, it’s hard to tell

which one caused the changes in the others. The experiment will probably still work, you just won’t learn much from the results! The The variable you change in an experiment is called the experimental experimental variable. This is usually the variable that you can freely manipulate. For the variable experiment with a car on a ramp, the angle of the ramp is the experimental

variable. Control The variables you keep the same are called control variables. If you are variables changing the angle of the ramp, you want to keep the mass of the car the

same each time you roll the car. Mass is a control variable. You also want to keep the position of the photogate the same. Photogate position is also a control variable. You will also want to have the same release technique for the car each time it rolls down the ramp. If you want to test different angles, the ramp angle should be the only variable you change.

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Figure 2.6: A car rolling downhill can be an experiment.

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Experimental techniques Experiments Many experiments are done over and over with only one variable changed. often have For example, you might roll a car down a ramp 10 times, each time with the several trials ramp at a different angle. Each time you run the experiment is called a trial.

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To be sure of your results, each trial must be as similar as possible to all the others. The only change should be the one variable you are testing. Experimental Your experimental technique is how you actually do the experiment. For technique example, you might release the car using one finger on top. If this is your

technique, you want to do it the same way every time. When you place the photogate on the track, you make sure the gate is always perpendicular to the track. By developing a good technique, you make sure your results accurately show the effects of changing your experimental variable. If your technique is sloppy, you might not be able to determine if your results are due to technique or changing your variable.

trial - each time an experiment is tried. experimental technique - the exact procedure that is followed each time an experiment is repeated.

procedure - a collection of all the techniques you use to do an experiment.

Procedures The procedure is a collection of all the techniques you use to do an

experiment. Your procedure for testing the ramp angle might have several steps. Good scientists keep careful track of their procedures so they can come back another time and repeat their experiments. Writing the procedures down in a lab notebook is a good way to keep track (Figure 2.7). Scientific results must always be repeatable

Scientific discoveries and inventions must always be testable by someone other than you. If other people can follow your procedure and get the same results, then most scientists would accept your results as being true. Writing good procedures is the best way to ensure that others can repeat and verify your experiments. This is a good thing to keep in mind when you write your own procedure for an experiment. Write it with enough detail that someone else could follow the procedure and do the experiment exactly the way you did it.

Communicating A lab report is a good way to communicate the results of an experiment to your results others. It should contain your research question, hypothesis, experiment

Figure 2.7: A notebook keeps your observations and procedures from getting lost or being forgotten.

procedures and data, and your conclusion. If you give an oral report to your class, colorful charts and graphs are a good way to show your data. This is how scientists present the results of their experiments to other scientists. 2.2 EXPERIMENTS AND VARIABLES

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Experiments: Then and now Electricity and Michael Faraday, a British scientist, made some important discoveries while magnetism in experimenting with electricity and magnets. This is a great example of how the 1800s one experiment often leads to another. Faraday’s original question was,

“How are electricity and magnetism related?”

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The original Faraday designed a controlled experiment with a loop of wire and a magnet. experiment When he moved the magnet through the loop of wire, an electric current was

produced in the wire. In previous experiments, he had generated electricity by using homemade batteries, but the magnet experiment was different. Moving a magnet through the wire loop was enough to produce an electric current in the wire, without using the chemical reactions of his homemade batteries. The opposite was also true. When Faraday rotated a wire through a magnetic field, an electric current was produced in the wire (Figure 2.8). A new experiment based on the old one

The world’s most amazing electricity generator

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NASA (National Aeronautics and Space Administration) has conducted a modern version of Faraday’s electromagnetism experiments. In simple terms, Earth is like a giant magnet. Magnetic field lines extend out from Earth into space. What would happen if Faraday’s experiment were performed in space? What if you dragged a wire through Earth’s magnetic field? Could an electric current be produced in the wire? This became an important mission for the space shuttle in 1996 (Figure 2.9). NASA scientists worked with Italian scientists to design equipment for the experiment. They made a special satellite and connected it to the space shuttle with over 20 kilometers of a special insulated copper cable. As the shuttle orbited Earth, scientists released the tethered satellite and conducted 12 different experiments while dragging the cable through Earth’s magnetic field at speeds over 15,000 miles per hour! The satellite was equipped with many instruments to study the electricity generated in the cable. As the cable cut through Earth’s magnetic field, 3,500 volts of electricity was produced, and a current of 0.5 amperes was generated. Faraday’s experiment worked in outer space! Unfortunately, the tether broke during the experiment and the satellite was lost, but not before scientists gathered enormous amounts of interesting data.

Figure 2.8: Electric current is created when a coil rotates in a magnetic field.

Figure 2.9: NASA’s tethered satellite experiment from shuttle mission STS-75. An electric current was created when the cable was dragged through Earth’s magnetic field.

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Section 2.2 Review

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1. Why is experimentation so important to science?

Science and Serendipity

2. Why is it important, in an ideal, simple experiment, to change only one variable from trial to trial?

Not all discoveries in science are made using the scientific method! In fact, many important new discoveries and inventions happen by trial and error, a lucky experiment, or by accident. The word serendipity describes an event during which a valuable discovery is made by accident.

3. What is the difference between an experimental variable and a control variable? Give an example to explain your answer. 4. You are planning an experiment to find out which detergent is the best at removing grass stains from cotton fabric. Think about how you might do this experiment and what kinds of variables are involved. Make a list of two variables that would be a part of the experimental system and two variables that would not be a part of this system. 5. Suppose you have three drinking cups that are identical except for the material they are made of. One is made of plastic, one of foam, and one of paper. You want to find out which cup will keep your hot cocoa hot for the longest time. a. Phrase a formal question for this experiment. b. What is your hypothesis? c. What is the experimental variable? d. What are three important control variables? e. What type of evidence will you collect to test your hypothesis? f. Challenge: Conduct your experiment and summarize your findings. 6. Think of an experiment you did in a past science class. a. Describe the experiment. b. What was the experimental variable? c. What were two control variables? d. What was the outcome of the experiment?

1. Describe a situation in which you made a serendipitous discovery. 2. Think about an object that you use every day. Find out how it was invented. Was this invention the result of serendipity? Why or why not?

For Question 5, predict what a graph or graphs of the data you collect would look like. Sketch the graph or graphs. The graph(s) should support the hypothesis you made in 5b.

7. Water in an open container will eventually evaporate. Do all liquids evaporate at the same rate? Suppose you conduct an experiment to see how quickly water, rubbing alcohol, and nail polish remover evaporate. Describe three important techniques you will have to follow to make sure your experimental procedure is repeatable and objective. 2.2 EXPERIMENTS AND VARIABLES

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2.3 The Nature of Science and Technology Science is a way of knowing that is based on evidence, logic, and skepticism. The purpose of scientific study is to learn about our natural world. Technology is a way of using scientific knowledge to create devices, such as mobile phones and medical instruments, which meet needs and solve problems. Science and technology are closely related, as you will see in this section.

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Ethical traditions Truthful Scientists all over the world conduct experiments every day, in colleges and reporting universities, in industry, and for government agencies. Truthful reporting is

the most important tradition of science. When scientists collect data, organize it, report it, and write about their results and conclusions, they must be unbiased and honest in their communication. Scientific How do scientists communicate their findings? Often, scientists write a journals and report about their experiments and submit it to a scientific journal. A peer review scientific journal is a publication, like a magazine, that comes out on a

regular basis. There are hundreds of major scientific journals in print. Before a paper is published in a scientific journal, the work is reviewed by peers. Only if the work is approved by independent scientists can the paper be published. Science news Scientific journals can be very technical, and cannot be read like an ordinary for everyone magazine. Other periodicals such as Popular Science or Scientific American

are also published. Their articles are less technical. They are selected from the thousands of papers that are published each month in scientific journals. These magazines are not scientific journals, but they are good sources of current science research findings. Daily news broadcasts on television, radio, and the Internet also carry headlines about recent scientific discoveries. Sometimes these headlines are unintentionally misleading, because they are just quick summaries of technical research explanations. Keep this in mind when you hear science news “sound bytes.” Remember, good science is always repeatable, reliable, based on evidence, and unbiased.

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Scientific Journals Perhaps you are keeping a journal for your science class. Your science journal can contain notes, thoughts, reflections, scientific data, experimental procedures, tables, graphs, and lab reports. A scientific journal is a specific kind of publication that is different from a science journal you might create in class. A scientific journal is a periodical publication that contains the results and conclusions of many different experiments. All of the papers (you might think of them as articles) submitted to a scientific journal must be reviewed by peers and accepted before they are published. Have you heard of any of these scientific journals? • • • • • •

Nature Science Proceedings of the National Academy of Sciences Journal of the American Medical Association Journal of the American Chemical Society Advances in Physics

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Science and technology Inventions solve You are surrounded by inventions, from the toothbrush you use to clean your problems teeth to the computer you use to do your school projects (and play games).

Where did these inventions come from? Most of them came from a practical application of scientific knowledge.

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What is Science helps us understand the natural world. Technology is the application technology? of science to meet human needs and solve problems. All technology—from

the windmill to the supersonic jet—arises from someone thinking, “There must be a better way to do this!” Although technology is widely different in the details, there are some general principles that apply to all forms of technological design or innovation. People who design technology to solve problems are called engineers. Scientists study the natural world to learn the basic principles behind how things work. Engineers use scientific knowledge to create or improve inventions that solve problems.

technology - the application of science to meet human needs and solve problems. engineer - a professional who uses scientific knowledge to create or improve inventions that solve problems and meet needs.

GPS Technology GPS stands for Global Positioning System. A GPS receiver can determine its position to within a few meters anywhere on Earth’s surface. How does this work? How does the GPS receiver “know” its position? There are 24 satellites in orbit around Earth that transmit radio signals as part of a global navigation system. The satellites are in the sky, all transmitting their unique codes and locations. At any given time, a GPS receiver can receive signals from 6 to 11 of these 24 satellites. A GPS receiver determines its own position on Earth by comparing the signals from four different GPS satellites.

2.3 THE NATURE OF SCIENCE AND TECHNOLOGY

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Engineering A sample Suppose you are given a box of toothpicks and some glue and are told to engineering build a bridge that can support a brick without breaking. After doing problem research, you come up with an idea for how to make the bridge. Your idea is

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to make the bridge from four structures connected together. Your idea is called a conceptual design.

prototype - a working model of a design that can be tested to see if it works.

engineering cycle - a process used to build and test devices that solve technical problems.

The importance You need to test your idea to see if it works. If you could figure out how of a prototype much force it takes to break one structure, you would know if four structures will hold the brick. Your next step is to build a prototype and test it. Your

prototype should be close enough to the real bridge so that what you learn from testing the prototype can be applied to the actual bridge. Testing the You test the prototype by applying more and more force until it breaks. You prototype learn that your structure (called a truss) breaks at a force of 5 newtons. The

brick weighs 25 newtons. Four trusses are not going to be enough. You have two choices now. You can make each truss stronger by using thread to tie the joints. Or, you could use more trusses in your bridge (Figure 2.10). The evaluation of test results is a necessary part of any successful design. Testing identifies potential problems in the design in time to correct them.

EVA

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keep testing them until they are successful under a wide range of conditions. The process of designing, prototyping, testing, and evaluating is the engineering cycle. The best inventions go through the cycle many times, being improved after each cycle until all the problems are worked out.

Engineering cycle

YPE OT

Changing the If you decide to build a stronger structure, you will design and need to make another prototype and test it again. testing again Good engineers often build many prototypes and

Figure 2.10: By testing the

prototype, you find out if it is strong enough. Testing often leads to an updated design, such as this one of a bridge that uses more trusses.

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Section 2.3 Review 1. Why are scientific journals such as Nature and Journal of the American Medical Association extremely important to scientific progress?

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2. Suppose a scientist conducts a series of experiments and the results are so amazing she wants to share them with other experts in the field. Why would it be risky for her to make the results public on her own website before publishing them in a scientific journal? 3. Identify whether each item below is an example of science or technology. a. digital music player b. Newton’s laws of motion c. atomic theory d. windmill e. universal law of gravitation f. GPS g. biochemistry h. maglev train 4. Discuss what might happen if an automobile manufacturer began making and selling cars based on a prototype that went through only one engineering design cycle.

Magnetic Levitation In the previous section, you read about Michael Faraday’s experiments with electromagnetism. A powerful new technology based on Faraday’s experiments is currently in development. Magnetically levitated, or maglev, train technology uses electromagnetic force to lift a train a few inches above its track (see the figure below). By “floating” the train on a powerful magnetic field, the friction between wheel and rail is eliminated. Maglev trains can reach high speeds using less power than an ordinary train. In 2003, a Japanese prototype three-car maglev train carrying 12 people reached a record speed of 360 miles per hour! Maglev trains are now being developed and tested in Germany and the United States. Many engineers believe maglev technology will become the standard for mass transit systems over the next 100 years. Perhaps someday you will commute to work on a maglev train!

A maglev train track has electromagnets in it that both lift the train and pull it forward. See the Technology box in the sidebar.

2.3 THE NATURE OF SCIENCE AND TECHNOLOGY

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Chapter 2 Assessment Vocabulary

Section 2.2

9.

Select the correct term to complete the sentences.

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control variable

experimental variable

prototype

deduce

hypothesis

repeatable

engineer

inquiry

scientific method

engineering cycle

natural laws

technology

experiment

objective

theory

experimental technique

procedure

trials

Section 2.1

1. 2.

To ____ is to figure something out from known facts using logical evidence. A scientific explanation supported by lots of evidence collected over a long period of time is a(n) ____.

When you run an experiment multiple times, you conduct several ____.

10. The thing you are testing (changing) in an experiment is the ____. 11. Something you keep the same from trial to trial in an experiment is called the ____. 12. A step-by-step account of all that you do when conducting a particular experiment is called the ____. 13. The way you release a cart on a ramp while conducting an experiment is an example of ____. 14. A(n) ____ is a situation specifically set up to investigate relationships between variables. Section 2.3

3.

Scientific evidence that is ____ can be seen by others if they repeat the same experiment in the same way.

15. A(n) ____ is a working model of a design that can be tested to see if it works.

4.

Learning by asking questions and seeking the answers is called ____.

5.

A(n) ____ is a possible scientific explanation that can be tested by comparison with scientific evidence.

16. A process used to build and test devices that solve technical problems is ____.

6.

____ evidence describes only what actually happened in an experiment as exactly as possible.

7.

Scientists believe the universe follows a set of “rules” known as ____.

8.

The ____ is a process of learning that begins with a hypothesis and proceeds to collect evidence to confirm or disprove the hypothesis.

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17. ____ is the application of science to meet human needs and solve problems. 18. A professional who uses scientific knowledge to create or improve technology is a(n) ____.

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Concepts

7.

1.

Explain the difference between a theory and a hypothesis.

2.

For each example, write whether it could be considered scientific evidence (S) or not (N).

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a. b. c. 3.

Indicate which of the following hypotheses are testable and scientific (S) and which are not (N). a. b. c.

4.

_____ An artist’s watercolor painting of an oak leaf _____ The time for a car to drive once around a track _____ The number of each different color of candy-coated chocolate in a bag of candy

_____ Your brain produces undetectable energy waves. _____ Life forms do not exist in other galaxies. _____ Earth completes one rotation every 24 hours.

A student designs an experiment and gets favorable results after one trial. The student should a. b. c. d.

write a paper and publish the results. redesign the experiment to get more-favorable data. repeat the experiment several times to verify the results. form a new experiment that supports a related hypothesis.

Explain the difference between experimental variables and control variables.

6.

What is the difference between experimental technique and procedure? Give an example to support your explanation.

the experiment is a failure. the results are of no use. the design of the experiment was bad. the data may be useful, but further testing and redesign of the experiment may be needed.

Section 2.3

8.

Science and technology are related, but they are not the same. What is the difference?

9.

Scientist and engineer are two different career options. How does their work differ?

Problems Section 2.1

1.

Suppose you turn on your digital music player and it doesn’t work. Describe how you could use the scientific method to figure out what’s wrong.

Section 2.2

2.

Design an experiment using a ruler, a stopwatch, a tennis ball, a 1-meter long piece of string, a rubber band, tape, and 10 pieces of paper. Document a question, a hypothesis, the independent variable, the dependent variable, the control variables, and the procedure for your experiment.

3.

A botanist wants to understand if exposure to St. John’s wort, a flowering roadside plant, causes skin irritation. In this experiment, several types of plants, including St. John’s wort, are rubbed onto the arms of 10 volunteers. A skin rash develops in all 10 individuals. Can the scientist clearly say that St. John’s wort causes skin irritation? Why or why not? Identify any variables and state any changes that could be made to make this experiment more valid.

Section 2.2

5.

After testing, a hypothesis appears to be false. This indicates that a. b. c. d.

Section 2.1

CHAPTER 2 ASSESSMENT

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4.

THE SCIENTIFIC PROCESS

Monique wants to see what happens when she drops a marble from different heights into a baking tray that has a thick layer of very soft modeling dough pressed inside. She predicts that the closer the marble is to the dough when she drops it, the deeper the marble’s indentation will be.

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a. b. c. d. e. f.

Applying Your Knowledge 1.

Write a caption for the illustration below. Your caption should include one or more vocabulary terms from the chapter that best describe the illustration.

What is Monique’s hypothesis? What is the experimental variable? What are two control variables? What evidence will be collected? Write a step-by-step procedure for the experiment. Do you think the data Monique collects will confirm or disprove her hypothesis? Explain your reasoning.

Section 2.3

5.

You have an idea for making a homemade shoe that will allow you to walk on open egg cartons without crushing any eggs. How could you use the engineering cycle to design and test your idea?

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CHAPTER

3

CHAPTER 3

Mapping Earth FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

According to archaeologists, mapmaking is thousands of years old. The early maps are rough but show amazingly accurate drawings of surroundings. Some of the earliest known maps showed hunting and fishing areas with detailed drawings. Mapmaking is also known as cartography. Early European cartographers were often painters and other artists. In the past, cartography was considered more of an art than a science. Now, thanks to sophisticated measuring devices, computers, and satellites, cartography is truly a science. One thing that hasn’t changed is the importance of and the need for maps. A picture really is worth a thousand words when it comes to finding your way.

4 What is the prime meridian? 4 What does the topographic map of a mountain look like?

4 How are bathymetric maps made?

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MAPPING EARTH

3.1 Position, Coordinates, and Maps

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Where are you right now? You could answer that question by saying, “In my classroom” or “At my desk.” Someone might then ask where your classroom or desk is located. To answer the question precisely, you can use the concepts of position, coordinates, and mapping. These ideas can be used to describe the location of ordinary objects, such as cars, bicycles, and people. They can also describe the location of tiny objects, such as atoms, and the location of enormous objects, such as planets and stars. Let’s begin by studying the position variable.

position - a variable that tells location relative to an origin.

origin - a place where the position has been given a value of zero.

The position variable Position as You might do an experiment that uses a car on a track. How do you tell a variable someone exactly where the car is at any given moment? You can do this by measuring the car’s position. Position is a variable. The position of the car

describes where the car is relative to the track. In the diagram below, the position of the car is 50 centimeters (cm). This means the center of the car is at the 50 cm mark on the track. Figure 3.1: If the car moves 20 cm to the right, its position will be 70 cm.

Position and Position and distance are similar but not the same. Both use units of length. distance However, position is given relative to an origin. The origin is the place

where position equals 0 (near the left end of the track above). Here’s an example of the difference between position and distance. Assume the track is 1 meter long. Suppose the car moves a distance of 20 cm away from the 50 cm mark. Where is it now? You know a distance (20 cm) but you still don’t know where the car is. It could have moved 20 cm to the right (Figure 3.1) or 20 cm to the left (Figure 3.2). Saying the car is at a position of 70 cm tells you where the car is. A position is a unique location relative to an origin.

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Figure 3.2: If the car moves 20 cm to the left, its position will be 30 cm.

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CHAPTER 3

Vectors and position

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Telling the difference between “in front” and “behind”

How can you tell the difference between one meter in front of you and one meter behind you? The variable of distance is not the answer. The distance between two points can only be positive (or zero). You can’t have a negative distance. For example, the distances between the ants in Figure 3.3 are either positive or zero. Likewise, 1 meter in front of you and 1 meter behind you both have the same distance: 1 meter.

vector - a variable that gives direction information included in its value.

Using positive The solution is to use position, which allows positive and negative numbers. and negative In the diagram below, positive numbers describe positions to the right (in numbers front) of the origin. Negative numbers are to the left (or behind) the origin.

Figure 3.3: Distance is always a positive value or zero.

Vectors Position is an example of a kind of variable called a vector. A vector is a

variable that tells you a direction as well as an amount. Positive and negative numbers provide enough information for a variable when the only directions are forward and backward. When up-down and right-left are also possible directions, vectors get more complicated. Mars Pathfinder The Mars Pathfinder is an unmanned spacecraft launched in 1996. Pathfinder mission and its robot, called Sojourner, landed on one of the ancient floodplains of

Figure 3.4: Sojourner, the robotic rover for Pathfinder.

Mars (Figure 3.4). Sojourner collected data about the climate, atmosphere, and geology of Mars. Information collected by scientific instruments on both the lander and Sojourner suggest that Mars was once warm and wet, with liquid water and a thicker atmosphere than it has now. Sojourner used As it moved, Sojourner needed to keep track of its position. The robot used vectors speed and time data to calculate the position vector, and then added up

position vectors to come up with a final position. If it moved forward +2 meters and then backward –0.8 meters, its final position would be +1.2 meters. In this way, Sojourner kept track of each move (Figure 3.5).

Figure 3.5: Each change in position is added up using positive and negative numbers.

3.1 POSITION, COORDINATES, AND MAPS

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Maps and coordinates Two dimensions If Sojourner had been crawling on a narrow, straight board, it would have

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had only two choices for direction: positive, or forward, and negative, or backward. Out on the surface of Mars, Sojourner could also turn and go sideways. The possible directions included north, east, south, west, and anything in between. A flat surface has two dimensions. We say two because it takes two lines of direction to describe every point (Figure 3.6).

axis - one of two (or more) number lines that form a graph.

coordinates - values that give a position relative to an origin.

map - a representational drawing of a location.

North, south, One way to describe two dimensions is to use number lines, or axes. One east, and west axis goes north–south. Positive positions are north of the origin and negative

positions are south. The other axis goes east−west. Positive positions on this axis are east of the origin and negative positions are west. Sojourner’s exact position at any given time can be described with two numbers. These numbers are called coordinates. The graph at the left shows Sojourner at the coordinates of (4, 2) m. The first number (or coordinate) gives the position on the east−west axis. Sojourner is 4 m east of the origin. The second number gives the position on the north−south axis. Sojourner is 2 m north of the origin.

Coordinates describe position

Figure 3.6: A flat surface has two perpendicular dimensions: north−south and east−west. Each dimension has positive and negative directions.

Maps A graph using north−south and east−west axes can accurately show where

Sojourner was. The graph can also show any path Sojourner took, curved or straight. This kind of graph is called a map. Many street maps use letters on the north−south axis and numbers for the east−west axis. For example, the coordinates F-4 identify the square that is in row F, column 4 of the map shown in Figure 3.7. A popular way to present a map of the world is to use a globe, as you will see on the next page.

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Figure 3.7: Street maps often use letters and numbers for coordinates.

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CHAPTER 3

Position on a globe A model of Earth A globe is a model of Earth. Looking at a globe, you can see the oceans and

continents on Earth’s surface. Because a globe is a sphere, Earth’s land masses are represented accurately. Key features of a globe are shown below.

globe - a map of Earth that models its shape and the locations and relative sizes of oceans and continents.

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EarthaTM—the World’s Largest Revolving and Rotating Globe EarthaTM, the world’s largest revolving and rotating globe, is located in Yarmouth, Maine, at the DeLorme headquarters (a company that makes maps). If you go to DeLorme’s headquarters, you can see EarthaTM in its three-story glass room. The globe’s diameter is 41 feet 1.5 inches (0.01 km). The diameter of our planet is 12,756 km. How much bigger is Earth compared to EarthaTM; 10 times, 1,000 times, or 1 million times bigger?

How is a A simple classroom globe is relatively easy to manufacture. First, flat, round globe made? maps of the northern and southern hemispheres are glued to cardboard

backings. The cardboard hemisphere circles are cut into pinwheel-like shapes then glued onto dome-shaped molds (Figure 3.8). Once the two hemispheres are shaped, they are glued together and the seam is covered with tape. The tape hides the seam and also shows exactly where the equator is located on the model.

Figure 3.8: You can cut a flat paper map to form it into a hemisphere for a globe.

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Latitude What are those Horizontal and vertical lines on a globe or map form a grid that is useful for lines? identifying the location of any place on our planet. Let’s first look at the most

well-known horizontal line—the equator. The equator The equator is an imaginary line around Earth’s middle that lies between

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

the North and South Poles. Earth’s equator is 40,075.0 kilometers (24,901.5 miles) long. Places located at or near the equator experience about 12 hours of daylight and 12 hours of night every day of the year.

equator - an imaginary line around Earth’s middle; lies between the North and South poles.

latitude - east–west lines that are north or south of the equator.

Latitude lines The equator is a line of latitude. Latitude lines appear horizontal on a map.

They are east–west lines that are north or south of the equator (Figure 3.9). Lines of latitude are also called parallels. The equator is at 0° latitude. Degrees, Each line of latitude represents one degree on Earth’s surface. The average minutes, and distance between each degree is 111 kilometers (69 miles). Each degree is seconds divided into 60 minutes and each minute is divided into 60 seconds. Minutes

and seconds in this context represent distances, not time! The latitude of the equator is written as 0° 0' 0". Minutes are indicated by an apostrophe (') and seconds are indicated by a double apostrophe ("). Latitude lines The equator is one line of latitude you know about. Other latitude lines that with names you may have heard of are listed below. Can you find these on a globe? Name of latitude line Arctic Circle Tropic of Cancer Tropic of Capricorn Antarctic Circle

Figure 3.9: Latitude lines.

Approximate location 66.5° N 23.5° N 23.5° S 66.5° S

How latitude Following is the process used to draw latitude lines on a globe. First, draw a lines are drawn line from the North Pole straight down to the equator so you have a line that

forms a 90-degree angle with the equator (Figure 3.10). Next, draw 30- and 60-degree angles between the equator and the North Pole. Finally, draw lines parallel to the equator along these measured angles. These are the 30-degree north and 60-degree north latitude lines. The same process is used to draw latitude lines south of the equator.

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Figure 3.10: How latitude lines are drawn.

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Longitude Prime meridian Longitude lines (or meridians) run north–south and are east or west of the prime meridian, which is an imaginary line that passes through Greenwich,

England, and is perpendicular to the equator. The prime meridian is the 0° line of longitude (Figure 3.11).

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

The The international date line is an imaginary longitude line located mainly at international 180°. Each new day begins at 12:00 a.m. at this line. As a result, you lose a date line day when you travel east across the line. For example, just before you cross

the line it might be 3:00 p.m. on Sunday, but when you cross it, the time is 3:00 p.m. on Monday! If you travel westward across the line, you gain a day. Since this situation can be confusing, the international date line zigzags to avoid crossing through countries or territories.

longitude - north–south lines that are east or west of the prime meridian. prime meridian - an imaginary line through Greenwich, England, and perpendicular to the equator; 0° longitude.

international date line - an imaginary longitude line located at 180° from the prime meridian.

Time zones For every 15° of longitude past the international date line, time changes by

one hour. For example, when it is 2:00 p.m. at the international date line, it is noon in Sydney, Australia (about 30° west of the line).

Longitude labels Longitude lines east of the prime meridian are numbered from 1 to 179 degrees

east, while lines west of the prime meridian are numbered from 1 to 179 degrees west. The 0- and 180-degree lines are not labeled east or west.

Figure 3.11: Longitude lines.

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Projections Globes On a globe, you can see how the size of Greenland compares to the size of

South America (Figure 3.12). Greenland is much smaller. But, look at the map below. On this flat map, Greenland looks larger than South America. Why does it appear that way?

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From a globe People often prefer flat maps to globes, but it is difficult to accurately take a to a flat map three dimensional (3-D) object like Earth and display it on a two dimensional

(2-D) map. When you project Earth’s surface onto a flat map, you end up with some degree of distortion in distance, direction, scale, or area. To show grid lines accurately on a two-dimensional map, map makers have to distort the sizes of the landforms and oceans. Different methods of representing Earth’s surface on a two-dimensional map are called projections. There are dozens of different projections, and each group of map-users has a favorite. Mercator A Mercator projection is a popular map-making method that converts a projection section of a globe to a rectangular, flat map. A Mercator projection map

shows a section of the world as though it were projected on a cylinder. Mercator projections are most accurate where the cylinder touches the globe, which would be at the equator. This is why landforms and oceans are more accurate in size and shape near the equator, while landforms and oceans near the poles are distorted and appear much larger than they actually are. Mercator projection Converting a 3-D map to a 2-D map

Figure 3.12: The image above shows Greenland

how the size of Greenland compares to the size of South America in reality and on a globe.

South America

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Features of maps legend - a special area on a map that lists and explains the symbols that are used.

Direction On maps, there is usually a symbol that symbols indicates direction—north, south, east, and

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west. An example of this direction symbol is shown at the right. Sometimes only the arrow pointing north is shown. Map legends Maps usually have a legend that lists and explains the symbols that are used

on the map. For example, the legend on a globe might include special lines to indicate the boundaries between countries, and circles of different sizes to represent the population sizes of cities. A legend on a road map might include special lines to indicate different kinds of roads (Figure 3.13) and the locations of places of interest, such as parks, airports, and hospitals. Scale of maps The scale of a map helps you relate the distances on the map to the larger,

real-life distances. There are three kinds of map scales. A fractional scale shows the ratio of the map distance to the real-life distance as a fraction. The scale 1/100,000 means that one unit on the map is equal to 100,000 units in real life. A verbal scale expresses the relationship in words, for example, “1 centimeter is equal to 1 kilometer.” A bar scale is simply a bar drawn on the map with the size of the bar proportional to a distance in real life. Types of map scales Fractional 1/100,000

Verbal 1 cm = 1 km

Bar 0

1

2

3

4

5

kilometers

What type of scale does the map in Figure 3.13 have? You are correct if you answered “bar scale.” This scale is shaded in increments of 10 miles. If a road map contains an inset portion to show details of a certain area, be aware that the scale for that portion of the map will probably be different from the scale for the part of the map that covers a wider area.

Figure 3.13: A road map with a legend and a scale.

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Section 3.1 Review 1. What is the difference between distance and position? 2. From an origin, you walk 3 meters east, 7 meters west, and then 6 meters east. What is your position now?

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3. A globe is a more accurate map of the sizes and shapes of landforms on Earth’s surface than a flat, paper map. Why?

The location of the Tropic of Cancer is 23.5° N. How far is the Tropic of Cancer from the equator? Use this conversion factor: one degree latitude = 111 km

4. What is the difference between latitude and longitude lines? 5. How is the prime meridian like the equator? 6. How is the prime meridian different from the equator?

STUDY SKILLS

7. Give the degree location for the international date line.

Remembering the definitions of terms is an important task in science. One way to make this task easier is to come up with a unique way to remember them.

8. You can find Omaha, Nebraska, at 41° 18' north and 95° 54' west. You can find Poughkeepsie, New York, at 41° 38' north and 73° 55' west. Are Poughkeepsie and Omaha near the same line of longitude or near the same line of latitude? 9. What is a Mercator projection? 10. Answer the following questions using the map below. a. Using only two-lane roads, how many kilometers is it from point A to point B? b. Which point is the furthest east on the map—A, B, C, or D? c. Which of the map locations would be most likely to have few or no cars—A, B, C, or D?

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For example, can you think of a way to remember the difference between latitude and longitude? Give it a try! Suggestions: Latitude lines are like the rungs on a ladder (ladder and latitude both start with la-). Longitude lines run the long way from one pole to the other.

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3.2 Topographic Maps Is it possible to show a mountain on a flat map? In this section, you will learn about special map lines called contour lines that show mountains and other land features. Relief maps and topographic maps are used to show mountains and valleys.

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Relief and elevation Relief Relief describes the distance between high and low places on a map. Shaded

relief maps (see below) show mountains and other land features using bumps and colors. In the map below, the western edges of North and South America have bumpy, dark-orange ridges indicating mountain ranges.

Elevation The high, low, and flat places on Earth’s surface can be further described using numbers. Elevation is the height of an object measured from a reference level, usually sea level. Sea level is the average level of the

ocean (Figure 3.14). The highest mountain on Earth is Mt. Everest in Nepal, with an elevation of 8,850 meters. The highest mountain in North America is Mt. McKinley in Alaska, with an elevation of 6,194 meters. The lowest point on land is the Dead Sea shore at 417.5 meters below sea level. The lowest point in North America is Death Valley, California, at about 86 meters below sea level.

relief - the distance between a high and low place on a map.

elevation - the height of an object measured from a reference level such as sea level.

sea level - the average level of the ocean; the halfway point between high tide and low tide.

Figure 3.14: Elevation and sea level. You might know that oceans experience tides—sea level is the halfway point between high tide and low tide.

3.2 TOPOGRAPHIC MAPS

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What is a topographic map? Mapping the Bumps or ridges can show mountains on a map. But to know exactly how height of a high a mountain is, the best kind of map to look at would be a topographic mountain map. A topographic map (or topo map for short) is a map that uses

contour lines to show elevation.

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Contour lines Contour lines indicate all points where the elevation is the same. The zero

contour line on a topo map indicates all the points on the map that are at sea level. A 100-meter contour line indicates points that are 100 meters above sea level (Figure 3.15). Contour lines also show the slope of land. Slope (also called gradient) is a measure of how steep land is. Legends for The legends for topo maps (and other maps) use a range of symbols to show topographic rivers and lakes, roads, railroad tracks, airports, types of vegetation, maps buildings, and many other things.

topographic map - a map that uses contour lines to show elevation.

contour lines - curved lines on a map that indicate all the points where the elevation or depth is the same.

slope - a measure of how steep land is; also called gradient.

Topographic map 100 m

100 0 Sea level

National Map The United States Geological Survey (USGS) publishes about Accuracy 57,000 topographic maps of the United States. These maps are drawn Standards according to the National Map Accuracy Standards. The standards define

accurate measurements for mapmaking so that any map you read can be compared to another map. What are some uses of topographic maps?

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Topographic maps are very useful for emergency responders. When a search and rescue team plans a mission, the team members must use topo maps to help them become familiar with the area, particularly if the terrain is rugged and unpopulated. Topo maps are also useful for hiking, orienteering, scientific research, and outdoor resource management.

Figure 3.15: The 0 contour line is

always at sea level. A 100-meter contour line shows all places on the map where the elevation is exactly 100 meters above sea level.

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Making a topographic map Drawing contour To understand how contour lines relate to the shape of a land form, imagine lines that you have a three-dimensional form in a box. The form represents an

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island. You pour water into the box to a starting level that represents sea level or the 0-meter contour line. By adding more water to the box, the edges of the island get covered. If you look down at the form from above, you will see the shape of the island at an elevation of 10 meters (Figure 3.16).

What does the Figure 3.16 illustrates how contour lines are used to make a topographic map. map look like? The 0 contour line shows the outline of the island at sea level. At the 10-meter

mark, the outline of the island is smaller and lies inside the 0-meter contour. Only the highest of the two peaks is shown on topographic map 3. The second peak is less than 40 meters high but taller than 30 meters. A contour line at 35 meters would be needed to see this peak. Showing the The spaces between the 0-, 10-, and 20-meter contours are wider on the right slope of land side of the map than on the left. This shows that the right side of the island is

not as steep as the left side. When contour lines are close together, you know that the land is steep. When contour lines are farther apart, the land is not as steep—it slopes gradually. Using a When you look at a mountain trail map that has contour lines, you can quickly topographic evaluate the difficulty of a hiking trail if you know how to read the map. If map for hiking you have to choose between two trails to a summit, and you want an easier

Figure 3.16: Drawing contour lines

to make a topographic map. Note that the space between the 10- and 20-meter contour lines is narrower on the left than the right. This shows that the left side of the island is steeper.

climb, pick the trail that crosses contour lines that are more widely spaced. 3.2 TOPOGRAPHIC MAPS

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Technology and making a topographic map The birth of In 1879, the United States Geological Survey (USGS) was created by an act the USGS of the U.S. Congress. The USGS was given the task of mapping public lands.

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Early employees of the USGS had to travel to places that were often difficult to reach in order to carry out this task. Their means of transportation was often a team of pack mules. Plane table Of course, mapmakers in the 1800s surveying did not have computers, electronic

equipment, or airplanes to help them make their maps. They used a technique called plane table surveying. A plane table is a horizontal table on a tripod. From the plane table, a surveyor uses a viewing instrument to gauge the height of land at a particular distance. To help with measurements of elevation, another surveyor holds up a tall measuring stick at the area being measured. This technique was used up until the 1970s. Topographic Starting in the 1940s, scientists began using aerial photographs and other mapping today techniques to make topographic maps. Today, scientists have computers,

electronic devices, and airplanes to help them make maps. Although these tools make it easier to draw an accurate map, it is still a complex process. Today, overlapping aerial photographs are used to create a 3-D image of an area. Special software, computer technology, and stereo glasses are used to make topographic maps (Figure 3.17).

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Figure 3.17: A pair of aerial

photographs is used to make a 3-D image that can be translated into a topographic map. Stereo glasses allow the mapmaker to see 3-D images.

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Section 3.2 Review 1. House A is located at 100 meters above sea level. House B is located at 350 meters above sea level. a. What is the elevation of House B? b. What is the relief between House A and House B?

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

2. How is elevation related to sea level? What is sea level? 3. True or false: Contour lines are lines on a map that show locations of equal relief. If this statement is false, rewrite it to make it true. 4. On a topographic map, what clue tells you that the land has a very steep slope?

Mapping Challenges 1. Make a map that includes a legend and a scale. Your map can be of your town, school, street, or home. 2. Find a map (in a book or atlas) that has a legend and a scale. Write directions for getting from one place to another, using real-life measurements (miles or kilometers) and indicating landmarks along the way.

5. Match each island (A, B, and C) with its topographic map. 6. The scale of a topographic map is 1:24,000, which means one centimeter on the map equals 24,000 centimeters on land. How many kilometers is 24,000 centimeters? 7. What does a scale of 1:500,000 mean on a topographic map? 8. The most common type of topographic map created by the USGS is a 7.5 minute by 7.5 minute quadrangle map (Figure 3.18). This means that each side of the map is 7 minutes and 30 seconds. Each minute of latitude is 1,852 meters and each second of latitude is 31 meters. How many meters does this map cover in a north-south direction?

Figure 3.18: Question 8. These blue contour lines represent the elevation of ice on the mountain top!

3.2 TOPOGRAPHIC MAPS

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3.3 Bathymetric Maps

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You just learned how mountains and valleys on land are represented on a topographic map. Mountains and valleys also occur on the bottom of the ocean. A bathymetric map shows the depths of a body of water, such as an ocean, and indicates mountains and valleys where the water is shallower or deeper. Imagine if all the water was drained out of an ocean, and then a map was drawn of how the ocean bottom looks. That’s what a bathymetric map (bath map for short) shows.

bathymetric map - a map that shows the depths of a body of water such as a lake or an ocean.

Showing depth Contour lines As with elevation, the depth of a body of water is compared to sea level.

Bathymetric maps often use contour lines to show depth. Look at Figure 3.19. Can you tell which part of the lake is deepest? Keep in mind that the numbers you see in this graphic are meters below sea level! Using color Color is also used to show depth in a lake or an ocean. In the image below,

shallow areas are light blue and deep areas are darker blue. Find the long undersea mountain chain in the middle of the North Atlantic Ocean. This is called the Mid-Atlantic Ridge. You’ll learn more about this ridge in a later chapter.

Figure 3.19: A bathymetric map of a lake. Where is the deepest part of the lake? Where is the shallowest part?

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Technology and making bathymetric maps How do you A bathymetric map is a map that shows a body of water with all the water map the bottom missing. You can’t drain all the water out of an ocean or a lake. So, how do of the ocean? scientists make bathymetric maps?

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

How deep is The average ocean depth is 3,711 meters (12,175 feet) and the deepest place the ocean? of all is the Challenger Deep in the Mariana Trench (located in the Pacific

Ocean, near Guam) which is 10,923 meters (35,838 feet). Scientists measure these depths using a technology called echo sounding or sonar.

Echo sounding Echo sounding uses sound waves to measure the distance to the bottom of

a body of water. A device on a ship sends sound waves outward from the bottom of the ship (Figure 3.20). The sound waves “echo” off the ocean floor. The time it takes for the echo to return to the ship and the speed of sound in water are used to calculate the depth of the ocean in that location. The combined data for many areas can be used to map the ocean floor (Figure 3.21).

Figure 3.20: Echo sounding.

Nautical charts Nautical charts are important tools for

people who are interested in navigating bodies of water. The nautical chart to the right shows a harbor of Puerto Rico. Land is indicated in yellow and water in blue. The contour lines on the yellow region show elevation on land. The contour lines in the blue region show depth of the water. Depths at single locations are indicated by numbers.

Figure 3.21: A bathymetric map of

the ocean floor. Color is used to show elevation and depth. The islands are green and mountains on these islands are yellow. The deep Puerto Rico Trench is purple and the other parts of the ocean floor are bright blue. See if you can find this location on a globe!

3.3 BATHYMETRIC MAPS

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Section 3.3 Review 1. Name two ways that you could show depth on a bathymetric map. 2. Describe how sound waves are used to map the bottom of a lake. What is this technique called?

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3. Look at the bathymetric map below. a. Which region is 200 meters deep on average at its edge? b. What single feature is 4,000 meters deep on the abyssal plain? c. What is the range of depth for the region of the ocean floor called the continental rise? d. Which ocean is featured in this bathymetric map? e. Which coast of the United States is featured on this map—the east or the west coast?

Search a local or national newspaper for articles about the bottom of the ocean. Gather your articles and any other information you find into a folder. Use the facts you find to write a story about the ocean floor.

3.3 BATHYMETRIC MAPS

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Chapter 3 Assessment Vocabulary

11. The _____ is a line that is perpendicular to the equator and that represents 0° longitude.

Select the correct term to complete the sentences.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

12. You are halfway around the world from the prime meridian at the _____.

axis

bathymetric map

topographic map

coordinates

contour line

elevation

legend

map

sea level

13. A(n) _____ is list of symbols used on a map.

equator

origin

globe

Section 3.2

latitude

position

slope

14. On a mountain top, the _____ is higher than at sea level.

longitude

prime meridian

vector

international date line

relief

15. The average water level of the ocean along a coastline is called _____.

Section 3.1

16. _____ describes the distance between high and low places on a map.

1.

A variable that is described using both a number and a direction is called a(n) ____.

2.

A(n) _____ is a representational drawing of a location.

3.

Because a(n) _____ represented accurately.

4.

The x-____ is horizontal on a graph or grid.

5.

The ____ of the origin of a graph are (0, 0).

6.

The ____ is the place where position equals zero.

Concepts

7.

The _____ is a line that falls between the North and South Poles on Earth and represents 0° latitude.

Section 3.1

8.

_____ lines are imaginary, horizontal lines on Earth’s surface that run east–west and represent north and south locations.

9.

The ____ of an object is given relative to an origin.

is

a

sphere,

Earth’s

landforms

18. A flat region of land has a(n) _____ of zero. are

10. _____ lines are imaginary lines on Earth’s surface that run north–south and represent east and west locations.

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17. A(n) _____ is a map that shows the surface features of an area and shows elevation by using contour lines. 19. A(n) _____ on a topographic map shows a region of equal elevation. Section 3.3

20. A(n) _____ is a map that shows the depths of bodies of water.

1.

Are the following directions usually considered positive or negative? Write + for positive or − for negative. a. b.

____ up ____ down

e. f.

____ north ____ south

c.

____ left

g.

____ east

d.

____ right

h.

____ west

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11. How are plane table surveying and photogrammetry similar and different? Answer this question as a short paragraph.

3.

The word hemisphere means “half a sphere.” Which latitude divides Earth into the northern and southern hemispheres?

12. Look at the topographic map below.

4.

On what continent is the sign shown to the right located?

5.

Lines of latitude are parallel to which imaginary line? prime meridian international date line equator the Mid-Atlantic Ridge

6.

Fill in the blanks. All the places in Australia have _____ (north or south) latitude lines and _____ (east or west) longitude lines.

7.

If you wanted to see an accurate representation of the sizes of the continents, would you use a Mercator projection map? Why or why not?

8.

Why is a legend an important part of a map? What would happen if a map did not include a legend?

9.

A verbal scale is 1 centimeter = 1 meter. Use this information to make a bar scale that shows a distance of 4 meters.

Section 3.2

10. Label this diagram using the following terms. One term will not be used. a. slope b. relief

c. elevation d. sea level

Lake

00 88

a. b. c. d.

00 96

If you are given x-y axes coordinates of (4, 9), which axis is represented by the number 9?

8400

8800

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2.

Elevation in feet

a. b. c. d.

Where are the steepest slopes on the map? Where is the lowest elevation shown on this map? What is the lowest elevation? Where are the gentlest slopes?

Section 3.3

13. List two differences bathymetric map.

between

a

topographic

and

a

14. Briefly describe how scientists measure the depths of various parts of the ocean. 15. A topographic map of a mountain with one high peak would look most like which type of bathymetric map? a. b. c. d.

a map of a circular lake that is very deep a harbor on the west coast of the United States a long, shallow river a mountain stream

CHAPTER 3 ASSESSMENT

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Problems

6.

Section 3.1

1.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

2.

The location of the Tropic of Cancer is about 23.5° north of the equator. The location of the Tropic of Capricorn is about 23.5° south of the equator. About how far apart are these two lines of latitude in kilometers? Hint: Each degree of latitude represents 111 kilometers. When it is 4:00 a.m. at the international date line, at which longitude will a new day be beginning? a. b. c. d.

3.

4.

30° west 60° north of the equator 15° east of the international date line 60° west of the international date line

Look at the topographic map from Concepts Question 12. How many feet does each contour line represent? (Hint: Subtract 8,400 from 8,800 and divide the answer by the number of lines between these two elevations.)

Section 3.3

7.

Imagine you want to know the depth of a lake. You have a really long pole and a measuring tape. How could you use these tools to find out how deep the lake is?

Applying Your Knowledge Section 3.1

1.

Look at a globe or another kind of world map. Pick a place that you have never been. Answer the following questions.

A map is drawn with 1 centimeter equal to 2 miles.

a.

What is the name of this place?

a. b.

b.

What is its location in latitude and longitude?

c.

What hemisphere is it in—the north or the south? The east or the west?

d.

Make a hypothesis about the kind of weather that is common in this place. Justify your answer.

How many centimeters equal 10 miles? How many miles does 4 centimeters represent?

Use the world map following questions.

a.

on

the

next

page

to

answer

the

Where would you be at Lat. 0° Long. 0°—on water or on land?

b.

Through what continent does the international date line cross?

c.

Give the locations of the marked cities to the closest whole degree. Use this format for writing the locations: New York, Lat. 41° N Long 74° W. The space between each line represents 10 degrees.

Section 3.2

2.

Make a sketch that shows a topographic map of a mountain that has a very steep slope on one side and a very gradual slope on the other side.

Section 3.2

5.

The scale of a topographic map is 1:250,000, which means 1 centimeter on the map equals 250,000 centimeters on land. How many kilometers is 250,000 centimeters?

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MAPPING EARTH

CHAPTER 3

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE CHAPTER 3 ASSESSMENT

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Unit 2 Motion, Force, and Energy FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

CHAPTER 4 Motion CHAPTER 5  Force CHAPTER 6 Newton’s Laws of

Motion

CHAPTER 7 Work and Energy

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‹ Try this at home Find a toy car, a piece of cardboard, and three to five books that are nearly the same thickness. Make a ramp for the car by tilting the cardboard against one of the books. Set this up on a flat surface. Let the car roll down the ramp and see how far it goes once it leaves the ramp. Now, put a second book on top of the first to make the ramp steeper. See how far the car goes once it leaves the ramp. Using a ruler or measuring tape, record the distance the car travels. Continue stacking the books to make the ramp steeper. Does the car go farther each time? Why or why not?

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4

CHAPTER 4

Motion FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

How long can you stand perfectly still? Ten seconds? A minute? Even if you stand still, things inside your body, such as your heart and lungs, are moving. Even when you are fast asleep your body is not really at rest. The 24-hour rotation of Earth is carrying you around at several hundred miles per hour. Every 365 days, Earth completes a 584-million-mile orbit around the Sun. To make this trip, Earth (with you on its surface) is rushing through space at the astounding speed of 67,000 miles per hour! In order to understand nature, we need to think about motion. How do we describe going from here to there? The ideas in this chapter apply to all motion, whether it is a toy car rolling along a track or Earth rushing through space. Position, speed, and acceleration are basic concepts of motion we need to understand in order to understand the physical world. We will explore these concepts, and more, in this chapter.

4 How do we accurately describe our position?

4 How do we show motion on a graph? 4 What is special about the motion of falling objects?

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4.1 Speed and Velocity The term speed describes how quickly something moves. In this section, you will learn about speed and speed with direction, called velocity.

Speed FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

Calculating To calculate the speed of a moving object, you divide the distance the object speed moves by the time it takes to move. For example, if you drive 120 miles (the

distance) and it takes you 2 hours (the time), your speed is 60 miles per hour (60 mph = 120 miles ÷ 2 hours). The lowercase letter v is used to represent speed, as shown in the formula below.

speed - describes how quickly an object moves, calculated by dividing the distance traveled by the time it takes. average speed - the total distance divided by the total time for a trip.

instantaneous speed - the actual speed of a moving object at any moment.

Units for speed The units for speed are distance units over time units. If distance is in

kilometers and time is in hours, then speed is in kilometers per hour (km/h). Other SI units for speed are cm per second (cm/s) and meters per second (m/s). Your family’s car probably shows speed in miles per hour (mph). Average speed When you divide the total distance of a trip by the time taken, you get the and instantaneous average speed. Figure 4.1 shows an average speed of 100 km/h. But think speed about what happens when you are riding in a car. On a real trip, your car

will slow down and speed up. Sometimes your speed will be higher than 100 km/h, and sometimes lower (even 0 km/h). The speedometer shows you the car’s instantaneous speed. The instantaneous speed is the actual speed an object has at any moment.

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Figure 4.1: A driving trip with an average speed of 100 km/h.

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MOTION

Solving Problems: Speed

CHAPTER 4

The Speed Limit of the Universe

How far will you go if you drive for 2 hours at a speed of 100 km/h?

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

1. Looking for:

You are asked for a distance.

2. Given:

You are given the speed and the time.

3. Relationships:

speed = distance ÷ time distance = speed × time

4. Solution:

distance = (100 km/h) × (2 h) = 200 km Your turn...

The fastest speed in the universe is the speed of light. Light moves at approximately 300 million meters per second (3 ×108 m/s). If you could make light travel in a circle, it would go around the Earth 7.5 times in one second! Scientists believe the speed of light is the ultimate speed limit in the universe.

a. You travel at an average speed of 20 km/h in a straight line to get to your grandmother’s house. It takes you 3 hours to get to her house. How far away is her house from where you started? b. What is the speed of a snake that moves 20 meters in 5 seconds? c. A train is moving at a speed of 50 km/h. How many hours will it take the train to travel 600 kilometers?

a. Your grandmother’s house is 60 km away from where you started. b. The snake’s speed is 4 m/s. c. It will take the train 12 hours to travel 600 kilometers.

4.1 SPEED AND VELOCITY

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Velocity What is Recall that position is an example of a kind of variable called a vector. We velocity? use the term velocity to mean speed with direction. Velocity (Figure 4.2) is

velocity - a variable that tells you both speed and direction.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

usually defined as positive when moving forward (to the right from an outside observer), and negative when moving backward (to the left to an outside observer). The difference Velocity is a vector, speed is not. In regular conversation, you might use the between velocity two words to mean the same thing. In science, they are related but different. and speed Speed can have only a positive value (or zero) that tells you how far you

move per unit of time (like meters per second). Velocity is speed and direction. If the motion is in a straight line, the direction can be shown with a positive or negative sign. The sign tells the direction and the quantity (speed) tells you how quickly you are moving. Use two Any formula that involves speed can also be used for velocity. For example, variables to find you move 2 meters if your speed is 0.2 m/s and you keep going for the third one 10 seconds. But did you move forward or backward? You move −2 meters

Figure 4.2: Velocity can be a positive or a negative value.

(backward) if you move with a velocity of −0.2 m/s for 10 seconds. Using the formula with velocity gives you the change of position instead of distance. Word formulas

Equation d v= t

speed = distance ÷ time

velocity = distance ÷ time

distance = speed × time

distance = velocity × time

d = vt

time = distance ÷ speed

time = distance ÷ velocity

t= d v

Direction of Suppose an object moves forward at 0.2 m/s for 10 seconds. Its velocity is movement +0.2 m/s. In 10 seconds, its position changes by +2 meters.

Now, suppose the object goes backward at 0.2 m/s for 4 seconds. This time the velocity is −0.2 m/s. The change in position is −0.8 meters. A change in position is velocity × time (Figure 4.3).

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Figure 4.3: The change in position or distance is the velocity multiplied by the time.

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MOTION

Solving Problems: Velocity

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

A train travels at 100 km/h heading east to reach a town in 4 hours. The train then reverses and heads west at 50 km/h for 4 hours. What is the train’s position now? 1. Looking for:

You are asked for position.

2. Given:

You are given two velocity vectors and the times for each.

3. Relationships:

change in position = velocity × time

4. Solution:

The first change in position is (+100 km/h) × (4 h) = +400 km The second change in position is (−50 km/h) × (4 h) = −200 km The final position is (+400 km) + (−200 km) = +200 km. The train is 200 km east of where it started.

CHAPTER 4

Fast Trains! The bullet train of Japan was the world’s first high-speed train. When it came into use in 1964, it went 210 km/h. Research today’s high-speed trains of the world. How fast can they go? Research to find out why the United States lags behind in having high-speed trains. Find out the advantages and disadvantages of having high-speed trains in the United States. .

Your turn...

a. A car travels south on a highway for 2 h at 90 km/h. The car reverses direction and heads north for 0.5 h at 80 km/h. What is the car’s position relative to where it started? b. A ship needs to sail to an island that is 1,000 km south of where the ship starts. If the captain sails south at a steady velocity of 30 km/h for 30 h, will the ship make it?

a. The car is 140 km south of where it started. b. No, because 30 km/h × 30 h = 900 km. The island is still 100 km away.

4.1 SPEED AND VELOCITY

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Section 4.1 Review 1. What is your average speed if you walk 2 kilometers in 20 minutes? 2. Give an example where instantaneous speed is different from average speed.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

3. A weather report says winds blow at 5 km/h from the northeast. Is this description of the wind a speed or velocity? Explain your answer. 4. What velocity vector will move you 200 miles east in 4 hours traveling at a constant speed?

Look at the graphic below and answer the following questions. 1. How fast is each cyclist going in units of meters per second*? 2. Which cyclist is going faster? How much faster is this cyclist going compared to the other one?

5. Explain how a bicycle can be fast compared to walking and slow compared to driving. How can two opposite words (fast and slow) describe the same speed?

Cyclist A Time (s)

6. What is the speed of the duck in the picture below if it takes 15 seconds to move the distance shown? 0

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Position (m)

Cyclist B Time (s)

7. Can you go 500 kilometers in 8 hours without driving faster than 55 mph? Explain your answer. 8. A boat sails an average speed of 20 km/h for 2 days. How far does the boat travel? 9. What is the difference between speed and velocity? 10. A bird flies west for 1 hour at a velocity of 15 km/hr. The bird switches direction and flies east for 1 hour at a velocity of 10 km/hr. What is the bird’s position relative to where it started?

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0

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Position (m)

*The word per means “for every” or “for each.” Saying “5 kilometers per hour” is the same as saying “5 kilometers for each hour.” You can also think of per as meaning “divided by.” The quantity before the word per is divided by the quantity after it.

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MOTION

CHAPTER 4

4.2 Graphs of Motion constant speed - speed that

Consider the phrase “a picture is worth a thousand words.” A graph is a special kind of picture that can quickly give meaning to a lot of data (numbers). You can easily spot relationships on a graph. It is much more difficult to see these same relationships by looking at columns of numbers. Compare the table of numbers to the graph in Figure 4.4 and see if you agree!

stays the same.

Recording data Imagine you are helping a runner who is training for a track meet. She wants to know if she is running at a constant speed. Constant speed means the

Time (s)

Position (m)

0

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speed stays the same. You mark the track every 50 meters. Then you measure her time at each mark as she runs. The data for your experiment is shown in Figure 4.4. This is position vs. time data because it tells you the runner’s position at different points in time. She is at 50 meters after 10 seconds, 100 meters after 20 seconds, and so on.

Runner’s position vs. time 150

Graphing data To graph the data, you put position on the vertical (y) axis and time on the

horizontal (x) axis. Each row of the data table makes one point on the graph. Notice the graph goes over to the right 10 seconds and up 50 meters between each point. This makes the points fall exactly in a straight line. The straight line tells you the runner moves the same distance during each equal time period. An object moving at a constant speed always creates a straight line on a position vs. time graph. Calculating The data shows that the runner took 10 seconds to run each 50-meter segment. speed Because the time and distance was the same for each segment, you know her

speed was the same for each segment. You can use the formula v = d/t to calculate the speed. Dividing 50 meters by 10 seconds tells you her constant speed was 5 meters per second.

Position (m)

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

Position and time data for a runner

The position vs. time graph

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Figure 4.4: A data table and a position vs. time graph for a runner.

4.2 GRAPHS OF MOTION

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Graphs show relationships between variables

Angle Average (degrees) speed (cm/s)

Relationships Think about rolling a toy car down a ramp. You theorize that steeper angles between on the ramp will make the car go faster. How do you find out if your theory variables is correct? You need to know the relationship between the variables angle

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and speed.

Figure 4.5, the x-axis (angle) has values between 0 and 60 degrees. The y-axis (average speed) has values between 0 and 300 cm/s. You can tell there is a relationship because all the points on the graph follow the same curve that slopes up and to the right. The graph tells you instantly that the average speed increases as the ramp gets steeper. Recognizing a Recall that the relationship between variables may be strong, weak, or there relationship may be no relationship at all. In a strong relationship, large changes in one from a graph variable make similarly large changes in the other variable, like in

Figure 4.5. In a weak relationship, large changes in one variable cause only small changes in the other. The graph on the right (below) shows a weak relationship. When there is no relationship, the graph looks like scattered dots (below left). The dots do not make an obvious pattern (a line or curve).

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Bands Tel. # named Ends in 10 06 15 85 19 15 6 22 22 96 9 10 25 63 12 34 11 79

Last 2 digits of phone #

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Weak relationship between variables 250

Speed (cm/s)

Bands named

No relationship between variables

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Mass (kg) 10 20 30 40 50 60 70 80 90

Speed (cm/s) 126 125 123 122 123 124 126 127 128

Speed vs. angle Average speed (c/s)

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Patterns on a Recall that in a graph, the dependent variable is usually plotted on the graph show vertical (or y) axis and the independent variable is usually on the horizontal relationships (or x) axis. Each axis is marked with the range of values the variable has. In

106 144 181 205 224

300 200 100

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Figure 4.5: This graph shows that the average speed between A and B increases as the angle of the track increases.

Mass (kg)

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MOTION

CHAPTER 4

Slope slope - the ratio of the rise (vertical

Comparing You can use position vs. time graphs to quickly compare speeds. Figure 4.6 speeds shows a position vs. time graph for two people running along a jogging path.

change) to the run (horizontal change) of a line on a graph.

Calculating The “steepness” of a line is called its slope. The slope is the ratio of the rise slope (vertical change) divided by the run (horizontal change). The diagram below

shows how to calculate the slope of a line. Visualize a triangle with the slope as the hypotenuse. The rise is the height of the triangle. The run is the length along the base. Here, the x-axis is time and the y-axis is position. The slope of the graph is therefore the distance traveled divided by the time it takes, or the speed. The units are the units for the rise (meters) divided by the units for the run (seconds), meters per second, or m/s. Position vs. time for two runners Slope =

600 500

Runner A

=

400

Rise = 600 m

300

Position vs. time for two runners 600 500

Position (m)

A steeper line on a position vs. time graph means a faster speed.

Position (m)

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

Both runners start at the beginning of the path (the origin) at the same time. Runner A (blue) takes 100 seconds to run 600 meters. Runner B (red) takes 150 seconds to go the same distance. Runner A’s speed is 6 m/s (600 ÷ 100) and Runner B’s speed is 4 m/s (600 ÷ 150). Notice that the line for Runner A is steeper than the line for Runner B. A steeper line on a position vs. time graph means a faster speed.

Runner A 400 300 Runner B 200 100 0 0

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100

125 150

Time (s)

Figure 4.6: A position vs. time graph for two runners.

Rise Run 600 m 150 s

= 4 m/s

200 100

Run = 150 s

Runner B’s speed is 4 m/s

0 0 Runner B

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Time (s)

125 150

The speed is the slope of the position vs. time graph.

4.2 GRAPHS OF MOTION

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Speed vs. time graphs

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

two graphs? The blue runner has a speed of 5 m/s. The speed vs. time graph shows a horizontal line at 5 m/s for the entire time. On a speed vs. time graph, constant speed is shown with a straight horizontal line. At any point in time between 0 and 60 seconds the line tells you the speed is 5 m/s.

Position vs. time 300 250

Position (m)

Constant speed The speed vs. time graph has speed on the y-axis and time on the x-axis. The on a speed vs. bottom graph in Figure 4.7 shows the speed vs. time for the runner. The top time graph graph shows the position vs. time. Can you see the relationship between the

200 150 100 50

Another The red runner’s line on the position vs. time graph has a less steep slope. example That means her speed is slower. You can see this immediately on the speed

0 0

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80

100

80

100

Time (s)

vs. time graph. The red runner shows a line at 4 m/s for the whole time. Calculating A speed vs. time graph can also be used to find the distance the object has distance traveled. Remember, distance is equal to speed multiplied by time. Suppose

Speed vs. time 6

Speed (m/s)

we draw a rectangle on the speed vs. time graph between the x-axis and the line showing the speed. The area of the rectangle (shown below) is equal to its length times its height. On the graph, the length is equal to the time and the height is equal to the speed. Therefore, the area of the graph is the speed multiplied by the time. This is the distance the runner traveled.

40

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Speed vs. time

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Speed (m/s)

5 4

5 m/s 3 2 1 0

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Figure 4.7: The position vs. time graph (top) shows the exact same motion as the speed vs. time graph (bottom).

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60 s speed  time  distance 5 m/s  60 s  300 m

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CHAPTER 4

Section 4.2 Review Position vs. time for two runners

1. On a graph of position vs. time, what do the x-values represent? What do the y-values represent?

3. What does the slope of the line on a position vs. time graph tell you about an object’s speed? 4. The graph in Figure 4.8 shows the position and time for two runners in a race. Who has the faster speed, Robin or Joel? Explain how to answer this question without doing calculations. 5. Calculate the speed of each runner from the graph in Figure 4.8.

Position (m)

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

2. Explain why time is an independent variable and position is a dependent variable in a position vs. time graph.

100 80 Joel 60 Robin

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Time (s)

Figure 4.8: Questions 4, 5, and 6.

6. The runners in Figure 4.8 are racing. Predict which runner will get to the finish line of the race first. 7. Maria walks at a constant speed of 2 m/s for 8 seconds. a. Draw a speed vs. time graph for Maria’s motion. b. How far does she walk? 8. Which of the three graphs below corresponds to the position vs. time graph in Figure 4.9?

Figure 4.9: Questions 8 and 9.

9. Between which times is the speed zero for the motion shown on the position vs. time graph in Figure 4.9? 4.2 GRAPHS OF MOTION

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4.3 Acceleration

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Constant speed is easy to understand. However, almost nothing moves with constant speed for long. When a driver steps on the gas pedal, the speed of the car increases. When the driver brakes, the speed decreases. Even while using cruise control, the speed goes up and down as the car’s engine adjusts for hills. Another important concept in physics is acceleration. Acceleration is how we describe changes in speed or velocity.

acceleration - the rate at which velocity changes.

An example of acceleration Definition of What happens if you coast down a long hill on a bicycle? At the top of the acceleration hill, you move slowly. As you go down the hill, you move faster and faster—you accelerate. Acceleration is the rate at which your speed

(or velocity) changes. If your speed increases by 1 meter per second (m/s) each second, then your acceleration is 1 m/s per second.

Acceleration Your acceleration depends on the steepness of the hill. If the hill is a gradual can change incline, you have a small acceleration, such as 1 m/s per second. If the hill is

steeper, your acceleration is greater, perhaps 2 m/s per second. Acceleration on Acceleration is easy to spot on a speed vs. time graph. If the speed changes a speed vs. time over time then there is acceleration. Acceleration causes the line to slope up graph on a speed vs. time graph (Figure 4.10). The graph on the top shows constant

speed. There is zero acceleration at constant speed because the speed does not change.

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Figure 4.10: Speed vs. time graphs showing constant speed (top) and acceleration (middle and bottom).

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Speed and acceleration The difference Speed and acceleration are not the same thing. You can be moving in one between speed direction (nonzero speed) and have no acceleration (think cruise control). But and acceleration if the brakes are applied and the car slows down, it is accelerating because the

speed is now changing (faster to slower).

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

Example: Acceleration describes how quickly speed changes. More precisely, acceleration Acceleration is the change in velocity divided by the change in time. For example, suppose a in cars powerful sports car changes its speed from 0 to 60 mph in 5 seconds. In English

units, the acceleration is 60 mph ÷ 5 seconds = 12 mph/s. In SI units, 60 mph is about the same as 100 km/h. The acceleration is 100 km/h ÷ 5 seconds, or 20 km/h/s (Figure 4.11). A formula you can use to calculate acceleration is shown below.

Figure 4.11: The acceleration of a sports car.

Acceleration To calculate acceleration, you divide the change in velocity by the amount of units time it takes for the change to happen. If the change in speed is in kilometers

per hour, and the time is in seconds, then the acceleration is in km/h/s or kilometers per hour per second. An acceleration of 20 km/h/s means that the speed increases by 20 km/h every second. What is a meter The time units for acceleration are often written as seconds squared or s2. per second For example, acceleration might be 50 meters per second squared or 50 m/s2. squared? The steps in Figure 4.12 show how to simplify the fraction m/s/s to get m/s2.

Saying seconds squared is just a math-shorthand way of speaking. It is better to think about acceleration in units of speed change per second (that is, meters per second per second). Figure 4.12: How do we get m/s2? 4.3 ACCELERATION

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Solving Problems: Acceleration A sailboat moves at 1 m/s. A strong wind increases its speed to 4 m/s in 3 seconds (Figure 4.13). Calculate the acceleration.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

1. Looking for:

You are asked for the acceleration in m/s2.

2. Given:

You are given the initial speed in m/s (v1), final speed in m/s (v2), and the time in seconds. v −v Use the formula for acceleration: a = 2 1 t

3. Relationships: 4. Solution:

a=

4 m/s − 1 m/s 3 m/s = = 1 m/s 2 3s 3s Figure 4.13: An acceleration example.

Your turn...

a. Calculate the acceleration of an airplane that starts at rest and reaches a speed of 45 m/s in 9 seconds. b. Calculate the acceleration of a car that slows from 50 m/s to 30 m/s in 10 seconds.

a. 5 m/s2 b. −2 m/s2

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Acceleration on motion graphs

Speed is constant when there is zero acceleration. Speed

Speed

Acceleration on A speed vs. time graph is useful for showing how the speed of a moving a speed vs. time object changes over time. Think about a car moving on a straight road. If the graph line on the graph is horizontal, then the car is moving at a constant speed (top

CHAPTER 4

get slower. People sometimes use the word deceleration to describe slowing down. Acceleration on The position vs. time graph is a curve when there is acceleration. Think about a position vs. a car with a speed that increases each second. Because it is speeding up, it time graph covers more distance each second. The position vs. time graph gets steeper

Speed increases with positive acceleration. Speed

Speed

Positive and Acceleration can be positive or negative. Positive acceleration in one negative direction adds more speed each second. Things get faster. Negative acceleration acceleration in one direction subtracts some speed each second, Things

Time

Acceleration

each second. The opposite happens when a car is slowing down. The speed decreases so the car covers less distance each second. The position vs. time graph gets shallower with time, becoming horizontal when the car is stopped.

Time

Speed decreases with negative acceleration. Speed

Speed

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

of Figure 4.14). The upward slope in the middle graph shows increasing speed. The downward slope of the bottom graph tells you the speed is decreasing. The word acceleration is used for any change in velocity, either an increase or a decrease.

Acceleration

Time

Figure 4.14: Three examples of

motion showing constant speed (top) and acceleration (middle, bottom).

4.3 ACCELERATION

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Free fall

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instant it leaves your hand until it reaches the ground. The “almost” is because there is a little bit of air friction that does make an additional force on the ball. A ball thrown upward is also in free fall after it leaves your hand. Even going up, the ball is in free fall because gravity is the only significant force acting on it. If air friction is ignored, objects in free fall on Earth accelerate downward, increasing their speed by 9.8 m/s every second. The value 9.8 m/s2 is called the acceleration due to gravity. The lowercase letter g is used to represent its value. When you see the lowercase letter g in a physics question, you can substitute the value 9.8 m/s2.

The acceleration due to gravity

free fall - accelerated motion that happens when an object falls with only the force of gravity acting on it.

acceleration due to gravity the value of 9.8 m/s2, which is the acceleration in free fall at Earth’s surface, usually represented by the lowercase letter g.

Free fall speed vs. time 50 40

Speed (m/s)

The definition An object is in free fall if it is accelerating due to the force of gravity and no of free fall other forces are acting on it. A dropped ball is almost in free fall from the

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0 9.8 19.6 29.4 39.2 49.0

Figure 4.15: A dropped ball Constant The speed vs. time graph in Figure 4.15 is for a ball in free fall. Because the acceleration graph is a straight line, we know the speed increases by the same amount

each second. This means the ball has a constant acceleration. Don’t confuse constant speed with constant acceleration! Constant acceleration means an object’s speed changes by the same amount each second.

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increases its speed by 9.8 m/s each second, so its constant acceleration is 9.8 m/s2.

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Acceleration and direction A change in If an object’s acceleration is zero, the object can only move at a constant direction is speed in a straight line (or be stopped). A car driving around a curve at a acceleration constant speed is accelerating (in the “physics sense”) because its direction is

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changing (Figure 4.16). Acceleration occurs whenever there is a change in speed, direction, or both. What change in What do we mean by change in direction? Consider a car traveling east. Its direction means velocity is drawn as an arrow pointing east. Now suppose the car turns

southward a little. Its velocity vector has a new direction.

Drawing vectors When drawing velocity vectors, the length represents the speed. A 2-cm

vector stands for 10 m/s (22 mph). A 4-cm vector is 20 m/s, and so on. At this scale, each centimeter stands for 5 m/s. You can now find the change in velocity by measuring the length of the vector that goes from the old velocity vector to the new one.

Turns are caused by sideways accelerations

Figure 4.16: A car can change its

velocity by speeding up, slowing down, or turning. The car is accelerating in each of these cases.

The small red arrow in the graphic above represents the difference in velocity before and after the turn. The change vector is 1 centimeter long, which equals 5 m/s. Notice the speed is the same before and after the turn! However, the change in direction is a sideways change of velocity. This change is caused by a sideways acceleration. 4.3 ACCELERATION

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Curved motion Acceleration Like velocity, acceleration has direction and is a vector. Curved motion is and curved caused by sideways accelerations. Sideways accelerations cause velocity to motion change direction, which results in turning. Turns create curved motion.

projectile - an object moving through space and affected only by gravity.

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An example of As an example of curved motion, imagine a soccer ball kicked into the air. curved motion The ball starts with a velocity vector at an upward angle (Figure 4.17). The

acceleration of gravity bends the trajectory more toward the ground during each second the ball is in the air. Therefore, gravity accelerates the ball downward as it moves through the air. Near the end of the motion, the ball’s velocity vector is angled down toward the ground. The path of the ball makes a bowl-shaped curve called a parabola. Projectiles A soccer ball is an example of a projectile. A projectile is an object moving

under the influence of only gravity. The action of gravity is to constantly turn the direction of the velocity vector more and more downward. Flying objects such as airplanes and birds are not projectiles, because they are affected by forces generated from their own power. Circular motion

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Circular motion is another type of curved motion. An object in circular motion has a velocity vector that constantly changes direction. Imagine whirling a ball around your head on a string. You have to pull the string to keep the ball moving in a circle. Your pull accelerates the ball toward you. That acceleration is what bends the ball’s velocity into a circle with you at the center. Circular motion always has an acceleration that points toward the center of the circle. In fact, the direction of the acceleration changes constantly so it always stays pointed toward the center of the circle.

Figure 4.17: A soccer ball in the air is a projectile. The path of the ball is a bowl-shaped curve called a parabola.

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CHAPTER 4

Section 4.3 Review 1. Nearly all physics problems will use the unit m/s2 for acceleration. Explain why the seconds are squared. Why isn’t the unit given as m/s, as it is for speed?

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2. Suppose you are moving forward with a velocity of 10 m/s. What happens to your speed if you have a negative acceleration? Do you speed up or slow down? 3. A rabbit starts from a resting position and is moving at 6 m/s after 3 seconds. What is the acceleration of the rabbit? (Figure 4.18) 4. You are running a race and you speed up from 3 m/s to 5 m/s in 4 seconds. a. What is your change in speed? b. What is your acceleration?

Figure 4.18: Question 3.

5. Does a car accelerate when it goes around a corner at a constant speed? Explain your answer. 6. A sailboat increases its speed from 1 m/s to 4 m/s in 3 seconds. What will the speed of the sailboat be at 6 seconds if the acceleration stays the same? (Figure 4.19) 7. The graph at the right shows the speed of a person riding a bicycle through a city. Which point (A, B, or C) on the graph is a place where the bicycle has speed but no acceleration? How do you know? 8. What happens to the speed of an object that is dropped in free fall? 9. A ball is in free fall after being dropped. What will the speed of the ball be after 2 seconds of free fall? 10. What happens when velocity and acceleration are at right angles to each other? What kind of motion occurs?

Figure 4.19: Question 6.

11. The Earth moves in a nearly perfect circle around the Sun. Assume the speed stays constant. Is Earth accelerating?

4.3 ACCELERATION

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Chapter 4 Assessment Vocabulary

Concepts

Select the correct term to complete the sentences.

Section 4.1

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

average speed

projectile

slope

1.

What is the speed of an object that is standing still?

acceleration due to gravity

speed

free fall

2.

Name three common units for measuring speed.

velocity

constant speed

acceleration

3.

Section 4.1

Write the form of the speed equation that you would see in each of the following scenarios. Let v = speed, t = time, and d = distance.

1.

Speed with direction is called _____.

a.

You know distance and speed and want to find the time.

2.

The formula for _____ is distance divided by time.

b.

You know time and distance and want to find the speed.

3.

_____ is the total distance divided by the total time of a trip.

c.

You know speed and time and want to find the distance.

instantaneous speed

4.

Section 4.2

4.

The actual speed of a moving object at any moment is called _____.

5.

Speed that stays the same is called _____.

How are the variables speed and velocity different? How are they similar?

Section 4.2

5.

Which of the graphs below shows an object that is stopped?

6.

Which of the graphs above shows an object moving at a constant speed?

7.

Look at the graph following questions.

Section 4.3

6.

The rate at which velocity changes is defined as _____.

7.

An object in _____ is accelerating due to the force of gravity with no other forces acting on it.

8.

An object moving in a curved path affected only by gravity is called a(n) _____.

9.

An object in free fall will accelerate toward Earth at 9.8 m/s2, the _____.

a. b.

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on

the

next

page

and

answer

the

What is the average speed of Runner B at 100 seconds? How much time did Runner A take to get to the 300-meter mark?

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c.

Make a sketch of this graph in your notebook. Add a line to the graph that represents a third runner who has a speed that is slower than the speeds of Runners A and B. This new line should begin at the origin of the graph. Position vs. time for two runners

Problems Section 4.1

A high-speed train travels at 300 km/h. How long (in hours) would it take the train to travel 1,500 km at this speed?

2.

Lance Armstrong’s teammate, George Hincapie, averaged a speed of 33.6 km/h in the 15th stage of the Tour de France, which took 4.00 hours. How far (in kilometers) did he travel in the race?

3.

You are traveling on an interstate highway at a speed of 65 mph. What is your speed in km/h? The conversion factor is 1.0 mph = 1.6 km/h.

4.

A pelican flies at a speed of 52 km/h for 0.25 hours. How many miles does the pelican travel? The conversion factor is 1.6 km/h = 1.0 mph.

5.

A snail crawls 300 cm in 1 hour. Calculate the snail’s speed in each of the following units.

500

Position (m)

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1.

600

Runner A 400 300 Runner B 200 100 0 0

25

50

75

100

125 150

Time (s)

a.

centimeters per hour (cm/h)

Section 4.3

b.

centimeters per minute (cm/min)

8.

How would it be possible for an object to be traveling with constant speed and still be accelerating?

c.

meters per hour (m/h)

9.

Can an object have a speed of zero while it has an acceleration that is not zero? Explain.

6.

10. Which of these graphs show acceleration occurring?

You want to arrive at your friend’s house by 5:00 p.m. Her house is 240 kilometers away. If your average speed will be 80 km/h on the trip, when do you need to leave your house in order to get to her house in time?

Section 4.2

7.

Draw the position vs. time graph for a person walking at a constant speed of 1 m/s for 10 seconds. On the same axes, draw the graph for a person running at a constant speed of 4 m/s.

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8.

MOTION

Calculate the speed represented by each position vs. time graph below.

Section 4.2

2.

Oliver is warming up for a track meet. First he walks 1 m/s for 100 seconds. Then he runs at 3 m/s for 200 seconds. His shoe comes untied, so he stops for 20 seconds to tie it. Finally he runs at 4 m/s for 200 seconds. a.

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Draw a position vs. time graph of Oliver’s motion. Hint: Use the table below to calculate the distance he travels during each segment. speed (m/s)

9.

×

time (s)

= distance (m)

Draw the speed vs. time graph that shows the same motion as each position vs. time graph above.

Section 4.3

b.

Draw a speed vs. time graph of Oliver’s motion.

10. When a ball is first dropped off a cliff in free fall, it has an acceleration of 9.8 m/s2. What is its acceleration as it gets closer to the ground? Assume no air friction.

c.

What is the total distance that Oliver travels?

d.

What is Oliver’s average speed during his 520-second warm-up?

11. Why is the position vs. time graph for an object in free fall a curve? 12. Draw a speed vs. time graph for each of the following situations. a. b. c.

Section 4.3

3.

Look at the graph below and make up a story involving motion that would create a graph shaped like this.

4.

Draw a speed vs. time graph that shows the same motion as the position vs. time graph above.

A person walks along a trail at a constant speed. A ball is rolling up a hill and gradually slows down. A car starts out at rest at a red light and gradually speeds up.

Applying Your Knowledge Section 4.1

1.

If you take a one-hour drive at an average speed of 65 mph, is it possible for another car with an average speed of 55 mph to pass you? Explain your answer.

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5

CHAPTER 5

Force FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

Every year, all over the world, competitions are held that require strength and a knowledge of force. Athletes compete in events with names like the Giant Log Lift, the Pillars of Hercules, the Atlas Stones, and the Plane Pull. As you might imagine, moving a giant log or a plane requires a tremendous amount of force. How can athletes achieve these amazing feats? There is a good chance that during their training, they thought about how best to apply force so that they could lift a giant log, pull a plane, or lift a 160-kilogram Atlas Stone. Forces are created and applied every time something moves. Forces, such as weight, are even present when objects are not moving. Your body uses forces even when your heart is beating and when you are walking upstairs. And force is necessary when you want to pick up or move something that is very heavy. Understanding forces is fundamental to understanding how tasks are best accomplished in nature and by people. Read this chapter to learn more about how forces are created, measured, described, and used in daily life.

4 How are you affected by forces right now? 4 What is friction and how is it useful? 4 What happens when an object experiences net force?

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5.1 Forces Force is a very important concept in physics and in everyday life. In this chapter, you will learn where forces come from, how they are measured, and how they are added and subtracted.

force - a push or a pull, or any action that involves the interaction of objects and has the ability to change motion.

The cause of forces FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

What are A force is a push or a pull. Technically, force is the action that has the ability forces? to change motion. You need force to start an object moving. You also need

force to change an object’s motion if it is already moving. Forces can increase or decrease the speed of a moving object. Forces can also change the direction in which an object is moving. How are forces Forces are created in many ways. For example, your muscles create force created? when you swing a baseball bat. On a windy day, the movement of air can

create forces. Earth’s gravity creates a force called weight that pulls on everything around you. Each of these actions creates forces, and through those forces, each can change an object’s motion.

The four elementary forces Strong nuclear force Electromagnetic force Weak force Gravity

Strong nuclear force This force holds the nucleus of an atom together. This force is very strong but only reaches a very short distance.

Electromagnetic force

Some causes of forces

This force acts between positive and negative charges. This force holds atoms together in molecules. g

Weak force This force causes some kinds of radioactivity.

Gravity

Muscles

Moving matter

Massive objects

(like wind)

(like planets)

The four All of the forces we know of in the universe come from four elementary elementary forces. Figure 5.1 describes the four elementary forces. If you study physics forces or chemistry, you will learn more about the strong and weak forces. These

This force causes all masses to attract each other. Your weight comes from the mass of Earth attracting the mass of your body.

Figure 5.1: All forces in the universe come from only four elementary forces.

forces are only important inside the atom and in certain types of radioactivity. However, the electromagnetic force and gravity are important in almost all areas of human life, including technology.

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Units of force Pounds Imagine mailing a package at the post office. How does the postal clerk know

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how much you should pay? You are charged a certain amount for every pound of weight. The pound (lb) is a unit of force commonly used in the United States. When you measure weight in pounds on a scale, you are measuring the force of gravity acting on an object (Figure 5.2). For smaller amounts, pounds are divided into ounces (oz). There are 16 ounces in 1 pound.

pound - the English unit of force equal to 4.448 newtons.

newton - the SI unit of force, equal to the force needed to make a 1-kg object accelerate at 1 m/s2.

The origin of The pound is based on the Roman unit libra, which means “balance.” This is the pound why the abbreviation for pound is lb. The word pound comes from the Latin

pondus, meaning “weight.” The definition of a pound has varied over time and from country to country. Newtons Although we use pounds all the time in our everyday life, scientists prefer to measure forces in newtons. The newton (N) is an SI of force. The newton is

defined by how much a force can change the motion of an object. A force of 1 newton is the exact amount of force needed to cause a mass of 1 kilogram to speed up (or slow down) by 1 m/s each second (Figure 5.2). We call the SI unit of force the newton because force is defined by Newton’s laws. The newton is a useful way to measure force because it connects force directly to its effect on motion.

Unit The newton is a smaller unit of force than the pound. One pound of force equals conversions 4.448 newtons. That makes the newton a little less than a quarter of a pound.

This is about the weight of a stick of butter. As another example, a 100-pound person weighs 444.8 newtons. In SI units, the mass of a 100-pound person (on Earth) is about 45 kilograms. If you do the math (444.8 ÷ 45) you will find that 1 kg of mass has a weight of 9.8 newtons of force.

Figure 5.2: The definitions of newton and pound.

5.1 FORCES

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The force vector Force is a vector The direction of a force makes a big difference in what the force can do. That

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means force is a vector, like velocity or position. To predict the effect of a force, you need to know both its strength and its direction. Strength is usually measured in newtons. Direction may be given in words, such as 5 newtons down, or in symbols. Arrows are often used to show the direction of forces in diagrams (Figure 5.3). Using positive Forces may be assigned positive and negative values to tell their directions. and negative For example, suppose a person pushes with a force of 10 newtons to the right numbers (Figure 5.3). The force vector is +10 N. A person pushing with the same

force to the left would create a force vector of −10 N. The negative sign indicates that the −10 N force is in the opposite direction from the +10 N force. We usually choose positive values to represent forces directed up, to the right, to the north, or to the east.

Figure 5.3: Positive and negative numbers are used to indicate the direction of force vectors.

Drawing a It is sometimes helpful to show both the strength and direction of a force force vector vector as an arrow on a graph. The length of the arrow represents the strength

of the force. The arrow points in the direction of the force. The x- and y-axes show the strength of the force in the x and y directions. Scale When drawing a force vector to show its strength, you must choose a scale.

For example, suppose you want to draw a force of 5 N pointing straight up (y-direction). You might use a scale of 1 cm = 1 N. At this scale, the force vector is a 5-cm long arrow pointing up, along the y-axis on your graph (Figure 5.4). A 5-N horizontal force would be drawn along the x-axis with a 5-cm-long arrow pointing to the right.

Figure 5.4: You must use a scale when drawing a vector.

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How forces act Contact forces There are two ways that objects can affect each other through forces. One way

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is the result of direct contact. The force between two people pulling on a rope is a good example of a force that occurs through direct contact (Figure 5.5). A contact force is transmitted by matter directly touching other matter. The wind acting to slow a parachute is also a contact force because air is matter. The force comes from air contacting the parachute. In the next section, you will learn about friction, another contact force. Forces that act Now think about Earth and the Moon. If Earth were to disappear, the Moon through space would sail off into space by itself. The Moon doesn’t fly off because a force

exists between Earth and the Moon. That force is called gravity. Gravity provides the force that keeps Earth and the Moon together in orbit. But, exactly how does “gravity” get from Earth to the Moon? Space is empty of matter, so the force cannot be a contact force.

Figure 5.5: Contact forces and a force that acts through a force field.

Some examples The force of gravity between Earth and the Moon appears to be what people

once called “action-at-a-distance.” The force between two magnets is another force that acts at a distance. So is the force that causes electricity. Table 5.1 summarizes the two types of forces. Table 5.1: Types of Forces Contact forces

“At-a-distance” forces

friction normal force tension, air resistance, spring

gravity electricity magnetism

STUDY SKILLS Defining Forces Pick a term that is listed in Table 5.1 but that is not described on this page (friction, normal force, or spring force). Find out what the term means.You can do research and find the answer on your own or ask someone who is knowledgeable on the subject.

The force field Today, we know that a true “action-at-a-distance” force is impossible. The

force of gravity actually acts in two steps. First, the mass of Earth creates a gravitational field that fills the space around Earth with potential energy. Second, the gravitational field of Earth creates a force on the Moon. The gravitational force is carried from Earth to the Moon by a force field. In fact, if Earth were to vanish instantly, the Moon would continue to be affected by Earth’s gravity for a few seconds. This is because the force field “flows” between Earth and the Moon quickly, but not instantly. 5.1 FORCES

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Contact forces from ropes and springs Two ways Ropes and springs are often used to make and apply forces. Ropes are used contact forces to transfer forces or change their direction. Springs are used to make and occur control forces.

The pulling force carried by a rope is called tension. Tension always acts along the direction of the rope. A rope carrying a tension force is stretched tight. The two people in the diagram at the left are each pulling on the rope with a force of 100 newtons. Tension is defined as the force with which a rope is pulled in each direction, so the tension in the rope is 100 newtons. Ropes do not carry pushing forces. This is obvious if you have ever tried pushing a rope!

Tension

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Springs are used to make or control forces. A spring creates a force when you stretch it or squeeze it away from its resting shape. The force from a spring always acts to return the spring to its resting shape. If you stretch a spring (extension), the spring acts to make itself shorter, pulling back on your hand. If you squeeze a spring (compression), the spring tries to get longer again and pushes back on your hand.

Spring forces

tension - a pulling force that acts in a rope, string, or other object.

extension - a “stretch,” or increase in size.

compression - a “squeeze,” or decrease in size.

Springs Two of the many types of springs are extension springs and compression springs. Extension springs are designed to be stretched. They often have loops on either end. Compression springs are designed to be squeezed. They are usually flat on both ends. Can you find both types in springs in your classroom? 1. What is the spring used for? 2. What would happen if the spring broke?

Spring forces The force created by a spring is proportional to the ratio of the extended or vary in strength compressed length divided by the original (resting) length. If you stretch a

spring twice as much, it makes a force that is twice as strong.

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Gravity Gravitational The force of gravity on an object is called weight. At Earth’s surface, gravity force depends exerts a force of 9.8 N on every kilogram of mass. Therefore, on Earth, the on mass weight of any object is its mass multiplied by 9.8 N/kg. For example, a

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

1-kilogram mass has a weight of 9.8 N, a 2-kilogram mass has a weight of 19.6 N, and so on. Because weight is a force, it is measured in units of force such as newtons and pounds.

Weight vs. mass Weight and mass are not the same. Mass is a fundamental property of matter

measured in kilograms (kg). Weight is a force measured in newtons (N). Weight depends on mass and gravity. For example, how much you weigh depends on your mass and the strength of gravity at your location. It is easy to confuse mass and weight because they seem similar. Heavy objects (more weight) have lots of mass and light objects (less weight) have little mass. But, it’s important to remember the difference when doing physics.

Weight is a force that depends on mass and gravity.

Figure 5.6: A 10-kilogram rock weighs 98 newtons on Earth but only 16 newtons on the Moon.

Weight is less A 10-kilogram rock has the same mass no matter where it is in the universe. on the Moon The rock’s weight, however, depends on where it is located. On Earth, the

rock weighs 98 newtons. But on the Moon, it weighs only 16 newtons (Figure 5.6). On the Moon, the rock’s weight would be one-sixth the rock’s weight on Earth because the strength of gravity on the Moon is one-sixth the strength of gravity on Earth. 5.1 FORCES

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Calculating weight

STUDY SKILLS

The weight The weight formula lets you calculate the weight of an object if you know formula the object’s mass and the strength of gravity at the object’s location. Three

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forms of the weight formula are given in Table 5.2. Use the appropriate form to find weight, mass, or the strength of gravity if you know any two of the three values.

g is the symbol The strength of gravity at Earth’s surface is so important to our everyday life for gravity that we give it a special symbol, the lowercase letter g. When you see a g in a

formula you can usually substitute the value g = 9.8 N/kg. Of course, that assumes the formula is being applied at the surface of Earth! Elsewhere in the universe g has different values. You sometimes see g written with units of m/s2, for example, g = 9.8 m/s2. This is really the same g expressed as the acceleration of a 1-kg mass under the influence of gravity. Table 5.2: Different forms of the weight formula

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Use. . .

if you want to find. . .

and you know. . .

W = mg

weight (W)

mass (m) and strength of gravity (g)

m = W/g

mass (m)

weight (W) and strength of gravity (g)

g = W/m

strength of gravity (g)

weight (W) and mass (m)

Different Ways to Show “Divided By” Below are three different ways to show the equation “mass equals weight divided by gravity.” Notice the different ways to show “divided by.” You should familiarize yourself with all three versions.

Some Notes about Drawing Force Vectors 1. Force vectors should always be drawn in the direction of the force they represent. 2. Force vectors should be drawn to scale if possible, with length proportional to strength. 3. A force on a surface can be shown as pointing toward the surface or away from it. What matters is that the direction is clear so you know what the net force is in a certain direction.

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Solving Problems: Weight and Mass

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Calculate the weight of a 60-kilogram person (in newtons) on Earth and on Mars (g = 3.7 N/kg on Mars) (Figure 5.7). 1. Looking for:

You are asked for a person’s weight on Earth and on Mars.

2. Given:

You are given the person’s mass and the value of g on Mars.

3. Relationships:

W = mg

4. Solution:

For the person on Earth: W = mg W = (60 kg)(9.8 N/kg) = 588 newtons

Figure 5.7: How does the weight of a person on Earth compare to the weight of the same person on Mars?

For the person on Mars: W = mg W = (60 kg)(3.7 N/kg) = 222 newtons Notice that while the masses are the same, the weight is much less on Mars. Your turn...

a. Calculate the mass of a car that weighs 19,600 N on Earth. b. A 70-kg person travels to a planet where he weighs 1,750 N. What is the value of g on that planet?

a. 2,000 kg b. 25 N/kg

5.1 FORCES

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Section 5.1 Review 1. Name three situations in which force is created. Describe the cause of the force in each situation. 2. Which of the following are units of force?

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a. kilograms and pounds b. newtons and pounds c. kilograms and newtons 3. Which is greater: a force of 10 N or a force of 5 lbs? 4. A rope is used to apply a force to a box. Which drawing shows the force vector drawn correctly?

5. What is the difference between contact forces and forces that act through a force field? 6. A spring is stretched as shown. Which drawing shows the force exerted by the spring? (Hint: Not the force on the spring.)

7. If the strength of gravity is 9.8 newtons per kilogram, that means: a. b. c. d.

each newton of force equals 9.8 pounds. each pound of force equals 9.8 newtons. each newton of mass weighs 9.8 kilograms. each kilogram of mass weighs 9.8 newtons.

Calculating Mass from Weight Use the steps on page 105 to solve the following problems. 1. What is the mass of an object with a weight of 35 newtons? Assume the object is on Earth’s surface. 2. Which is greater: A force of 100 N or the weight of 50 kilograms on Earth’s surface? 3. The mass of a bag of potatoes is 0.5 kg. Calculate the weight of the potatoes in newtons.

Contact forces are actually acting through force fields too! When you push a box, the atoms in your hand are electrically repelling the atoms in the box. The force is carried between the atoms of your hand and the atoms of the box by trillions of tiny electrical force fields. In reality, all forces act through force fields once you get to the atomic level! We don’t notice because atoms are so small.

8. An astronaut in a spacesuit has a mass of 100 kilograms. What is the weight of this astronaut on the surface of the Moon where the strength of gravity is approximately one-sixth that of Earth? 9. What is the weight (in newtons) of a bowling ball that has a mass of 3 kilograms?

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5.2 Friction Friction is a force that resists motion. Friction is found everywhere in our world. You feel the effects of friction when you swim, ride in a car, walk, and even when you sit in a chair. Friction can act when an object is moving or when it is at rest. Many types of friction exist. Figure 5.8 shows some common examples.

friction - a force that resists motion.

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Some causes of friction The cause of Imagine looking through a microscope at friction two smooth surfaces touching each other.

You would see tiny hills and valleys on both sides. As surfaces slide (or try to slide) across each other, the hills and valleys grind against each other. This is a cause of friction. The tiny hills may change shape or wear away. If you rub sandpaper on a piece of wood, friction affects the wood’s surface and makes it either smoother (hills wear away) or rougher (hills change shape). Two surfaces Friction depends on both of the surfaces that are in contact. The force of are involved friction on a rubber hockey puck is very small when it is sliding on ice. But

the same hockey puck sliding on a piece of sandpaper experiences a large friction force. When the hockey puck slides on ice, a thin layer of water between the rubber and the ice allows the puck to slide easily. Water and other liquids, such as oil, can greatly reduce the friction between surfaces.

Figure 5.8: There are many types

of friction.

5.2 FRICTION

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Identifying friction forces Direction of the We think of friction as a force, measured in newtons just like any other force. friction force You draw the force of friction with a force vector. To figure out the direction

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of the vector, always remember that friction resists motion between surfaces. The force of friction acting on a surface always points opposite the direction of the motion of that surface. Imagine pushing a heavy box across the floor (Figure 5.9). If the box is moving to the right, then friction acts to the left, against the surface of the box touching the floor. If the box were moving to the left instead, the force of friction would act toward the right. This is what we mean when we say friction resists motion.

sliding friction - the friction force that resists the motion of an object moving across a surface. static friction - the friction force that resists the motion between two surfaces that are not moving.

Sliding friction Sliding friction is a force that resists dry sliding motion between any two

surfaces. If you push a box across the floor toward the right, sliding friction acts toward the left, slowing down the motion of the box. The friction force acts between the floor and the bottom surface of the box. Let’s say you stop pushing the box, but it keeps moving. Sliding friction continues to work and eventually slows the box to a stop. Static friction Static friction keeps an object that is standing still (at rest) from starting to

move. Imagine trying to push a heavy box with a small force. The box stays at rest because the static friction force acts against your force and cancels it out. As you increase the strength of your push, the static friction also increases. Eventually, your force becomes strong enough to overcome static friction and the box starts to move (Figure 5.9). The force of static friction balances your force up to a limit. The limit of the static friction force depends on the types of surfaces, the weight of the object you are pushing, and the angle of incline of the surface. Comparing How does sliding friction compare with static friction? If you have ever tried sliding and to move a heavy sofa or refrigerator, you probably know the answer. It is static friction harder to get something moving than it is to keep it moving. This is because

static friction is almost always greater than sliding friction at slow speeds.

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Figure 5.9: The direction of the force of friction is opposite the direction the box is pushed.

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A model for friction Different The amount of friction generated when a box is pushed across a smooth floor amounts is very different from when it is pushed across a carpet. This is because of friction friction depends on materials, roughness, how clean the surfaces are, and

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other factors. Even the friction between two identical surfaces changes as the surfaces are polished by sliding motion. No single formula can accurately describe all types of friction. An example An easy experiment to measure friction is to pull a piece of paper across a

table with a force scale. The paper slides smoothly, and the scale measures almost no force. Now put a brick on the piece of paper (Figure 5.10). Friction increases and you must pull with a greater force to move the paper. Friction depends on the force between surfaces

Why does the brick have an effect on friction? The two surfaces in contact are still the paper and the tabletop, but the brick causes the paper to press harder into the table’s surface. The tiny hills and valleys in the paper and in the tabletop are pressed together with a much greater force, so the friction increases. The same is true of most dry sliding friction. Increasing the force that pushes surfaces together increases the amount of friction.

The greater the force squeezing two surfaces together, the greater the friction force. Why sliding friction increases with weight

Figure 5.10: Friction increases greatly when a brick is placed on the paper.

The friction force between two smooth, hard surfaces is approximately proportional to the force squeezing the surfaces against each other. Consider sliding a heavy box across a floor. The force between the bottom of the box and the floor is the weight of the box. Therefore, the force of friction is proportional to the weight of the box. If the weight doubles, the force of friction also doubles. This rule is not true if one or both surfaces are wet, or if they are soft.

5.2 FRICTION

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Reducing the force of friction All surfaces Unless a force is constantly applied, friction will slow all motion to a stop experience eventually. For example, bicycles have low friction, but even the best bicycle some friction slows down as you coast on a level road. It is impossible to completely

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eliminate friction. However, many clever inventions have been devised to reduce friction. You use them every day. Lubricants Putting a liquid, such as oil, between two sliding surfaces keeps them from reduce friction touching each other. The tiny hills and valleys don’t become locked together, in machines so there is less friction. The liquid also keeps the surfaces from wearing

away as quickly. You add oil to a car’s engine so that the moving parts slide or turn with less friction. Even water can be used to reduce friction between objects if they are not too hot. Ball bearings

Ball bearings reduce friction in rotating motion (Figure 5.11). Ball bearings change sliding motion into rolling motion, which has much less friction. For example, a metal shaft rotating in a hole rubs and generates a lot of friction. Ball bearings that go between the shaft and the inside surface of the hole allow the shaft to spin more easily. The shaft rolls on the bearings instead of rubbing against the walls of the hole. Well-oiled bearings rotate easily and greatly reduce friction.

Figure 5.11: The friction between a

shaft (the long pole in the picture) and the inner surface of the hole produces a lot of heat. Friction can be reduced by placing ball bearings between the shaft and the hole surface.

Magnetic Another method of decreasing friction is to separate the two surfaces with a levitation cushion of air. A hovercraft floats on a cushion of air created by a large fan.

Magnetic forces can also be used to separate surfaces. A magnetically levitated (or maglev) train uses magnets that run on electricity to float on the track once the train is moving (Figure 5.12). There is no contact between train and track, so there is far less friction than with a standard train on tracks. The ride is smoother, so maglev trains can move at very fast speeds. Maglev trains are not widely used yet because they are much more expensive to build than regular trains. They may become more popular in the future.

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Figure 5.12: With a maglev train,

there is no contact between the moving train and the rail—and thus there is little friction.

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Using friction Friction is useful for brakes and tires

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There are many occasions when friction is very useful. For example, the brakes on a bicycle create friction between the brake pads and the rim of the wheel. Friction makes the bicycle slow down or stop. Friction is also needed to make a bicycle move. Without friction, the bicycle’s tires would not grip the road.

Tires designed Friction is also important to anyone driving a car. Tires are specially designed for bad weather to maintain friction on pavement in rain or snow. Tire treads have grooves that

allow space for water to be channeled away where the tire touches the road (Figure 5.13). This allows good contact between the rubber and the road surface. Special groove patterns along with tiny slits are used on snow tires to increase traction in snow. These grooves and slits keep snow from getting packed into the treads.

Figure 5.13: Grooved tire treads

allow space for water to be channeled away from the road−tire contact point, allowing for more friction in wet conditions.

Nails Friction even keeps nails in place (Figure 5.14). When a nail is hammered

into wood, the wood pushes against the nail on all sides. The force of the wood against the nail surface creates a lot of friction. Each hit of the hammer pushes the nail deeper into the wood. The deeper the nail goes, the more surface there is for friction to grab onto. Cleated shoes

Shoes are designed to increase the friction between your foot and the ground. Many athletes, including football and soccer players, wear shoes with cleats. Cleats are like teeth on the bottom of the shoe that dig into the ground. Players wearing cleats can apply much greater force against the ground to help them move and to keep them from slipping.

Compression force

Friction

Figure 5.14: Friction is what

makes nails hard to pull out, and what gives nails the strength to hold things together.

5.2 FRICTION

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Friction and energy Earlier, we learned that energy moves through the action of forces. Energy also changes into different forms. For example, friction changes energy of motion into heat energy. You may have noticed that rubbing your hands together quickly can make them warmer. You are feeling the effect of friction changing energy of motion into heat.

Friction changes energy of motion into heat

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Heat in Friction is always present in any machine with moving parts. In small machines machines, the forces are low and the amount of heat produced by friction

may be small. A sewing machine is an example of a small machine. Larger machines have more problems with heat. In many machines, oil is pumped around moving parts. The oil does two important things. First, oil reduces friction so less heat is generated. Second, the oil absorbs the heat and carries it away from the moving parts. Without the flow of cooling oil, moving parts in an engine would heat up too much and melt. Friction causes wear

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Another way friction changes energy is by wearing away moving parts. You have probably noticed that objects that slide against each other often get rounded or smoothed. Each time two moving surfaces touch each other, tiny bits of material are broken off by friction. Breaking off bits of material uses energy. Sharp corners and edges are rounded off and flat surfaces may be scratched or even polished smooth and shiny.

Heat and Machines Every machine releases heat from friction. The faster the parts move, and the larger the forces inside the machine, the more heat is released. Electronic machines, such as computers, are no exception, even though they may have no moving parts! Electricity moving through wires also creates friction. If a machine gets too hot, parts can melt and the machine may stop working. Because of this, many machines have special systems, parts, and designs to get rid of unwanted heat energy. Here are three machines you probably see every day. How is excess heat removed from each one?

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Section 5.2 Review

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1. It is a common practice to put oil in a car and to change the car’s oil once in a while. Why do cars need oil?

You Can Count on Friction!

2. Which two of the following statements are true? a. Sliding friction is typically greater than static friction. b. Static friction is typically greater than sliding friction. c. Sliding friction occurs at rest and static friction occurs in motion. d. Static friction occurs at rest and sliding friction occurs in motion.

Write a paragraph telling how the events of your day would not have been possible without friction.

3. If the force squeezing two surfaces together is decreased, the force of dry sliding friction between the two surfaces will most likely a. increase. b. decrease. c. stay about the same. 4. Name three devices or inventions that are designed to decrease friction. 5. Name three devices or inventions that are designed to increase friction. 6. True or false? A well-oiled machine has no friction. Explain your answer. 7. A box is sliding across the floor from left to right. Which diagram correctly shows the force of friction acting on the box?

Friction is a part of your daily life.

Then, imagine the world suddenly had much more friction than normal. Write a paragraph telling how your day would have been affected.

Design a New Shoe! If it weren’t for friction it would be hard to walk! We need to be able to place our feet on a hard surface and push off from it to move forward. Invent a new shoe that would be suitable for an environment of your choice. For example, you might want to design a shoe for mountain climbing or for walking on the Moon! Make a sketch of your shoe and write an explanation about the research you did to develop the best design.

8. True or false: Friction makes energy vanish. Explain your answer. 9. True or false: Electronic machines with no moving parts experience friction and get hot because electricity is moving through the wires.

5.2 FRICTION

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5.3 Forces and Equilibrium We almost never feel only one force. For example, friction and weight are two forces that both act on us when we’re walking. It is the total of all forces acting on our bodies that determines how we move. This section is about how forces can be added and subtracted.

net force - the sum of all forces acting on an object.

balanced forces - combined forces that result in a zero net force on an object.

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Adding forces An example The sum of all the forces acting on an object is called the net force. The

word net means “total.” Net force also means that the direction of each force is considered when multiple forces are added. Consider a flying airplane (Figure 5.15). Four forces act on the plane: weight, drag (air friction), the thrust of the engines, and the lift force caused by the flow of air over the wings. For a plane to fly at a constant speed on a level path, the forces must all balance. Balanced forces result in a net force of zero. A pilot must always be aware of these four forces and know how to change them in order to speed up, slow down, lift off, and land. For example, to speed up there must be a net force in the forward direction. The thrust must be greater than the drag. To climb, there must be an upward net force. The lift force must be greater than the weight.

Figure 5.15: Four forces act on a plane as it flies.

Adding x-y To calculate the net force on an object, you must add the forces in each components direction separately. Remember to define positive and negative directions for

both the x-direction and y-direction. In the diagram above, +x is to the right and +y is up. The net force in the x-direction is zero because the +20,000 N and −20,000 N add up to zero. The net force in the y-direction is +5,000 N (+55,000 N − 50,000 N). The plane climbs because there is a positive (upward) net force.

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Equilibrium equilibrium - the state in which the net force on an object is zero.

Net force can be When many forces act on the same object, either: zero or not zero

the net force is zero, or

the net force is not zero.

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Definition of When the net force on an object is zero, we say the object is in equilibrium. equilibrium Equilibrium does not mean there are no forces! Equilibrium means all forces

cancel each other out leaving zero net force. For example, when the net force is zero, an object at rest will stay at rest. Interestingly, an object can be in motion at constant speed and still be in equilibrium. This happens when a pushing force and a friction force are equal but opposite in direction so the object does not speed up or slow down (Figure 5.16). Using equilibrium to find unknown forces

The idea of equilibrium is often used in reverse. Instead of thinking “an object in equilibrium stays at rest,” we think “an object at rest must be in equilibrium.” If an object is at rest, the net force on it must be zero. This fact often allows us to find the strength and direction of forces that must be there even if we don’t directly cause them.

Figure 5.16: Objects are in

equilibrium when the net force is zero.

When net force If the net force is not zero, then the motion of an object will change. An object is not zero at rest will start moving. An object that is moving may change its velocity. In

other words, unbalanced forces cause acceleration. 5.3 FORCES AND EQUILIBRIUM

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Normal forces Definition of Imagine a book sitting on a table (Figure 5.17). Gravity pulls the book normal force downward with the force of the book’s weight. The book is at rest, so the net

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force must be zero. But what force balances the weight? The table exerts an upward force on the book called the normal force. The word normal here has a different meaning from what you might expect. In mathematics, normal means “perpendicular.” The force that the table exerts is perpendicular to the table’s surface. The normal force is also sometimes called the support force.

normal force - the perpendicular force that a surface exerts on an object that is pressing on it.

When normal A normal force is created whenever an object is in contact with a surface. force is created The normal force has equal strength to the force pressing the object into the

surface, which is often the object’s weight. The normal force has opposite direction to the force pressing the object into the surface. For example, the weight of a book presses down on the table’s surface. The normal force is equal in strength to the book’s weight but acts upward on the book, in the opposite direction from the weight. What normal The normal force acts on the object pressing into the surface. That means, in force acts on this example, the normal force acts on the book. The normal force is created

Figure 5.17: The normal force

and the weight are equal in strength and opposite in direction on a horizontal surface.

by the book acting on the table. Strength of the What happens to the normal force if you put a brick on top of the book? The normal force brick makes the book press harder into the table. The book does not move, so

the normal force must be the same strength as the total weight of the book and the brick (Figure 5.18). The normal force acting on the book increases to keep the book in balance. How the normal How does a table “know” how much normal force to supply? The answer is force is created that normal force is very similar to the force exerted by a spring. When a

book sits on a table, it squeezes the atoms in the table together by a tiny amount. The atoms resist this squeezing and try to return the table to its natural thickness. The greater the table is compressed, the larger the normal force it creates. The matter in the table acts like a bunch of very stiff springs. You don’t see the table compress because the amount of compression is very small.

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Figure 5.18: The normal force is

greater if a brick is placed on the book.

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The free-body diagram Forces on a free- How can you keep track of many forces with different directions? The answer body diagram is to draw a free-body diagram. A free-body diagram contains only a single

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object, like a book or a table. All connections or supports are taken away and replaced by the forces they exert on the object. An accurate free-body diagram includes every force acting on an object, including weight, friction, and normal forces.

free-body diagram - a diagram showing all the forces acting on an object.

An example As an example of a free-body diagram, consider a stack of books weighing

30 newtons resting on a table that weighs 200 newtons. The books are on one corner of the table so that their entire weight is supported by one table leg. Figure 5.19 shows a free-body diagram of the forces acting on the table. Finding the Because the table is in equilibrium, the net force on it must be zero. The forces weight of the books acts on the table making a 30 N force. The weight of the

table acts on the floor. At every point where the table touches the floor (each leg) a normal force is created. The correct free-body diagram shows six forces. The normal force at each of the four legs is one-quarter the weight of the table (50 newtons). The leg beneath the book also supports the weight of the book (50 N + 30 N = 80 N). The purpose of a By separating an object from its physical connections, a free-body diagram free-body helps you identify all forces and where they act. A normal force is usually diagram present when an object is in contact with another object or surface. Forces due

to weight may be assumed to act directly on an object, often at its center. Positive and There are two ways to handle positive and negative directions in a free-body negative forces diagram. One way is to make all upward forces positive and all downward

forces negative. The second way is to draw all the forces in the direction you believe they act on the object. When you solve the problem, if you have chosen correctly, all the values for each force are positive. If one comes out negative, it means the force points in the opposite direction from what you guessed.

Figure 5.19: A free-body diagram showing the forces acting on a table that has a stack of books resting on one corner.

5.3 FORCES AND EQUILIBRIUM

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Solving Problems: Equilibrium

\\

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Two chains are used to support a small boat weighing 1,500 newtons. One chain has a tension of 600 newtons (Figure 5.20). What is the force exerted by the other chain? 1. Looking for:

You are asked for an unknown tension in a chain.

2. Given:

You are given the boat’s weight in newtons and the tension in one chain in newtons.

3. Relationships:

The net force on the boat is zero.

4. Solution:

Draw a free-body diagram. The force of the two chains must balance the boat’s weight. 600 N + Fchain2 = 1,500 N Fchain2 = 900 N

Figure 5.20: What is the force exerted by the other chain that is supporting the boat?

Your turn...

a. A person with a weight of 400 N is sitting motionless on a swing (Figure 5.21). For the swing to be in equilibrium, what is the tension force in each rope holding up the swing? b. A heavy box weighing 1,000 N sits on the floor. You press down on the box with a force of 450 N. What is the normal force on the box? c. A cat weighing 40 N stands on a chair. If the normal force on each of the cat’s back paws is 12 N, what is the normal force on each front paw? (You can assume the force is the same on each front paw.)

Figure 5.21: What is the tension

force in each rope holding up the swing?

(a) The upward force from both ropes must be 400 N, so the force in each rope is 200 N. (b) 1,450 N; (c) 8 N

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Section 5.3 Review 1. What is the relationship between net force and balanced forces? 2. Make two diagrams. The first diagram should show a net force of zero on an object and the other diagram should show a net force that is not zero.

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3. If an object is accelerating, can the net force acting on it ever be zero? Explain your answer. 4. If you push down on a table with a force of 5 newtons, what is the normal force pushing back on you?

Figure 5.22: Question 5.

5. The diagram in Figure 5.22 shows three forces acting on a pencil. What is the net force acting on the pencil? 6. If an object is in equilibrium, a. the net force on the object is zero. b. the object has zero total mass. c. no forces are acting on the object. d. only normal forces are acting on the object. 7. A train is climbing a gradual hill. The weight of the train creates a downhill force of 150,000 newtons. Friction creates an additional force of 25,000 newtons acting in the same direction (downhill) (Figure 5.23). How much force does the train’s engine need to create so the train is in equilibrium (going uphill at constant speed)? 8. Draw a free body diagram of your own body sitting on a stool. Include all forces acting on your body.

Figure 5.23: Question 7.

9. If a force has a negative value, such as −100 N, that means the force a. is less than 100 N in strength. b. acts in the opposite direction from a +100 N force. c. is a normal force. 10. A child weighing 200 newtons is sitting in the center of a swing. The swing is supported evenly by two ropes, one on each side. What is the tension force in one of the ropes? 5.3 FORCES AND EQUILIBRIUM

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Chapter 5 Assessment Vocabulary Select the correct term to complete the sentences.

12. A drawing representing all forces acting on an object is called a(n) ____. 13. The sum of all forces acting on an object is called the ____.

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balanced forces

compression

equilibrium

free-body diagram

friction

net force

newton

normal force

pound

Concepts

sliding friction

static friction

tension

Section 5.1

weight

force

1.

Describe one situation in which forces are created.

2.

A(n) ____ is an action that can change an object’s speed, direction, or both.

Name the four fundamental forces of nature, the forces from which all others are derived.

3.

Why is weight considered a force?

2.

The English unit of force equal to 4.448 newtons is the ____.

4.

3.

The SI unit of force needed to accelerate a 1-kg mass at 1 m/s each second is the ____.

Forces cause changes to the motion of objects. Name a force and describe two changes it makes.

5.

What two pieces of information do you need to describe a force?

4.

Squeezing creates ____ in a spring.

6.

Draw the following force vectors and show the scale you use.

5.

A pulling force carried by a rope is called ____.

Section 5.1

1.

Section 5.2

6. 7. 8.

____ is a force that always resists the relative motion of objects or surfaces. A frictional force that occurs when one surface slides over another is called ____. ____ is a frictional force between two nonmoving surfaces.

a.

20 N west

b.

4 N southeast

7.

Name one contact force and one force that acts through a force field.

8.

What happens to a spring’s force if you stretch it more?

9.

Distinguish between tension, compression, and extension.

10. Which of the following is most often used to change the direction of a force, but not the strength of the force?

Section 5.3

a.

a ball bearing

c.

a spring

9.

b.

a rope

d.

a parachute

When forces add up to a net force equal to zero they are called ____.

10. When all forces on an object are balanced, the object is in ____. 11. The perpendicular force exerted by a surface on an object pressing against it is called the ____.

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11. You know the relationship between weight and mass at the surface of the Earth. Describe this relationship on the Moon.

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12. Identify which of the following are units of force (F) and which are units of mass (M). a.

____ kilogram

c.

____ pound

b.

____ newton

d.

____ gram

CHAPTER 5

22. Describe the motion of the race car shown in the graphic. Assume the car is moving forward. Is it speeding up or slowing down?

Section 5.2

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13. Give a reasonable explanation for why the friction is so low between an ice skate blade and the ice. 14. Does it require more force to start an object sliding or to keep it sliding? Explain your answer. 15. Why is it much easier to slide a cardboard box when it is empty compared to when it is full of heavy books? 16. Explain two ways friction can be reduced.

23. What are the four main forces acting on an airplane in flight? If the plane accelerates forward, which two forces must be out of balance? In order for the plane to fly on a level path, which two forces must be in balance? 24. Which of the following diagrams correctly shows the normal force on the block of wood sliding down the incline?

17. Explain how friction keeps a nail in place in a block of wood. If you try to pull out the nail, which way does the friction act? 18. Name two types of energy generated by friction and give an example of each. 19. Is friction something we always want to reduce? Explain. Section 5.3

20. If the net force on an object is zero, can the object be moving? Explain.

25. Draw a free-body diagram for the forces acting on the parachutist shown. Don’t forget about air friction!

21. Standing on Earth, gravity exerts a downward force on you, yet you don’t fall toward the center of the planet. a.

Name the other force that acts on you and keeps you in equilibrium.

b.

What is the direction of the other force?

c.

What do you know about the strength of this other force?

CHAPTER 5 ASSESSMENT

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Problems

Section 5.2

Section 5.1

1.

Calculate the weight of a 66-newton bowling ball in pounds.

2.

A frozen turkey bought in Canada is labeled “5.0 kilograms.” This is a measurement of its mass. What is its weight in newtons?

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3.

What is the mass, in kilograms, of a large dog that weighs 441 newtons?

4.

How much does a 40-kg student weigh on Earth in newtons?

5.

How much mass, in kilograms, does a 50,000-N truck have?

6.

An astronaut has a mass of 70 kilograms on Earth. What would her mass be on Mars? What would her weight be on Mars? The value of gravity (g) on Mars is 3.7 m/s2.

7.

Using a scale of 1 cm = 5 N, draw force vectors representing a +20 N force and a –10 N force.

8.

A spring is stretched 15 cm by a 45-N force. How far would the spring be stretched if a 60-N force were applied?

9.

You and your friend pull on opposite ends of a rope. You each pull with a force of 10 newtons. What is the tension in the rope?

10. Two friends decide to build their strength by having a tug of war each day. They each pull with a force of 200 N. a.

How much tension is in the rope?

b.

One day, one of the friends is sick and cannot work out. The other friend decides to build strength by tying the rope around a tree and pulling on the rope. How much must the single friend pull in order to get the same workout as he normally does? What is the tension on the rope? Explain. In both cases above, what is the net force on the rope if (a) neither person is moving, and (b) the tree does not move?

c.

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11. Thomas pushes a 250-N box across a wooden floor at a constant speed using 75 N of force. If a second box of the same weight is stacked on top of the first, how much force would Thomas need to push the two boxes across the same floor? 12. Your backpack weighs 50 N. You pull it across a table at a constant speed by exerting a force of 20 N to the right. Draw a free-body diagram showing all four forces on the backpack. State the strength of each force. 13. You exert a 50-N force to the right on a 300-N box that is on a table. However, the box does not move. Draw a free-body diagram for the box. Label all the forces and state their strengths. Explain why the box doesn’t move. Section 5.3

14. Find the net force on each box.

15. A 20-kilogram monkey hangs from a tree limb by both arms. Draw a free-body diagram showing the forces on the monkey. Hint: 20 kilograms is not a force! 16. The weight of a book resting on a stationary table is 9 N. How much is the normal force on the book? What would you need to do to increase the normal force on the book? 17. Is it possible to arrange three forces of 100 N, 200 N, and 300 N so they are in equilibrium? If so, draw a diagram.

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FORCE

18. You weigh a bear by making him stand on four scales as shown. Draw a free-body diagram showing all the forces acting on the bear. If his weight is 1,500 newtons, what is the reading on the fourth scale?

Section 5.2

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3.

When an ice skater is on ice, a small amount of melting occurs under the blades of the skates. How does this help the skater glide? Your answer should discuss at least one type of friction.

4.

Joints, such as knees and elbows, are designed to move freely. Find out how friction is reduced in a joint.

5.

When on a mission, astronauts experience weightlessness. a.

Research weightlessness. Define it in terms of the forces experienced by an astronaut.

b.

Research the effects of weightlessness on people and what astronauts do to counter those effects.

Applying Your Knowledge Section 5.1

Section 5.3

1.

6.

2.

What is the weight of your favorite animal at different places in the universe? a.

First, find your favorite animal’s mass in kilograms. (1 pound = 0.454 kilogram; 2.2 pounds = 1 kilogram)

b.

Then, find the values of gravitational force (g) on five different planets or moons. The next page has values for g for the planets in our solar system in units of N/kg.

c.

Make a table that lists g for each planet or moon and your animal’s weight in Newtons on each.

Use the data in the table on the next page to answer the following questions.

CHAPTER 5

Use the diagram to answer the following questions.

a.

You know that mass is related to the strength of an object’s gravitational force. Does the data in the table support this statement? Support your answer with an explanation.

Is the object shown in the diagram in equilibrium? Why or why not?

b.

Redraw this free-body diagram in a way that shows that the box will move to the right.

b.

Is gravitational force related to the number of moons that a planet has?

c.

Redraw this free-body diagram so that the box will move downward.

c.

Is gravitational force related to how far a planet is from the Sun?

d.

Now, come up with your own question and answer it using the data in the table.

a.

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6

CHAPTER 6

Newton’s Laws of Motion FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

In January 1993, the 53rd space shuttle mission crew brought some toys on board. During the flight, crew members played with the toys to see how they would work in “microgravity.” Can you imagine trying to shoot a ball through a hoop while floating around in the space shuttle? Would a toy car be able to race around a loop track in space? You can learn how the toys behaved in space by doing an Internet search using the keywords “toys in space.” But by reading this chapter first, you may be able to predict how the toys worked in space. This chapter presents the laws of motion as stated by Sir Isaac Newton (1642–1727). Newton discovered answers to many questions about motion. Many historians believe Newton’s ideas about motion were the beginning of modern science.

4 Why is a bowling ball harder to move than a golf ball?

4 How is acceleration related to force and mass?

4 What would happen if Sir Isaac Newton had a skateboard contest with an elephant?

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6.1 Newton’s First Law

MOV E!

People who study science consider Sir Isaac Newton to be one of the most brilliant scientists who has ever lived. His three laws of motion are among the most widely used natural laws in all of science. Newton’s laws are not complicated math equations. They are brilliantly simple rules that show us an elegant way to make sense of how our world works.

This will not work.

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Force changes motion Force changes When playing miniature golf, what do you do to move the golf ball toward an object’s the hole? Do you tell the ball to move? Of course not! You hit the ball with motion the golf club to get it rolling. In physics, “hit the ball” means the golf club

Only force has the ability to change motion.

applies a force to the ball. This force is what changes the ball from being at rest to being in motion (Figure 6.1). Motion can change only through the action of a force. This statement is the beginning of Newton’s first law. Why do things Once moving, the ball rolls some, slows down, and eventually stops. For a stop moving? long time, scientists thought the natural state of all things was to be at rest

(stopped). They believed force had to be applied to keep an object moving and that constant motion required a constant force. They were wrong!

Force

Change in motion

Figure 6.1: Force has the ability to change the motion of an object.

The real The golf ball stops because the force of friction keeps acting on it until there explanation is no longer any motion. Suppose the golf course were perfectly level and

had no friction. After being hit with the golf club, the ball would keep moving in a straight line at a constant speed forever. The ball would neither slow down nor change direction unless another force acted on it. Being stopped or moving with constant speed and direction are both natural states of motion and neither one requires any force to sustain it. Net force When you hit a golf ball, the force from the club is not the only force that

acts on the ball (Figure 6.2). The ball’s weight, the normal force from the ground, and friction are also acting. The ball moves according to the net force acting on the ball. The golf club causes the ball to move because its force overcomes the friction force keeping the ball in place. Newton’s first law is written in terms of the net force because that is what affects motion.

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Figure 6.2: Four forces act on a golf ball. The net force determines how the ball moves.

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The first law: The law of inertia Newton’s first Newton’s first law says objects continue the motion they already have law unless they are acted on by a net force (the sum of all forces acting on an

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object at any given time). When the net force is zero, objects at rest stay at rest, and objects that are moving keep moving in the same direction with the same speed.

When the net force is zero, objects at rest stay at rest and objects in motion keep moving with the same speed and direction. Force is The first law says there can be no change in motion without a net force. That required to includes slowing down! It takes a net force (often friction) to make things change motion slow down. If forces are truly balanced, a moving object will keep moving

Newton’s first law - a law of motion that states that an object at rest will stay at rest and an object in motion will stay in motion with the same velocity unless acted on by an unbalanced force.

unbalanced forces - forces that result in a net force on an object and can cause changes in motion. inertia - the property of an object that resists changes in its motion.

forever with the same speed, in the same direction. Balanced and Changes in motion come from unbalanced forces. Forces are “unbalanced” unbalanced when the net force is not exactly zero. A rolling golf ball on a grassy golf forces course is not in equilibrium because friction is an unbalanced force. Forces

are “balanced” when they add up to zero net force. An object is in equilibrium if all of the forces on it are balanced. Inertia The first law is often called the “law of inertia” because inertia is the

property of an object that resists changes in motion. Inertia comes from mass. Objects with more mass have more inertia. To understand inertia, imagine moving a bowling ball and a golf ball that are both at rest (Figure 6.3). A golf ball has a mass of 0.05 kilograms, and suppose the bowling ball has a mass of 5 kilograms. The bowling ball has 100 times more mass than the golf ball, so it has 100 times more inertia too. Which needs more force to start moving? If you push for the same distance, the bowling ball takes much more force to get it moving the same speed as the golf ball. The bowling ball needs more force because the bowling ball has more inertia than the golf ball. The greater an object’s inertia, the greater the force needed to change its motion.

Figure 6.3: The bowling ball has more mass than the golf ball. The bowling ball is harder to move because it has more inertia.

6.1 NEWTON’S FIRST LAW

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Solving Problems: Net Force and the First Law

Forward force between road and tires = 2,000 N

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A car drives along the highway at constant velocity. Find the car’s weight and the friction force if the engine produces a force of 2,000 N between the tires and the road and the normal force on the car is 12,000 N (Figure 6.4). 1. Looking for:

You are asked for the car’s weight and the friction force.

2. Given:

You are given the normal force and forward force between the road and tires. The normal force is 12,000 N and the forward force is 2,000 N. The car is moving at a constant velocity.

3. Relationships:

Newton’s first law states that if the car is moving at a constant velocity, the net force must be zero.

4. Solution:

The weight of the car balances the normal force. Therefore, the weight of the car is a downward force: 12,000 N. The forward force balances the friction force so the friction force is 2,000 N in the opposite direction of the car’s motion. Your turn...

a. Identify the forces on the same car if it is stopped at a red light on level ground. b. While the car is moving forward, a gust of wind gives it a big push from behind. Since most of the friction on a car (at highway speeds) is from the air, the friction force is reduced from 2,000 N to 1,500 N. What is the net force on the car if the engine force remains at 2,000 N? Does it still move at constant velocity?

Friction force Normal force = 12,000 N

Weight

Figure 6.4: The forces on the car.

a. When stopped, the car experiences a normal force of 12,000 N and its weight of 12,000 N. b. The net force is 500 N. No, while the wind is blowing, the car is not moving at constant velocity since it is experiencing a net force. c. The normal force is 13,000 N. d. The normal force of the floorboard on your feet is 50 N.

c. What is the normal force on the car if 1,000 N of luggage is added? d. As you sit on the passenger seat of the car, the seat exerts a normal force of 550 N on you. If you weigh 600 N, what is the normal force of the car’s floorboard on your feet?

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Section 6.1 Review

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1. For each of the following situations, identify what creates one of the forces that creates the motion described (there may be many). a. A flag flaps back and forth at the top of a flagpole. b. A soccer ball is passed from one player to another. c. A large piece of hail falls toward the ground. d. The ocean tide goes from high to low at the seashore. (You might have to do a little research to get this one if you don’t know already.) 2. Which has more inertia—a shopping cart full of groceries or an empty shopping cart? 3. In the following situation, which diagram (A, B, C, or D) best illustrates the net force experienced by the cart when the weight pulls downward?

Mass Transportation Cars and planes with more inertia take more force to accelerate. Since inertia is related to mass, in order to reduce inertia you must reduce mass. The mass of a car or plane is a trade-off between inertia and the strength of materials of the car or plane. We want strong materials, but we don’t want them so heavy that it takes too much energy (fuel) just to get the car or plane moving! 1. Research how cars or planes have been designed to have less mass. 2. How is the balance between strength and mass resolved when designing cars or planes?

4. Forces contribute to the net force on a car rolling down a ramp. a. Which force supports the car’s weight? b. Which force accelerates the car down the ramp? c. Which force acts against the motion of the car? 5. Imagine whirling a ball on a string over your head. Suppose the knot holding the ball comes loose and the ball is instantly released from the string. What path does the ball take after leaving the string? Use Newton’s first law to explain your answer.

6.1 NEWTON’S FIRST LAW

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6.2 Newton’s Second Law What kind of change happens when forces are not balanced? The answer is acceleration. Acceleration is a change in velocity (speed or direction). Newton’s second law describes how acceleration depends on both force and mass.

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The three main ideas of the second law What is the Newton’s first law tells us that motion cannot change without a net force. second law The second law tells us exactly what kind of change is caused by unbalanced about? forces. The second law answers questions like: “How much force does it take

to change the speed of a 1,000-kg car from 0 to 80 km/h?” Anyone who does anything involving motion needs to understand the second law. The three main Here are the three big ideas covered by the second law. ideas

1.

Acceleration is the result of unbalanced forces.

2.

A larger force makes a proportionally larger acceleration.

3. Acceleration is inversely proportional to mass. Unbalanced The first law tells us that objects in motion can continue to move even forces cause without any net force. This is true as long as the motion is at a constant speed acceleration and in a straight line. The second law says that any unbalanced force results in acceleration. We know that acceleration causes changes in velocity (speed or direction). Putting these two ideas together tells us two things about force and motion: (1) Unbalanced forces cause changes in speed, direction, or both; and (2) any time there is a change in speed or direction, there must be an unbalanced force acting. Force and motion connect through acceleration

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Figure 6.5: The newton, a unit of force, is defined in terms of the acceleration it can create.

The second law is the connection between force, mass, and motion. The connection occurs through acceleration, which results in changes in speed and/or direction. In fact, the unit of force (newton) is defined by the second law (Figure 6.5).

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Acceleration and force Acceleration is The second law says that acceleration is proportional to force. What does this proportional to mean? It means that, all other things being equal, if the force doubles, the force acceleration also doubles. If the force is reduced by half, the acceleration is

also reduced by half (Figure 6.6).

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Example: A Here is an example. Two engineers are each asked to design a battery-operated robot mail cart motor for a robot mail cart. The cart is supposed to drive around to people’s

offices and stop so they can collect their mail. One engineer chooses a motor that produces a force of 50 newtons. The other chooses a motor that produces a force of 100 newtons. The acceleration The robot with the smaller motor goes from rest to a top speed of 4 m/s in of the mail cart 4 seconds. The acceleration is 1 m/s2. The robot with the larger motor

accelerates to the same top speed in 2 seconds. Its acceleration is 2 m/s2. Both robots reach the same top speed. The one with the bigger motor accelerates to its top speed twice as fast because it uses twice as much force. Of course, the one with the bigger motor drains its batteries faster too, because there is also a trade-off between acceleration and energy.

Acceleration is Another important factor of the second law is that the acceleration is always in the direction in the same direction as the net force. A force in the positive direction causes of the net force acceleration in the positive direction. A force in the negative direction

causes acceleration in the negative direction. A sideways net force causes a sideways acceleration and makes the object turn.

Figure 6.6: “Acceleration is proportional to force” means that if force is increased or decreased, acceleration will be increased or decreased by the same factor.

STUDY SKILLS Reviewing the Newton One newton is the force needed to change the speed of 1 kilogram by 1 m/s in 1 second. This means that: 1 N = 1 kg

· m/s2

Or you can say 1 newton equals 1 kilogram-meter per second squared.

6.2 NEWTON’S SECOND LAW

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Acceleration and mass Mass and The greater the mass, the smaller the acceleration for a given force acceleration (Figure 6.7). This means that acceleration is inversely proportional to mass.

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When the forces stay the same, increasing the mass decreases the acceleration. For example, an object with twice the mass will have half the acceleration if the same force is applied. An object with half the mass will have twice the acceleration.

Newton’s second law - a law of motion that states that acceleration is equal to force divided by mass.

Why mass Acceleration decreases with mass because mass creates inertia. Remember, reduces inertia is the property of matter that resists changes in motion (acceleration). acceleration More mass means more inertia, and therefore more resistance to acceleration. Newton’s Force causes acceleration and mass resists acceleration. Newton’s second law second law relates the force on an object, the mass of the object, and the

object’s acceleration.

The acceleration caused by a net force is proportional to force and inversely proportional to mass.

Figure 6.7: How acceleration is affected by mass.

The formula for The relationships between force, mass, and acceleration are described in the the second law formula for Newton’s second law. Answer the following questions to test your understanding of Newton’s second law. 1. Force is tripled but mass stays the same. What happens to acceleration? 2. Acceleration decreases but the force is the same. What must have happened to the mass?

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Summarizing the second law Writing the You can use Newton’s second law to calculate force, mass, or acceleration if second law two of the three values are known. As you solve problems, keep in mind the

Newton vs. Einstein

concepts shown below. Larger force leads to larger acceleration. Larger mass leads to smaller acceleration.

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Net force and Newton’s second law explains the effect of the net force on motion. You must the second law consider all the forces that are acting and add them up to find the net force.

Then you use the net force to calculate any acceleration. You can also use the second law to calculate net force from a given mass and acceleration.

In 2005, The Royal Society of London took a poll of scientists and members of the public to see whether Sir Isaac Newton or Albert Einstein contributed more to science and humankind. The results were close in this heated debate! But, Sir Isaac Newton came out the winner! Here are the results.

Now, take your own poll to find out what people think about Newton and Einstein and their impact on science and our world.

To use Newton’s second law properly, keep the following important ideas in mind. 1.

The net force is what causes acceleration.

2.

If there is no acceleration, the net force must be zero.

3.

If there is acceleration, there must also be a net force.

4.

The force unit of newtons is based on kilograms, meters, and seconds.

6.2 NEWTON’S SECOND LAW

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Solving Problems: Newton’s Second Law

Race Car Design

A car has a mass of 1,000 kg. If a net force of 2,000 N is exerted on the car, what is the car’s acceleration? You are asked for the car’s acceleration.

2. Given:

You are given mass (kg) and net force (N). Recall that 1 N = 1 kg · m/s2.

3. Relationships:

acceleration = force ÷ mass

4. Solution:

acceleration = (2,000 N) ÷ (1,000 kg) = 2 m/s2 Your turn...

a. As you coast down a hill on your bicycle, you accelerate at 0.5 m/s2. If the total mass of your body and the bicycle is 80 kilograms, what is the net force pulling you down the hill? b. What is the mass of an object that is experiencing a net force of 200 N and an acceleration of 500 m/s2? c. Recall that speed = distance ÷ time. The ratio of distance ÷ time is the same as the slope of a distance vs. time graph. That means speed is the slope of the distance vs. time graph. Acceleration is speed ÷ time. Use this graph of speed vs. time to find acceleration (the slope of this graph).

a. 40 N b. 0.40 kg

Speed vs. time 40

Speed (m/s)

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1. Looking for:

Race cars are designed to have strong engines that produce large forces between the car and the road. They are also designed to be lightweight. Why is this combination of high forces and low mass useful for the design of a race car? Use Newton’s second law to explain.

c. 10 m/s2

30 20 10 0

1

2

3

4

Time (s)

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Section 6.2 Review 1. What are the three main ideas associated with Newton’s second law of motion? List them using your own words. 2. What conditions are necessary for acceleration to occur?

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3. One kilogram-meter per second squared is also equal to what unit? 4. How much force would you need to cause a 20-kilogram object to accelerate in a straight line to 20 m/s2? 5. Different forces are applied to cars of different masses. The acceleration is measured for each combination of force and mass. Graph the data and determine the acceleration. Force goes on the y-axis and mass goes on the x-axis. Be sure to label each axis and give your graph a title. Force (N)

Mass (kg)

5 10 15 20

1 2 3 4

Figure 6.8: Question 6.

6. A 2-kilogram rabbit starts from rest and is moving at 6 m/s after 3 seconds. What net force must be exerted on the rabbit (by the ground) to cause this change in speed (Figure 6.8)? 7. Explain how changing force or mass affects the acceleration of an object. Provide one example to support your answer. 8. A tow truck pulls a 1,500-kilogram car with a net force of 4,000 newtons. What is the acceleration of the car? 9. A potato launcher uses a spring that can apply a force of 20 newtons to potatoes. A physics student launched a 100-gram potato, a 150-gram potato, and a 200-gram potato with the launcher. Which potato had the greatest acceleration?

Figure 6.9: Question 10.

10. An experiment measures the speed of a motorcycle and rider (total mass = 250 kg) every 2 seconds (Figure 6.9). The motorcycle moves in a straight line. What is the net force acting on the motorcycle and rider? 6.2 NEWTON’S SECOND LAW

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6.3 Newton’s Third Law and Momentum

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Newton’s first and second laws apply to the motion of an individual object. Newton’s third law applies to forces between interacting objects. Think about throwing a basketball (Figure 6.10). You feel the ball push back against your hand as you throw it. You apply a force to the ball to make it move. Where does the force against your hand come from? Can you predict your hand’s motion and the basketball’s motion after the throw?

Forces always come in matched pairs An imaginary Imagine a skateboard contest between Isaac Newton and an elephant. They skateboard can push against each other, but not against the ground. The one whose contest skateboard moves the fastest wins. The elephant is much stronger and pushes

off Newton with a huge force thinking he will surely win. But will he?

The winner Newton flies away with a great speed and the puzzled elephant moves

backward with a much smaller speed. Newton wins—and will always win this contest against the elephant. No matter how hard the elephant pushes, Newton will always move away faster. Why?

Figure 6.10: You experience

Newton’s third law (action-reaction) whenever you apply force to any object, such as a basketball.

Think of three examples of action-reaction pairs that you experienced before class today. Write each one down and identify the action and reaction forces. Also write down what object each force acted on. Hint: The action and reaction forces never act on the same object.

Forces always It takes force to make both Newton and the elephant move. Newton wins come in pairs because forces always come in pairs. The elephant pushes against Newton

and that action force pushes Newton away. The elephant’s force against Newton creates a reaction force against the elephant. The action and reaction forces are equal in strength. Newton has much less mass so he has much more acceleration, therefore his speed is always greater.

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The third law: Action and reaction The first and The first two laws of motion apply to individual objects. The first law says an second laws object will remain at rest or in motion at a constant velocity unless acted upon

by a net force. The second law states that acceleration equals the force on an object divided by the mass of the object.

Newton’s third law - a law of motion that states that for every action force there is a reaction force equal in strength and opposite in direction.

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The third law The third law of motion deals with pairs of objects. This is because all forces come in pairs. Newton’s third law states that every action force creates a

reaction force that is equal in strength and opposite in direction.

Every action force creates a reaction force that is equal in strength and opposite in direction. Force pairs There can never be a single force acting alone, without its action-reaction

partner. Forces only come in action-reaction pairs. In the skateboard contest, the net force is the difference between the force created by the elephant in one direction and the force created by Newton in the opposite direction. The action of this force acts on Newton and moves Newton. The reaction of the same force acts on the elephant and moves the elephant. The combined strength of Newton and the elephant create two equal and opposite forces, an action and a reaction.

Figure 6.11: It doesn’t matter which force you call the action and which you call the reaction.

The labels The words action and reaction are just labels. It does not matter which force action and is called action and which is called reaction. You simply choose one to call reaction the action and then call the other one the reaction (Figure 6.11). Why action and reaction forces do not cancel each other out

Why don’t action and reaction forces cancel each other out? The reason is action and reaction forces act on different objects. For example, think again about throwing a ball. When you throw a ball, you apply the action force to the ball, creating the ball’s acceleration. The reaction is the ball pushing back against your hand. The action acts on the ball and the reaction acts on your hand. The forces do not cancel each other out because they act on different objects. You can only cancel out forces acting on the same object (Figure 6.12).

Figure 6.12: Action and reaction

forces do not cancel each other out. One force acts on the ball, and the other force acts on the hand.

6.3 NEWTON’S THIRD LAW AND MOMENTUM

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Action and reaction forces A skateboard Think carefully about propelling a skateboard with your foot. Your foot example presses backward against the ground (Figure 6.13). The force acts on the

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ground. However, you move, so a force must act on you, too. Why do you move? What force acts on you? You move because the action force of your foot against the ground creates a reaction force of the ground against your foot. You “feel” the ground because you sense the reaction force pressing on your foot. The reaction force is what makes you move because it acts on you. Draw diagrams When sorting out action and reaction forces, it is helpful to draw diagrams.

Draw each object apart from the other. Represent each force as an arrow in the appropriate direction. The illustration in Figure 6.13 is a good example of a diagram that shows a pair of action and reaction forces. The Solve It! box in the sidebar gives you an opportunity to think of your own example and draw a diagram. Action and Below are some guidelines to help you sort out action and reaction forces. reaction guidelines Guidelines for action–reaction forces

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Examples

Both forces are always there whenever any force occurs.

Your foot pushes (action) and the ground pushes back (reaction).

They always have the exact same strength.

The force arrows are the same length.

They always act in opposite directions.

The force arrows point in opposite directions.

They always act on different objects.

Your foot and the ground.

Both are real forces and can cause changes in motion.

You move forward on your skateboard. d.

Figure 6.13: You move forward because of the reaction force of the ground on your foot.

Think of an action-reaction pair situation. Then, draw a diagram illustrating the action-reaction pair. Use the tips in the text for drawing your diagram.

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Solving Problems: Action and Reaction

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A woman with a weight of 600 newtons is sitting on a chair (Figure 6.14). Describe one action-reaction pair of forces in this situation. 1. Looking for:

You are asked for a pair of action and reaction forces.

2. Given:

You are given an action force—the woman’s force on the chair. Her force is 600 N.

3. Relationships:

Action-reaction forces are equal and opposite and act on different objects.

4. Solution:

The downward force of 600 N exerted by the woman on the chair is an action. Therefore, the chair acting on the woman provides an upward force of 600 N and is a reaction.

Figure 6.14: An action is sitting on a chair.

Your turn...

a. 640 N

a. A dog jumps up and sits on the lap of the woman who is sitting in the chair in Figure 6.14. The dog’s weight is 40 newtons. What is the reaction force provided by the chair now?

b. The weight of the chair is 60 N. Action-reaction pairs include the dog-woman’s lap, the woman-chair, the chair-strongman, and the strongman-ground.

b. A strong man now picks up the chair with the woman and the dog and holds them all above his head. If the upward force from the strong man is 700 newtons, what is the weight of the chair in newtons? Describe the different action-reaction pairs in this scenario. c. A baseball player hits a ball with a bat. Describe an action-reaction pair of forces in this situation.

c. The force of the bat on the ball (action) accelerates the ball. The force of the ball on the bat (reaction) slows down the swinging bat.

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Collisions and momentum The effect of Newton’s third law tells us that when two objects collide, they exert equal forces and opposite forces on each other. However, the effect of the force is not

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always the same. Imagine two hockey players moving at the same speed toward each other, one with twice the mass of the other. The force on each during the collision is the same strength, but they do not have the same change in motion during the collision.

momentum - the mass of an object times its velocity.

law of conservation of momentum - a law that states that as long as interacting objects are not influenced by outside forces, the total amount of momentum is constant.

Force = 200 N Force = 200 N

m = 80 kg

m = 40 kg

Momentum When studying motion related to collisions, we can predict how two

colliding objects might move using Newton’s third law of motion and momentum. Momentum is the mass of a object times its velocity. The units for momentum are kilogram-meter per second (kg · m/s). MOMENTUM Mass (kg) Momentum (kg · m/s)

p = mv

Calculate: Use the momentum formula to find the momentum of each hockey player before they collide. Player 1: m = 80 kg; v = 2 m/s Player 2: m = 40 kg; v = 3 m/s Predict: Let’s say the motion of Player 1 is in the positive direction and the motion of Player 2 is in the negative direction. Based on your momentum calculations, in which direction do you think the two combined players will move after the collision?

Velocity (m/s)

The law of Using this information, we can determine the momentum of each player in conservation of the example above. The law of conservation of momentum states that as momentum long as the interacting objects are not influenced by outside forces (like

friction) the total amount of momentum is constant (does not change). This means that the total amount of momentum for the colliding hockey players before the collision equals the total amount of momentum afterward. Also, any momentum lost by one player is gained by the other one.

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Understanding the law of conservation of momentum Positive The forces on any two interacting objects are always equal and opposite. and negative Similarly, the momentum of two interacting objects is equal and opposite. momentum Therefore, it makes sense to use positive and negative values to tell the

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direction of motion (Figure 6.15). Momentum can be positive (moving to the right) or negative (moving to the left). A ball example Let’s say a skateboarder is standing on a skateboard and is holding a ball.

Before he throws the ball, his velocity (and the ball’s) is zero. Since momentum is mass times velocity, the total momentum is also zero. The law of conservation of momentum says that after the ball is thrown, the total momentum still has to be zero. Here’s where positive and negative values help us. Conservation of If the ball has a mass of 1 kilogram and the skateboarder throws it at a momentum velocity of –20 m/s to the left, the ball takes away –20 kg · m/s of momentum.

Figure 6.15: The direction is

important when using the law of conservation of momentum. We use positive and negative numbers to represent opposite directions.

To make the total momentum zero, the skateboarder must take away +20 kg · m/s of momentum. If his mass is 40 kilograms and you ignore friction, then his speed is +0.5 m/s to the right (Figure 6.16). More mass Because of his greater mass, the skateboarder will have a slower speed. The results in less ball, which has less mass, has the greater speed. They each have equal and acceleration opposite momentum after the throw. The two objects, the skateboarder and the

ball, have different speeds because they have different masses, not because the forces are different! Jet planes and Rockets and jet planes use the law of conservation of momentum to move. In rockets a process called jet propulsion, a jet moves forward when the engine pushes

exhaust air at very high speed out of the back of the engine. The momentum lost by the air going backward is compensated for by the momentum gained by the jet moving forward. Similarly, a rocket accelerates in space because it pushes mass at high speed out the end of the engine in the form of exhaust gases from burning fuel. The forward momentum of a rocket is equal to, but in the opposite direction from, the momentum of the escaping mass ejected from the end of the engine.

Figure 6.16: The result of a

skateboarder throwing a 1-kg ball at a velocity of –20 m/s is that he and the skateboard, with a total mass of 40 kg, move backward at a velocity of +0.5 m/s if you ignore friction. If you account for friction, would the calculation for velocity of the skateboarder on the skateboard end up being less or more than 0.5 m/s?

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Solving Problems: Conservation of Momentum

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An astronaut in space throws a 2-kilogram wrench away from her at a velocity of –10 m/s. If the astronaut’s mass is 100 kilograms, at what velocity does the astronaut move backward after throwing the wrench? 1. Looking for:

You are asked for the astronaut’s speed. Since the astronaut is in space, we can ignore friction.

2. Given:

You are given the mass and velocity of the wrench and the mass of the astronaut.

3. Relationships:

This is enough information to apply the law of conservation of momentum. The momentum of the wrench (m1v1) and the momentum of the astronaut (m2v2) add up to zero before the wrench is thrown. m1 v1 + m2 v2 = 0

4. Solution:

The momentum of the wrench and the astronaut also add up to zero after the wrench is thrown. [2 kg × (–10 m/s)] + [(100 kg) × v2] = 0; v2 = +20 ÷ 100 = +0.2 m/s The astronaut moves backward at a velocity of +0.2 m/s to the right. Your turn...

a. Two hockey players have a total momentum of +200 kg·m/s before a collision (+ is to the right). After their collision, they move together. In what direction do they move and what is their momentum?

Figure 6.17: Your turn... Question b.

a. The two hockey players move in the positive direction (or to the right). Their momentum after the collision is +200 kg·m/s. b. The car has less mass and therefore less inertia, so it accelerates more (and may become more damaged) than the truck in this collision.

b. When a large truck hits a small car, the forces are equal (Figure 6.17). However, the small car experiences a much greater change in velocity than the big truck. Explain why.

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Section 6.3 Review 1. Emilio tries to jump to a nearby dock from a canoe that is floating in the water. Instead of landing on the dock, he falls into the water beside the canoe. Use Newton’s third law to explain why this happened. Hint: First identify the action-reaction pair in this example.

Squid Science

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2. You push backward against the ground to move a skateboard forward. The force you make acts against the ground. What force acts against you to move you forward? 3. Explain why action-reaction forces do not cancel each other out, resulting in zero net force. 4. The momentum of an object depends on what two factors? 5. The engine of a jet airplane pushes exhaust gases from burning fuel backward. What pushes the jet forward?

6. A small rubber ball is thrown at a heavier, larger basketball that is not moving. The small ball bounces off the basketball. Assume there are no outside forces acting on the balls. a. How does the force on the small ball compare to the force on the basketball? b. Compare the total momentum of the two balls before and after the collision. c. The mass of the basketball is 600 grams and its velocity before the small ball hits is 0 m/s. The mass of the small ball is 100 grams and its velocity is +5 m/s before the collision and –4 m/s afterward. What is the velocity of the basketball after the collision?

Airplanes are not the only things that use jet propulsion. Several animals have adapted jet propulsion in order to get around. A squid takes water into its body chamber and rapidly pushes it out of a backward-facing tube. The water squirts backward and the squid jets forward. What are the action-reaction forces in this example? Draw a diagram to illustrate your answer. Most species of squid are small, but Architeuthis, the giant squid, is not! In September 2004, Japanese scientists took over 500 photos of a giant squid. The animal was nearly 25 feet long! This was the first record of a live giant squid in the wild. Conduct an Internet search using the key phrase “giant squid” to find more information and photos.

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Chapter 6 Assessment Vocabulary

2.

Two identical-looking, large, round balls are placed in front of you. One is filled with feathers and the other is filled with sand. Without lifting the balls, how could you use Newton’s first law to distinguish between them?

3.

Which motion is possible for an object that has no unbalanced forces?

Select the correct term to complete the sentences.

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Newton’s first law

unbalanced forces

inertia

momentum

Newton’s second law

Newton’s third law

a. b. c. d.

Section 6.1

being stopped moving with constant direction moving with changing speed moving with constant velocity

1.

____ says that objects continue the motion they already have unless they are acted on by an unbalanced force.

2.

If the net force acting on an object is not zero, then the forces acting on the object are ____.

Section 6.2

Objects with more mass have more ____.

4.

3.

a. b.

Section 6.2

4.

The relationship between the force on an object, the mass of the object, and its acceleration is described by ____.

Section 6.3

5. 6.

____ states that every action force creates a reaction force that is equal in strength and opposite in direction. The law of conservation of ____ can be used to predict motion of interacting objects after they collide.

c.

If you are applying the brakes on your bicycle, and you are slowing down, are you accelerating? Why or why not?

6.

What is the formula that summarizes Newton’s second law?

Section 6.3

7.

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Identify each statement as correct or incorrect. If incorrect, rewrite the sentence so that it is correct. a. b.

Section 6.1

Newton’s first law states that no force is required to maintain motion in a straight line at constant speed. If Newton’s first law is true, why must you continue to pedal a bicycle on a level surface in order to keep moving?

the time it takes to move 1 kilogram the force it takes to change the speed of 1 kilogram by 1 m/s in 1 second the speed it takes to move a 1 kilogram mass in 1 hour

5.

Concepts 1.

What is a newton?

8.

In an action-reaction pair, the forces work on the same object. Every action force creates a reaction force and the two forces are different in strength but act in the same direction.

Give an example of the law of conservation of momentum from everyday life.

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9.

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When a bug traveling west collides with the windshield of a car traveling east, which statement about the collision is true?

6.

What is the acceleration of a truck with a mass of 2,000 kg when its brakes apply a force of 10,000 N?

a. b. c. d.

7.

Gina is pushing a 10-kg box with 50 N of force toward the east. Dani is pushing the same box at the same time with 100 N of force toward the west. Assuming there is no friction, what is the acceleration of the box?

8.

A car speeds up from 5 m/s to 29 m/s over 4 seconds.

The bug feels a stronger force than the car. The bug and the car feel the same size force. The car accelerates more than the bug. The bug does not accelerate due to the force.

Problems

a. b.

Section 6.1

1.

While an object is moving at a constant 20 m/s, a 5-N force pushes the object to the left. At the same time, a 5-N force is pushing the object to the right. What will the object’s velocity be after 10 seconds?

2.

A bowling ball has a mass of 6 kilograms. A tennis ball has a mass of 0.06 kilograms. How much inertia does the bowling ball have compared to the tennis ball?

3.

What is the net force on the refrigerator shown below?

4.

Make a free-body diagram of someone pushing a refrigerator that shows: a. b.

What is the car’s acceleration? If the car had started at 29 m/s and ended at 5 m/s after 4 seconds, what would its acceleration be? How is this different from the answer above?

Section 6.3

9.

Jane has a mass of 40 kg. She pushes on a 50-kg rock with a force of 100 N. What force does the rock exert on Jane?

10. Look at the picture below. a. b.

Identify at least three action-reaction pairs. Why might it be hard for the firefighter to hold the hose steady when the water gushes out of the hose? Think about the law of conservation of momentum.

A net force of 100 N with the refrigerator being pushed to the right. The refrigerator in equilibrium.

Section 6.2

5.

CHAPTER 6

What force is needed to accelerate a 1,000-kg car from a stop to 5 m/s2?

11. A 3,000-kg car bumps into a stationary 5,000-kg truck. The velocity of the car before the collision was +4 m/s and –1 m/s after the collision. What is the velocity of the truck after the collision? CHAPTER 6 ASSESSMENT

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Applying Your Knowledge

4.

Section 6.1

1.

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2.

You are watching a magic show. During one trick, the magician rolls a ball down a hill. Suddenly, the ball stops moving down the hill. It is as if the ball is defying gravity! Come up with an explanation for how the magician might have accomplished his trick. Hint: Think of all the forces that might be acting on the ball.

b. c.

d.

List all the forces that are acting on a hot air balloon to keep it on the ground. List all the forces that act on a hot air balloon when it is in the sky. Sketch a free-body diagram for a hot air balloon that is rising straight off the ground. Indicate the magnitude of forces with the length of the force vectors. Sketch a free-body diagram for a hot air balloon that is in a neutral position in the sky (neither rising nor sinking) but being blown eastward by the wind. Indicate the magnitude of forces with the length of the force vectors. What force might be opposing the wind?

Section 6.2

3.

a. b.

Answer the following motion questions for a hot air balloon. a.

The text stated that anyone who does anything involving motion needs to understand Newton’s second law. Think of a job or career that might involve using and understanding motion and answer the following. a. b.

Name the job or career. Describe the types of motion-related tasks that are involved in this job or career. Pick one task listed in your answer above and explain how understanding Newton's laws of motion might help accomplish the task better.

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Describe the design features you would incorporate into a battery-operated motor for a robot mail cart for the following situations. The design features to consider include the mass of the motor, rate of acceleration, and speed.

c.

A robot mail cart is needed to collect mail from offices located in a large warehouse. The warehouse has a lot of open space. A robot mail cart is needed in a small office space that has many offices that are close together. A robot mail cart is needed in an elementary school that has long hallways and many offices. However, many children are often in the hallways.

Section 6.3

5.

At the beginning of the chapter, you read about astronauts investigating how toys work in space. Describe how you think the following toys would work in space based on what you have learned in this chapter. a. b. c. d.

a ball that can be thrown through a hoop building blocks a board game with game pieces for each player a deck of cards

6.

Auto manufacturers design cars to withstand collisions. Research design features that allow a car and the people inside the car to survive a crash. Write a paragraph about one design feature that interests you.

7.

If you push a very large object, such as a building, it doesn’t move before or after the interaction. Explain why.

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CHAPTER

7

CHAPTER 7

Work and Energy FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

What would it take to throw a ball all the way to the Moon? The Moon is 384,000 kilometers away. Even the best baseball pitcher could not accomplish that feat because it takes much more energy than the pitcher can give. You could, however, throw a ball to the top of a telephone pole, which is only about 0.01 kilometers tall. The concept of energy explains how far a ball can be thrown above the ground, or how much light comes out of a bulb, or how hot the Sun gets. In fact, energy is responsible for all changes that happen in the physical world. Energy is what makes the universe active, and so to understand why things happen, and how they happen, we need to look at the flow of energy. If you have energy, you can make things change. The more energy you have, the bigger the changes can be, and the more work you can do. Changing the location of a ball from the ground to the Moon is a much larger change than moving it to the top of a telephone pole, and that’s why it takes more energy. The converse is also true: If you have no energy at all, nothing changes. Energy is everywhere! As you read this chapter, think about how energy is responsible for the changes that take place around you and even inside your body. For starters, can you identify the different forms of energy in the picture on this page?

4 What is work to a physicist? 4 What is energy, and what does it mean to conserve energy?

4 Which is a more efficient machine: a bicycle or an automobile?

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7.1 Force, Work, and Machines

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In the last chapter, you saw how force and motion are related through Newton’s laws of motion. Forces can be manipulated to accomplish physical tasks. How did ancient people move huge stones to build monuments, such as the Great Pyramid of Giza, long before the invention of trucks and engines? The ancient builders developed simple machines that allowed them to multiply by many times the force from their muscles. All simple machines obey a rule that says any advantage in force is compensated for by applying the force over a proportionally longer distance. This rule is an example of one of the most powerful laws in all of physics. The law involves the physics meaning of work, which you will explore in this section.

machine - a device with moving parts that work together to accomplish a task. input - forces, energy, or power supplied to make a machine accomplish a task.

output - forces, energy, or power provided by the machine.

Using machines What Machines allow us to do incredible things. Moving huge steel beams, technology digging tunnels that connect two islands, and building 100-story skyscrapers allows us to do are examples. Clever human inventions of machines make this possible. A machine is a device, such as a bicycle, with moving parts that work together

to accomplish a task (Figure 7.1). All the parts of a bicycle system work together to transform forces from your muscles into motion. A bicycle allows you to travel at faster speeds than you could on foot.

The concepts of For the machines in this chapter, the input includes everything you do to input and output make the machine accomplish a task, such as pushing on the bicycle pedals. The output is what the machine does for you, such as going fast or climbing

a steep hill. The input and output might be force, energy, or power. An electric saw uses your hand and electricity for input, and cuts wood for its output.

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Figure 7.1: A bicycle is a machine that allows you to travel faster than you can on foot.

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CHAPTER 7

Simple machines The beginning The development of cars, airplanes, and other modern machines began with of technology the invention of simple machines, such as levers. A simple machine is an

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unpowered mechanical device that accomplishes a task with only one movement. For example, a lever allows you to open a paint can, sweep the floor, or move a heavy rock (Figure 7.2). A variety of simple machines is shown below.

Input force and Simple machines work with forces. The input force is the force you apply to output force the machine. The output force is the force the machine applies to what you are

trying to move. Figure 7.3 shows how a lever is arranged to create a large output force from a small input force. A lever is a stiff structure that rotates around a fixed point called a fulcrum. Machines within Most of the machines we use today are made up of combinations of different machines types of simple machines. For example, a bicycle is a complex machine made

up of simple machines. A bicycle uses wheels and axles, levers (the pedals and kickstand), and gears. A gear is a rotating wheel with teeth that receives or transfers motion and forces to other gears or objects. If you take apart a complex machine such as a clock, a food processor or blender, or a car engine, you will find it is made of simple machines, such as gears.

simple machine - an unpowered mechanical device that accomplishes a task with only one movement. lever - a stiff structure that rotates around a fixed point called a fulcrum. gear - a rotating wheel with teeth that transfers motion and forces to other gears or objects.

Figure 7.2: Levers accomplish a task with one motion.

Output force 500 N Fulcrum

Figure 7.3: If arranged like this, a lever can create a large output force.

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Mechanical Advantage Mechanical Simple machines can manipulate input and output forces to create advantage mechanical advantage for the user. Mechanical advantage is the ratio of

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output force to input force. If the mechanical advantage is bigger than one, the output force is bigger than the input force (Figure 7.4). A mechanical advantage smaller than one means the output force is smaller than the input force. For a typical automotive jack, the mechanical advantage is 30 or more. For a mechanical advantage of 30, a force of 100 newtons (22.5 pounds) applied to the input arm of the jack produces an output force of 3,000 newtons (675 pounds)—enough to lift one corner of an automobile.

mechanical advantage - ratio of output force to input force for a simple machine.

How mechanical If you use a jack to lift a car, you will notice that you have to move the arm advantage is of the jack a lot to raise the car only a little. Machines create mechanical created advantage with trade-offs between force and distance. On the input of the

jack, a small force has to move a large distance. On the output of the jack, a much larger force moves only a small distance. This trade-off, or inverse relationship between force and distance, is characteristic of all simple machines and is due to a powerful natural law in physics (conservation of energy).

Figure 7.4: This jack is an example of a lever. The input force is applied to the rigid bar. The output force is then applied by the machine to lift the car.

Types of simple There are a few basic kinds of simple machines that create mechanical machines advantage. The lever, wheel and axle, rope and pulleys, screw, ramp, and

gears are the most common types. Complex machines such as a bicycle combine many simple machines into mechanical systems. A mechanical system is an assembly of simple machines that work together to accomplish a task.

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Levers Parts of All levers include a stiff structure that rotates around a fulcrum. For example, the lever you can make a lever by balancing a board on a log. The log is the fulcrum.

The side of the lever where the input force is applied is called the input arm. The output arm is the end of the lever that applies the output force.

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Mechanical Levers are useful because you can arrange the fulcrum and the input and advantage output arms to adjust the mechanical advantage of the lever. By changing the

position of the fulcrum, you can alter the amount of input force needed to produce the desired output. For example, if the input arm is three times longer than the output arm, the output force is three times greater than the input force. This lever has a mechanical advantage of three. Using the length of the lever arms, mechanical advantage can be calculated by dividing the length of the input arm by the length of the output arm. The three Pliers, a wheelbarrow, and your arm each represent one of the three classes of classes of levers levers. These objects all look different, so how are they similar? For starters,

they all accomplish a task with one movement. They also all operate using a fulcrum and lever arms. Each class of levers is defined by the location of the input and output forces relative to the fulcrum (Figure 7.5 and Table 7.1). Table 7.1: Classes of levers Class of Lever

Fulcrum

Force

Length of arms

1st

Between input and output forces

Vary in magnitude

Vary in length

2nd

One end of lever

Output > input

Input > output

3rd

One end of lever

Input > output

Output > input

Mechanical First-class levers can be set up to have a mechanical advantage of less than advantage of one, equal to one, or greater than one, depending on how long the input arm lever classes is compared to the output arm. Second-class levers have a longer input arm

than output arm, and will have a mechanical advantage greater than one. Third-class levers have a mechanical advantage of less than one since the input arm is shorter than the output arm.

Figure 7.5: These diagrams show the three classes of levers. What is the mechanical advantage of each of these levers: 1, > 1, or < 1?

7.1 FORCE, WORK, AND MACHINES

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Work and machines What work Simple machines obey a rule that says any advantage in force is compensated means for by applying the force over a proportionally longer distance. When a force in physics is applied over a distance, work can be done. The word work is used in many

work - a form of energy that comes from force applied over distance.

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different ways. You can work on science problems, your toaster might not work, and taking out the trash might be too much work. In physics, however, work has a very specific meaning. Work is the transfer of energy that results from applying a force over a distance (Figure 7.6). If you push a box with a force of 1 newton for a distance of 1 meter, you do 1 joule of work. Both work and energy are measured in the same units (joules) because work is a form of energy. Work is done by forces that cause movement

When thinking about work, remember that work is done by forces that cause movement. If nothing moves (distance is zero), no work is done, even if a huge force is applied. Work is done only by the part of a force that acts in the same direction as the resulting motion. Force A in Figure 7.7 does no work at all because it does not cause the block to move sideways. Force B is applied at an angle to the direction of motion of the block. Only part of force B (in the direction the block moves) does work. The most effective force is force C. All of force C does work because force C acts in the same direction the block moves.

Figure 7.6: Work is a form of energy you either use or get when a force is applied over a distance.

Lifting force Many situations involve work done by or against the force of gravity. To lift equals the something off the floor, you must apply an upward force with a strength weight equal to the object’s weight. It does not matter whether you lift the object

straight up or you carry it up the stairs in a zig-zag pattern. The work is the same in either case.

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Figure 7.7: All of force C does work.

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CHAPTER 7

Solving Problems: Work

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How much work is done by a person who pushes a cart with a force of 50 newtons if the cart moves 20 meters in the direction of the force (Figure 7.8)? 1. Looking for:

You are asked for work.

2. Given:

You are given values for force and distance.

3. Relationships:

Work = force × distance.

4. Solution:

The work done is: 50 N × 20 m = 1,000 J.

Figure 7.8: How much work is this person doing by pushing the cart?

Your turn...

a. How far does a 100-newton force have to move to do 1,000 joules of work? b. An electric hoist does 500 joules of work lifting a crate 2 meters. How much force does the hoist use? c. An athlete does one push-up. In the process, she moves half of her body weight, 250 newtons, a distance of 20 centimeters. This distance is the distance her center of gravity moves when she fully extends her arms. How much work did she do after one push-up?

a. 10 m b. 250 N c. 50 J d. You didn’t do any work because the wall did not move.

d. You decide to push on a brick wall with all your strength for 5 minutes. You push so hard that you begin to sweat. However, the wall does not move. If you end up pushing with a force of 500 newtons, how much work did you do?

7.1 FORCE, WORK, AND MACHINES

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Section 7.1 Review 1. List two reasons from the section that explain why a simple machine is a useful device.

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2. The arrangement of the lever in Figure 7.9 is similar to the arrangement you need to pry open the lid of a paint can. For the diagram to the right, label each part as fulcrum, output force, or input force. 3. Describe the term mechanical advantage. Why is it an important value to know when working with machines?

Output force 500 N

Input force

Fulcrum

Figure 7.9: Question 2.

4. You might be surprised to learn that a broom is a lever. What kind of lever is it: first, second, or third class? Explain your answer. 5. What is the best way to define work? a. applying a force for a period of time b. moving a certain distance c. applying a force over a distance d. applying a force at a given speed 6. If you push a box across a table with a force of 5 newtons and the box moves 0.5 meters, how much work has been accomplished? 7. If you do 200 joules of work using a force of 50 newtons, over what distance was the force applied? 8. A cart was pulled for a distance of 1 kilometer. The amount of work accomplished equaled 40,000 joules. With what force was the work accomplished?

Figure 7.10: Question 9.

9. In which of these cases (Figure 7.10) is a waiter doing work on the object? Explain your answer. Situation 1: The waiter is carrying a tray of glasses across a room. Situation 2: The waiter is pushing a cart across a room.

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7.2 Energy and the Conservation of Energy Energy appears in many forms, such as motion and heat. Energy can also travel in different ways, such as light and electricity. Without energy, nothing could ever change. In fact, the workings of the entire universe (including all of our technology) depend on energy flowing and changing back and forth from one form to another.

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Defining energy

energy - a quantity that describes the ability of an object to change or cause changes.

joule - a unit of energy. One joule is enough energy to push with a force of 1 newton for a distance of 1 meter.

What is energy? Energy describes the ability of things to change or to cause change in other

things. What types of changes are we talking about? Some examples are changes in temperature, speed, position, pressure, or any other physical variable. Energy can also cause changes in materials, such as when burning wood changes into ashes and smoke. What has The list below describes objects that have energy. Read through this list and energy? notice how many different forms of energy exist.

• A gust of wind has energy because it can move objects in its path. • A piece of wood burning in a fireplace has energy because it can produce heat and light. • You have energy because you can change the motion of your body. • Batteries have energy; they can be used in a radio to make sound. • Gasoline has energy; it can be burned in an engine to move a car. • A ball at the top of a hill has energy because it can roll down the hill and move objects in its path. Measuring A joule (J) is the unit of measurement for energy. One joule is the energy energy needed to push with a force of 1 newton for a distance of 1 meter (Figure 7.11). So, 1 joule is equivalent to 1 newton multiplied by 1 meter (or 1 newton-meter). If you push a toy car forward with a force of 1 newton over a distance of 1 meter, you have applied 1 joule of energy to the car. One joule is a pretty small amount of energy. An ordinary 100-watt electric light bulb uses 100 joules of energy every second.

Figure 7.11: Pushing an object with a force of 1 newton for a distance of 1 meter uses 1 joule of energy.

Units Related to the Joule 1 joule = 1 newton-meter 1 newton = 1 kg·m/s2 therefore... 1 joule = 1 kg·m2/s2

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Some forms of energy Understanding One way to understand energy is to think of it as nature’s money. Energy can energy be spent and saved in a number of different ways. It takes energy to “buy”

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changes such as going faster, moving higher, or getting hotter. These three changes use energy. The opposite changes, such as slowing down, falling, or cooling off, release energy. Just like a checkbook, nature keeps perfect track of energy. What you “spend” diminishes what you have left. You can only “buy” as much change as you have energy to “pay for.”

mechanical energy - a form of energy that is related to motion or position. chemical energy - a form of potential energy that is stored in molecules.

Mechanical Mechanical energy is the energy possessed by an object due to its motion energy or its position. Turning windmill blades have mechanical energy. Chemical energy Chemical energy is a form of energy

stored in molecules. Batteries are really storage devices for chemical energy. The chemical energy in a battery changes to electrical energy when you connect wires and a light bulb to the battery. Your body also uses chemical energy when it converts food into energy so that you can walk or think. A car and many other types of machines use chemical energy when they burn fuel to operate.

STUDY SKILLS Keeping Track of Energy In this section, you will learn about different forms of energy. Keep track of these in a table. List the name of each form of energy and write down any information you learn about it.

Electrical energy Electrical energy comes from electric charge, which is one of the

fundamental properties of all matter. The electrical energy we use in our homes is transformed from other forms of energy, such as the chemical energy released by burning oil and gas, or the mechanical energy released by falling water in a hydroelectric dam or power plant. Pressure energy Pressure in gases and liquids is also a form of energy. An inflated bicycle tire

has more energy than a flat tire. An inflated tire can hold up a bicycle (with you on it) against the force of gravity while a flat tire cannot.

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More forms of energy Elastic energy Elastic energy is energy that is stored or released when an object changes

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shape (or deforms). For example, you use energy to stretch a rubber band. Some of the energy from your muscles is stored as elastic energy in the stretched (changed) shape of the rubber band. The energy is released again when the rubber band changes back to its original (unstretched) shape. Objects that are commonly used to store and release elastic energy include rubber bands, springs, and archery bows (Figure 7.12).

nuclear energy - a form of energy that is stored in the nuclei of atoms. radiant energy - a form of energy that is represented by the electromagnetic spectrum.

Nuclear energy Every second, about 5 million tons of mass is converted to energy through and radiant nuclear reactions in the core of the Sun. In the Sun, nuclear energy is energy transformed to heat that eventually escapes the Sun as radiant energy. Nuclear energy is a form of energy stored in the nuclei of atoms (particles

of matter). You will read more about nuclear energy and nuclear reactions in Chapter 14. Radiant energy is energy that is carried by electromagnetic waves. Light is one form of radiant energy, and so are radio waves that carry music through the air. The Light and radio waves are a traveling form of energy. In fact, they are only electromagnetic two of a whole family of energy waves called the electromagnetic spectrum. spectrum The electromagnetic spectrum includes infrared radiation (heat), visible light

(what we see), and ultraviolet light. In other words, light energy and heat energy are included in the electromagnetic spectrum. You will recognize other components of the spectrum as well. You have listened to radio waves, might have cooked with microwaves, and maybe you have had an image made of a part of your body with X-rays.

Figure 7.12: A stretched bowstring

on a bent bow has elastic energy, so it is able to create change in itself and in the arrow.

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The Sun and gravity The Sun and Living things and human technology derive virtually all of their energy from energy the Sun. Without the Sun’s energy, Earth would be a cold, icy place. The

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Sun’s energy not only warms the planet, it also drives the entire food chain (Figure 7.13). Plants store the energy as carbohydrates, such as sugar. Animals eat the plants to get energy. Other animals eat those animals for their energy. It all starts with the Sun. Life on Mars and A very important question in science today other planets is whether there is life on other planets

such as Mars. Mars is farther from the Sun than Earth. For this reason, Mars receives less energy from the Sun than does Earth. In fact, the average temperature on Mars is well below the freezing point of water. Can life exist on Mars? Recent research suggests that it might be possible. Scientists have found bacteria in the Antarctic ice living at a temperature colder than the average temperature of Mars.

Gravity and A falling rock gains speed as it falls. Energy must be supplied to increase energy speed. The falling water that turns a hydroelectric turbine must also have

Figure 7.13: The flow of energy

from the Sun supports all living things on Earth.

The planet Venus is closer to the Sun than Earth. Should this make Venus warmer or colder than Earth? Research your answer to see what scientists think Venus is like on its surface.

energy, otherwise no electrical energy could be produced. Where does this energy come from? The answer has to do with Earth’s gravity. If an object, or any matter, is lifted against gravity, energy is stored. This stored energy is transformed into energy of motion, such as the object falling back down. Many forms of human technology, including roller coasters, swings, water wheels, and hydroelectric power plants, rely on gravity.

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Energy and work What work You learned in the previous section that work has a very specific meaning. means Work is the transfer of energy that results from applying a force over a in physics distance. Work is a product of the force applied times the distance traveled

Work done stretching a rubber band is stored as potential energy. Distance

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(work = force × distance). For example, if you push a block with a force of 1 newton for a distance of 1 meter, you do 1 joule of work. Both work and energy are measured in the same units (joules) because work is a form of energy.

Work and Doing work always means transferring energy. The energy might be potential energy transferred to the object to which force is applied, or it might go elsewhere.

For example, you can increase the energy of a rubber band by exerting a force that stretches it. The work you do stretching the rubber band is stored as elastic potential energy by the rubber band. The rubber band can then use that stored energy to do work on a paper airplane, giving it energy (Figure 7.14).

Force

The potential energy can be used to do work launching a paper airplane.

Work is done When thinking about work, you should always be clear about which force is on objects doing the work on which object. Work is done on objects. If you lift a block

Distance

1 meter with a force of 1 newton, you have done 1 joule of work on the block. Energy is An object that has energy is able to do work; without energy, it is impossible needed to do work. In fact, energy can sometimes be thought of as stored work. As to do work the block you lifted earlier falls, it has energy that can be used to do work. If

Force e

the block hits a ball, it will do work on the ball and change the ball’s motion. Some of the block’s energy is transferred to the ball during the collision.

Figure 7.14: You can do work to

increase an object’s energy. Then that energy can do work on another object, giving it energy.

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Potential energy What is potential Potential energy is energy due to position. The word potential means that energy? something is capable of becoming active. Systems or objects with potential

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energy are able to exert forces (exchange energy) as they change to other arrangements. For example, a stretched spring has potential energy. If released, the spring will use this energy to move itself (and anything attached to it) back to its original length.

potential energy - energy due to position.

force = weight = mass × acceleration due to gravity (mg)

Gravitational A block suspended above a table has potential energy. If released, the force potential energy of gravity moves the block down to a position of lower energy. The term

gravitational potential energy describes the energy of an elevated object. The term is often shortened to potential energy because the most common type of potential energy in physics problems is gravitational. Unless otherwise stated, you can assume potential energy means gravitational potential energy. How to How much potential energy does a raised block have? The block’s potential calculate energy is exactly the amount of work it can do as it goes down. Work is force potential energy multiplied by distance. The force is the weight (mg or mass × acceleration

due to gravity) of the block in newtons. The distance the block can move down is its height (h) in meters. Multiplying the weight (mg) by the distance (h) gives you the block’s potential energy (mgh) at any given height (Figure 7.15).

mg (weight)

mg 0.2 kg The potential energy of the block is mgh.

distance block can fall = height

h = 0.5 m

Figure 7.15: The potential energy of the block is equal to the product of its mass, the strength of gravity, and the height from which the block can fall.

Ep = (0.2 kg)(9.8 m/s2 )(0.5 m) =0.98 J

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Kinetic energy Kinetic energy is Objects that are moving also have the ability to cause change. Energy of energy of motion is called kinetic energy. A moving billiard ball has kinetic energy motion because it can hit another ball and change its motion. Kinetic energy can

kinetic energy - energy of motion.

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easily be converted into potential energy. The kinetic energy of a basketball tossed upward converts into potential energy as the height increases. Kinetic energy The amount of kinetic energy an object has equals the amount of work the can do work object can do by exerting force as it stops. Consider a moving skateboard and

rider (Figure 7.16). Suppose it takes a force of 500 newtons applied over a distance of 10 meters to slow the skateboard to a stop (500 N × 10 m = 5,000 J). The kinetic energy of the skateboard and rider is 5,000 joules since that is the amount of work it takes to stop the skateboard. Kinetic energy If you had started with twice the mass—say, two skateboarders—you would depends on have to do twice as much work to stop them both. Kinetic energy increases mass and speed with mass. If the skateboard and rider are moving faster, it also takes more

work to bring them to a stop. This means kinetic energy also increases with speed. Kinetic energy is related to both an object’s speed and its mass. The formula for The kinetic energy of a moving object is equal to one-half its mass kinetic energy multiplied by the square of its speed. This formula comes from a combination

of relationships, including Newton’s second law, the distance equation for acceleration (d = 1/2at2), and the calculation of energy as the product of force and distance.

Figure 7.16: The amount of kinetic

energy the skateboard has is equal to the amount of work that must be done to stop the skateboard.

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Solving Problems: Kinetic Energy

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A 2-kilogram rock is at the edge of a cliff 20 meters above a lake. The rock becomes loose and falls toward the water below. Its speed is 14 m/s at the halfway point. Calculate the rock’s kinetic energy at the halfway point. 1. Looking for:

You are asked for the rock’s kinetic at the halfway point.

2. Given:

You are given the mass in kilograms, the height at each location in meters, and the speed halfway down in m/s.

3. Relationships:

Ek = mv 2

4. Solution:

Kinetic energy halfway down: m = 2 kg and v = 14 m/s

1

2

Ek = (1/2)(2 kg)(14 m/s)2 Ek = (1/2)(2 kg)(196 m2/s2)

Kinetic Energy and Speed Kinetic energy increases as the square of the speed. This means that if you go twice as fast, your energy increases by four times (22 = 4). If your speed is three times as fast, your energy is nine times bigger (32 = 9). A car moving at a speed of 100 km/h (62 mph) has four times the kinetic energy it had when going 50 km/h (31 mph). At a speed of 150 km/h (93 mph), it has nine times as much energy as it did at 50 km/h. The stopping distance of a car is proportional to its kinetic energy. A car going twice as fast has four times the kinetic energy and needs four times the stopping distance. This is why driving at high speeds is so dangerous.

Ek = 196 kg × m2/s2 = 196 J Your turn...

a. Calculate the potential energy of a 4-kilogram cat crouched 3 meters off the ground. b. Calculate the kinetic energy of a 4-kilogram cat running at 5 m/s.

a. 117.6 J b. 50 J

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Transforming energy An example of Systems change as energy flows and changes from one part of the system to energy flow another. Parts of the system might speed up or slow down, get warmer or

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colder, or change in other measurable ways. Each change transfers energy or transforms energy from one form to another. An example of a flow of energy is illustrated below. This example involves transforming chemical energy into electrical energy. The chemical energy (a fuel) is a gas called methane. It is burned in a chemical reaction and heat energy is released. The heat energy makes hot steam. The steam turns a device called a turbine, making mechanical energy. Finally, the turbine turns an electric generator, producing electrical energy. You can obtain this electrical energy by “plugging in” to an electrical outlet.

From high to How can we predict how energy will flow? One thing we can always be sure low energy of is that systems tend to move from higher to lower energy. For example, at

the top of a roller coaster hill, the car has more potential energy (Figure 7.17). The potential energy is transformed to kinetic energy as the car rolls down the hill. Once it reaches the bottom, the car has less potential energy and is more stable. Friction and the law of conservation of energy

At the bottom of a hill, a roller coaster car has more kinetic energy. Without friction, due to Newton’s first law of motion, the car would roll on a straight path forever. However, on a straight path, the kinetic energy of the car eventually decreases due to friction slowing it down. Friction transforms energy of motion to energy of heat or to the wearing away of the material of the wheels. The energy converted to heat or wear is no longer available as potential energy or kinetic energy, but it was not destroyed.

Figure 7.17: This roller coaster car

illustrates how systems go from high to low energy to become more stable. Potential energy decreases as the car rolls down the hill. Kinetic energy eventually decreases due to friction along the track and is transformed to heat and the wear of the wheels.

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The law of conservation of energy An energy What happens when you throw a ball straight up in the air (Figure 7.18)? The transformation ball leaves your hand with kinetic energy it gained while your hand accelerated

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it from rest. As the ball goes higher, it gains potential energy. However, the ball slows down as it rises, so its kinetic energy decreases. The increase in potential energy is exactly equal to the decrease in kinetic energy. The kinetic energy converts into potential energy, and the ball’s total energy stays the same.

law of conservation of energy energy can never be created or destroyed, only transformed into another form. The total amount of energy in the universe is constant.

Law of The idea that energy transforms from one form into another without a change conservation in the total amount is called the law of conservation of energy. The law of energy states that energy can never be created or destroyed, just transformed from

one form into another. The law of conservation of energy is one of the most important laws in physics. It applies not only to kinetic and potential energy, but to all forms of energy.

Energy can never be created or destroyed, just transformed from one form into another. Using energy The law of conservation of energy explains how a ball’s launch speed affects conservation its motion. As the ball in Figure 7.17 moves upward, it slows down and loses

kinetic energy. Eventually, it reaches a point where all the kinetic energy has been converted to potential energy. The ball has moved as high as it will go and its upward speed has been reduced to zero. If the ball had been launched with a greater speed, it would have started with more kinetic energy. It would have had to climb higher for all of the kinetic energy to be converted into potential energy. If the exact launch speed is given, the law of conservation of energy can be used to predict the height the ball reaches. Energy converts The ball’s energy on the way down is the opposite of what it was on the way from kinetic to up. As the ball falls, its speed increases and its height decreases. The potential potential energy decreases as it converts into kinetic energy. If gravity is the

only force acting on the ball, it returns to your hand with exactly the same speed and kinetic energy it started with—except that now it moves in the opposite direction.

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Figure 7.18: When you throw a

ball in the air, the energy transforms from kinetic to potential and then back to kinetic.

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“Using” and “conserving” energy in the everyday sense

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Lighting Choices

“Conserving” Almost everyone has heard that it is good to “conserve energy” and not waste energy it. This is useful advice because energy from gasoline or electricity costs

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money and uses resources. But what does it mean to “use energy” in the everyday sense? If energy can never be created or destroyed, how can it be “used up”? Why do people worry about “running out” of energy? “Using” energy When you “use” energy by turning on a light, you are really converting

energy from one form (electricity) to other forms (light and heat). What gets “used up” is the amount of energy in the form of electricity. Electricity is a valuable form of energy because it is easy to move over long distances (through wires). In the physics sense, the energy is not used up—it is converted into other forms. The total amount of energy stays constant. Power plants Electric power plants don’t make electrical energy. Energy cannot be created.

What power plants do is convert other forms of energy (chemical, solar, nuclear) into electrical energy. When someone asks you to turn out the lights to conserve energy, they are asking you to use less electrical energy. If people used less electrical energy, power plants would burn less oil, gas, or other fuels in “producing” the electrical energy they sell. “Running out” Many people are concerned about running out of energy. What they actually of energy worry about is running out of certain forms of energy that are easy and

economical to use, such as fossil fuels like oil and gas. It took millions of years to accumulate these fuels because they are derived from decaying, ancient plants that obtained their energy from the Sun when they were alive. Fossil fuels are a limited resource because it took a long time for plants to grow, decay, and become oil, coal, and gas. Transitioning to When you use gas in a car, the chemical energy in the gasoline mostly new resources becomes heat energy. It is impractical to put the energy back into the form of

gasoline, so we say the energy has been “used up,” even though the energy itself is still there, in a different form. Energy from flowing water, wind, or the Sun is not as limited. Many scientists hope our society will make a transition to these forms of energy over the next 100 years.

The "old fashioned" incandescent light bulb patented by Thomas Edison in 1879 was the primary lighting source in the US for well over a century. Despite this, there is a good chance that you've never even seen one! These bulbs have been gradually phased out in our country since Congress passed the "light bulb law" in 2007, which set energy efficiency standards for light bulbs. There are two new types of energy-efficient bulbs: compact fluorescent lamps (CFLs) and light emitting diodes (LEDs). Both types of lighting are more energy efficient than Edison's, and both fit the sockets in all current lighting fixtures. But how do these two types of lights compare, and which should you choose? Research lighting choices and prepare a chart that compares CFLs to LEDs in terms of power output, price, cost to operate, environmental impact, versatility, and safety.

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Section 7.2 Review

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1. Martha wakes up at 5:30 a.m. and eats a bowl of corn flakes. It’s a nice day, so she decides to ride her bicycle to work, which is uphill from her house. It is still dark outside. Martha’s bike has a small electric generator that runs from the front wheel. She flips on the generator so that her headlight comes on when she starts to pedal. She then rides her bike to work. Draw a diagram that shows the energy transformations that occur in this situation.

2. Imagine you are the teacher of a science class. A student brings in a newspaper article that claims the world will run out of energy by the year 2050 because all the oil will be pumped out of the planet. The student is confused because she has learned in your class that energy can never be created or destroyed. How would you explain to her what “running out of energy” means in the article? 3. Some, but not all, of the gasoline used by a car’s engine is transformed into kinetic energy. Where else might some of the energy go in this system? 4. A 0.5-kg ball moving at a speed of 3 m/s rolls up a hill. How high does the ball roll before it stops?

Energy Projects Conduct Internet research on energy conservation. Use your favorite search engine and the following keywords to help you find information: green communities, local energy conservation, and local electricity costs. The United States Environmental Protection Agency is another good resource (www.epa.gov). 1. Research what is going on in your community regarding energy conservation. Write about a project designed to save energy that is being planned or is already implemented. How much energy has been or might be saved? 2. Every month your family pays an electric bill for energy you have used. Research the cost of electricity in your area. How much does it cost for 1 million joules? This is the amount of energy used by a single electric light bulb in three hours.

5. Explain in your own words why energy is considered to be “nature’s money.” Give an example to support your explanation.

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7.3 Efficiency and Power One day your science teacher declares, “Today we are going to do our work with greater efficiency and greater power.” That sounds like a good idea, but what does your teacher mean? Read on and you will find out.

on an object.

work output - the work that an object does as a result of work input.

Input work and Every process that transforms energy can be output work thought of as a machine. Work or energy ete

2 meters × 5 newtons = 10 joules

rs

Input work 2m

goes in one end and work or energy comes out the other end. The “machine” might be a toaster heating bread, which transforms electrical energy into heat, or even a human consuming food in order to have the energy to exercise. Using this concept, the work input is the work or energy supplied to the process (or machine). The work output is the work or energy that comes out of the process (or machine).

5N

A rope and As an example, consider using a rope and pulley machine to lift a load pulley example weighing 10 newtons (Figure 7.19). If you lift the load a distance of 1 meter,

the machine has done 10 joules of work and the work output is 10 joules. For this particular machine, you need to pull with a force of only 5 newtons, but you need to pull the rope a distance of 2 meters. Your work input is 5 newtons × 2 meters or 10 joules. How work input The example of a rope and pulley machine illustrates a rule that is true for all and output are machines and all processes that transform energy. The total energy of work related output can never be greater than the total energy of work input.

The energy output of a process or machine can never exceed the energy input.

Output work 1 meter × 10 newtons = 10 joules

1 meter

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Work input and output

work input - the work that is done

Figure 7.19: Assuming no friction,

the work input of the rope and pulley machine is the same as the work output.

You might recognize this statement as just another way of saying the law of conservation of energy. You are right! If you carefully account for all the work and energy in any process, you find that the total work and energy output of the process is exactly equal to the total work and energy input. 7.3 EFFICIENCY AND POWER

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Efficiency Real machines Suppose you measure the forces on an actual rope and pulley machine.

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Figure 7.20 shows what you find. Notice that the work input is a little more than the work output. It took 11 joules of input work applied to the rope to produce 10 joules of output work lifting the weight. This kind of behavior is true of all real machines. The work output is less because some work is always converted to heat and other kinds of energy by friction. Everyday machines Energy use in a typical car

65% Waste heat 13% Work output 10% Friction 7% Idling 5% Accessories

efficiency - the ratio of usable output work divided by total input work. Efficiency is often expressed as a percent, with a perfect machine having 100 percent efficiency.

The diagram at the left shows how the chemical energy (input) released by burning gasoline is used in a typical car. Only 13 percent of the energy in a gallon of gas is transformed into output work! Car engines in use get hot. That’s because 65 percent of the energy in gasoline is converted to heat. In terms of moving the car, this heat energy is “lost.” The energy doesn’t vanish, it just does not appear as useful output work.

Efficiency The efficiency of a machine is the ratio of usable output work divided by

total input work. Efficiency is usually expressed in percent. The car in the diagram has an efficiency of 13 percent. That means 13 out of every 100 joules released from gasoline go to making the car move. A “perfect” car would have an efficiency of 100 percent. Since all real machines have some friction, perfect machines are technically impossible. Calculating You calculate efficiency by dividing the usable output work by the total input efficiency work. The rope and pulley machine in Figure 7.20 has an efficiency of

91 percent. That means that 1 joule out of every 11 (9 percent) is “lost” to friction. The work isn’t really “lost,” but it is converted to heat and other forms of energy that are not useful in doing the job the rope and pulley machine is designed to do.

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Figure 7.20: If the input work is 11 joules, and the output work is 10 joules, then the efficiency is 91 percent.

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Efficiency in natural systems The meaning of Energy drives all the efficiency processes in nature, from

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winds in the atmosphere to nuclear reactions occurring in the cores of stars. In the environment, efficiency is defined as the fraction of incoming energy that goes into a process. For example, Earth receives energy from the Sun. Earth absorbs this solar energy with an average efficiency of 78 percent. The energy that is not absorbed is reflected back into space.

Figure 7.21: Dust and clouds reflect light back into space, decreasing the efficiency with which Earth absorbs energy from the Sun.

Earth’s Earth’s efficiency at absorbing solar energy is critical to living things. If the temperature efficiency decreased by a few percent, Earth’s surface would become too cold

for life. Some scientists believe that many volcanic eruptions or nuclear war could decrease the absorption efficiency by spreading dust in the atmosphere. Dust reflects solar energy (Figure 7.21). On the other hand, if the efficiency increased by a few percent, Earth would get too hot to sustain life. Adding carbon dioxide (and other greenhouse gases) in the atmosphere increases absorption efficiency. Scientists are concerned that the average annual temperature of Earth has already warmed 1°C degree since the 1880s mostly as a result of carbon dioxide released by human activities (Figure 7.22). Conservation of In any system, all of the energy goes somewhere. Another way to say this is energy that energy is conserved. For example, rivers flow downhill. Most of the

Figure 7.22: Human activities

potential energy lost by water moving downhill becomes kinetic energy in the motion of the water. Erosion takes some of the energy and slowly changes the land by wearing away rocks and dirt. Friction takes some of the energy and heats up the water. If you could add up the efficiencies for every single process in which this water is involved, that total would be 100 percent.

have increased the amount of carbon dioxide and other greenhouse gases in Earth’s atmosphere. These gases increase the absorption efficiency of Earth’s atmosphere.

7.3 EFFICIENCY AND POWER

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Power Energy vs. If you lift a book over your head, the book gets potential energy from your power action. Even if you lift the book faster, it has the same amount of potential

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

energy. This is because the height is the same. But it feels different to transfer the energy to the book at different speeds. Power describes how fast energy is transferred to an object. What is power? Power is the rate at which work is done. Here’s an example. Suppose

Michael and Jim each lift a barbell weighing 100 newtons from the ground to a height of 2 meters (Figure 7.23). Michael lifts quickly and Jim lifts slowly. Michael and Jim do the same amount of work (100 N × 2 m = 200 joules of work). However, Michael’s power is greater because he gets the work done in less time. Watts and Power is calculated in watts. One watt (W) is equal to 1 joule of work per horsepower second. One kilowatt equals 1,000 watts. The watt was named after James

Watt, the Scottish engineer who invented the steam engine. Another unit of power is horsepower (hp). Watt expressed the power of his engines as the number of horses an engine could replace. One horsepower equals 746 watts or 746 joules of work per second.

power - the rate of doing work or moving energy. Power is equal to energy (or work) divided by time. watt - a unit of power equal to 1 joule per second.

horsepower - a unit of power equal to 746 watts.

100 N

Michael 2m

seconds

100 N

Jim 2m

Calculating Now, let’s calculate and compare the power output of Michael and Jim. power Michael’s power is 200 joules divided by 1 second, or 200 watts. Jim’s

power is 200 joules divided by 10 seconds, or 20 watts. Jim takes 10 times as long to lift the barbell, so his power is one-tenth as much. The maximum power output of an average person is a few hundred watts.

seconds

Figure 7.23: Michael and Jim do the same amount of work but do not have the same power.

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Section 7.3 Review Are You Really Doing Work When You Do Your Homework?

1. You read about a rope and pulley machine that was able to produce equal amounts of output work and input work. Was this a realistic example? Why or why not?

Answer this question in your own words, based on what you know about work.

2. What do you need to do to calculate the efficiency of any machine?

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3. A car’s efficiency is only 13 percent. a. If the input work for a car is 200 joules, what is the output work? b. List two things that car manufacturers do to improve a car’s efficiency.

Think about this question from different angles before you answer it.

4. A simple machine produces 25 joules of output work for every 50 joules of input work. What is the efficiency of this machine? 5. How is work related to power? 6. If you know the power for a machine and the amount of time it was running, what value can you calculate? 7. How does 1 horsepower compare to 1 watt of power? 8. A gallon of gasoline contains about 36 kilowatt-hours of energy. Suppose a gallon of gas costs $2 and a kilowatt-hour of electricity costs 8¢. Which form of energy is less expensive?

Energy-Efficient Technologies

9. A 100-newton object is lifted 100 meters in 100 seconds. What is the power generated in this situation? 10. Which situation would produce 200 watts of power? a. 100 J of work done in 2 s c. 2,000 J of work done in 5 s b. 400 J of work done in 2 s d. 2 J of work done in 100 s 11. An average car engine can produce about 100 horsepower. How many 100-watt light bulbs does it take to use the same amount of power? 12. A half-cup of ice cream contains about 200 food Calories. How much power can be produced if the energy in a cup of ice cream is expended over a period of 10 minutes (600 seconds)? Each food Calorie is equal to 4,184 joules. Write your answer in watts and then in horsepower.

Engineers are always trying to improve the efficiency of the machines we use every day. Do an Internet search using the key phrase “energy efficient technologies” and see what you find. Or, you might want to go directly to the U.S. government website www.energystar.gov. Pick a topic and present your findings to your class. Extension: Be a reporter within your home and see how many energy-efficient appliances you can find.

7.3 EFFICIENCY AND POWER

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Chapter 7 Assessment Vocabulary

Section 7.2

Select the correct term to complete the sentences.

8.

This energy is related to Earth’s gravity: ____. Energy that is due to motion is called ____.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

chemical energy

law of conservation of energy

potential energy

9.

efficiency

lever

power

10. The ____ is the SI unit of energy.

energy

machine

radiant energy

11. A fossil fuel is a good example of this kind of energy: ____

gear

mechanical advantage

watt

horsepower

mechanical energy

work

input

nuclear energy

work input

13. ____ from the Sun depends on this kind of energy: ____

joule

output

work output

kinetic energy

simple machine

14. The ____ states that the total amount of energy does not change over time.

12. Potential and kinetic energy are types of this kind of energy: ____

Section 7.1

15. To do work, you need ____.

1.

In physics, _____ is the product of the force applied and the distance moved in the direction of the force.

Section 7.3

2.

A(n) ____ is a stiff structure that pivots on a fulcrum.

17. A unit of power equal to 746 watts is a(n) ____.

3.

If the output force is 2 newtons and the input force is 1 newton, the ____ for a machine is 2.

18. The unit for one joule per second is one ____.

4.

A(n) ____ is a wheel with teeth that transfers motion or force.

19. You calculate the ____ of a machine by dividing its ____ by its work input and multiplying by 100.

5.

A rope and pulley system or a lever is an example of a(n) ____.

20. The work output of a machine can never be greater than the ____.

6.

To travel 150 kilometers in less than 2 hours, I need a(n) ____, a device that has moving parts that work together to help me travel that far in that amount of time.

Concepts

7.

The force you use when you pedal a bicycle is the ____ and the motion of the wheels and distance traveled is the ____.

1.

16. The rate at which work is done is called ____.

Section 7.1

Correct or incorrect? Explain your answer in each case. a. b.

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You know the input arm length and the output arm length of a lever. Therefore, you can calculate the mechanical advantage. You know the input arm length, output arm length, and the output force for a lever. Therefore, you can determine the input force.

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2.

d.

Copy the table below onto a piece of paper. Then, use the graphic to fill it in. In the Work Done? column, write yes, no, or some. In the Motion of the Block column, describe how the block would move under each force.

e.

CHAPTER 7

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

Which involves more work in the scientific sense: moving the boxes and furniture down from the second floor or up to the fifth floor? Explain your reasoning. You take one box up to the fifth floor by taking the stairs. If the elevator had taken the same box up to the fifth floor, would it have done more, less, or the same amount of work as you? Explain your reasoning.

4.

Name two simple machines that are found on a bicycle.

5.

How does the mechanical advantage of a second-class lever compare to the mechanical advantage of a third-class lever?

Section 7.2

6.

Force

Work done?

a. b. c. d.

Motion of the block

A B C

3.

It’s moving day and you need to move boxes and furniture from your old second-floor apartment on Main Street to your new fifth-floor apartment on Harmony Street. You have to take the stairs to move your furniture from the old apartment. But, you can use the elevator to get up to your new apartment on the fifth floor. a. b. c.

Describe one way in which your muscles do do work while moving your boxes and furniture down from the second floor. Describe one way in which your muscles don’t do work while moving your boxes and furniture down from the second floor. Does the elevator do work moving your boxes and furniture up to the fifth-floor apartment?

Identify at least one way that energy is involved in the following situations.

7.

A wave at the ocean knocks over a sand castle. Your houseplant grows better when it is placed in sunlight. When you drop a plate, it breaks into pieces. Your hair dryer works when you plug it in to an electrical outlet.

Copy the following table onto a piece of paper and fill it in based on your understanding of potential and kinetic energy. Potential energy Formula What happens to energy when the mass of an object increases? What happens when the object is lifted to a higher height (without a change in speed)? What happens when the speed of an object increases (without a change in height)?

CHAPTER 7 ASSESSMENT

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8.

WORK AND ENERGY

A roller coaster track is a good example of the law of conservation of energy. Use this law to explain these facts about a roller coaster track. a. b.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

c.

The largest hill for a roller coaster track is the first hill on the track. The hills after the first are smaller. To get to the top of the first (highest) hill, a motor pulls the cars up to the top. After the top of the first hill a motor is not needed to keep the cars going. The roller coaster cars move really fast at the bottom of a hill on the track but slow down as they move up a hill (not including the first hill).

3.

Section 7.2

4.

Section 7.3

9.

A lever has an input arm that is 2 meters and an output arm that is 3 meters. What is the mechanical advantage? Does this lever multiply force? Why or why not?

Your lab partner shows you results from an experiment with a simple machine. The output work is 10 joules and the input work is 8 joules. She asks, “Does this data look correct?” What would be your response and why?

A bottle rocket is a toy that is made from an empty soda bottle. A bicycle pump is used to pump air into the bottle. The rocket shoots upward when it is released from the launcher, allowing the high-pressure air to come out. a.

10. Mikhail lifts a 500-newton weight 2 meters in 2 seconds. Tobias lifts the same 500-newton weight 2 meters in 4 seconds. a. b. c.

Which boy does more work? Which boy uses greater power? The human body is only 8 percent efficient. To obtain the amount of work accomplished by Mikhail or Tobias, how much input work was required?

b.

c.

Work is done as the pump is pushed, forcing air into the bottle. What happens to this work? Does it just disappear? Suppose a person does 2,000 joules of work using the pump. What is the maximum kinetic energy the rocket can have after it is launched? Do you think the rocket could actually have this much kinetic energy? Explain why or why not.

Problems

5.

What is the minimum energy required to lift an object weighing 200 newtons to a height of 20 meters?

Section 7.1

6.

If 300 joules of energy are used to push an object with a force of 75 newtons, what is the maximum distance the object can move?

7.

Calculate the potential energy of a bird sitting on a tree limb. The mass of the bird is 0.1 kilogram and it is 5 meters off the ground.

1.

2.

Sara’s mother gets a flat tire on her car while driving Sara to school. They use a jack to change the tire. It exerts a force of 5,000 newtons to lift the car 0.25 meters. How much work is done by the jack? How far does Isabella lift a 50-newton box if she does 40 joules of work lifting the box from the floor to a shelf?

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Section 7.3

8.

9.

A machine is used to lift an object a distance of 2 meters. If the power of the machine is increased, what happens to the time it takes for the object to be lifted 2 meters?

4.

Nuclear energy is a controversial energy resource. Find out why. List two pros and two cons for this form of energy.

5.

Here is some data for kinetic energy versus speed for a moving object. Make a graph of this data and answer the following questions. Place kinetic energy on the y-axis and speed on the x-axis.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

During construction, a crane lifts a 2,000-newton weight to the top of a 50-meter-tall building. How much power must the crane have to perform this task in 5 seconds? Give your answer in watts, kilowatts, and horsepower.

10. What is the minimum time needed to lift a 1,000-newton weight 20 meters using a motor with a maximum power rating of 8,000 watts? a. b.

Applying Your Knowledge Section 7.1

1.

Spend one day recording a variety of tasks that you do that involve doing work in the scientific sense. Also record the machines that allow you to do certain tasks. Then, spend the next day doing one or two of these tasks without using the machine. Answer the following questions. a. b. c.

2.

Was more or less work done using the machine? How do you know? Was the power output more or less with the machine? How do you know? What are your thoughts about using machines to accomplish work?

CHAPTER 7

c. 6.

Speed (m/s)

Kinetic energy (J)

12

720

24

2,880

48

11,520

60

18,000

What is the mass of the object represented by this data? Use your graph to find the kinetic energy at 30 m/s. Then use the kinetic energy formula to check yourself. Should the relationship between kinetic energy and speed be described as linear or exponential? Explain your answer.

A water-powered turbine makes electricity using the energy of falling water. At the location of one turbine, 100 kilograms of water fall every second from a height of 20 meters. a. b. c.

How much potential energy does 100 kilograms of water have at a height of 20 meters? How much power in watts could you get out of the turbine if it was perfectly efficient? Research the efficiency of modern water-powered turbines. How efficient are these devices?

Does mechanical advantage have units? Why or why not?

Section 7.2

3.

Solar energy and hydroelectric energy are important sources of energy. Find out more about either one of these forms of energy. What’s being done to make it a more efficient source of energy, and where is it being used in the United States? CHAPTER 7 ASSESSMENT

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Unit 3 Matter, Energy, and Earth FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

CHAPTER 8 Matter and

Temperature

CHAPTER 9  Heat CHAPTER 10 Properties of

Matter

CHAPTER 11 Earth’s Atmosphere

and Weather

‹ Try this at home Get a metal spoon and a plastic spoon, a cup, some ice, and water. Fill the cup with ice and then add water until the cup is about half full with water. Place both spoons in the cup and wait for two minutes. Touch the metal spoon and then the plastic spoon. Record your observations on a piece of paper. Which spoon feels colder? Warmer? Why do the spoons feel like they do? Write a paragraph about what you felt and why you think that happened.

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CHAPTER

8

CHAPTER 8

Matter and Temperature FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

Have you ever imagined what it would be like to live in an atom-sized world? You may have seen movies where the characters are shrunk to the size of a flea or an even tinier animal. If you were that small, what would the matter around you look like? What if you were even smaller, say the size of an atom? At that size, even the air around you could be dangerous. Everywhere you looked you would see atoms and molecules whizzing around at amazingly fast speeds and occasionally colliding with one another. Watch out! One of those particles might collide with you! If you were the size of an atom, you would notice that the particles that make up everything are in constant motion. In liquids, the particles slide over and around one another. In solids, the particles vibrate in place. In gases, the particles move around freely. Ordinary air would look like a crazy, three-dimensional bumpercar ride where you are bombarded from all sides by giant beach balls. It will be helpful to imagine life as an atom as you study this chapter.

4 What is the smallest particle of sugar that is still sugar?

4 What does temperature measure? 4 What happens at the molecular level when water melts, freezes, and boils?

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8.1 The Nature of Matter From a distance, a sugar cube looks like a single piece of matter. But up close, you can see it is made up of tiny, individual crystals of sugar fused together. Can those sugar crystals be broken into even smaller particles? What is the smallest particle of sugar that is still sugar (Figure 8.1)?

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

Matter is made of tiny particles in constant motion The idea of Matter is a term used to describe anything that has mass and takes up space. atoms The idea that matter is made of tiny particles goes back to 430 BCE. The

Greek philosophers Democritus and Leucippus proposed that matter is made of tiny particles called atoms. For over 2,000 years, few people believed this theory. In 1803, John Dalton revived the idea of atoms, but he lacked proof. Brownian motion provides evidence for particles

In 1827, Robert Brown, a Scottish botanist, was looking through a microscope at tiny grains of pollen in water. He saw that the grains moved in an irregular, jerky manner. After observing the same motion in tiny dust particles, he theorized that all tiny particles move in the same way. The irregular, jerky motion was named Brownian motion in Brown’s honor.

Figure 8.1: What is the smallest particle of sugar that is still sugar?

A human-sized Imagine throwing marbles at a tire tube floating in the water. The impact of comparison any single marble is too small to make the tire tube move. If you throw

enough marbles, the tube will start moving slowly. The motion of the tire tube will appear smooth because the mass of a single marble is tiny compared to the mass of the tire tube (Figure 8.2). Why Brownian Now, imagine throwing marbles at a foam cup floating in water. The motion motion is jerky, is jerky and the impact of individual marbles can be seen. The mass of the not smooth cup is not huge compared to the mass of a marble. A pollen grain in water

moves around in a jerky manner much like the foam cup. That motion is caused by the impact of individual water molecules on the pollen grain. Like the cup, the mass of the pollen grain—while larger than a water molecule—is not so much larger that impacts are completely smoothed out. Matter is made In 1905, Albert Einstein explained how Brownian motion is caused by of atoms collisions between visible particles like pollen grains, and smaller, invisible

Figure 8.2: Throwing marbles at a tire tube moves the tube smoothly. Throwing the same marbles at a foam cup moves the cup in a jerky manner, like Brownian motion.

particles. His work provided strong evidence that matter was made of atoms.

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Atoms and elements element - a pure substance that

Elements An element is defined as a pure substance that cannot be broken down into

cannot be broken down into simpler substances by physical or chemical means.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

simpler substances by physical or chemical means. For example, water is made from the elements hydrogen and oxygen. If you add energy, you can break water down into hydrogen and oxygen, but you cannot break the hydrogen and oxygen down into simpler substances (Figure 8.3).

atom - the smallest particle of an

Defining atoms A single atom is the smallest particle of an element that retains the chemical

identity of the element. For example, you can keep cutting a piece of the element gold into smaller and smaller pieces until you cannot cut it any more. That smallest particle you can divide it into is one atom. A single atom of gold is the smallest piece of gold you can have. If you split the atom, it will no longer be gold.

element that retains the chemical identity of the element.

How small are A single atom has a diameter of about 10–10 meters. This means that you can atoms? fit 10,000,000,000 (1010) atoms side-by-side in a one-meter length. You may

think a sheet of aluminum foil is thin, but it is actually more than 200,000 atoms thick! Atoms of an element are similar to each other

Each element has a unique type of atom. Sodium atoms are different from carbon atoms, carbon atoms are different from aluminum atoms, etc. But all atoms of a given element are similar to each other. If you could examine a million atoms of carbon, you would find them all to be similar. You will learn much more about atoms in Chapter 9.

Sodium atom

Carbon atom

Aluminum atom

Oxygen atom

Figure 8.3: You can break water down into oxygen and hydrogen by adding energy.

Hydrogen atom

8.1 THE NATURE OF MATTER

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Compounds contain two or more elements Compounds Sometimes elements are found in their pure form, but more often they are

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combined with other elements. Most substances contain several elements combined together. A compound is a substance that contains two or more different elements chemically joined and that has the same composition throughout. For example, water is a compound that is made from the elements hydrogen and oxygen. Figure 8.4 shows some familiar compounds. Molecules If you could magnify a sample of pure

water so you could see its atoms, you would notice that the hydrogen and oxygen atoms are joined together in groups of two hydrogen atoms to one oxygen atom. These groups are called molecules. A molecule is a group of two or more atoms joined together by chemical bonds. A compound is made up of only one type of molecule. Some compounds, like table salt (sodium chloride), are made of equal combinations of different atoms instead of individual molecules.

Salt crystal

compound - a substance that contains two or more different elements chemically joined and that has the same composition throughout. mixture - matter that contains a combination of different elements and/or compounds and can be separated by physical means. molecule - a group of two or more atoms joined together by chemical bonds.

COMPOUNDS contain more than one type of atom joined together. 8 Hydrogen atoms

Chlorine atom (Cl)

Sodium atom (Na)

Propane ne (C3H8)

Mixtures Most of the things you see and use in everyday life are mixtures. A mixture

3 Carbon atoms

contains more than one kind of atom, molecule, or compound. Hot cocoa and soil are examples of mixtures.

2 Hydrogen atoms

Water ter (H2O) 1 Oxygen atom

Figure 8.4: Examples of compounds.

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Classifying matter pure substance - matter that

Pure substances Matter can be divided into two categories: pure substances and mixtures. A pure substance cannot be separated into different kinds of matter by

cannot be separated into other types of matter by physical means. Includes all elements and compounds.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

physical means such as sorting, filtering, heating, or cooling. Elements and compounds are pure substances. Examples include water, table salt, gold, and oxygen. Mixtures contain A mixture contains a combination of different elements and/or compounds. more than one All mixtures share one common property: They can be separated into kind of matter different types of matter by physical means such as sorting, filtering, heating,

or cooling. For example, cola is a mixture that can be separated into carbonated water, corn syrup, caramel color, phosphoric acid, natural flavors, and caffeine. A homogeneous mixture is the same throughout

Two samples of a heterogeneous mixture could be different

A homogeneous mixture is the same throughout. In other words, all samples of a homogeneous mixture are the same. For example, an unopened can of cola is a homogeneous mixture. The cola in the top of the unopened can is the same as the cola at the bottom. Once you open the can, however, carbon dioxide begins to escape from the cola, making the first sip a little different from your last sip. Brass is another example of a homogeneous mixture. It is made of copper and zinc. If you cut a brass candlestick into 10 pieces, each piece would contain the same percentage of copper and zinc.

homogeneous mixture - a mixture that is the same throughout. All samples of a homogeneous mixture are the same. heterogeneous mixture - a mixture in which different samples are not necessarily made up of the same proportions of matter.

Figure 8.5: Chicken soup is a heterogeneous mixture.

A heterogeneous mixture is one in which different samples are not necessarily made up of exactly the same proportions of matter. One common heterogeneous mixture is chicken noodle soup (Figure 8.5). One spoonful might contain broth, noodles, and chicken, while another contains only broth. Can you think of a way to separate this mixture?

8.1 THE NATURE OF MATTER

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Summary Keep track of at least 20 types of matter you use in one day. List each item and classify it according to the diagram at the left. You may need to do some research for some of your items. Make a poster showing how the matter you used is classified. Use pictures from the Internet or magazines.

M AT T E R FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

Cannot be separated by physical means

Can be separated by physical means

Pure substances

Mixtures

Elements Diamond

Compounds

Homogeneous

Heterogeneous Chocolate chip cookie kie batter

Propane

STUDY SKILLS

Olive oil

Gold Water

Granite Granit te

A graphic organizer is a chart that shows how ideas and topics are related. Draw a graphic organizer that depicts the diagram to the left.

Brass

Salad

Sugar Aluminum

Air

Blood

Helium alt Table salt Window cleaner

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CHAPTER 8

Section 8.1 Review Edouard Benedictus

1. Explain why Brownian motion provides evidence for the existence of atoms and molecules. 2. Describe the difference between elements, compounds, and mixtures.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

3. Which would be easier to separate, a mixture or a compound? Explain your answer. 4. Give an example of an element, a compound, and a mixture. Use examples that are not mentioned in the reading. 5. Identify each of the following as element, compound, homogeneous mixture, or heterogeneous mixture. Explain your reasoning for each. a. milk b. iron nail c. glass d. sugar e. bottled spring water f. distilled water g. air h. metal bicycle frame i. propane j. baking soda

In 1903, a French chemist named Edouard Benedictus dropped a glass flask in the lab. The flask was full of cracks, but surprisingly, the pieces did not scatter across the floor. The shape of the flask remained intact. The flask had been used to store a compound called cellulose nitrate. Although the chemical had evaporated, it left a plastic film on the inside of the glass. Initially, Benedictus tried to sell his shatter-resistant glass to automobile manufacturers but they weren’t interested. During World War I, he sold it for use in gas mask lenses. Soon after the war, the auto industry began using his glass.

6. Most things you use every day are: a. compounds b. elements c. mixtures 7. Your teacher has mixed salt, pepper, and water. Describe a procedure that you could use to separate this mixture. Be sure to list all of the materials you would need, your set up, and your expected results.

8.1 THE NATURE OF MATTER

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8.2 Temperature You have probably used a thermometer. Did you ever stop to think about how it works? In this section, you will learn what temperature is, how it is measured, and how the devices we use to measure temperature work.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

Temperature scales Fahrenheit There are two common temperature scales. On the Fahrenheit scale, water

Fahrenheit - a temperature scale in which water freezes at 32 degrees and boils at 212 degrees. Celsius - a temperature scale in which water freezes at 0 degrees and boils at 100 degrees.

freezes at 32 degrees and boils at 212 degrees (Figure 8.6). There are 180 Fahrenheit degrees between the freezing point and the boiling point of water. Temperature in the United States is commonly measured in Fahrenheit; 68°F (68 degrees Fahrenheit) is a comfortable room temperature. Celsius The Celsius scale divides the interval between the freezing and boiling

points of water into 100 degrees (instead of 180). Water freezes at 0°C (0 degrees Celsius) and boils at 100°C. Most scientists and engineers use Celsius because 0 and 100 are easier to work with than 32 and 212. Converting A weather report of 21°C in London, England, predicts a pleasant day, good between the for shorts and a T-shirt. A weather report of 21°F in Minneapolis, Minnesota, scales means a heavy winter coat, gloves, and a hat will be needed. Because the

United States is one of only a few countries that use the Fahrenheit scale, it is useful to know how to convert between Fahrenheit and Celsius.

Figure 8.6: The Fahrenheit and Celsius temperature scales.

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CHAPTER 8

Solving Problems: Temperature Conversions

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A friend in Paris sends you a recipe for a cake. The French recipe says to bake the cake at a temperature of 200°C for 45 minutes. At what temperature should you set your oven, which uses the Fahrenheit scale (Figure 8.7)? 1. Looking for:

You are asked for the temperature in degrees Fahrenheit.

2. Given:

You are given the temperature in degrees Celsius.

3. Relationships:

Use the conversion formula: TF = 9/5 TC + 32.

4. Solution:

TF = (9/5)(200) + 32 = 392°F Your turn...

a. You are planning a trip to Iceland where the average July temperature is 11.2°C. What is this temperature in Fahrenheit?

Figure 8.7: A French recipe says to bake a cake at 200°C. At what temperature would you set the oven in degrees Fahrenheit?

b. You are doing a science experiment with a Fahrenheit thermometer. Your data must be in degrees Celsius. If you measure a temperature of 125°F, what is this temperature in degrees Celsius? c. The temperature on the Moon varies from –230°C at night to 120°C during the day. What is the range in temperatures on the Moon in degrees Fahrenheit?

a. 52.2°F b. 51.7°C c. –382°F to 248°F

8.2 TEMPERATURE

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Defining temperature Atoms are Imagine you had a microscope powerful enough to see individual molecules always in in a compound (or atoms in the case of an element). You would see that the motion molecules are in constant motion, even in a solid object. In a solid, the

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molecules are not fixed in place, but act like they are connected by springs (Figure 8.8). Each molecule stays in the same average place, but constantly jiggles back and forth in all directions. The “jiggling” is motion, and motion means energy. The back-and-forth jiggling of molecules is caused by thermal energy, which is a kind of kinetic energy.

thermal energy - energy due to temperature.

temperature - a quantity that measures the kinetic energy per molecule due to random motion.

Temperature Thermal energy is proportional to temperature. When the temperature goes and energy up, the energy of motion increases. This means the molecules jiggle around

more vigorously. The higher the temperature, the more thermal energy molecules have and the faster they move around. Temperature measures a particular kind of kinetic energy per molecule.

Temperature measures the kinetic energy per molecule due to random motion. Random versus If you throw a rock, the rock gets more kinetic energy, but the temperature of average motion the rock does not go up. How can temperature measure kinetic energy then?

The answer is the difference between random motion of the molecules, and average motion of the object. For a collection of many molecules (like a rock), the kinetic energy has two parts. The kinetic energy of the thrown rock comes from the average motion of the whole collection, or the whole rock. This kinetic energy is not what temperature measures.

Figure 8.8: Molecules in a solid are connected by bonds that act like springs.

Random motion Each molecule in the rock is also jiggling back and forth independently of

the other molecules in the rock. This jiggling motion is random motion. Random motion is motion that is scattered equally in all directions. On average, there are as many molecules moving one way as there are moving the opposite way. Temperature measures the kinetic energy of the random motion. Temperature is not affected by any kinetic energy associated with average motion. This is why throwing a rock does not make it hotter (Figure 8.9).

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Figure 8.9: A collection of molecules can have both average motion and random motion. That is why a rock has both a velocity and a temperature.

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Thermometers Thermometers If you touch an object, you can sense whether it is hot or cold but you cannot tell the exact temperature. A thermometer is an instrument that measures

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exact temperature. The most common thermometers contain either a red fluid, which is alcohol containing a small amount of red dye; or a silvery fluid, which is mercury. You may have also used a thermometer with a digital readout.

thermometer - an instrument that measures temperature.

How a thermometer works Molecules move around more as the temperature increases. So, the same number of molecules take up more space at higher temperatures.

Using a liquid to Thermometers can detect the physical changes in materials caused by change sense the in temperature. Different types of thermometers measure different physical temperature changes. In a thermometer that uses a liquid to sense temperature, the

expansion of the liquid is directly proportional to increase in temperature. As the temperature increases, the liquid expands and rises up a long, thin tube (Figure 8.10). The height that the liquid rises indicates the temperature. The tube is long and thin so a small change in volume makes a large change in the height of the liquid. Digital Another physical property that changes with temperature is electrical thermometers resistance. The resistance of a metal wire will increase as temperature

increases. Since the metal is hotter and the metal atoms are shaking more, there is more resistance to electrons passing through the wire. A thermistor is a device that changes its electrical resistance as the temperature changes. Some digital thermometers sense temperature by measuring the resistance of a thermistor. Liquid-crystal Some thermometers, often used on the outside of aquariums, contain liquid thermometers crystals that change color based on temperature. As temperature increases, the

Alcohol molecules at 0ºC

Figure 8.10: How a thermometer works.

molecules of the liquid crystal bump into each other more and more. This causes a change in the structure of the crystals, which in turn affects their color. These thermometers are able to accurately determine the temperature between 65°F and 85°F.

8.2 TEMPERATURE

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Alcohol molecules at 22ºC

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Absolute zero and the Kelvin temperature scale Absolute zero There is a limit to how cold matter can get. As the temperature is reduced,

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molecules move more and more slowly. When the temperature gets down to absolute zero, molecules have the lowest energy they can have and the temperature cannot get any lower. You can think of absolute zero as the temperature at which molecules are completely frozen, with no motion. Technically, molecules never become absolutely motionless, but the amount of kinetic energy is so small it might as well be zero. Absolute zero occurs at –273°C (–459°F).

absolute zero - the lowest possible temperature, at which thermal energy is as close to zero as it can be, approximately –273°C. Kelvin scale - a temperature scale that starts at absolute zero and has units the same size as Celsius degrees.

Absolute zero is the temperature at which molecules are completely frozen, with no motion. The Kelvin scale A temperature in Celsius measures only relative thermal energy, relative to zero Celsius. The Kelvin scale is useful in science because it starts at

absolute zero. A temperature in Kelvins measures the actual energy of molecules relative to zero energy. Converting to The Kelvin (K) unit of temperature is the same size as the Celsius degree. If Kelvin a room’s temperature increases by 2°C, it also increases by 2K. Water freezes

at 273K and boils at 373K. Most of the outer planets and moons have temperatures closer to absolute zero than to the freezing point of water (Figure 8.11). To convert from Celsius to Kelvins, you add 273 to the temperature in Celsius. For example, a temperature of 21°C is equal to 294K (21 + 273). High While absolute zero is the lower limit for temperature, there is no practical temperatures upper limit. Temperature can go up almost indefinitely. As the temperature

increases, exotic forms of matter appear. For example, at 10,000°C, atoms start to come apart and become a plasma. In a plasma, atoms are broken apart into separate positive ions and negative electrons. Plasma conducts electricity and is formed in lightning and inside stars. You’ll read more about plasma in the next section.

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Figure 8.11: The average surface

temperature of Saturn’s largest moon, Titan, is 93K.

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Section 8.2 Review 1. People in the United States know that water boils at 212°F. In Europe, people know that water boils at 100°C. Is the water in the United States different than the water in Europe? What explains the two different temperatures?

What is absolute zero in degrees Fahrenheit?

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0K

-273 ºC

? ºF

Kelvin

Celsius

Fahrenheit

2. A comfortable room temperature is 20°C. What is this temperature in degrees Fahrenheit? 3. Which is colder, 0°C or 20°F? 4. Explain the scientific meaning of the word random. 5. Temperature measures: a. the kinetic energy of the random motion of molecules in an object. b. the kinetic energy of the average motion of molecules in an object. c. the potential energy of an object. d. the motion of an object.

Absolute zero

6. A thermometer that uses a liquid to measure temperature works because: a. the electrical resistance in the liquid changes with temperature. b. the liquid changes color as temperature changes. c. the expansion of the liquid is directly proportional to the increase in temperature. 7. Which statement best describes the relationship between temperature and thermal energy? a. Temperature and thermal energy mean the same thing. b. As temperature increases, thermal energy increases. c. As temperature increases, thermal energy decreases. d. Thermal energy is not related to temperature. 8. Would thermal energy be greater at 0°C or 48°F? Explain your answer. 9. Why can’t there be a temperature lower than absolute zero?

8.2 TEMPERATURE

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8.3 The Phases of Matter

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You will notice that on a hot day, a glass of iced tea (or any cold beverage) has liquid water on the outside (Figure 8.12). The water does not come from inside the glass. The ice (the solid form of water) and cold liquid inside the glass cause the outside of the glass to also become cold. This “outside” cold temperature causes water vapor in the air—a gas—to condense into liquid water on the exterior of the glass. What is happening at the level of atoms and molecules? Why can water take the form of solid, liquid, or gas?

Solid, liquid, and gas Phases of On Earth, pure substances are usually found as matter solids, liquids, or gases. These are called phases of

solid - a phase of matter that holds its shape and does not flow. liquid - a phase of matter that holds its volume, does not hold its shape, and flows.

gas - a phase of matter that flows, does not hold its volume, and can expand or contract to fill a container.

matter. Another phase of matter called plasma is discussed later in the section. Solids A solid holds its shape and does not flow. The

molecules in a solid vibrate in place, but, on average, don’t move far from their places. Liquids A liquid holds its volume but does not hold its

shape—it flows. The molecules in a liquid are about as close together as they are in a solid. But they have enough energy to change positions with their neighbors. Liquids flow because the molecules can move around. Gases A gas flows like a liquid, but can also expand or

contract to fill a container. A gas does not hold its volume. The molecules in a gas have enough energy to completely break away from each other and are much farther apart than molecules in a liquid or a solid.

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Figure 8.12: Why can water take the form of solid, liquid, and gas?

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Intermolecular forces What are When they are close together, molecules are attracted through intermolecular intermolecular forces. These forces are not as strong as the chemical bonds between atoms, forces? but are strong enough to attach neighboring molecules to each other.

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Intermolecular forces have different strengths in different elements and compounds. Iron is a solid at room temperature. Water is a liquid at room temperature. This tells us that the intermolecular forces between iron atoms are stronger than those between water molecules.

intermolecular forces - forces between atoms or molecules in a substance that determine the phase of matter.

Temperature vs. Within all matter there is a constant competition between temperature and intermolecular intermolecular forces. The kinetic energy from temperature tends to push forces atoms and molecules apart. When temperature wins the competition,

molecules break away from each other and you have a gas. Intermolecular forces tend to bring molecules together. When intermolecular forces win the competition, molecules clump tightly together and you have a solid. Liquid is somewhere in the middle. Molecules in a liquid are not stuck firmly together, but, at the same time, they cannot escape and break away from each other (Figure 8.13).

Figure 8.13: The relationship

between temperature, intermolecular forces, and phase of matter.

8.3 THE PHASES OF MATTER

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Changing phase Melting and The melting point is the temperature at which a substance changes from freezing solid to liquid (melting) or from liquid to solid (freezing). The melting point

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is sometimes called the freezing point. Different substances have different melting points because intermolecular forces vary. When these forces are strong, it takes more energy to separate molecules from each other. Water melts at 0°C. Iron melts at a much higher temperature, about 1,500°C. The difference in melting points tells us the intermolecular forces between iron atoms are stronger than those between water molecules. Boiling and condensing

melting point - the temperature at which a substance changes from solid to liquid (melting) or liquid to solid (freezing).

boiling point - the temperature at which a substance changes from liquid to gas (boiling) or from gas to liquid (condensing).

When enough energy is added, the intermolecular forces are completely pulled apart and a liquid becomes a gas. The boiling point is the temperature at which a substance changes from liquid to gas (boiling) or from gas to liquid (condensing). When water boils, you can easily see the change within the liquid as bubbles of water vapor (gas) form and rise to the surface. The bubbles in boiling water are not air, they are water vapor.

Changes in It takes energy to break the intermolecular forces between particles. This phase require explains a peculiar thing that happens when you heat an ice cube. As you add energy heat energy, the temperature increases. Once it reaches 0°C, the temperature

stops increasing as ice starts to melt and form liquid water (Figure 8.14). As you add more heat energy, more ice becomes liquid but the temperature stays the same. This is because the energy you are adding is being used to break the intermolecular forces and change solid into liquid. Once all the ice has become liquid, the temperature starts to rise again as more energy is added. Figure 8.14 shows the temperature change in an experiment. When heat energy is added or subtracted from matter, either the temperature changes, or the phase changes, but usually not both at the same time.

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Figure 8.14: Note how the

temperature stays constant as the ice is melting into water.

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Melting and boiling points, sublimation, and plasmas All substances can exist as a solid, liquid, or gas

plasma - a phase of matter in which the matter is heated to such a high temperature that some of the atoms begin to break apart.

On Earth, elements and compounds are usually found as solids, liquids, or gases. Each substance can exist in each of the three phases, and each substance has a characteristic temperature and pressure at which it will undergo a phase change. Figure 8.15 lists some examples.

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Sublimation and Sometimes a solid can change directly to a gas with no liquid phase when heat deposition energy is added. This process is called sublimation. Solid iodine is a

substance that readily undergoes sublimation at room temperature. This is evident by the formation of a purple cloud above the crystals (Figure 8.16). A more common example is the shrinking of ice cubes (solid water) over time in the freezer. The ice doesn’t melt in the freezer, but some of the molecules turn directly from solid to gas and the ice cubes shrink. The opposite of sublimation is deposition. One example of deposition is when water vapor changes directly into a solid—such as frost on a window on a cold winter night. Plasma is a At temperatures greater than fourth phase 10,000°C, the atoms in a gas start to of matter break apart. In the plasma phase,

Melting point

Boiling point

–269°C –183°C

Mercury

–272°C –218°C –39°C

Water

0°C

100°C

Lead

327°C

1,749°C

Aluminum

660°C

2,519°C

Substance Helium Oxygen

357°C

Figure 8.15: The melting and boiling points of some common substances.

matter becomes ionized as electrons are broken loose from atoms. Because the electrons are free to move independently, plasma can conduct electricity. The Sun is made of plasma, as is most of the universe, including the Orion nebula (shown right). Where else do A type of plasma is used to make neon and fluorescent lights. Instead of we find plasma? heating the gases to an extremely high temperature, an electrical current is

passed through them. The current strips the electrons off the atoms, producing plasma. You also see plasma every time you see lightning!

Figure 8.16: Solid iodine

readily undergoes sublimation at room temperature.

8.3 THE PHASES OF MATTER

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Summarizing the phases of matter

Atoms start to break apart.

Can expand or contract to fill a container. Does not hold its volume. The molecules in a gas break away from each other and are much farther apart than molecules in a liquid or a solid.

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Strongest

Intermolecular forces

Gas Solid

Liquid

Temperature

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Plasma

Evaporation

Holds its volume, but does not hold its shape—it flows. Liquids flow because the molecules can move around.

Holds its shape and does not flow. The molecules in a solid vibrate in place, but on average, don’t move far from their places.

If you leave a pan of water in a room, eventually it will dry out. Why does this happen? Evaporation occurs when molecules go from liquid to gas at temperatures below the boiling point. Remember, temperature measures the average random kinetic energy of molecules. Some molecules have energy above the average and some below the average. Some of the highest-energy molecules have enough energy to overcome the intermolecular forces between them and their neighbors and become a gas if they are near the surface of the liquid. Molecules with higher than average energy are the source of evaporation. Evaporation takes energy away from a liquid. The molecules that escape are the ones with the most energy. The average energy of the molecules left behind is lowered. Evaporation cools the surface of a liquid because the fastest molecules escape and carry energy away. This is how your body cools off on a hot day. The evaporation of sweat from your skin cools your body.

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Section 8.3 Review

2. Explain why particles in a gas are free to move far away from each other. 3. Explain why liquids flow but solids do not.

One of the ways to make car engines more efficient is to let them reach higher temperatures. Unfortunately, steel melts at about 1,500°C. Steel gets soft before it melts, so engines typically can’t operate at temperatures even close to the melting point. Some new engine technologies use cylinders and pistons made of ceramic. Ceramic stays hard and strong at a much higher temperature than steel.

4. Would you expect a substance to be a solid, liquid, or gas at absolute zero? Explain your answer. 5. Describe what happens at the molecular level during melting. 6. Describe what happens at the molecular level when a substance boils. 7. What is the most common phase of matter in the universe? 8. What is plasma? Where can you find plasma? 9. List the four phases in order of increasing temperature (lowest to highest).

50

10. Put the following terms in order from strongest intermolecular forces to weakest intermolecular forces: liquid, gas, solid.

40

11. Which would you expect to have stronger intermolecular forces? a. hydrogen, which exists as a gas at room temperature b. iron, which exists as a solid at room temperature 12. Identify the segment(s) of the graph (A–B, B–C, C–D, D–E) in Figure 8.17 where a phase change is occurring. There could be more than one place. Explain your reasoning.

Temperature (ºC)

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1. Identify the phase or phases of matter (solid, liquid, gas) that apply to each description. More than one phase of matter may apply to each description. a. molecules vibrate in place but are not free to move around b. has volume but no particular shape c. flows d. molecules break free of intermolecular forces e. does not maintain a volume or shape f. molecules can move around and switch places, but remain close together

D

20 10 0

B

C

1

2

A 3

4

5

6

Time (min)

Figure 8.17: Question 12.

8.3 THE PHASES OF MATTER

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E

30

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Chapter 8 Assessment Vocabulary

10. ____ is a temperature scale in which water freezes at 0 degrees.

Select the correct term to complete the sentences.

11. Energy due to temperature is called ____.

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atom

Fahrenheit

heterogeneous mixture

12. You measure temperature with a(n) ____.

Celsius

absolute zero

element

13. The lowest possible temperature is called ____.

gas

plasma

intermolecular forces

compound

pure substance

solid

14. The ____ is a temperature scale that starts with absolute zero.

melting point

thermal energy

thermometer

Section 8.3

homogeneous mixture

liquid

mixture

15. A(n) ____ holds its shape.

Kelvin scale

boiling point

molecule

16. A(n) ____ does not hold its shape but has a fixed volume.

Section 8.1

1.

A pure substance that cannot be broken down into simpler substances by physical or chemical means is a(n) ____.

2.

The smallest particle of an element is a(n) ____.

3.

A(n) ____ is a substance that contains two or more elements that are chemically joined.

4.

A(n) ____ is a group of two or more atoms joined together by chemical bonds.

5.

A(n) ____ cannot be separated into other types of matter by physical means.

6.

Matter that contains a combination of different elements and/or compounds and can be separated by physical means is called a(n) ____.

7.

A(n) ____ is a mixture that is the same throughout.

8.

A(n) ____ is a mixture that is not the same throughout.

Section 8.2

9.

17. A(n) ____ does not hold its shape and takes on the volume of its container. 18. The forces that determine the phase of matter are known as ____. 19. The temperature at which a substance changes from solid to liquid is called ____. 20. The temperature at which a substance changes from liquid to gas is called ____. 21. ____ is a phase of matter in which some of the atoms begin to break apart.

Concepts Section 8.1

1.

What is Brownian motion? How does it provide evidence that matter is made of atoms and molecules?

2.

Explain the differences between elements and compounds.

3.

What are the two major categories of matter?

____ is a temperature scale in which water freezes at 32 degrees.

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4.

Name three foods not mentioned in the text that would be classified as heterogeneous mixtures, and three foods that are homogeneous mixtures.

5.

Explain the difference between the two kinds of pure substances.

6.

Explain the difference between an atom and a molecule.

CHAPTER 8

14. Why doesn’t a solid flow? 15. Name one similarity between gases and liquids. 16. Identify the phase represented by each diagram below and describe its basic properties.

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Section 8.2

7.

Compare the Celsius temperature scale with the Fahrenheit scale by answering the following questions. a. b. c.

8. 9.

Which is the larger change in temperature, 1°C or 1°F? What are the melting points and boiling points of water on each scale? Why are two different scales used?

What are the formulas for converting Fahrenheit to Celsius and Celsius to Fahrenheit? Since it is fairly easy to tell when the temperature is high or low, why do we need thermometers, thermistors, and other devices for measuring temperature?

10. Compare the Celsius temperature scale with the Kelvin scale by answering the following questions. a. b. c.

Which is the larger change in temperature, 1K or 1°C? What are the freezing points and boiling points of water on each scale? Why are two different scales used?

11. What is the difference between 0° on the Celsius scale and absolute zero? 12. Absolute zero is considered the lowest possible temperature. What is the highest possible temperature? Section 8.3

13. A liquid takes the shape of its container, but why doesn’t a liquid expand to fill the container completely?

(A)

(B)

17. What is sublimation? 18. Explain how a liquid can enter the gas phase without reaching its boiling point. 19. Which has more thermal energy: gas, plasma, or liquid? 20. What is the most common phase of matter in the universe?

Problems Section 8.1

1.

Describe a method you would use to separate chicken soup into the individual forms of matter from which it is made.

2.

Describe a method you would use to separate a mixture of sugar and water.

Section 8.2

3.

Calculate the average human body temperature, 98.6°F, on the Celsius scale.

4.

Convert −20°C to the Kelvin scale.

5.

What is the Celsius equivalent of 100K?

6.

A pizza box says to bake the pizza at 450°F but your oven measures temperature in Celsius. At what temperature should you set the oven?

CHAPTER 8 ASSESSMENT

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3.

Section 8.3

7.

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The diagram to the right shows a graph of temperature vs. time for a material that starts as a solid. Heat is added at a constant rate. Using the diagram, answer the following questions. a. b. c. d.

8.

During which time interval does the solid melt? During which time interval is the material all liquid? What is the boiling point of the substance? Does it take more heat to melt the solid or boil the liquid?

About 70 percent of the Earth’s surface is covered by water. There is water underground, and even in the atmosphere. What is water’s state at each of the following temperatures? a. b. c.

temperatures below 0 degrees Celsius temperatures between 0 and 100 degrees Celsius temperatures above 100 degrees Celsius

Applying Your Knowledge Section 8.1

1.

Identify each of the following in your classroom, school cafeteria, or home. a. b. c. d.

2.

5 homogeneous mixtures 5 heterogeneous mixtures 3 elements 5 compounds

Air is a homogeneous mixture. Conduct research to find out the gases found in air and the percentage of each. Make a pie chart illustrating your findings.

Section 8.2

4.

If you keep lowering the temperature of a material, the molecules vibrate less and less. If you could eventually reach a low enough temperature, the molecules might not vibrate at all. Is this possible, and what does it mean for the temperature scale? Is it possible to keep lowering the temperature indefinitely?

5.

In the 1860s, English physicist James Clerk Maxwell and Austrian physicist Ludwig Boltzmann first gave a rigorous analysis of temperature in terms of the average kinetic energy of the molecules of a substance. Explore their lives and their contributions to the development of the theory of temperature.

Section 8.3

6.

Design a poster or model to summarize the differences between a solid, liquid, gas, and plasma.

7.

Create a chart that illustrates the following phase changes: melting, boiling, freezing, evaporation, condensation, and sublimation.

8.

Plasmas, or ionized gases as they are sometimes called, are of great interest both physically and technologically. Do some research to find out why plasmas are of great interest to scientists and manufacturers. Describe at least two current uses of plasmas, and describe one way scientists and engineers hope to use plasmas in the future.

Design a poster to illustrate the classification of matter. Provide examples of everyday materials that belong in each category.

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CHAPTER

9

CHAPTER 9

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There is a new kind of farm that is unlike any other. Instead of food, they produce energy from wind. These farms can help solve the world’s energy shortages by generating electricity from the powerful forces in wind. Most of Earth’s energy comes from thermal radiation from the Sun, called solar radiation. A small fraction of that energy is used to drive Earth’s winds. Huge turbines that collect wind energy are becoming a familiar sight, silhouetted against the skies. Wind power in Texas, for example, has more than quadrupled in recent years. Currently there are over 2,000 wind turbines in western Texas alone, most of them situated on land leased from crop farmers and ranchers. Not long ago, most farms in the United States had a windmill. They were used to pump water from wells. These days, an electric motor pumps the water, and the old windmills are gone or just displayed as antiques. Tower-mounted wind turbines that are far larger and more efficient have replaced the old models. When these big turbines are grouped, they form a wind farm. Wind farms are being built on land that is still used for crop farming. With support from industry and the government, wind farms are sprouting up across the country. In this chapter, you will learn how winds are produced through solar radiation and the transfer of heat.

4 Why does chocolate melt in your hand? 4 How does water help stabilize Earth’s temperature?

4 What produces winds?

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HEAT

9.1 Heat and Thermal Energy To change the temperature, you usually need to add or subtract energy. For example, when it’s cold outside, you turn up the heat in your home and the temperature goes up. You know that adding heat increases the temperature, but have you ever thought about exactly what heat is? What does heat have to do with temperature?

heat - thermal energy that is moving or is capable of moving.

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Heat, temperature, and thermal energy What is heat?

What happens when you hold a chocolate bar in your hand? Thermal energy flows from your hand to the chocolate and it begins to melt. We call this flow of thermal energy heat. Heat is really just another word for thermal energy that is moving. In the scientific sense, heat flows any time there is a difference in temperature. Heat flows naturally from a warmer object (higher energy) to a cooler one (lower energy). In the case of the melting chocolate bar, the thermal energy lost by your hand is equal to the thermal energy gained by the chocolate bar. What makes chocolate melt in your hand?

Figure 9.1: It takes twice as much energy to heat a 2,000-gram mass of water compared to a 1,000-gram mass.

Heat flows naturally from a warmer object (higher energy) to a cooler one (lower energy). Thermal energy depends on mass and temperature

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Heat and temperature are related but they are not the same thing. The amount of thermal energy depends on the temperature but it also depends on the amount of matter you have. Think about heating two pots of water. One pot contains 1,000 grams of water and the other contains 2,000 grams of water. The water in both pots starts out at the same temperature and is heated to the same final temperature (Figure 9.1). Which takes more energy to heat? Or do both require the same amount of energy? The pot holding 2,000 grams of water takes twice as much energy as the pot with 1,000 grams, even though both start and finish at the same temperature. The two pots illustrate the difference between temperature and thermal energy. The pot of water with more mass has more energy even though both are at the same temperature.

Like many words used in science, the word heat has many other meanings beside the one above. Write down three sentences that contain the word heat. Try to use a different meaning of heat in each sentence.

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Units of heat and thermal energy The joule The metric unit for measuring heat is the joule. This is the same joule used to

measure all forms of energy, such as potential energy and kinetic energy. A joule is a small amount of heat. The average hair dryer puts out 1,200 joules of heat every second!

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The calorie One calorie is the amount of energy (heat) needed to increase the temperature

of 1 gram of water by 1 degree Celsius. One calorie is a little more than 4 joules (Figure 9.2). You might have noticed that most food packages list “Calories per serving.” The unit used for measuring the energy content of the food we eat is the kilocalorie, which equals 1,000 calories. The kilocalorie is often written as Calorie (with a capital C). If a candy bar contains 210 Calories, it contains 210,000 calories, or 879,060 joules! The British Still another unit of heat energy you might encounter is the British thermal thermal unit unit, or Btu. The Btu is often used to measure the heat produced by heating

systems or the heat removed by air-conditioning systems. One Btu is the quantity of heat it takes to increase the temperature of 1 pound of water by 1 degree Fahrenheit. One Btu is a little more than 1,000 joules. Calorie

Btu 50ºF

10ºC

11ºC

+ 1 gram of water at 10ºC

+

51ºF

+

=

= calorie 1c alorie l ie heat off h eat

=

1 gram of water at 11ºC

1 pound of water at 50ºF

+

1 Btu of heat

=

1 pound of water at 51ºF

Why so many The calorie and Btu units were being used to measure heat well before units? scientists knew that heat was really energy. The calorie and Btu are still used,

CHAPTER 9

Unit

Is equal to

1 calorie

4.186 joules

1 kilocalorie

1,000 calories

1 Btu

1,055 joules

1 Btu

252 calories

Figure 9.2: Conversion table for

units of heat.

Heat and Work Work can be done whenever heat flows from a higher temperature to a lower temperature. Since heat flows from hot to cold, to get output work you need to maintain a temperature difference. Many inventions use heat to do work. The engine in your car uses the heat released by the burning of gasoline. In a car engine, the high temperature is inside the engine and comes from the burning gasoline. The low temperature is the air around the car. The output work produced by the engine is extracted from the flow of heat. Only a fraction of the heat is used to do work, and that is why a running car gives off so much heat through the radiator and exhaust.

even 100 years after heat was shown to be energy, because people give up familiar ways very slowly!

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Specific heat Temperature, If you add heat to an object, how much will its temperature increase? It mass, and depends in part on the mass of the object. If you double the mass of the material object, you need twice as much energy to get the same increase in

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temperature. The temperature increase also depends on what material you are heating up. It takes different amounts of energy to raise the temperature of different materials.

specific heat - the amount of heat needed to raise the temperature of 1 kilogram of a material by 1 degree Celsius.

The temperature increase of an object depends on its mass and the material from which it is made. Temperature You need to add 4,184 joules of heat to 1 kilogram of water to raise the and type of temperature by 1°C (Figure 9.3). You only need to add 470 joules to raise the material temperature of 1 kilogram of steel by 1°C. It takes nine times more energy to

raise the temperature of water by 1°C than it does to raise the temperature of the same mass of steel by 1°C. Specific heat Specific heat is a property of a material that tells us how much heat is

needed to raise the temperature of 1 kilogram of that material by 1 degree Celsius. Specific heat is measured in joules per kilogram per degree Celsius (J/kg°C). A large specific heat means you have to put in a lot of energy for each degree of increase in temperature. Uses for specific Knowing the specific heat of a material tells us how quickly the temperature heat of the material will change as it gains or loses energy. If the specific heat is

low (like for steel), then temperature will change relatively quickly because each degree of temperature change takes less energy. If the specific heat is high (like for water), then the temperature will change relatively slowly because each degree of temperature change takes more energy. For instance, hot apple pie filling stays hot for a long time because it is mostly water, and therefore has a high specific heat. Pie crust has a much lower specific heat and cools much more rapidly. Figure 9.4 lists the specific heat for some common materials.

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Figure 9.3: Water and steel have different specific heats. Material

Specific heat (J/kg°C)

Water

4,184

Wood

1,800

Aluminum

900

Concrete

880

Glass

800

Steel

470

Figure 9.4: Specific heat values of some common materials.

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Why is specific heat different for different materials? Why specific In general, elements made of more massive atoms tend to have low specific heat varies heats compared to elements with less massive atoms. This is because

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temperature measures the average kinetic energy per atom. Elements with more massive atoms usually have fewer atoms per kilogram. When the added energy is divided between fewer atoms, there is more energy per atom and therefore more temperature change.

An example: Suppose you add 4,000 joules of energy to a kilogram of silver and silver and 4,000 joules to a kilogram of aluminum. Silver’s specific heat is 235 J/kg°C aluminum and adding 4,000 joules is enough to raise the temperature of the silver by

17°C. Aluminum’s specific heat is 900 J/kg°C. Adding 4,000 joules only raises the temperature of the aluminum by 4.4°C. The silver has fewer atoms than the aluminum because silver atoms are more massive than aluminum atoms. When energy is added, each atom of silver gets more energy than each atom of aluminum because there are fewer silver atoms in a kilogram. Because the energy per atom is greater, the temperature increase in the silver is also greater.

Water has a higher specific heat than many other common materials. Its specific heat is more than four times greater than the specific heat of rocks and soil. The high specific heat of water is very important to our planet. Water covers about 70 percent of Earth’s surface. One of the fundamental reasons our planet is habitable is that the huge amount of water on it helps regulate the temperature. Land, because it has a low specific heat, experiences large changes in temperature when it absorbs heat from the Sun. Water tends to have smaller changes in temperature when it absorbs the same amount of heat. During the day, oceans help keep Earth cool, while at night, they keep Earth warm by slowing the rate at which heat is emitted back into space.

9.1 HEAT AND THERMAL ENERGY

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Calculating energy changes from heat How could you figure out how much energy it would take to heat a swimming pool or boil a pot of water? The heat equation below shows how much energy (E) it takes to change the temperature (T ) of a mass (m) of a substance with a specific heat value (Cp). Figure 9.5 shows the specific heat values for some common materials.

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Solving Problems: Heat Equation

Material

Specific heat (J/kg°C)

Water

4,184

Wood

1,800

Aluminum

900

Concrete

880

Glass

800

Steel

470

Silver

235

Gold

129

Figure 9.5: Use these specific heat values to solve the problems on this page.

How much heat is needed to raise the temperature of a 250 kg of water in a hot tub from 20°C to 40°C? 1. Looking for:

You are looking for the amount of heat energy needed in joules.

2. Given:

You are given the mass in kg, temperature change in °C, and specific heat of water in J/kg°C.

3. Relationships:

E = mCp(T2 – T1)

4. Solution:

E = 250 kg × 4,184 J/kg°C (40°C − 20°C) = 20,920,000 J

a. 35,200 J b. 116 J

Your turn...

a. How much heat energy is needed to raise the temperature of 2.0 kg of concrete from 10°C to 30°C? b. How much heat energy is needed to raise the temperature of 5.0 g of gold from 20°C to 200°C? (Hint: you will have to do a unit conversion.)

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Section 9.1 Review A fast-food hamburger contains 870 kilocalories. Calculate the quantity of energy in calories, Btu, and joules.

1. When you hold a piece of chocolate in your hand, why does the chocolate melt? 2. Which is a larger unit of heat: calorie, kilocalorie, Btu, or joule?

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3. Which of the following would require more energy to heat it from 10°C to 20°C? a. 200 kg of water b. 200 kg of aluminum c. 100 kg of steel 4. What is the difference between temperature and heat?

STUDY SKILLS

5. What conditions are necessary for thermal energy to flow? 6. How much heat is required to raise the temperature of 20 kilograms of water from 0°C to 35°C? 7. Heat is added to an object. Its temperature increase depends on: a. its mass. b. its velocity. c. the material from which it is made. d. answers a and c e. none of the above

Temperature Thermometer

8. When night falls at the beach, which would you expect to cool faster: the ocean water or the beach sand? Explain your answer. 9. Why is the high specific heat of water important to our planet?

You have learned many terms associated with heat and temperature. It is important to be able to distinguish between the meanings of each term. Make a set of flash cards for the terms below. Write the term on one side and the definition on the other. Use the term in a sentence. Write the sentence underneath the definition.

Heat Thermal energy Specific heat

10. Which material would have a higher specific heat? a. a material made of heavier particles b. a material made of lighter particles c. the mass of the particles does not affect specific heat

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9.2 Heat Transfer Thermal energy flows from higher temperature to lower temperature. This process is called heat transfer. How is heat transferred from material to material, or from place to place? There are three ways heat flows: heat conduction, convection, and thermal radiation.

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Heat conduction What is Heat conduction is the transfer of heat by the direct contact of particles of conduction? matter. If you have ever held a warm mug of hot cocoa, you have

experienced heat conduction. Heat is transferred from the mug to your hand. Heat conduction only occurs between two materials that are at different temperatures and only when they are touching each other. In conduction, heat can also be transferred through materials. If you stir hot cocoa with a metal spoon, heat is transferred from the cocoa, through the spoon, and to your hand.

heat transfer - the flow of thermal energy from higher temperature to lower temperature.

heat conduction - the transfer of heat by the direct contact of particles of matter. thermal equilibrium - when two objects are at the same temperature and no heat flows.

Heat conduction is the transfer of heat by the direct contact of particles of matter. How does Imagine placing a cold spoon into a mug of hot cocoa (Figure 9.6). The conduction molecules in the cocoa have a higher average kinetic energy than those of the work? spoon. The molecules in the spoon exchange energy with the molecules in

the cocoa through collisions. The molecules within the spoon spread the energy up the stem of the spoon through the intermolecular forces between them. Heat conduction works through collisions and also through intermolecular forces between molecules. Thermal As collisions continue, the molecules of the hotter material (the cocoa) lose equilibrium energy and the molecules of the cooler material (the spoon) gain energy. The

kinetic energy of the hotter material is transferred, one collision at a time, to the cooler material. Eventually, both materials are at the same temperature. When this happens, they are in thermal equilibrium. Thermal equilibrium occurs when two objects have the same temperature. No heat flows when objects are in thermal equilibrium.

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Figure 9.6: Heat flows by conduction from the hot cocoa into, and up, the spoon.

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Thermal conductors and insulators Which state of Heat conduction can happen in solids, liquids, and gases. Solids make the best matter conducts conductors of heat because their particles are packed closely together. heat the best? Because the particles in a gas are spread so far apart, relatively few collisions

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occur, making air (a gas) a poor conductor of heat. This explains why many materials used to keep things warm, such as fiberglass insulation and down jackets, contain air pockets (Figure 9.7). Thermal Materials that conduct heat easily are called thermal conductors and those conductors and that conduct heat poorly are called thermal insulators. For example, metal is a insulators thermal conductor and a foam cup is a thermal insulator. The words conductor

and insulator are also used to describe a material’s ability to conduct electrical current. In general, good electrical conductors like silver, copper, gold, and aluminum are also good thermal conductors.

Heat conduction cannot occur through a vacuum

Heat conduction happens only if there are particles available to collide with one another. Heat conduction does not occur in the vacuum of space. One way to create an excellent thermal insulator on Earth is to make a vacuum. A vacuum is empty of everything, including air. A vacuum bottle keeps liquids hot for hours. This container consists of a bottle surrounded by a slightly larger bottle. Air molecules are removed from the space between the bottles to create a vacuum (Figure 9.8).

Figure 9.7: Because air is a poor conductor of heat, a down jacket keeps you warm in cold weather.

Figure 9.8: This container uses a vacuum to prevent heat transfer by conduction and convection. 9.2 HEAT TRANSFER

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Convection What is Have you ever watched water boil in a pot? Bubbles form on the bottom and convection? rise to the top. Hot water near the bottom of the pan circulates up, forcing

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cooler water near the surface to sink. This circulation carries heat through the water (Figure 9.9). This heat transfer process is called convection. Convection is the transfer of heat through the motion of matter such as air and water.

convection - the transfer of heat by the motion of matter, such as by moving air or water.

Natural Fluids expand when they heat up. Since expansion increases the volume but convection not the mass, a warm fluid has a lower mass-to-volume ratio (called density)

than the surrounding cooler fluid. In a container, warmer fluid floats to the top and cooler fluid sinks to the bottom. This is called natural convection.

Convection currents

Forced In many houses, a boiler heats water and then pumps circulate the water to convection the rooms. Since the heat is being carried by a moving fluid, this is another

example of convection. However, since the fluid is forced to flow by the pumps, it is called forced convection. Natural and forced convection often occur at the same time. Forced convection transfers heat to a hot radiator. The heat from the hot radiator then warms the room air by natural convection. Convection is mainly what distributes heat throughout the room. Figure 9.9: Convection currents in water. The hot water at the bottom of the pot rises to the top and replaces the cooler water.

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Thermal radiation What is thermal If you stand in a sunny area on a cold, calm day, you will feel warmth from radiation? the Sun. Heat from the Sun is transferred to Earth by thermal radiation. Thermal radiation is electromagnetic waves (including light) produced by

thermal radiation electromagnetic waves produced by an object because of its temperature.

Thermal radiation is heat transfer by electromagnetic waves, including light. Thermal Thermal radiation comes from the thermal energy of atoms. The power in radiation comes thermal radiation increases with higher temperatures because the thermal from atoms energy of atoms increases with temperature (Figure 9.10). Because the Sun is

extremely hot, its atoms emit lots of thermal radiation. Unlike conduction or convection, thermal radiation can transfer heat through the vacuum of space. All the energy that Earth receives from the Sun comes from thermal radiation. Objects emit Thermal radiation is also absorbed by objects. Otherwise all objects would and absorb eventually cool down to absolute zero by radiating their energy away. The radiation temperature of an object rises if more radiation is absorbed. The temperature

Thermal radiation power Power (W)

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an object because of its temperature. All objects with a temperature above absolute zero (–273°C or –459°F) emit thermal radiation. To emit means to give off.

100,000 10,000 1,000 100 10 1 0.1 10

100

1,000

10,000

Temperature (ºC)

Figure 9.10: The higher the

temperature of an object, the more thermal radiation it emits.

falls if more radiation is emitted. The temperature adjusts until there is a balance between radiation absorbed and radiation emitted. Some surfaces absorb more energy than others

The amount of thermal radiation absorbed depends on the surface of a material. Black surfaces absorb almost all the thermal radiation that falls on them. For example, black asphalt pavement gets very hot in the summer sun because the black surface effectively absorbs thermal radiation. A silver mirror surface reflects most thermal radiation, absorbing very little (Figure 9.11). You might have seen someone put a silver screen across his windshield after parking his car on a sunny day. This silver screen can reflect the Sun’s heat back out the car window, helping the parked car stay cooler on a hot day.

Figure 9.11: Dark surfaces absorb most of the thermal radiation they receive. Silver or mirrored surfaces reflect thermal radiation.

9.2 HEAT TRANSFER

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Heat transfer, winds, and currents Thermals are small convection currents in the atmosphere

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Have you ever seen a hawk soaring above a highway and wondered how it could fly upward without flapping its wings? The hawk is riding a thermal—a convection current in the atmosphere (Figure 9.12). A thermal forms when a surface, such as a blacktop highway, absorbs solar radiation and emits energy as heat. That heat warms the air near the surface. The warmed air molecules gain kinetic energy and spread out. As a result, the heated air near the highway becomes less dense than the colder air above it. The heated air rises, forcing the colder air to move aside and sink toward the ground. Then this colder air is warmed by the heat from the blacktop, and it rises. A convection current is created.

Giant There are also giant convection currents in the atmosphere. These form as a convection result of the temperature difference between the equator and the poles. Warm currents air at the equator rises and flows toward the poles. Cooler, denser air from

Figure 9.12: Hawks ride convection currents called thermals.

the poles sinks and flows back toward the equator. When air flows horizontally from an area of high density and pressure into an area of low density and pressure, we call the flowing air wind. Global wind While it might seem logical that air would flow in giant circles from the cells equator to the poles and back, the reality is more complicated than that. The

warm air from the equator doesn’t make it all the way to the poles because of Earth’s rotation. In fact, the combination of global convection and Earth’s rotation sets up a series of wind patterns called global wind cells in each hemisphere (Figure 9.13). These cells play a large role in shaping weather patterns on Earth. Ocean currents The global wind patterns and Earth’s rotation cause surface ocean currents to

move in large circular patterns. Ocean currents can also occur deep within the ocean. These currents move slower than surface currents and are driven by temperature and density differences in the ocean. Surface and deep currents work together to move huge masses of water around the globe. Ocean currents play a big role in heating and cooling some parts of Earth.

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Figure 9.13: These circular wind

patterns exist in both the northern and southern hemispheres. They are called global wind cells.

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Section 9.2 Review 1. What is thermal equilibrium?

Where Does Solar Radiation Go?

2. Which state of matter—solid, liquid, or gas—is the best at conducting heat? Why?

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3. Cooking pots are made of metal but often the handle of a cooking pot is made of plastic or rubber. Explain why this design makes sense. 4. A down jacket keeps your body warm mostly by reducing which form of heat transfer? a. conduction b. convection c. thermal radiation 5. What is the advantage of designing a Thermos® so that it has a vacuum layer surrounding the area where hot liquids are stored? 6. What is the difference between forced and natural convection? 7. Examine the scene below. Explain what types of heat transfer are occurring in the scene and where each is occurring:

Most of Earth’s energy comes from thermal radiation from the Sun called solar radiation. Of the total amount of incoming solar radiation: • • • • •

8. How does heat from the Sun get to Earth? a. conduction b. convection c. thermal radiation 9. Explain the roles of density and temperature in convection.

30% is returned to outer space. 47% is absorbed by Earth. 22.78% is used to drive the hydrologic cycle. 0.2% drives the winds. 0.02% is absorbed by plants and used in photosynthesis.

Create a graph with the data in the Science Fact above. Think about the best type of graph to use.

10. A sailor on a sailboat depends on the process of convection. Explain why this is so.

9.2 HEAT TRANSFER

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Chapter 9 Assessment Vocabulary Select the correct term to complete the sentences.

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convection

heat transfer

thermal equilibrium

heat conduction

thermal radiation

heat

3.

The amount of thermal energy in an object depends on what two factors?

4.

Name three units for measuring heat.

5.

What is the relationship between the calorie used by scientists and the Calorie used by nutritionists?

6.

Compare the size of a calorie to a joule.

7.

Why does specific heat vary for different substances?

specific heat Section 9.1

1.

Thermal energy that is moving or capable of moving is called ____.

2.

The amount of heat needed to raise the temperature of 1 kilogram of a material by 1 degree Celsius is called its ____.

Section 9.2

3.

____ is the flow of thermal energy from higher temperature to lower temperature.

4.

Heat stops flowing when ____ is reached.

5.

The transfer of heat by the direct contact of particles of matter is called ____.

6.

When heat is transferred by the motion of matter such as by moving air or water, it is called ____.

7.

Heat is transferred from the Sun to Earth by ____.

Concepts Section 9.1

1.

Distinguish between heat and thermal energy.

2.

When you hold a cold glass of water in your warm hand, which way does the heat flow?

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Section 9.2

8.

Name the three methods by which heat can be transferred and give an example of each.

9.

A metal cup containing water at 100°F is placed in an aquarium containing water at 80°F. a. b. c.

Which way will heat flow? Why? When will the flow of heat stop? What is it called when heat no longer flows?

10. How do vacuum bottles keep cold beverages contained inside them from getting warm? 11. Name three good thermal insulators. 12. How do we know that we receive heat from the Sun by thermal radiation and not by conduction or convection? 13. Explain the difference between natural and forced convection. Give an example of each.

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Problems Section 9.1

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1.

How much energy, in joules, does it take to raise the temperature of 1.5 kg of aluminum from 20°C to 40°C?

2.

Relative to 0°C, the amount of thermal energy in a quantity of water is its mass × specific heat × temperature. The specific heat of water is 4,184 J/kg°C.

3.

a.

How much thermal energy is in 100 grams of water at 50°C?

b.

How much thermal energy is in 100 grams of water at 0°C?

c.

How much energy is there when both quantities of water are mixed together?

d.

How much mass is this energy spread out over (in the mixture)?

e.

What do you think the temperature of the mixture should be, assuming no heat is lost to the air?

How much energy will it take to increase the temperature of 0.2 L of water by 12°C? (Hint: 1 L of water = 1 kg.)

4.

Two beakers each contain 1 kilogram of water at 0°C. One kilogram of gold (specific heat = 129 J/kg°C) at 100°C is dropped into one beaker. One kilogram of aluminum (specific heat = 900 J/kg°C) at 100°C is dropped into the other beaker.

a. b.

c.

Compare the amount of thermal energy contained in the aluminum and gold. After each beaker has reached thermal equilibrium, describe whether the temperatures in the two beakers are the same or different. If they are different, describe which is warmer and which is colder. Explain your answer to part b. Use the concept of specific heat in your explanation.

CHAPTER 9 ASSESSMENT

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Section 9.2

Section 9.2

5.

You pour some hot water into a metal cup. After a minute, you notice that the handle of the cup has become hot. Explain, using your knowledge of heat transfer, why the handle of the cup heats up. How would you design the cup so that the handle does not heat up?

3.

6.

A computer CPU chip creates heat because of the electric current it uses. The heat must be carried away, or the chip will melt. To keep the chip cool, a finned heat sink (shown right) is used to transfer heat from the chip to the air. Which of the materials below would make the best heat sink (transfer the most heat)? Which would be the worst material to use? Note: Thermal conductivity is a measure of a material’s ability to conduct heat and is measured in units of watts per meter Kelvin.

In an automobile, a mixture of water and antifreeze is pumped through the engine block as a coolant. The mixture is pumped back to the radiator where a fan blows air. Explain—using the concepts of conduction, convection, and radiation—how this system works to transfer heat from the engine to the air.

4.

In a home aquarium, regulating the temperature of the water is critical for the survival of the fish. To keep a fish tank warm, a heating element with a thermostat is often placed on the bottom of the tank. Why is a heating element placed on the bottom of the tank instead of at the top?

5.

A thermostat controls the switch on a furnace or air conditioner by sensing the temperature of the room. Explain—using the concepts of conduction, convection, and radiation—where you would place the thermostat in your science classroom. Consider windows, inside and outside walls, and where the heating and cooling ducts are located. You can also sketch your answer. Draw your classroom, showing room features and placement of the thermostat.

6.

Building materials such as plywood, insulation, and windows are rated with a number called the “R value.” The R value has to do with the thermal conductivity of the material. Higher R values mean lower conductivity and better insulation properties. Design a window with a high R value. Sketch your window and label its features and the materials it is made from. Explain the reasons for each of your design choices.

Thermal conductivity of materials (W/m · K) Concrete = 1.7

Aluminum = 240

Asbestos = 0.1

Glass = 0.8

Copper = 400

Gold = 310

Wood = 0.1

Rubber = 0.2

Silver = 430

Applying Your Knowledge Section 9.1

1.

The first settlers in Colorado were very concerned about fruits and vegetables freezing in their root cellars overnight. They soon realized that if they placed a large tub of water in the cellar, the food would not freeze. Explain why the food would not freeze.

2.

Scottish chemist Joseph Black developed the theory of specific heat. Research his life and how he made the discoveries.

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10

CHAPTER 10

Properties of Matter

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Would you believe that someone has invented a solid material that has about the same density as air? It’s so light, if someone put a chunk of it your hand you might not even notice. Silica aerogel is a foam that’s like solidified smoke. Aerogel is mostly air and has remarkable thermal, optical, and acoustical properties. Aerogels are fantastic insulators. You could hold a flame under a chunk of the material and touch the top without being burned. Aerogels have the potential to replace a variety of materials used in everyday life. If researchers could make a transparent version of an aerogel, it would almost certainly be used in doublepane windows to keep heat inside your house in the winter and outside in the summer. Opaque aerogels are already being used as insulators. Aerogels have been put to use by NASA in several projects, including the Mars Pathfinder, Soujourner and Stardust missions. Read this chapter to find out more about various types of matter and their properties.

4 What are some important properties of solids?

4 What is a fluid and how are fluids different from solids?

4 What is pressure? 4 Why does a steel cube sink while a steel boat floats?

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PROPERTIES OF MATTER

10.1 Density

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Mass and volume are different properties of matter, but they are related. For instance, a solid block of wood and a solid block of steel can have the same volume, but they would not have the same mass. The steel block has a lot more mass than the wood block. Because of the mass difference, the wood block floats in water and the steel block sinks. Whether an object floats or sinks is related to the object’s density. This section will explain density, a property of all matter.

density - the mass per unit volume of a given material. Units for density are often expressed as g/mL, g/cm3, or kg/m3.

Density is a property of matter Density is mass Density describes how much mass is in a given volume of a material. per unit volume Steel has high density; it contains 7.8 grams of mass per cubic centimeter

(7.8 g/cm3). Aluminum, as you might predict, has a lower density; a 1-centimeter cube has a mass of only 2.7 grams (2.7 g/cm3).

The density of Liquids and gases are matter, therefore, they have density. The density of water and air water is about 1 gram per cubic centimeter. The density of air is lower, of

course—much lower. The air in your classroom has a density of about 0.001 grams per cubic centimeter (0.001 g/cm3). Density units can be expressed as g/cm3 g/mL, or kg/m3 (Figure 10.1).

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Figure 10.1: The density of steel,

aluminum, water, and air expressed in grams per milliliter (1 mL = 1 cm3).

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Units of density Density in units Your laboratory investigations will typically express density in units of grams of g/mL per milliliter (g/mL). The density of water is one gram per milliliter. This

means 1 milliliter of water has a mass of 1 gram.

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Density in units Some problems express density in units of grams per cubic centimeter (g/cm3). of g/cm3 and Since 1 milliliter is exactly the same volume as 1 cubic centimeter, the units 3 it is easier to kg/m3 of g/cm and g/mL are the same. For measuring large objects, 3

express density in units of kilograms per cubic meter (kg/m ). Figure 10.2 gives the densities of some common materials in both units.

Converting units To convert from one unit of density to the other, remember that 1 g/cm3 is of density equal to 1,000 kg/m3. To go from g/cm3 to kg/m3, you multiply by 1,000. For

example, the density of ice is 0.92 g/cm3. This is the same as 920 kg/m3. To go from kg/m3 to g/cm3, you divide by 1,000. For example, the density of aluminum is 2,700 kg/m3. Dividing by 1,000 gives a density of 2.7 g/cm3.

Material

(kg/m3)

(g/cm3)

Platinum Lead Steel Titanium Aluminum Glass Granite Concrete Plastic Rubber Liquid water Ice Ash (wood) Pine (wood) Cork Air (avg.)

21,500 11,300 7,800 4,500 2,700 2,700 2,600 2,300 2,000 1,200 1,000 920 670 440 120 0.9

21.5 11.3 7.8 4.5 2.7 2.7 2.6 2.3 2.0 1.2 1.0 0.92 0.67 0.44 0.12 0.0009

Figure 10.2: Density of some common materials.

Ipe (pronounced ee-pay) is a Brazilian hardwood that can be used as a durable (but expensive!) construction material for decks, docks, and other outdoor projects. Every cubic foot of ipe weighs 69 pounds. Use dimensional analysis to convert the density of ipe to g/cm3. How does the density of ipe compare to other woods and materials in the list above?

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Density of solids and liquids Density of a material does not change with quantity or shape

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Density is a property of material that is independent of quantity or shape. For example, a steel nail and a steel cube have different amounts of matter and therefore different masses (Figure 10.3). They also have different volumes and shapes. But they have the same density. Dividing mass by volume gives the same density for the nail and the cube, because both are made of steel.

Density of a material is the same no matter what the size or shape of the material Liquids tend to The density of a liquid is usually a little less than the density of the same be less dense material in solid form. Take the example of solder (pronounced sod-der). than solids of Solder is a metal alloy used to join metal surfaces. the same 500 g of solid solder fills a volume of 50 mL. material

The density of solid solder is 10 g/mL. The same mass (500 g) of melted (liquid) solder has 52.6 mL of volume. Liquid solder has a lower density of 9.5 g/mL. The density of a liquid is lower because the atoms are not packed as tightly as they are in a solid. Imagine a brand-new box of toy blocks. When you open the box, the blocks are tightly packed, like the atoms in a solid. Now imagine dumping the blocks out of the box, and then pouring them back into the original box again. The same number of jumbled blocks take up more space, like the atoms in a liquid (Figure 10.4).

Water is an Water is an exception to this rule. The density of solid water, or ice, is less exception than the density of liquid water. When water molecules freeze into ice

crystals, they form a pattern that has an unusually large amount of empty space. The water molecules in ice are actually farther apart than they are in liquid water. Because of this, ice floats in liquid water.

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Steel density Steel cube

Volume: 10.0 cm3 Mass: 78 g Density: 7.8 g/cm3

Nail Volume: 1.6 cm3 Mass: 12.5 g Density: 7.8 g/cm3

Figure 10.3: The density of a steel

nail is the same as the density of a solid cube of steel.

Figure 10.4: The same number (or mass) of blocks arranged in a tight, repeating pattern take up less space than when they are jumbled up.

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Determining density Finding density To find the density of a material, you need to know the mass and volume of a

sample of the material. You can calculate density using the formula below.

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m V Density gives information about atoms and molecules

Density gives us information about how tightly the atoms or molecules of a particular material are “packed.” Diamond is made of carbon atoms and has a density of 3.5 g/cm3. The carbon atoms in diamond are relatively tightly packed. Paraffin wax is also made mostly of carbon atoms, but the density is only 0.87 g/cm3. The density of paraffin is low because the carbon atoms are mixed with hydrogen atoms in long molecules that take up a lot of space. The molecules in paraffin are not as tightly packed as the atoms in diamond.

The density of Suppose you have a piece of aluminum foil, a length of aluminum wire, and solid objects an aluminum brick. At the same temperature and pressure, the aluminum

making each of these has the same density. It does not matter whether the aluminum is shaped into a brick, flat sheet, or long wire. The density is 2.7 g/cm3 as long as the object is made of solid aluminum. The average If an object is hollow, its average density is less than the density of the density of a material from which the object is made. Suppose a small block of aluminum hollow object with a mass of 10.8 grams is used to make a soda can (Figure 10.5). Both the

solid block of aluminum and the soda can have a mass of 10.8 grams, but the hollow can has a much larger volume. The can has 100 times the volume of the block, so its density is 100 times less.

Figure 10.5: The aluminum block

and the soda can have the same mass but different volumes and densities. The density of the aluminum can is called its average density because it also includes the air inside the can as part of the volume.

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Solving Problems: Calculating Density A solid wax candle has a volume of 1,700 mL. The candle has a mass of 1.5 kg (1,500 g). What is the density of the candle?

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

1. Looking for:

You are asked for the density.

2. Given:

You are given the mass and volume.

3. Relationships:

Density is mass divided by volume.

4. Solution:

Density = 1,500 g ÷ 1,700 mL = 0.88 g/mL

To find:

Use:

Density

D= m V

Volume

V= m D

Mass

m=D×V

Figure 10.6: Using the density equation.

Your turn...

a. Look at Figure 10.7. A student measures the mass of five steel hex nuts to be 96.2 g. The hex nuts displace 13 mL of water. Calculate the density of the steel in the hex nuts. b. The density of granite is about 2.60 g/cm3. How much mass would a solid piece of granite have that measures 2.00 cm × 2.00 cm × 3.00 cm? c. Ice has a density of about 0.920 g/cm3. What is the volume of 100.0 g of ice? Figure 10.7: A student measures the volume and mass of five steel hex nuts.

a. 7.4 g/mL; b. 31.2 g; c. 109 cm3

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Section 10.1 Review 1. Define density, write the formula (from memory!), and give two different units used to measure density. 3. A material’s density is the same, no matter how large or small the sample is, or what its shape is, as long as it is a solid, uniform piece of the material. Explain how this is possible and give an example. 4. The density of balsa wood is about 170 kg/m3. Convert to g/cm3. Why do you think balsa wood, rather than oak or ash, is commonly used for building models? (Use evidence from Figure 10.2 on page 217.) 5. A certain material has a density of 0.2 g/cm3. Is this material better for building a bridge or for making sofa cushions? Explain, using evidence from Figure 10.2 on page 217.

20.0 grams

4.0

cm

2.0 cm

2.0 cm

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

1.0 cm

2. One cubic centimeter (cm3) is the same volume as one ________.

Mass =

? 3.0

cm

4.0 cm

Two toy blocks are made of the same type of material. One has a mass of 20.0 grams and its dimensions are 2.0 cm × 4.0 cm × 1.0 cm. The second block measures 4.0 cm × 3.0 cm × 2.0 cm. Calculate the mass of the second block.

6. The piece of wood shown above has a mass of 20 grams. Calculate its volume and density. Then, use Figure 10.2 on page 217 to determine which type of wood it is. What are the two factors that determine a material’s density? 7. The density of maple wood is about 755 kg/m3. What is the mass of a solid piece of maple that has a volume 640 cm3?

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10.2 Properties of Solids All matter is made up of tiny atoms and molecules. In a solid, the atoms or molecules are closely packed, and they stay in place. This is why solids hold their shape. In this section, you will learn how the properties of solids are a result of the behavior of atoms and molecules.

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Matter has physical and chemical properties Characteristics Different kinds of matter have different characteristics. They melt and boil at of matter a wide range of temperatures. They might be different colors or have

physical properties characteristics that can be observed directly.

chemical properties characteristics that can only be observed when a substance changes into a different substance.

different odors. Some can stretch without breaking, while others shatter easily. These, and other properties, help us distinguish one substance from another. These properties also help us choose which kind of material to use for a specific purpose. Physical Characteristics that can be observed directly are called physical properties properties. Physical properties include color, odor, texture, density,

brittleness, and state (solid, liquid, or gas). Substances can often be identified by their physical properties. For example, water is a colorless, odorless substance that exists as a liquid at room temperature. Gold is shiny, exists as a solid at room temperature, and can be pounded into very thin sheets. Physical A physical change is any change in the size, shape, or phase of matter in changes which the identity of a substance does not change. For example, when water

is frozen, it changes from a liquid to a solid. This does not change the water into a new substance. It is still water, only in solid form which we call ice. The change can easily be reversed by melting the solid water. Bending a steel bar causes another example of a physical change. Chemical Properties that can only be observed when a substance changes into a properties different substance are called chemical properties. For example, if you

leave an iron nail outside, it will eventually rust. A chemical property of iron is that it reacts with oxygen in the air to form iron oxide (rust). Any change that transforms one substance into a different substance is called a chemical change (Figure 10.8). Chemical changes are not easily reversible. Rusted iron will not turn shiny again, even if you remove it from oxygen in the air.

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Figure 10.8: Physical and chemical properties of iron.

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The arrangement of atoms and molecules in solids Crystalline and The atoms or molecules in a solid can be arranged in two ways. If the particles amorphous are arranged in an orderly, repeating pattern, the solid is called crystalline. solids Examples of crystalline solids include salts, minerals, and metals. If the particles are arranged in a random way, the solid is amorphous. Examples of

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

amorphous solids include rubber, wax, and glass. Crystalline solids

Most solids on Earth are crystalline. Some materials, like salt, exist as single crystals and you can see the arrangement of atoms reflected in the shape of the crystal. If you look at a crystal of table salt under a microscope, you’ll see that it’s cubic in shape. If you could examine the arrangement of atoms, you would see that the shape of the crystal comes from the cubic arrangement of sodium and chlorine atoms. Metals are also crystalline. They don’t look like “crystals” because solid metal is made from very tiny crystals fused together in a jumble of different orientations (Figure 10.9).

Amorphous The word amorphous comes from the Greek word amorphos, meaning solids “without shape.” Unlike crystals, amorphous solids do not have a repetitive

crystalline - an orderly, repeating arrangement of atoms or molecules in a solid. amorphous - a random arrangement of atoms or molecules in a solid.

Figure 10.9: Metallic crystals in

steel. Single crystals are very small. This image was taken with an electron microscope at very high magnification.

pattern in the arrangement of molecules or atoms. The atoms or molecules are randomly arranged. While amorphous solids also hold their shape, they are often softer and more elastic than crystalline solids. This is because a molecule in an amorphous solid is not tightly connected to as many neighboring molecules as it would be in a crystalline solid. Glass is a common amorphous solid. Glass is hard and brittle because it is made from molten silica crystals that are cooled quickly, before they have time to recrystallize. The rapid cooling leaves the silica molecules in a random arrangement. Plastic is another useful amorphous solid. 10.2 PROPERTIES OF SOLIDS

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Mechanical properties of solids When you apply a force to an object, the object might change its size, shape, or both. The concept of strength describes the ability of a solid object to maintain its shape even when force is applied. The strength of an object can be determined based on the answers to the two questions in the illustration to the left.

The meaning of strength

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

Tensile strength Tensile strength is a measure of how much stress from pulling, or tension,

a material can withstand before breaking (Figure 10.10). Strong materials like steel have high tensile strength. Weak materials like wax and rubber have low tensile strength. Brittle materials also have low tensile strength.

strength - the ability to maintain shape under the application of force.

tensile strength - a measure of how much stress from pulling, or tension, a material can withstand before breaking.

hardness - a measure of a solid’s resistance to scratching.

elasticity - the ability to be stretched or compressed and then return to original size. brittleness - the tendency to crack or break; the opposite of elasticity.

Hardness Hardness measures a solid’s resistance to scratching. Diamond is the

hardest natural substance found on Earth. Geologists sometimes classify rocks based on hardness. Given six different kinds of rock, how could you line them up in order of increasing hardness? Elasticity If you pull on a rubber band, its shape changes. If you let it go, the rubber

band returns to its original shape. Rubber bands can stretch many times their original length before breaking, a property called elasticity. Elasticity describes a solid’s ability to be stretched and then return to its original size. This property also gives objects the ability to bounce and to withstand impact without breaking. Brittleness Brittleness is defined as the tendency of a solid to crack or break before

stretching very much. Glass is a good example of a brittle material. You cannot stretch glass even one-tenth of a percent (0.001) before it breaks. To stretch or shape glass you need to heat the glass until it is almost melted. Heating causes molecules to move faster, temporarily breaking the forces that hold them together.

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Figure 10.10: Tensile strength measures how much pulling, or tension, a material can withstand before breaking.

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Ductility One of the most useful properties of metals is that they are ductile. A ductile

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material can be bent a relatively large amount without breaking. For example, a steel fork can be bent in half and the steel will not break. A plastic fork cracks when it is bent only a small amount. Steel’s high ductility means steel can be formed into useful shapes by pulling, rolling, and bending. These processes would destroy a brittle material like glass. The ductility of many metals, such as copper, allow them to be formed into wire like the copper wire shown below. What is Malleability measures a solid’s ability to be pounded into thin sheets. malleability? Aluminum is a highly malleable metal. Aluminum foil and beverage cans are

ductility - the ability to bend without breaking. malleability - the ability of a solid to be pounded into thin sheets.

thermal expansion - the tendency of the atoms or molecules in a substance (solid, liquid, or gas) to take up more space as the temperature increases.

two good examples of how manufacturers take advantage of the malleability of aluminum.

Thermal As the temperature increases, the kinetic energy in the vibration of atoms and expansion molecules also increases. The increased vibration makes each particle take up a little more space, causing thermal expansion. Almost all solid materials

Figure 10.11: Bridges have

expansion joints to allow for thermal expansion of concrete.

expand as the temperature increases. Some materials (like plastic) expand a great deal. Other materials (like glass) expand only a little. All bridges longer than a certain size have special joints that allow the bridge surface to expand and contract with changes in temperature (Figure 10.11). The bridge surface would crack without these expansion joints. 10.2 PROPERTIES OF SOLIDS

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Section 10.2 Review

STUDY SKILLS

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1. Name one example of a physical change and one example of a chemical change.

Physical Property Flashcards

2. Name one example of a material for each set of properties.

Make flash cards that will help you remember the meanings of the physical properties discussed in this section.

a. b. c. d. e.

high elasticity and high tensile strength amorphous and brittle crystalline and brittle amorphous and elastic ductile and crystalline

3. The strength of a material determines: a. how dense the material is. b. how much force it can withstand before breaking. c. how good a thermal or electrical conductor it is.

Write a property on one side of a card and the definition and some examples on the other side. For example, write “amorphous” on one side of a card and “random arrangement of molecules in a solid” on the other side. In addition, list some examples of amorphous solids such as glass and wax.

4. Latex is a soft, stretchy, rubber-like material. Would you expect latex to be crystalline or amorphous? 5. Explain, from an atomic-level perspective, why expansion joints are used in bridges. 6. Which property of a metal describes why it can be formed into wire? 7. When installing wood floors, it is often recommended that you leave a half-inch of space between the flooring and the wall (Figure 10.12). Why do you think this space would be recommended? 8. Aluminum can be made into foil because aluminum has high ____.

Figure 10.12: Question 7.

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10.3 Properties of Fluids

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A fluid is defined as any matter that flows when force is applied. Liquids, such as water, are one kind of fluid. Gases, such as air, are also fluids. You might notice cool air flowing into a room when a window is open, or the smell of someone’s perfume drifting your way. These examples provide evidence that gases flow. What are some other properties of fluids?

fluid - any matter that flows when force is applied.

Pressure

equal to one newton of force per square meter of area.

pressure - the amount of force exerted per unit of area.

pascal - the SI unit of pressure

Forces in fluids When you push down on a bowling ball, what happens? Because the bowling

ball is a solid, the force is transmitted down in the same direction as the applied force. Now, what happens when you push down on an inflated balloon? The downward force you apply creates forces that act sideways as well as down. The balloon is filled with air, a fluid. Because fluids change shape, forces in fluids are more complicated than forces in solids.

Pressure A force applied to a fluid creates pressure. Pressure acts in all directions, not

just the direction of the applied force. When you inflate a car tire, you are increasing the pressure in the tire. This force acts up, down, and sideways in all directions inside the tire. Units of The units of pressure are force divided by area (Figure 10.13). If your car tires pressure are inflated to 35 pounds per square inch (35 psi), then a force of 35 pounds

acts on every square inch of area inside the tire. The pressure on the bottom of the tire is what holds up the car! The SI unit of pressure is the pascal (Pa). One pascal is one newton of force per square meter of area (N/m2). Figure 10.13: Comparing units of pressure.

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Pressure, energy, and force The atomic level What causes pressure? On the atomic level, pressure comes from collisions explanation between atoms and molecules. Look at Figure 10.14. Molecules move

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

around and bounce off each other and off the walls of the pitcher. It takes force to make a molecule reverse its direction and bounce the other way. The bouncing force is applied to the molecule by the inside surface of the pitcher. According to Newton’s third law, an equal and opposite reaction force is exerted by the molecule on the pitcher. The reaction force is what creates the pressure acting on the inside surface of the pitcher. Trillions of molecules per second are constantly bouncing against every square millimeter of the inner surface of the pitcher. Pressure comes from the collisions of those many, many molecules. Pressure is Differences in pressure create potential energy in fluids just like differences potential energy in height create potential energy from gravity. A pressure difference of one

newton per m2 is equivalent to a potential energy of one joule per m3. We get useful work when we allow a fluid under pressure to expand. In a car engine, high pressure is created by an exploding gasoline-air mixture. This pressure pushes the cylinders of the engine down, doing work that moves the car.

Figure 10.14: Pressure comes

from constant collisions of trillions of molecules.

Car tires are usually inflated to a pressure of 32–40 pounds per square inch (psi). Racing bicycle tires are inflated to a much higher pressure, 100–110 psi. A bicycle and rider are much lighter than a car. Why is the pressure in a bicycle tire higher than the pressure in a car tire?

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Bernoulli’s principle Bernoulli’s Everything obeys the law of energy conservation. But this energy conservation principle is more challenging to explain in a flowing fluid such as water coming out

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

of a hole in a container. In addition to potential and kinetic energy, the fluid also has pressure energy. If friction is ignored, the total energy stays constant for any particular sample of fluid. This relationship is known as Bernoulli’s principle.

Bernoulli’s principle - a relationship that describes energy conservation in a fluid.

Streamlines Streamlines are imaginary lines drawn to show the flow of fluid. We draw

streamlines so that they are always parallel to the direction of flow. If water is coming out of a hole in a container, the streamlines look like the one shown in Figure 10.15. Bernoulli’s principle tells us that the energy of any sample of fluid moving along a streamline is constant. Bernoulli’s principle Form of energy

Variable

Potential energy

height

Kinetic energy

speed

Pressure energy

=

Constant along any streamline in a fluid

Figure 10.15: Streamlines are

imaginary lines drawn to show the flow of a fluid.

pressure

The three Bernoulli’s principle says the three variables of height, pressure, and speed variables are related by energy conservation. Height is associated with potential energy,

speed with kinetic energy, and pressure with pressure energy. If one variable increases along a streamline, at least one of the other two must decrease. For example, if speed goes up, pressure goes down. The airfoil An important application of Bernoulli’s principle is the airfoil shape of wings

on a plane (Figure 10.16). The shape of an airfoil causes air flowing along the top (A) to move faster than air flowing along the bottom (B). According to Bernoulli’s principle, if the speed goes up, the pressure goes down. When a plane is moving, the pressure on the top surface of the wings is lower than the pressure beneath the wings. The difference in pressure is what creates the lift force that supports the plane in the air.

Figure 10.16: Streamlines showing

air moving from right to left around an airfoil (wing).

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Pressure, volume and density of gases How gases are Gases are fluids but they are different from liquids because the molecules in different from a gas are completely separated from each other. Because gas molecules act liquids independently, gases are free to expand or contract. Unlike liquids, a gas will

expand to completely fill its container.

Boyle’s law - in a fixed quantity of a gas, the pressure and volume are inversely related if the mass and temperature are held constant.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

Pressure and When you squeeze a fixed quantity of gas into a smaller volume, the pressure volume goes up (Figure 10.17). This rule is known as Boyle’s law. The pressure

increases because the same number of molecules are now squeezed into a smaller space. The molecules hit the walls more often because there are more of them per unit of area. The formula for Boyle’s law relates the pressure and volume of gas. If the mass and temperature are kept constant, the product of the pressure multiplied by the volume stays the same.

Pressure and The density of a gas usually increases when the pressure increases. (We say density “usually” because density and pressure are also affected by temperature.) By

increasing the pressure, you are doing one of two things: squeezing the same amount of mass into a smaller volume, or squeezing more mass into the same volume. Either way, the density goes up. For example, air has a density of 0.0009 g/cm3 at atmospheric pressure. When compressed in a diving tank to 150 times higher pressure, the density is about 0.135 g/cm3. The density of a gas can vary from near zero (in outer space) to greater than the density of some solids. This is very different from the behavior of liquids or solids.

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Figure 10.17: Compressing the

volume of air to increase the pressure.

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Boyle’s law The inverse relationship between pressure and volume for a gas, when graph temperature remains constant, is evident in the graph in Figure 10.18. The

example below shows you how to solve problems using Boyle’s law.

Solving Problems: Boyle’s Law FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

Another unit of pressure is the atmosphere (atm). One atm = 101,325 pa. A kit used to fix flat tires consists of an aerosol can containing compressed air and a patch to seal the hole in the tire. Suppose 5 liters of air at 1 atm is compressed into a 0.5 liter aerosol can. What is the pressure, in atm, of the compressed air in the can? Assume no change in temperature or mass. 1. Looking for:

You are looking for the pressure inside an aerosol can.

2. Given:

You are given initial volume (in liters), initial pressure (in atmospheres), and final volume.

3. Relationships:

Use Boyle’s law, P1V1 = P2V2; rearrange variables to solve for P2: P2 =

4. Solution:

Figure 10.18: This graph shows the relationship between the pressure and volume of a gas when the temperature does not change.

P1 × V1 V2

Plug in the numbers and solve: P2 =

1 atm × 5.0 L = 10 atm 0.5 L

a. 0.25 L

Your turn...

a. A total of 0.50 L of O2 is collected at a pressure of 0.50 atm. What volume will this gas occupy at sea level (1 atm) at constant temperature and mass? b. A total of 1.0 L of helium is stored at sea level (1 atm). If the gas is carried to the top of Mt. Washington (pressure = 0.80 atm), what volume will it occupy at constant temperature and mass?

b. 1.2 L

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Viscosity What is Viscosity is the measure of a fluid’s resistance to flow. High-viscosity fluids viscosity? take longer to pour from their containers than low-viscosity fluids. Ketchup,

viscosity - a measure of a fluid’s resistance to flow.

for example, has a high viscosity and water has a low viscosity.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

Viscosity and Viscosity is an important property of motor oils. If an oil is too thick, it might motor oils not flow quickly enough to parts of an engine. However, if an oil is too thin,

it might not provide enough “cushion” to protect the engine from the effects of friction. A motor oil must function properly when the engine is started on a bitterly cold day, and when the engine is operating at high temperatures (see Science Fact on the next page). Viscosity and Viscosity is determined in large part by the shape and size of the particles in a particles liquid. If the particles are large and have bumpy surfaces, a great deal of

friction will be created as they slide past each other. For instance, corn oil is made of large, chain-like molecules. Water is made of much smaller molecules. As a result, corn oil has greater viscosity than water. This is especially interesting when you consider that corn oil is less dense than water.

As a liquid gets warmer, its viscosity decreases

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As the temperature of a liquid is raised, the viscosity of the liquid decreases. In other words, warm liquids have less viscosity than cold liquids. Fudge topping, for example, is much easier to pour when it’s warm than when it’s chilled. Also, if you heat corn oil on the stove you would notice that the viscosity decreases. Why is this? When temperature rises, the vibration of molecules increases. This allows molecules to slide past each other with greater ease. As a result, the viscosity decreases (Figure 10.19).

Figure 10.19: Heating fudge topping decreases viscosity so it is much easier to pour.

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Section 10.3 Review Motor Oil Numbers

1. Explain why liquid silver is less dense than solid silver.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

2. The pressure at the bottom of Earth’s atmosphere is about 100,000 N/m2. This means there is a force of 100,000 N acting on every square meter of area! Your body has about 1.5 square meters of surface. Why aren’t you crushed by the atmosphere? 3. The pressure at the bottom of the ocean is great enough to crush submarines with solid steel walls that are 10 centimeters thick. At a depth of 1,000 meters, the weight of water pushing on each square meter of the submarine is 9.8 million newtons.

Numbers on the label of a quart of motor oil are based on a scale established by the Society of Automotive Engineers (SAE). The first number indicates the lowest temperature at which the oil will work well (–10°F in this case). The W means the oil works well in cold weather. The second number is a grade for the oil: 50 is best for hot-weather driving, 30 for cold-weather driving, and 40 for mild weather temperatures.

a. What is the pressure exerted on the submarine at 1,000 m? b. How does this pressure compare with the air pressure we experience every day on Earth’s surface (100,000 N/m2)? 4. What does pressure have to do with how a car engine works? 5. Bernoulli’s principle relates the speed, height, and pressure in a fluid. Suppose streamline speed goes up and height stays the same. What happens to the pressure? 6. Boyle’s law states that if you squeeze a fixed amount of a gas into a smaller volume, the pressure will increase. Explain why in your own words. 7. At the atomic level, what causes fudge topping to pour faster when it is heated?

10.3 PROPERTIES OF FLUIDS

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10.4 Buoyancy If you drop a steel marble into a glass of water, it will sink to the bottom. The steel does not float because it has a greater density than the water. And yet many ships are made of steel. How does a steel ship float in water when a steel marble sinks? The answer has to do with gravity, weight, and displacement.

buoyancy - the measure of the upward force that a fluid exerts on an object that is submerged.

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Weight and buoyancy Weight and We all tend to use the terms weight and mass interchangeably. In science mass are not the however, weight and mass are not the same thing. Mass is a fundamental same property of matter. Weight is a force caused by gravity. It is easy to confuse

mass and weight because often heavy objects (more weight) have lots of mass and light objects (less weight) have little mass. Buoyancy is a It is much easier to lift yourself in a swimming pool than to lift yourself on force land. This is because the water in the pool exerts an upward force on you that

acts in a direction opposite to your weight (Figure 10.20). We call this force buoyancy. Buoyancy is a measure of the upward force that a fluid exerts on an object that is submerged. Pushing a ball underwater

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The strength of the buoyant force on an object in water Weightt Weight depends on the volume of the object that is underwater. ronger Suppose you have a buoyant Buoyant force large beach ball that force you want to submerge in a pool. As you keep pushing downward on the ball, you notice the buoyant force getting stronger and stronger. The greater the part of the ball you manage to push underwater, the stronger the force trying to push it back up. The strength of the buoyant force is proportional to the volume of the part of the ball that is submerged.

Figure 10.20: The water in the pool

exerts an upward force on your body, so the net force on you is lessened.

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Archimedes’ principle What is In the third century BCE, a Greek mathematician named Archimedes realized Archimedes’ that buoyant force is equal to the weight of the fluid displaced by an object. principle? We call this relationship Archimedes’ principle. For example, suppose a

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

rock with a volume of 1,000 cubic centimeters is dropped into water (Figure 10.21). The rock displaces 1,000 cm3 of water, which has a mass of 1 kilogram. The buoyant force on the rock is the weight of 1 kilogram of water or 9.8 newtons. Free body diagram N

N

10

29.4 N

Scale 29.4 N

19.6 N

20

30

30

40

40

50

Mass = 3 kg Volume = 1000 cm3

that the buoyant force is equal to the weight of the fluid displaced by an object.

Free body diagram

10 20

Archimedes’ principle - states

50

Weight 29.4 N

Scale 19.6 N

Weight 29.4 N

Buoyant force 9.8 N

Water

A simple Look at the illustration above. A simple experiment can be done to measure buoyancy the buoyant force on a rock (or other small object) using a spring scale. experiment Suppose you have a rock with a volume of 1,000 cubic centimeters and a mass

of 3 kilograms. In air, the scale shows the rock’s weight as 29.4 newtons. The rock is then gradually immersed in a container of water, but not allowed to touch the bottom or sides of the container. As the rock enters the water, the reading on the scale decreases. When the rock is completely submerged, the scale reads 19.6 newtons.

Figure 10.21: A rock with a volume

of 1,000 cm3 experiences a buoyant force of 9.8 newtons.

Calculating the Subtracting the two scale readings—29.4 newtons and 19.6 newtons—results buoyant force in a difference of 9.8 newtons. This is the buoyant force exerted on the rock,

and it is the same as the weight of the 1,000 cubic centimeters of water the rock displaced. 10.4 BUOYANCY

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Sinking and floating Comparing Buoyancy explains why some objects sink and others float. A submerged buoyant force object floats to the surface if the buoyant force is greater than the object’s and weight weight (Figure 10.22). If the buoyant force is less than its weight, the

Buoyant force

object sinks.

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Equilibrium Suppose you place a block of foam in a tub of water. The block sinks

partially below the surface. Then it floats without sinking any farther. The upward buoyant force perfectly balances the downward force of gravity (the block’s weight). But how does the buoyant force “know” how strong it needs to be to balance the weight?

eight Buoyant force

Weight

uoyant rce

Denser objects You can find the answer to this question in the illustration above. If a float lower in foam block and a wood block of the same size are both floating, the wood the water block sinks farther into the water. Wood has a greater density, so the

wood block weighs more. A greater buoyant force is needed to balance the wood block’s weight, so the wood block displaces more water. The foam block has to sink only slightly to displace water with a weight equal to the block’s weight. A floating object displaces just enough water until the buoyant force is equal to the object’s weight.

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Weight

Figure 10.22: Whether an object sinks or floats depends on how the buoyant force compares with the object’s weight.

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Density and buoyancy Comparing If you know an object’s density, you can immediately predict whether it will densities sink or float—without measuring its weight. An object sinks if its density is

Buoyancy and Submarines

greater than that of the liquid it is submerged into. It floats if its density is less than that of the surrounding fluid.

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Two balls with the same volume but different densities

To see why, imagine dropping a steel ball and a wood ball into a pool of water. The balls have the same size and volume but have different densities. The steel ball has a density of 7.8 g/cm3, which is greater than the density of water (1.0 g/cm3). The wood ball has a density of 0.75 g/cm3, which is less than the density of water.

Why one sinks When they are completely underwater, both balls have the same buoyant force and the other because they displace the same volume of water. However, the steel ball has floats more weight since it has a higher density. The steel ball sinks because steel’s

higher density makes the ball heavier than the same volume of water. The wood ball floats because wood’s lower density makes the wood ball lighter than the same volume of displaced water.

Exploring the deep ocean requires sophisticated engineering. The U.S. Navy’s submarine Alvin is a research vessel that can dive to 4,500 meters below the ocean surface. Alvin’s depth is controlled by changing its average density. There is a chamber aboard the submarine that can be filled with air or water. To dive, water is pumped into the tank and air is released. The tank’s average density becomes greater than the density of water and the submarine sinks. When Alvin reaches the proper depth, the amount of air and water is adjusted with pumps until the average density of the whole vessel is the same as the density of water. This is called neutral buoyancy. When it is time for Alvin to head back to the surface, water is pumped out of the tank and replaced with air. Alvin’s average density decreases and the submarine rises.

10.4 BUOYANCY

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Boats and apparent density How do steel If you place a solid chunk of steel in water, it immediately sinks because the boats float? density of steel (7.8 g/cm3) is much greater than the density of water

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(1.0 g/cm3). So how is it that thousands of huge ships made of steel are floating around the world? The answer is that apparent density determines whether an object sinks or floats (Figure 10.23).

Making a steel object hollow decreases apparent density

Increasing volume decreases density

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To make steel float, you have to reduce the apparent density somehow. Making the steel hollow does exactly that. Making a boat hollow expands its volume a tremendous amount without changing its mass. Steel is so strong that it is quite easy to reduce the apparent density of a boat to 10 percent of the density of water by making the shell of the boat relatively thin.

Ah, you say, but that’s an empty ship. True, so the density of a new ship must be designed to be under 1.0 g/cm3 to allow for cargo. When objects are placed in a boat, the boat’s apparent density increases. The boat must sink deeper to displace more water and increase the buoyant force. If you have seen a loaded cargo ship, you might have noticed that it sat lower in the water than an unloaded ship nearby. In fact, the limit to how much a ship can carry is set by how low in the water the ship can get before rough seas cause waves to break over the sides of the ship.

apparent density - the total mass divided by the total volume of an object that is made up of more than one material including air.

An object with an apparent density GREATER than the density of water will sink. An object with an apparent density LESS than the density of water will float.

Figure 10.23: The meaning of

apparent density. Note: 1 mL = 1 cm3.

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Buoyancy, volume, temperature, and pressure of gases Sinking in a gas Like water, gases can create buoyancy forces. Because a gas can flow and has

a very low density, objects of higher density sink quickly. For example, if you drop a penny, it drops through the air quite easily. This is because the density of a penny is 9,000 times greater than the density of air.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

Floating in a gas

Charles’s law - at constant pressure and mass, the volume of a gas increases with increasing temperature and decreases with decreasing temperature.

Objects of lower density can float on gas of higher density. A hot air balloon floats because it is less dense than the surrounding air. What makes the air inside the balloon less dense? The word “hot” is an important clue. To get their balloons to fly, balloonists use a torch to heat the air inside the balloon. The heated air in the balloon expands and lowers the overall density of the balloon to less than the density of the surrounding cooler air.

Charles’s law The balloon example illustrates an important relationship, known as Charles’s law, discovered by Jacques Charles in 1787. According to

Charles’s law, the volume of a gas increases with increasing temperature (Figure 10.24). The volume decreases with decreasing temperature. Charles’s law explains why the air inside the balloon becomes less dense than the air outside the balloon. The volume increases as the temperature increases. Since there is the same total mass of air inside, the density decreases and the balloon floats. Stated another way, the weight of the air displaced by the balloon provides buoyant force to keep the balloon in flight.

Figure 10.24: The formula for Charles’s law.

Pressure and The pressure of a gas is also affected by temperature changes. If the mass and temperature volume are kept constant, the pressure goes up when the temperature goes up,

and the pressure goes down when the temperature goes down. This happens because the average kinetic energy of moving molecules is proportional to temperature. Hot molecules move faster and exert more force when they bounce off each other and off the walls of their container. The mathematical relationship between the temperature and pressure of a gas at constant volume and mass was discovered by Joseph Gay-Lussac in 1802 (Figure 10.25).

Figure 10.25: The pressure-

temperature relationship for gases.

10.4 BUOYANCY

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Use Kelvins for Any time you see a temperature in a formula in this section about gases, the problems temperature must be in Kelvins (Figure 10.26). This is because only the related to gas Kelvin scale starts from absolute zero. A temperature in Kelvins expresses

the true thermal energy of the gas above zero thermal energy. A temperature in Celsius measures only the relative energy, relative to zero Celsius.

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Solving Problems: Gases A can of hair spray has a pressure of 300 psi at room temperature (21°C). The can is accidentally moved too close to a fire and its temperature increases to 295°C. What is the final pressure in the can (rounded to the nearest whole number)? Note: This is why you should never put spray cans near heat (Figure 10.27). The pressure can increase so much that the can explodes! 1. Looking for:

You are asked for final pressure in psi.

2. Given:

You are given initial pressure in psi, and initial and final temperatures in °C.

3. Relationships:

Convert temperatures to K: °C + 273 Apply the pressure–temperature relationship: P1 ÷ T1 = P2 ÷ T2

4. Solution:

Convert °C to K: 21°C + 273 = 294 K and 295°C + 273 = 568 K Rearrange variables and solve: P2 = (P1 × T2) ÷ T1 = (300 psi × 568 K) ÷ 294 K = 580 psi. Your turn...

a. A balloon filled with helium has a volume of 0.50 m3 at 21°C. Assuming the pressure and mass remain constant, what volume will the balloon occupy at 0°C? b. A tire contains 255 cm3 of air at a temperature of 28°C. If the temperature drops to 1°C, what volume will the air in the tire occupy? Assume no change in pressure or mass.

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Figure 10.26: To convert degrees

Celsius to Kelvins, simply add 273 to the Celsius temperature.

Figure 10.27: Never put spray cans

near heat!

a. 0.46 m3 b. 232 cm3

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Section 10.4 Review 1. The buoyant force on an object depends on the _____ of the object that is underwater. 2. What happens to the buoyant force on an object as it is lowered into water? Why? 4. When the buoyant force on an object is greater than its weight, the object _____.

5 cm

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3. The buoyant force on an object is equal to the weight of the water it _____.

10

cm

20 cm

5. A rectangular object is 10 centimeters long, 5 centimeters high, and 20 centimeters wide. Its mass is 800 grams. a. Calculate the object’s volume in cubic centimeters. b. Calculate the object’s density in g/cm3. c. Will the object float or sink in water? Explain. 6. Solid iron has a density of 7.9 g/cm3. Liquid mercury has a density of 13.5 g/cm3. Will iron float or sink in mercury? Explain.

Legend has it that Archimedes added to his fame by using the concepts of volume and density to figure out whether a goldsmith had cheated Hiero II, the king of Syracuse. The goldsmith had been given a piece of gold of a known weight to make a crown. Hiero suspected the goldsmith had kept some of the gold for himself and replaced it with an equal weight of another metal. Explain the steps you could follow to determine whether or not the crown was pure gold.

7. Why is it incorrect to say that heavy objects sink in water? 8. Steel is denser than water, yet steel ships float. Explain. 9. If mass and pressure are constant, what is the relationship between temperature and volume? 10. A helium balloon has a pressure of 40.0 psi at 20°C. What will the pressure be at 40°C? Assume constant volume and mass.

10.4 BUOYANCY

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Chapter 10 Assessment Vocabulary Select the correct term to complete the sentences.

12. A measure of how much pulling a material can withstand before breaking is called _____. 13. When a heated material changes size it is said to undergo _____.

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brittleness

thermal expansion

amorphous

buoyancy

chemical properties

Archimedes’ principle

Section 10.3

elasticity

crystalline

pressure

14. _____ is a measure of a fluid’s resistance to flow.

Pascal

viscosity

Bernoulli’s principle

fluid

ductility

malleability

hardness

Boyle’s law

physical properties

15. Any matter that flows when force is applied is referred to as a(n) _____.

tensile strength

strength

Charles’s law

17. _____ is a relationship that describes energy conservation in a fluid.

density

18. The SI unit of pressure is the _____.

Section 10.1

1.

16. _____ is the measure of force per unit of area.

The mass-per-unit volume of a material is its _____.

19. _____ states that pressure and volume are inversely related. Section 10.4

Section 10.2

2.

____ are properties that can be observed directly.

3.

____ can only be observed when a substance is changed to another substance.

4.

A solid having randomly-arranged atoms or molecules is called ____.

5.

The tendency to crack or break is called _____.

6.

A(n) _____ solid has an orderly, repeating arrangement of particles.

7.

_____ is the ability to bend without breaking.

8.

A solid that can be bent and stretched and then return to its original shape has high _____.

9.

A solid’s ability to resist being scratched is called _____.

10. Gold has high _____ because it can be pounded into very thin sheets.

20. _____ is a measure of the upward force a fluid exerts on an object that is submerged. 21. _____ states that the buoyant force is equal to the weight of the fluid displaced by an object. 22. _____ describes the relationship between the temperature and volume of a gas.

Concepts Section 10.1

1.

In general, how do the densities of a material in solid and liquid form compare? Name a common exception to the general rule.

2.

Which makes better packing material: a high density or a low density material? Why?

11. The ability to maintain shape under the application of forces is called _____.

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3.

A cube of solid steel and a cube of solid aluminum are both covered with a thin plastic coating, making it impossible to identify the cubes based on color. Referring to Figure 10.2 on page 217, tell how you could determine which cube is steel and which is aluminum.

Section 10.2

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

4.

Explain the difference between physical and chemical properties. Use an example in your explanation.

5.

The density of a solid material depends on two things. Name those two things.

6. 7.

Compare the arrangement of atoms or molecules in an amorphous solid to the arrangement of atoms or molecules in a crystalline solid. Classify the following as a physical property (P) or a chemical property (C). a. b. c. d. e. f.

8.

Use the word amorphous or crystalline to describe each of the materials listed below. a. b. c. d.

9.

____ ice melts at room temperature ____ an apple turns brown when it is peeled ____ mercury is a metal that is liquid at room temperature ____ rust is orange ____ copper is shiny ____ copper forms a blue-green patina after being exposed to the air for a long period of time

metal glass rubber diamond

e. f. g. h.

taffy candy plastic sugar ice

Match the materials below with the mechanical property associated with the material. a. b. c.

____ gold ____ rubber ____ glass

1. 2. 3.

Section 10.3

10. Compare the terms liquid and fluid. 11. Describe how Newton’s third law is related to fluid pressure. 12. Explain how Bernoulli’s principle helps to explain the lift that airplane wings experience. Section 10.4

13. Compare the buoyant force to the weight of a floating block of foam. 14. Explain why a solid steel ball sinks in water but a steel ship floats in water. 15. A solid steel ball and a hollow steel ball of the same size are dropped into a bucket of water. Both sink. Compare the buoyant force on each. 16. Why does ice float in a glass of water? Explain in terms of density and buoyancy.

Problems Section 10.1

1.

A chunk of paraffin (wax) has a mass of 50.4 grams and a volume of 57.9 cm3. What is the density of paraffin?

2.

Gold has a density of 19,300 kg/m3. Calculate the mass of one gold bar that has dimensions of 1.00 cm × 2.00 cm × 10.0 cm.

Section 10.2

3.

Your teacher gives you two stainless steel ball bearings. The larger has a mass of 25.0 g and a volume of 3.2 cm3. The smaller has a mass of 10.0 g. Calculate the volume of the smaller ball bearing.

4.

At 20°C, the density of copper is 8.9 g/cm3. The density of platinum at the same temperature is 21.4 g/cm3. What does this tell you about how the atoms are “packed” in each material?

brittleness ductility elasticity CHAPTER 10 ASSESSMENT

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Section 10.3

m2?

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5.

What is the pressure if 810 N of force is applied on an area of 9

6.

A 4,000-pound car’s tires are inflated to 35 pounds per square inch (psi). How much tire area must be in contact with the road to support the car?

7.

Another unit of pressure is the atmosphere (atm). One atmosphere of pressure is equal to 101,325 pascals. A total of 1.00 L of helium at 1 atm is compressed to 350 mL. What is the new pressure of the gas in atmospheres? Assume that temperature and mass are constant.

8.

A total of 5.00 L of oxygen is pumped from a tank with a pressure of 20 atm into another tank. The new pressure is 80 atm. What is the new volume of the oxygen? Assume that temperature and mass are constant.

15. A 7.25 L sample of nitrogen is heated from 80.5°C to 86.0°C. Find its new volume if the pressure and mass remain constant.

Applying Your Knowledge Section 10.1

1.

Deep ocean currents are caused by differences in ocean water density. What two things can cause density differences in ocean water? How does the density difference actually cause the movement of deep ocean water? Do some research to find the answers to these questions. Be sure to cite your references.

Section 10.2

2.

Section 10.4

9.

14. At 210°C, a gas has a volume of 7.5 L. What is the volume of this gas at –20.0°C? Assume constant pressure and mass.

You hold a balloon with a volume of 2,000 mL under water. What is the buoyant force on the balloon?

You are an engineer who must choose a type of plastic to use for the infant car seat that you are designing. Name two properties of solids that would help you decide, and explain why each is important.

10. An object weighing 45 newtons in air is suspended from a spring scale. The spring scale reads 22 newtons when the object is fully submerged in water. Calculate the buoyant force on the object.

Section 10.3

3.

Describe how your body makes use of Boyle’s law in order to breathe.

11. A stone that weighs 6.5 newtons in air weighs only 5.0 newtons when submerged in water. What is the buoyant force exerted on the rock by the water?

4.

Many studies have been done about the viscosity of lava from various volcanic eruptions around the world. Do some research to find out how scientists determine the viscosity of lava, and find out if there is much variation in the viscosity of different lava flows.

12. A 100.0-mL oak object is placed in water. What volume of water is displaced by the oak object? The density of oak is 0.60 g/cm3. 13. At 225°C, a gas has a volume of 350 mL. What is the volume of this gas at 120°C? Assume constant pressure and mass.

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Section 10.4

5.

The Dead Sea is a body of water that lies between Israel and Jordan. It is so salty that almost no organisms other than a few types of bacteria can survive in it. The density of its surface water is 1.166 g/mL. Would you find it easier to float in the Dead Sea or in a freshwater lake? Give a reason for your answer.

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11

CHAPTER 11

Earth’s Atmosphere and Weather FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

Neither rain, nor sleet, nor cold shall keep a mail carrier from doing his or her job (or you from walking the dog). The same can be said of your local meteorologist. Every day, meteorologists broadcast weather reports. Millions of people plan what they will wear, what they will do after work or on the weekend, and if they will carry their umbrellas based on those reports. But only a very few meteorologists in the United States forecast the weather on radio or TV programs. Most meteorologists work for the National Weather Service (NWS), a government agency that is part of the National Oceanic and Atmospheric Administration (NOAA). Meteorologists observe and study Earth’s atmosphere and its phenomena. Many work to forecast the weather and changing climate conditions, while others do scientific research. They try to understand how the atmosphere affects the environment. They study the constant changes in our atmosphere. They create computer models to predict how storms will form, when rivers will flood, and what areas will suffer droughts. Their work goes beyond telling an audience whether it will be sunny or cloudy tomorrow.

4 What are the causes and effects of atmospheric pressure?

4 What variables affect our weather patterns? 4 Why is Earth neither too cold nor too hot? 245

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11.1 Earth’s Atmosphere Earth’s atmosphere is a layer of gases surrounding the planet, protecting and sustaining life. It insulates Earth so its inhabitants don’t freeze at night. Earth’s atmosphere also contains the carbon dioxide that plants need for photosynthesis and the oxygen that animals need to breathe.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

What’s in Earth’s atmosphere? Earth’s atmosphere is 78 percent nitrogen

Nitrogen (N2) gas makes up about 78 percent of Earth’s atmosphere. Nitrogen is released into the air by volcanoes and decaying organisms and is a vital element for living things. Protein, a substance in body tissues, contains nitrogen. However, this nitrogen is not absorbed directly from the air. Instead, the nitrogen is changed into nitrates (NO3) by nitrogen-fixing bacteria in the soil. Plants absorb nitrates from the soil and use them to make proteins. We eat plants (especially their seeds) or meat from plant-eating animals to obtain these proteins (Figure 11.1).

Earth’s atmosphere is 21 percent oxygen

The second most abundant gas is oxygen (O2), which makes up 21 percent of Earth’s atmosphere. Atmospheric oxygen enables us to process the fuel we need for life. The remaining 1 percent of Earth’s atmosphere is made up of 0.93 percent argon and 0.04 percent carbon dioxide. There are also tiny amounts of neon, helium, methane, krypton, and hydrogen, which are called trace gases.

Why Earth’s The atmosphere exists around Earth because our planet has just the right atmosphere balance of mass and distance from the Sun. Scientists explain that at the time exists of Earth’s formation, the heat from the Sun drove off most of the lightweight

elements such as hydrogen and helium. Earth would have remained a rocky, airless world except that, as it cooled, earthquakes and volcanoes spewed out heavier gases like nitrogen and carbon dioxide. Earth’s mass gave it enough gravitational pull to hold these gases around it. Although the planet Mercury was formed in a similar way, its mass is too small and it is too close to the Sun to have retained much of a layer of gas around it. Venus, Earth, and Mars, however, retained their atmospheres. Figure 11.1: The nitrogen cycle.

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CHAPTER 11

Atmospheres of Earth, Venus, and Mars atmosphere - a layer of gases that

Comparing An atmosphere is a layer of gases surrounding a planet or other body in atmospheres space. The atmospheres of Venus, Earth, and Mars were formed in similar

surrounds a planet.

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ways, so we might expect them to contain similar elements. Figure 11.2 compares the atmospheres of these three planets. As you can see, Earth’s atmosphere is very different from those of Venus and Mars.

Planet

Similarities Venus and Mars show striking similarities in the makeup of their between Venus atmospheres. They are mostly carbon dioxide, with a small amount of and Mars nitrogen. Earth, on the other hand, is very different. Ours is the only planet

Venus Earth

with a large amount of nitrogen and oxygen, and just a tiny amount of carbon dioxide in its atmosphere. Why is Earth so different?

Mars

Life changed Through photosynthesis, life on Earth has actually changed the planet’s Earth’s atmosphere. Many forms of life use photosynthesis to obtain energy from the atmosphere Sun. This process breaks down carbon dioxide, uses carbon to build the

Major gases in atmosphere 96% CO2

3% N2

0.04% 78% CO2 N2 95% 3% CO2 N2

0.1% H2O 21% 0.93% O2 Ar 1.6% Ar

Figure 11.2: Comparing the

atmospheres of Venus, Earth, and Mars.

organism, and releases oxygen into the air (Figure 11.3). Where does the When organisms die and decompose, some of the carbon from their bodies is carbon go? released as carbon dioxide back into the air. However, if all of the carbon used

by life processes returned to Earth’s atmosphere, the atmosphere would be like that of Venus and Mars. Instead, some of the carbon used to build living organisms ends up staying in the ground. Earth stores carbon in several ways. How Earth stores carbon

Many marine organisms such as microscopic phytoplankton use carbon dioxide dissolved in seawater to form shells of calcium carbonate (and lots of oxygen). A greatly magnified picture of a coccolithophore is shown at the left. When these organisms die, their shells sink to the bottom of the water and stay there. The carbon doesn’t return to the atmosphere. Massive piles of calcium carbonate have built up over the years, creating some of our land forms. Fossil fuels (oil, coal, and natural gas) also store carbon from decaying plants and animals in the ground. Another process stores carbon in a type of rock called limestone.

Figure 11.3: Photosynthesis is a

process that uses carbon dioxide and produces oxygen.

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What is atmospheric pressure? Air molecules The pressure of air molecules in the atmosphere is a result of the weight of a exert pressure column of air pressing down on an area. Atmospheric pressure is a

measurement of the force of air molecules per unit of area in the atmosphere at a given altitude.

measurement of the force of air molecules per unit of area in the atmosphere at a given altitude.

barometer - an instrument that measures atmospheric pressure (see page 249).

inside our bodies that is pushing out with the same amount of pressure, so the forces are balanced. Second, our skeletons are designed to withstand the pressure of our environment. Air pressure and altitude

Atmospheric pressure decreases as altitude Thermosphere increases. Why? The 90 molecules at the bottom of the atmosphere are packed 80 together more tightly Mesosphere 70 because the weight of the molecules above presses 60 down on them. The air pressure is greatest at sea 50 Stratosphere level (the bottom of the 40 atmosphere). As you get higher and higher above sea 30 level, the molecules are Top of Mt. Everest 20 more and more spread out, Sea level 334 mb 1013 mb so there are fewer molecules 10 Troposphere above you pushing down. The graph (left) shows the 0 0 200 400 600 800 1000 1200 relationship between Pressure (mb) altitude and pressure. At sea level, the air pressure averages 1,013 millibars (mb). On top of Mt. Everest (altitude 8.85 km), the air pressure averages 334 millibars. Air pressure vs. altitude

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Altitude (km)

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How we At sea level, the weight of the column of air above a person is about withstand air 9,800 newtons (2,200 pounds)! This is equal to the weight of a small car pressure (Figure 11.4). Why aren’t we crushed by this pressure? First, there is air

atmospheric pressure - a

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Figure 11.4: At sea level, the weight of the column of air above a person is equal to the weight of a small car!

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Barometers and units of pressure Barometers Atmospheric pressure is measured with an instrument called a barometer measure air (defined on page 248). The oldest type of barometer is the mercury barometer pressure (Figure 11.5). It consists of a tube that is sealed at one end and partially filled

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with mercury. The open end of the tube stands in a dish of mercury. As air presses down on the mercury in the dish, it forces the liquid in the tube to rise. When the air pressure is greater, the mercury travels farther up the tube. The air pressure at sea level generally causes the mercury in a barometer to rise 29.92 inches (760 millimeters). Table 11.1 compares units of pressure. Table 11.1: Units of Pressure Unit

Description

Relationship

pascal (pa)

SI unit commonly used to measure pressure of air in a container.

atmosphere (atm)

One atmosphere is the standard air pressure at sea level. Used by divers to compare pressure under water with surface pressure.

1 atm = 101,325 pa

millimeter of mercury (mm Hg)

Unit describing the height of a column of mercury in a barometer.

760 mm Hg = 1 atm

pounds per square inch (psi)

English unit commonly used to measure pressure of air in a container, like a tire or ball.

millibar (mb)

SI unit used to measure atmospheric pressure.

Figure 11.5: A mercury barometer.

1 pa = 1 N/m2

14.7 psi = 1 atm 1013.25 mb = 1 atm

Aneroid Mercury barometers have a downside: Mercury is a poisonous liquid, and it barometers creates unhealthy vapors. You would not want to have a mercury barometer in

your living room! Most barometers in use today are aneroid barometers (Figure 11.6). They have an airtight cylinder made of thin metal. The walls of the cylinder are squeezed inward when the atmospheric pressure is high. At lower pressures, the walls bulge out. A dial attached to the cylinder moves as the cylinder changes shape, indicating the change in air pressure.

Figure 11.6: Inside an aneroid

barometer. Letter A shows the airtight cylinder, to which a spring, B, is attached. C is a series of levers that amplify the spring’s movement. A small chain transfers the movement to the pointer, D.

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Layers of the atmosphere The atmosphere You probably know that temperature at the top of a high mountain is usually is divided into colder than at the base. But the temperature doesn’t just keep decreasing as layers you go farther and farther up in the atmosphere. The temperature first

Vocabulary terms are defined on the next page.

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decreases, then increases, then decreases, and then increases again. Scientists divide Earth’s atmosphere into layers based on these zigzags in temperature (Figure 11.7). The troposphere We live in the troposphere (defined on page 251), the layer that extends

from 0 kilometers to approximately 11 kilometers above Earth’s surface. About 75 percent of the atmosphere’s mass is found in the troposphere. Almost all of Earth’s water vapor, carbon dioxide, dust, airborne pollutants, and terrestrial life forms exist here. The Sun warms Earth’s surface. Heat radiates from the surface and warms the troposphere. As a result, the troposphere is warmest at Earth’s surface. The temperature drops about 6.5°C for every 1 kilometer you go up in the troposphere. The temperature at the top of the troposphere is about –60°C. Weather in the The name troposphere contains the Greek root tropo, meaning “to turn or troposphere change.” The troposphere is the region where clouds form and where all

weather happens. When you hear about airplanes “flying above the weather,” this means that they are flying above the troposphere. The Above the troposphere lies the stratosphere (defined on page 251), stratosphere extending from about 11 to 50 kilometers above Earth’s surface. The

temperature increases as you go up in the stratosphere because of a thin layer of ozone. The ozone layer absorbs the Sun’s high-energy ultraviolet (UV) radiation. As a result, the stratosphere increases in temperature with altitude, and we are protected from UV radiation. The mesosphere Above the stratosphere, the temperature begins to drop again. This marks the beginning of the mesosphere (defined on page 251), which extends from

Figure 11.7: Earth’s atmosphere is

divided into layers based on temperature.

50 to 85 kilometers above Earth. The mesosphere is the coldest layer of the atmosphere. At its outer reaches, the temperature can be as low as –90°C. Most meteors, or “shooting stars,” burn up in the mesosphere.

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The The thermosphere layer begins at about 85 kilometers above Earth’s surface. thermosphere This layer has a low density of air

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molecules—there are 100,000 times more air molecules in a cubic meter of air at Earth’s surface than in the thermosphere. These molecules have a lot of kinetic energy, because the energy from the Sun hits them first. Temperatures in this layer can reach 1,800°C. The ionosphere The ionosphere is part of the

thermosphere and is where the Sun’s ultraviolet light creates charged atoms and molecules called ions. The energy released in this process causes the high temperatures in the thermosphere. Ions easily transmit electricity and electromagnetic waves. The ionosphere makes it possible for you to tune into short wave radio stations that originate a thousand or more miles away. The radio signals are rebroadcast by the ions in the ionosphere back to Earth. The exosphere The exosphere begins at about

500 kilometers above Earth’s surface and does not have a specific outer limit. Lightweight atoms and molecules escape into space from this region. Satellites orbit Earth in the exosphere. Most satellites that we rely on orbit 36,000 kilometers above the equator and travel at the same speed that Earth rotates (called geostationary orbit). This orbital path is called the Clarke Belt.

troposphere - a layer of atmosphere that occurs from 0 kilometers to about 11 kilometers above Earth’s surface; where all weather occurs. stratosphere - a layer of atmosphere that occurs from about 11 kilometers to 50 kilometers above Earth’s surface; the location of the ozone layer.

mesosphere - a layer of atmosphere that occurs from about 50 kilometers to 85 kilometers above Earth’s surface; the coldest layer.

thermosphere - a layer of atmosphere that occurs from about 85 kilometers to about 500 kilometers above Earth’s surface; this layer has a low density of air molecules and a very high temperature. ionosphere - portions of the atmosphere in the region of the thermosphere where electricity can be transmitted. exosphere - the region of the atmosphere that begins at about 500 kilometers above Earth’s surface and extends into space; the location of the orbits of satellites.

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Section 11.1 Review 1. Earth’s atmosphere is 78 percent nitrogen.

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a. Where does nitrogen in the atmosphere come from? b. How does nitrogen from the air get into the bodies of plants and animals? 2. What is the second most abundant gas in Earth’s atmosphere? Where does it come from? 3. The atmospheres of Mars and Venus are mostly carbon dioxide. Earth’s atmosphere contains only a fraction of a percent of carbon dioxide. Why is Earth’s atmosphere so different from those of Mars and Venus? 4. 5. 6. 7.

What is atmospheric pressure? Why doesn’t Earth’s atmospheric pressure crush our bodies? What is a barometer? Explain how a mercury barometer works. Which statement is true about atmospheric pressure? a. As altitude increases, atmospheric pressure increases. b. Atmospheric pressure does not change with altitude. c. As altitude increases, atmospheric pressure decreases. d. None of the above are true.

Converting Units of Pressure Convert the following units of pressure. Use Table 11.1 on page 249 to find the conversion factors. 1. 2.00 atm = _____ mm Hg 2. 4.50 atm = _____ pa 3. 35 psi = _____ atm 4. 1,850 mm Hg = _____ atm 5. 45.0 psi = _____ pa

8. Use the graph on page 248 to estimate the following. a. What is the atmospheric pressure at an altitude of 22 kilometers? b. If the atmospheric pressure measures 500 millibars, what is the altitude? c. Mt. Rainier (Figure 11.8), in Washington State, has an elevation of about 14,000 feet. What is the atmospheric pressure at its summit? 9. Almost all of Earth’s weather occurs in which layer of the atmosphere? 10. In which layer of the atmosphere is the ozone layer located? How does the ozone affect the temperature of this layer? 11. Which layer of the atmosphere is the coldest?

Figure 11.8: Question 8c.

STUDY SKILLS Make up a game or activity that you can play with friends to help you remember the different layers of the atmosphere.

12. In which layer do most meteors, or “shooting stars,” burn up?

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11.2 Weather Variables

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Weather is a term that describes the condition of the atmosphere in terms of temperature, atmospheric pressure, wind, water vapor, and precipitation. The Sun is the major energy source for weather events on Earth. In this section, you will learn how and why weather occurs.

weather - a term that describes the

Convection, pressure, and wind

thermal - a small, upward flow of warm air caused by convection.

Convection and Convection occurs naturally in Earth’s atmosphere due to the heating and thermals cooling of air. As the Sun warms Earth’s surface, air near the surface warms,

expands, and becomes less dense. The less-dense air rises. Eventually the warm, less-dense air that rose from the surface cools. The same chain of events that made the air rise now works in reverse and the air sinks back to the ground (Figure 11.9). A thermal is a small, upward flow of warm air caused by convection. Gliding birds like hawks often ride a thermal as they hunt.

condition of the atmosphere in terms of temperature, atmospheric pressure, wind, water vapor, and precipitation.

air mass - a large body of air with consistent temperature and moisture content throughout. wind - the horizontal movement of air that occurs as a result of a pressure difference between two air masses.

High and low When warm air rises from Earth’s surface, an area of low atmospheric pressure pressure is created. This lower-pressure area draws in air from surrounding

higher-pressure areas. Eventually the warm air that rose from the surface cools and becomes denser. This dense, cool air sinks back to the surface causing an area of higher atmospheric pressure (Figure 11.9). What is wind? An air mass is a large body of air with consistent temperature and moisture content throughout. Wind is the horizontal movement of air that occurs as a

result of a pressure difference between two air masses. The greater the difference in pressure, the greater the speed of the air flow. Most of these pressure differences are due to unequal heating of the atmosphere. Sea and land Convection near coastlines causes sea breezes during the day and land breezes breezes at night because water has a higher specific heat than land. During the

daytime, the land heats up faster than the ocean. Rising warm air over the land creates a low-pressure area causing the rising air to move out over the sea, cool, and sink toward the sea surface. The cooling, sinking air mass creates a high-pressure area. Air flows from high- to low-pressure areas. So, during daytime hours, there is a cool sea breeze from sea to land. The opposite occurs at night causing land breezes.

Figure 11.9: Convection in the atmosphere.

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Global convection Global Convection also occurs on a global scale. Warm, less-dense air at the equator convection tends to rise and flow toward the poles. Then, cooler, denser air from the

poles sinks and flows back toward the equator. Convection cells Due to Earth’s rotation, rising warm air from the equator doesn’t make it all

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the way to the poles. The combination of global convection and Earth’s rotation sets up a series of wind patterns called convection cells in each hemisphere. Look at Figure 11.10 and follow the arrows. Do you see where air is rising and sinking?

convection cells - large wind patterns in Earth’s atmosphere caused by convection. Coriolis effect - the bending of currents of air or water due to Earth’s rotation.

The combination of global convection and Earth’s rotation causes wind patterns called convection cells in each hemisphere. The effects of Earth’s rotation also changes the direction of airflow. This causes the path of Earth’s rotation the wind to be curved as it moves between the poles and the equator. In the

northern hemisphere, winds bend to the right and move clockwise around a high-pressure center (H). In the southern hemisphere, winds bend to the left and move counterclockwise around a high-pressure center (H). The Coriolis This bending of currents of air due to the Earth’s rotation is called the effect Coriolis effect. It is named after the French engineer–mathematician

Gaspard Gustave de Coriolis, who first described the phenomenon in 1835. Due to the Coriolis effect . . . Winds bend to the right in the northern hemisphere.

N

W

Winds bend to the left in the southern hemisphere. E

S

Figure 11.10: This diagram shows

N

W

Earth’s convection cells and how winds curve due to the Coriolis effect.

E

S

To understand “right” and “left” directions in this graphic, imagine you are standing at the base of each arrow on the globes.

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Global surface wind patterns

STUDY SKILLS

Wind and human Three important global wind patterns exist in each hemisphere (Figure 11.11). history Sailors have used these winds to travel to and explore new lands throughout

human history. Trade winds The trade winds are surface wind currents that move between 30° north or

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south latitude and the equator. Remember, the air around the equator warms, rises, and flows toward the poles. At about 30° N and 30° S, it cools, sinks, and flows toward the equator again. The Coriolis effect bends the trade winds so that they flow from northeast to southwest in the northern hemisphere and from southeast to northwest in the southern hemisphere. Prevailing In the northern hemisphere, the trade winds set up a high-pressure area at westerlies about 30° N latitude. Air along the surface between 30° N and 60° N moves

northward, from high to low pressure. The air bends to the right due to the Coriolis effect, creating the prevailing westerlies. Most of the United States is between 30° N and 60° N, so most of our weather patterns move from southwest to northeast. In the southern hemisphere, the weather patterns between 30° S and 60° S tend to move from the northwest to the southeast. Polar easterlies Polar easterlies form when the air over the poles cools and sinks, creating a

Which way does the wind blow? Here are some facts about winds to help you study. – Winds are described by the direction from which they originate. That means that a west wind blows from the west, for example. – Trade winds are named after trade routes used by sailing merchants. – Prevailing westerlies are so named because they blow from the west. – Polar easterlies are so named because they come from polar regions and blow from the east.

90º W

0º

180º

Summer location 60º N Winter location 30º N 90º E

At an average of about 60 degrees latitude, the polar easterlies meet the prevailing westerlies, at a boundary called the polar front. Here, the dense, polar air forces the warmer, westerly air upward. Some warmer air flows toward the poles and some flows back toward the 30 degree latitude line. The diagram (left) shows a top view of the arctic polar front. During the winter, the polar front slides toward the equator while during the summer, it retreats northward.

N

Polar front

high-pressure area. Like the other global winds, this polar wind is bent by the Coriolis effect. The air flows from northeast to southwest in the northern hemisphere, and from southeast to northwest in the southern hemisphere. The polar front

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Polar easterlies 60º Prevailing westerlies Trade winds Trade winds

W

0º

Polar easterlies Polar front

E

30º

Prevailing westerlies 60º

S

Figure 11.11: Global surface wind patterns.

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Water in the atmosphere Three phases of Water in the atmosphere exists in all three phases (solid, liquid, and gas). Ice water in the crystals occur high in the troposphere. Tiny water droplets, much too small to atmosphere see, are suspended throughout the troposphere virtually all the time. They are

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considered liquid water and not gas because they are made of microscopic “clumps” of water molecules. Water in the atmosphere also occurs as water vapor—water in the gas phase.

dew point - the temperature at which more water condenses than evaporates in an air mass at a constant atmospheric pressure.

Temperature As temperature increases, the rate of evaporation increases (Figure 11.12). and pressure Higher temperatures cause the liquid water molecules to move fast so they

have enough energy to break free of their bonds with each other. These water molecules become water vapor in the atmosphere. In contrast, as atmospheric pressure increases, the rate of evaporation decreases (Figure 11.12). This is because the pressure makes it harder for water molecules to escape from the liquid to the gas phase. Dew point Both condensation and evaporation occur in the atmosphere all the time.

However, each process might happen at different rates. When the rate of evaporation is greater than the rate of condensation, we see clearing skies. When the rate of condensation exceeds the rate of evaporation, we say that the air’s dew point has been reached. This is the temperature at which more water vapor is condensing than evaporating in an air mass. The water in the air mass is getting colder, slowing down, and forming “dew” or droplets. Humidity Humidity describes the amount of water vapor present in an air mass and is

responsible for the “muggy” weather you often experience on a hot summer day. The hotter the air is, the more water vapor it can contain. There are several ways to measure humidity. Absolute humidity is the mass of water vapor divided by the mass of dry air in a volume of air at a given temperature. Most weather reports express humidity in terms of relative humidity. Relative humidity is the ratio of the current absolute humidity to the highest possible absolute humidity—which depends on the current temperature of the air. A measurement of 100 percent relative humidity means that the air is completely saturated with water vapor and cannot hold any more.

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Figure 11.12: The relationship

between temperature and pressure when evaporation occurs.

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Precipitation How much water An air mass can be compared to a sponge. Warm air is like a big sponge that vapor can air can contain a lot of water vapor. Cold air is like a small sponge that can hold? contain less water vapor. Air that contains the maximum amount of water is

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saturated. Like a soggy sponge, saturated air can’t hold more water vapor. When more water vapor is added, it condenses and forms droplets. Rain If air cools to a temperature lower than the dew point, and the pressure

remains constant, water vapor condenses into liquid. At first, the water molecules condense on particles such as dust, pollen, or volcanic ash. Once a few water molecules condense, they create a site for other molecules to condense, too. What starts as just a few water molecules quickly grows to millions of molecules that form water droplets. If the droplets become big enough, they form visible clouds. Clouds will produce rain when the drops get even bigger and have a volume of about 1 milliliter. At this size, they become heavy enough to fall as raindrops.

Condensation Warms the Air Condensation is actually a warming process. Why? Energy was needed when the water changed from a liquid to a gas. This energy is released when the water vapor changes back into the liquid form. An example: water condensing on a cool glass of lemonade warms the lemonade.

Snow and sleet Snow usually forms when both ice crystals and water droplets are present in

the sky. The water droplets attach to ice crystals and freeze there. When the ice crystals are large enough, they will fall to the ground as snow. However, if the air temperature near the ground is warm, the crystals will melt and the precipitation will fall as rain. Sometimes very cold air lies below warmer air, causing the water to refreeze and hit the ground as sleet. Dew and frost Because the ground cools quickly, the temperature of the ground is often

below the dew point late at night or early in the morning. Air near the ground gets cooled and some water vapor condenses in the form of dew. If the temperature is low enough, the dew freezes and turns to frost. Fog If air within a few hundred meters of the ground is cooled below the dew

point, fog will form. Fog can form under two conditions. Warm, moist air could move over a cooler surface, or the ground below could cool below the dew point at night. Either way, fog consists of suspended water droplets. Fog is a ground-level cloud.

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Climate and biomes Earth’s climate Climate is the type of weather that a place has, on average, over a long and biomes period of time. Climate depends on many variables, including latitude,

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precipitation, elevation, topography, and distance from large bodies of water. Scientists divide the planet into climate regions. Each region is called a biome. Earth has six major biomes: deserts, grasslands, temperate deciduous forests, rainforests, taigas, and tundras. These biomes generally differ in their latitude, weather and relative humidity, amount of sunlight, and topography. Each biome has a unique set of plants and animals that thrive in its climate.

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climate - the long-term record of weather patterns that includes the temperature, precipitation, and wind for a region. biome - a major climate region with particular plants and animals. Earth has six major biomes.

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Types of biomes Deserts Deserts average less than 35 centimeters of rainfall per year. Most deserts

are found around the latitudes of 30° N and 30° S. Deserts have large variations in daily high and low temperatures. Grasslands Grasslands are on every continent except Antarctica. There are two types:

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tropical grasslands, known as savannas; and temperate grasslands. Savannas occur where there is not enough rainfall to create a rainforest. Temperate grasslands are in the mid-latitudes and receive most of their precipitation in the spring and summer. Temperate Temperate deciduous forests are found in middle-latitude regions, where deciduous there are four distinct seasons. Average yearly rainfall is 75 to 150 centimeters; forests enough to support the growth of broad-leafed, deciduous trees like oak and

maple. Deciduous means these trees lose their leaves at the end of the growing season. Rainforests Tropical rainforests are near the equator—between the latitudes of 23.5° N

and 23.5° S. They have an average rainfall of at least 200 centimeters per year. The temperature of these rainforests is nearly constant and in a narrow range—20 to 25°C. Temperate rainforests, another kind of rainforest, are in the middle-latitude regions, and experience about 250 centimeters of rain per year.

deserts - climate regions that average less than 35 centimeters of rainfall per year. grasslands - climate regions with too little rainfall to support a forest. Grasslands have grasses as the main vegetation.

temperate deciduous forests climate regions in the mid-latitudes that have four seasons.

tropical rainforests - climate regions found near the equator that have a lot of rainfall and high biodiversity.

taiga - the largest climate region, found in the higher latitudes. tundra - a climate region located in high latitudes; the coldest land biome.

Taiga The taiga is the largest biome. The taiga can be found between the latitudes

of 50° N and 70° N in North America, Europe, and Asia. The average temperature in the taiga is below freezing for at least six months of the year. The taiga is also known as a boreal or coniferous forest. Tundras The tundra is the coldest biome on Earth. The word tundra comes from a

Finnish word for “treeless land.” There are two types of tundra—Arctic tundra, found in a band around the Arctic Ocean, and alpine tundra, found high in mid-latitude mountains.

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Plants and animals in biomes Communities A biome is characterized by its plant and animal communities. The plants

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and animals in a community interact with each other and survive in a shared environment. The plants and animals in the environment have adaptations that allow them to obtain enough resources (such as food, water, and sunlight) to survive in the environment. Adaptations For example, how might an animal survive in a hot desert? Jackrabbits have

an adaptation to keep cool—enormous ears with many blood vessels near the surface (Figure 11.13). Blood running through the vessels speeds up heat transfer from the jackrabbit’s body to the air so it stays cooler. Figure 11.14 shows an arctic hare that lives in a very cold biome. How is it different from the jackrabbit? How might its ears help it survive the arctic temperatures? Ecosystems Biomes are large geographic areas. Within a biome, there are many

interrelated ecosystems. An ecosystem is made up of the plants and animals that live there, plus nonliving things like soil, air, water, sunlight, and nutrients. The living and nonliving parts of an ecosystem work together, and each organism plays an important ecological role. On a baseball team, for example, important roles include coach, pitcher, catcher, outfielders, and infielders. Similarly, organisms play roles in an ecosystem.

Figure 11.13: The large ears of a jackrabbit help this desert animal to cool down.

How many The number and types of organisms that an ecosystem can support depends roles? on the resources available (food sources) and on environmental factors, such

as the amount of available sunlight, water, and the temperature. For plants, another important factor is soil composition. The roles within a biome ecosystem depend on the quantity and type of resources. Each ecosystem of a particular biome type has organisms that play similar roles. For example, both a rainforest in South America and a rainforest in Australia have predators, herbivores, and decomposers suited to surviving in the rainforest environment. Figure 11.14: An Arctic hare.

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Variables that shape biomes Sunlight at the Earth is hottest near the equator where the Sun is closest to being directly equator vs. high overhead year round. At the north and south poles, temperatures are much latitudes colder. This effect is related to the fact that light travels in straight parallel

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lines. To demonstrate what is happening, imagine shining a flashlight on a sheet of paper (Figure 11.15). The light makes a small, bright spot. By tilting the paper, you can make the light spot bigger and less intense. Latitude and At the equator, sunlight is direct and intense. Earth’s north and south poles are solar radiation tilted away from or toward the Sun depending on the time of year. The

locations of the poles relative to the Sun and Earth’s spherical surface mean that sunlight reaching these areas is spread out and less intense (Figure 11.15). As a result, the average yearly temperature at the equator is 27°C (80°F), while at the North Pole it is –18°C (0°F). Generally, as latitude (or distance from the equator) increases, the amount of incoming solar radiation decreases. Temperatures in ocean regions and in inland regions

Areas near the ocean do not get as hot in the summer or as cold in the winter as inland areas at the same latitude. For example, Portland, Oregon, and Minneapolis, Minnesota, are two cities near the same latitude. Portland averages 1 to 7°C in January, and 14 to 27°C in July. Minneapolis averages –16 to –6°C in January, and 17 to 29°C in July. Because of its higher specific heat, water warms up and cools down slowly. In contrast, land warms up and cools down quickly because of its lower specific heat. Therefore, regions near water—like Portland—do not have extremely hot or cold weather.

Figure 11.15: If you tilt the paper, the spot of light spreads out and becomes less intense, like at the poles.

Elevation Elevation is another important factor in determining the characteristics of a

biome. The range of biomes that exist on Earth from the equator to the poles also exists if one goes from the bottom of a mountain to the top of a mountain (Figure 11.16).

Figure 11.16: Latitude versus

elevation for the Northern Hemisphere.

11.2 WEATHER VARIABLES

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Section 11.2 Review 1. Define wind. Draw a diagram that illustrates how wind is created. 2. How does convection help birds fly? 3. Why is the path of the wind curved as it moves from the poles to the equator?

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4. Why are there three different wind patterns in each hemisphere? What are the names of these wind patterns? 5. Which wind pattern most affects the United States? 6. Which holds more water vapor, a warm or a cold air mass?

Throughout human history, sailors have used global wind patterns to travel to and explore new lands. Research one of the more famous ship captains—Capt. James Cook (1728–1779). Who was he? What is he known for? Write a short report about one or more of Captain Cook’s adventures or achievements.

7. When the air is filled to capacity with water vapor, it is said to be ___________. 8. What does it mean for an air mass to have 70 percent relative humidity? 9. An air mass cools to the point where it becomes saturated. What might happen next? 10. A cool (10°C) air mass warms to 30°C. a. Does the volume of the air mass decrease or increase when the temperature goes up? b. If the amount of water vapor in the air mass stays the same, does the relative humidity increase or decrease when the temperature goes up? 11. Name three variables that affect climate. 12. Are climate and weather the same thing? If not, explain how these terms are different. 13. What happens to the intensity of solar radiation and Earth’s average yearly temperature as you move from the equator to the South Pole or North Pole? 14. Refer to the Earth’s biome map on page 258. What kind of biome occurs at 30° S and 150° E? Describe what this biome is like. 15. Alpine and arctic tundra occur at a mid-latitude location near India (25° N 80° E). Why do you think this biome occurs here? (Hint: Find out what land form occurs at this location.)

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11.3 Weather Patterns We can learn about today’s or tomorrow’s weather by listening to a meteorologist—a person who forecasts the weather. You can also find out about weather on your own by looking at clouds in the sky and by taking your own weather data. Read on to find out more about weather and storms.

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Fronts

front - the border between two different air masses. cold front - a front that occurs when a cold air mass moves in and replaces a warm air mass.

Large bodies Air masses form when air is stationary over an area long enough to take on of air the characteristics of the surface below. Two common air masses affecting the

United States are the continental polar air mass, which forms over the Canadian plains, and the maritime tropical air mass, which forms over the Gulf of Mexico (Figure 11.17). The continental polar air mass contains cold, dry air. In contrast, the maritime tropical air mass contains warm, moist air.

Continental polar

Moving air and Changing atmospheric conditions and global wind currents cause air masses fronts to move. The continental polar air mass tends to slide south or southeast,

while the maritime tropical air mass tends to slide north or northwest. When two different moving air masses collide, the border between them is called a front. Cold fronts A cold front occurs when cold air moves in and replaces warm air. The warm

air is forced sharply upward by the cold, denser air. The rising warm air cools. This causes condensation. Often, rain or snow showers that can be shorter in duration, but intense, accompany a cold front. As a cold front moves through an area, the temperature and water content of the air decrease rapidly. The temperature can sometimes cool as much as 15°F in one hour.

N W

E S

Figure 11.17: Two air masses that affect the weather in the United States.

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Warm fronts A warm front occurs when warm air moves in and replaces cold air. The

warm air slides up over the colder air. The warm air rises and cools, but in this case the lifting is very gradual and steady. As a result, long bands of light precipitation often move ahead of a warm front. As a warm front moves through an area, there will be a noticeable increase in temperature and moisture in the air.

warm front - a front that occurs when a warm air mass moves in and replaces a cold air mass. jet streams - high-altitude, fast-moving winds.

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Weather map symbols for fronts CC ool dlda Airir

Jet streams High-altitude, fast-moving winds are called jet streams. There are two big

jet streams in each hemisphere, formed where there are sharp boundaries between cold and warm temperatures. A jet stream acts as a border between cold and warm air masses. When the jet stream changes its path, air masses to either side of it tend to move too.

Cold front

as 320 kilometers (200 miles) per hour. The jet streams flow around the globe from west to east. A jet stream attains its fastest speeds during the winter of its hemisphere when the temperature difference between that pole and the equator is greatest. The path and speed of a jet stream can be altered by land features such as mountain ranges, or by giant cumulus clouds that act like boulders in a rushing river.

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W

Speed and path The jet stream winds are found near the top of the troposphere, and have of a jet stream speeds of at least 87 kilometers (54 miles) per hour, and sometimes as great

air a rm A

Warm front On a weather map, a cold front is shown using a line marked with blue triangles. The triangles point in the direction the front is moving. A warm front is shown using a line marked with red semicircles, which point in the direction the front is moving.

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Low- and high-pressure areas Low-pressure When a cold front moves into a region and warm air is forced upward, a centers low-pressure center is created near Earth’s surface at the boundary of two

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air masses (Figure 11.18). Cold air rushes in to fill that low-pressure region. This cold air forces more warm air to be pushed upward. A cycle begins to develop. Due to the Coriolis effect, the air masses move in curved paths. As a result, the moving air begins to rotate around the low-pressure center (Figure 11.18). In the northern hemisphere, the moving air rotates counterclockwise, while in the southern hemisphere, the air rotates clockwise. Strong winds and precipitation often accompany these rotating systems.

low-pressure center - a low-pressure area created by rising warm air. high-pressure center - a high-pressure area created by sinking cold air. isobar - a line on a weather map that connects places that have the same atmospheric pressure.

High-pressure A high-pressure center tends to be found where a stable, colder air mass centers has settled in a region. Colder air is denser than warm air, and therefore

creates higher atmospheric pressure. Sinking air in a high-pressure center inhibits the development of the upward air movement needed to create clouds and precipitation. High-pressure centers, therefore, are associated with fair weather and blue skies. Winds rotate clockwise in the northern hemisphere and counterclockwise in the southern hemisphere. This is the opposite of what happens in a low-pressure center. Isobars

The wavy lines on a weather map are often associated with high-pressure (H) and low-pressure (L) centers. Each line, called an isobar, connects the places that have the same atmospheric pressure. Isobars help meteorologists pinpoint the location of highand low-pressure centers, and provide information about the movement of weather systems.

Figure 11.18: (1) Warm air is

forced upward when a cold front moves into an area. A low-pressure center is created. (2) The cold air moving toward the low- pressure center begins to rotate around it in a counterclockwise direction.

11.3 WEATHER PATTERNS

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Clouds What is a cloud? When more water in the atmosphere is condensing than evaporating, we begin to see clouds. A cloud is a group of water droplets or ice crystals that

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you can see in the atmosphere. The flat bottom of the cloud marks the level of the atmosphere where condensation first exceeds evaporation (when the dewpoint has been reached). Clouds are divided into two broad categories: cumuliform clouds (cumulus means “piled up”) and stratiform clouds (stratus means “layer”).

cloud - a group of water droplets or ice crystals that you can see in the atmosphere.

Cumuliform Cumuliform clouds, which look like heaps of popcorn, form as an air mass clouds rises because of convection (Figure 11.19). Air is commonly warmed over a

dark surface (like a road) that absorbs a lot of heat. It is rare to see a line of these clouds right above a dark surface though, because wind currents blow the rising air masses around before they condense and form clouds. Cirrocumulus: Small, puffy, “cotton ball” type clouds high in the atmosphere (above 6,000 meters) are called cirrocumulus. They usually indicate fair weather. Altocumulus: Altocumulus clouds form between 2,000 and 6,000 meters high. They usually form larger, darker puffs than cirrocumulus clouds. Sometimes they appear in rows. If the altocumulus clouds look like towers, they are called altocumulus castellatus. These clouds often appear before a storm. Cumulus: Cumulus clouds are the tall, puffy clouds that form when the air over land is heated. As a result, these clouds often break down as the Sun sets. Often, cumulus clouds have a flat base. They are found below 2,000 meters. Cumulonimbus: A dark and stormy cumulus cloud is called cumulonimbus. Thunderstorms develop from cumulonimbus clouds. These clouds are between 2,000 and 15,000 meters high. Figure 11.19: Cumuliform clouds.

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Stratiform Stratiform clouds form when a large mass of stable air gradually rises. As this clouds air rises, it expands and cools, allowing condensation to spread evenly

throughout the layer. Stratiform clouds look like smooth, flattened blankets (Figure 11.20). They can cover as much as 300,000 square miles! A sky with stratiform clouds appears uniformly gray.

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Cirrostratus: Cirrostratus clouds look like a translucent white coating across the sky. They are high clouds, located at least 6,000 meters above the ground. These clouds are made of ice crystals. As a result, sunlight shining through the crystals is refracted (bent) causing a halo-like effect around the Sun. Altostratus: Altostratus clouds are the most easily recognizable stratiform clouds. If the sky looks like a smooth gray sheet and no shadows form on the ground, you are seeing altostratus clouds located between 2,000 and 6,000 meters high. Stratus: Stratus clouds form below 2,000 meters. Stratus clouds look like fog that doesn’t quite reach the ground. Nimbostratus: When a stratus cloud turns dark gray, it signals the approach of rain. These rain clouds are called nimbostratus.

Figure 11.20: Stratiform clouds.

Stratocumulus Stratocumulus clouds have aspects of both cumuliform and stratiform clouds clouds (Figure 11.21). They form when convection occurs inside a stratiform

cloud. As rising air cools, the water in the cloud condenses, creating a cumuliform cloud within the stratiform cloud. This causes the smooth cloud to look lumpy. Cirrus clouds Cirrus clouds are thin lines of ice crystals high in the sky, above 6,000 meters

Figure 11.21: Stratocumulus clouds.

(Figure 11.22). A curved cirrus cloud is commonly called a “mare’s tail.” The curving is due to a change in wind direction, and might indicate that the weather is going to change.

Figure 11.22: Cirrus clouds. 11.3 WEATHER PATTERNS

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Thunderstorms Storm cells Thunderstorms occur because of convection

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in the atmosphere. Warm air rises from the ground to the top of the troposphere. This is called an updraft. As the updraft rises, it cools and condenses. This condensation releases heat, which warms the surrounding air, allowing it to rise and condense. This process forms a towering cumulonimbus cloud. Eventually, some of the cloud droplets become large enough to fall as rain. Cold air from the top of the troposphere is dragged down along with the rain. This cold, dense air is called a downdraft. The downdraft and updraft form a type of convection cell called a storm cell within the cloud (see diagram at right). A storm ends when cool air from the downdraft replaces all the warm air on the ground. The updraft stops flowing. Next, the rain stops and the thunderstorm ends.

storm cell - a convection cell within a cloud that is associated with a storm. lightning - a bright spark of light that occurs inside a storm cloud, between a cloud and Earth’s surface, or between two clouds.

thunder - a sound that occurs when a lightning spark heats and expands air.

Lightning and Lightning is a bright spark of light that occurs within a storm cloud, thunder between a cloud and Earth’s surface, or between two storm clouds. Lightning

occurs when the bottom of a storm cloud becomes negatively charged (–) and the top becomes positively charged (+). The negative charges on the bottom of the cloud repel negative charges on the ground so the ground becomes positive (Figure 11.23). In this situation, a spark can travel between the negatively and positively charged surfaces. Thunder is the sound we hear that is associated with lightning. Thunder is caused by the rapid heating and expanding of air that is near lightning. Hail Hail is a form of precipitation consisting of chunks or balls of ice called

hailstones. Hail forms in very tall thunderstorm clouds that have strong updrafts, where part of the cloud is below freezing (0°C), and when water droplets freeze on contact with dust particles. The hailstones are carried upward in the updraft and fall back down in the downdraft of the storm, gaining a layer of ice in each cycle. When hailstones become too heavy to be carried up by the storm’s updraft, they fall out of the cloud to the ground.

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Figure 11.23: Lightning occurs

when a spark travels between negative and positive charges.

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Hurricanes Cyclones and A cyclone is a low-pressure center that is surrounded by rotating winds. The hurricanes Coriolis effect causes these winds to rotate counterclockwise in the northern hemisphere and clockwise in the southern hemisphere. A hurricane is a

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tropical cyclone with wind speeds of at least 119 kilometers (74 miles) per hour. The Saffir-Simpson Hurricane Scale is one scale used for rating hurricanes (Figure 11.24). How hurricanes Warm, moist air over the tropical ocean provides the initial energy source for form a hurricane. As the warm air rises, the water vapor in it condenses. Clouds and

thundershowers form. The condensation releases heat, warming the surrounding air even more. As all of this air expands and rises, it creates an area of low pressure at the surface of the water. This pressure difference causes the surrounding air to rush toward the center. The path of this rushing air curves because of the Coriolis effect, and a rotating system forms. Hurricane conditions

On August 28, 2005, Katrina, one of the deadliest hurricanes on record, became a category 5 hurricane (photo, left). Several conditions must be present for a rotating system to become a hurricane. First, the ocean water must be warm (about 27°C). Second, the layer of warm ocean water must be deep enough so that cooler water does not get stirred up to the surface by the storm. Cooler water decreases the strength of the storm. Next, the air must be warm and moist to a point high above sea level. Water vapor from high-level air is pulled into the storm. When it condenses, heat is released, and the storm strengthens. Finally, the wind conditions must also be just right. The storm breaks apart when the source of warm, moist air is removed, mostly by moving over land.

cyclone - a low-pressure center surrounded by rotating winds.

hurricane - a tropical cyclone with wind speeds of at least 119 kilometers per hour.

Saffir-Simpson Hurricane Scale Name

Wind speed

Damage

Storm surge

Tropical < 63 km/h depression

Little

None

Tropical storm

Minor flooding

Very minor

Category 1 119–153 km/h Minimal hurricane damage

1.2–1.5 m

Category 2 154–177 km/h Moderate hurricane

1.6–2.4 m

Category 3 178–209 km/h Extensive hurricane

2.5–3.7 m

Category 4 210–249 km/h Extreme hurricane

3.8–5.5 m

Category 5 > 250 km/h hurricane

> 5.6 m

63–117 km/h

Catastrophic

km/h = kilometers per hour

Figure 11.24: The Saffir-Simpson Hurricane Scale.

11.3 WEATHER PATTERNS

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Tornadoes Comparing A tornado, like a hurricane, is a system of rotating winds around a hurricanes and low-pressure center. An average tornado is less than 200 meters in tornadoes diameter—tiny, compared with the 640 kilometer (640,000 meter) average

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diameter of a hurricane! However, the wind speeds of a tornado are much greater than those of a hurricane. A tornado’s wind speed can reach 400 kilometers per hour.

tornado - a system of rotating winds around a low-pressure center; a tornado is smaller than a hurricane, but has faster winds.

How tornadoes A tornado begins to form when the updrafts in a storm cell reach more than form 160 kilometers per hour. Winds near the top of the cumulonimbus cloud

begin rotating at a high speed. As more air flows into the low-pressure center of the storm, the rotation extends downward. The diameter of the rotating wind pattern narrows, causing the wind to speed up. As the rotating wind pattern narrows and lengthens, it forms a funnel cloud (Figure 11.25). If the funnel cloud reaches the ground, it becomes a tornado. High wind The rushing wind of a speeds cause tornado can flatten houses damage and even lift cars

completely off the ground. A tornado in Broken Bow, Oklahoma, once carried a motel sign 48 kilometers and dropped it in Arkansas! Most tornadoes last around 10 to 20 minutes, although the strongest tornadoes can last an hour or more. They travel along the ground at speeds of about 40 to 60 kilometers per hour.

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Figure 11.25: A funnel cloud forms when updrafts in a storm cell reach high speed and begin to rotate. As the diameter of the rotation narrows and extends downward, a funnel cloud takes shape.

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Section 11.3 Review 1. How is the weather associated with a cold front different from the weather associated with a warm front? 2. What are jet streams and where do they form?

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3. Indicate which characteristics below apply to a high-pressure center and which apply to a low-pressure center. a. rising warm air b. sinking cold air c. wind rotates counterclockwise around this pressure center in the northern hemisphere d. precipitation e. dry and clear 4. Name one type of cloud you would expect to see on a day when the weather is cool, dry, and clear. Name one type of cloud you would expect to see if a thunderstorm were about to happen. 5. Which kind of cloud has the characteristics of both cumuliform and stratiform clouds? Describe this cloud.

This photo of the jet stream was taken by the GOES-8 satellite in orbit 36,000 kilometers above Earth. Arrows were added to indicate wind direction. Research one important aspect of the jet stream and write a short report about what you learn.

6. How is convection of air involved in the development of a thunderstorm? 7. What conditions are necessary for hail to form? 8. What conditions are needed for a hurricane to develop? 9. List three differences between a hurricane and a tornado. 10. On the Saffir-Simpson Hurricane Scale, what is the difference between a category 1 hurricane and a category 5 hurricane?

When Hurricane Andrew hit Florida in 1992, its winds were 265 km/h and it produced a storm surge of 5.2 meters. What category was Hurricane Andrew on the Saffir-Simpson Scale? Research the answer to the following question. How does Hurricane Katrina, which hit New Orleans in 2005, compare to Hurricane Andrew?

11.3 WEATHER PATTERNS

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Chapter 11 Assessment Vocabulary

Section 11.2

Select the correct term to complete the sentences.

10. _____ occurs as a result of a pressure difference between two air masses.

atmospheric

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pressure weather storm cell

biome

isobar

jet streams

ionosphere

stratosphere

high-pressure

low-pressure

air mass

center

center

Coriolis effect

convection cells

climate

warm front

mesosphere

front

barometer

dew point

atmosphere

exosphere

cold front

thermal

wind

troposphere

thermosphere

11. A(n) _____ is a large body of air with consistent temperature and moisture throughout. 12. A(n) _____ is a small, upward flow of warm air caused by convection. 13. _____ describes the condition of the atmosphere in terms of temperature, atmospheric pressure, wind, and precipitation. 14. Large wind patterns in Earth’s atmosphere are called _____.

1.

The layer of gases that surrounds a planet is its _____.

15. The bending of currents of air or water due to Earth’s rotation is called the _____.

2.

_____ is a measure of the force of air molecules per unit area in the atmosphere at a given altitude.

16. The temperature at which more water condenses than evaporates in an air mass is called _____.

3.

An instrument that measures atmospheric pressure is called a(n) _____.

17. _____ is the long term record of weather patterns.

Section 11.1

18. A(n) _____ is a major climate region.

4.

All weather occurs in the layer of the atmosphere called the _____.

Section 11.3

5.

The ozone layer is located in the _____.

19. A(n) _____ is the border between two different air masses.

6.

The coldest layer of the atmosphere is the _____.

7.

The layer of the atmosphere that has a high temperature and low density of air molecules is the _____.

20. A front that occurs when a cold air mass moves in and replaces a warm air mass is called a(n) _____.

8.

The _____ is the location of satellites.

9.

The portion of the atmosphere where electricity can be transmitted is the _____.

21. A front that occurs when a warm air mass moves in and replaces a cold air mass is called a(n) _____. 22. High-altitude, fast-moving winds are called _____. 23. Rising warm air causes a(n) _____ to form. 24. Sinking cold air causes a(n) _____ to form.

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25. A(n) _____ is a line on a weather map that connects places with the same atmospheric pressure.

10. In what direction would you expect a global wind pattern to be blowing at 15° S latitude? What is the name of this global wind pattern?

26. A convection cell within a cloud that is associated with a storm is called a(n) _____.

11. Explain how temperature and pressure affect the amount of water in Earth’s atmosphere.

Concepts

12. A weather report states that the relative humidity is 40 percent. What does this value mean?

Section 11.1

13. What is a biome and how many main biomes are there on Earth?

1.

What gases are found in Earth’s atmosphere? How has life on Earth changed Earth’s atmosphere?

2.

Explain how Earth’s atmosphere formed.

14. Explain why the average yearly temperature at the equator is hot (27°C) and the average yearly temperature at the North Pole is cold (–18°C).

3.

What is atmospheric pressure? Explain how our bodies are adapted to survive Earth’s atmospheric pressure.

15. Name two things you would have to do in order to move into a different climate than the one you are in now.

4.

How does a mercury barometer measure atmospheric pressure? What is atmospheric pressure at sea level on a mercury barometer?

5.

Which statement is true?

16. You can expect to find tundra in the high northern latitudes of the northern hemisphere. Where would you expect to find a tundra ecosystem on a mountain?

a.

17. How many seasons are there in temperate deciduous forests?

b. c. d. e. 6.

The atmospheric pressure at sea level is greater than the atmospheric pressure at the top of Mt. Everest. Atmospheric pressure increases with altitude. Atmospheric pressure is not related to altitude. Atmospheric pressure decreases with altitude. Statements a and d are true.

Explain what happens to temperature as you go from sea level to the top of the thermosphere.

Section 11.2

7.

What causes wind?

8.

Why is atmospheric pressure low at the equator?

9.

What causes the Coriolis effect?

18. Identify whether these comments are talking about the weather or about the climate for an area. a. b. c. d.

A cold front is moving into the area. A region has two main seasons—a wet and a dry season. My region averages only 20 centimeters of rain per year. Tomorrow will be windy and sunny.

Section 11.3

19. A weather map shows a high-pressure area located over Town A and a low-pressure area located over Town B. Which direction will the wind blow: from Town A to Town B or from Town B to Town A?

CHAPTER 11 ASSESSMENT

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20. You hear a weather report that a warm front is moving through your town. What kind of weather do you expect?

4.

21. The ocean water temperature is 30°C, the wind is blowing from one direction, the layer of warm ocean water is 50 meters deep, and the air is warm and moist up to 5,750 meters. Would a hurricane form under these conditions? Why or why not?

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Section 11.3

22. Copy this table on to your own paper and fill it in:.

5. Cloud Category

How it Forms

You are a pilot who wants to fly an airplane from St. Paul, Minnesota, 700 miles south to Little Rock, Arkansas. If you set your compass and try to fly straight south, you will probably end up in New Mexico! Why?

Types

Cumuliform

Identify the following on the map below: a high-pressure center, a low-pressure center, one or more isobars, a warm front, and a cold front.

Stratiform

Problems Section 11.1

1.

Would you expect a barometer to have a higher reading in Alaska’s Denali National Park or in Florida’s Everglades National Park? (Hint: An atlas may help you.)

2.

Convert the following barometric readings to atmospheres (atm). a. b. c. d.

1,890 mm Hg 306,000 pa 100 psi 5,000 mb

Section 11.2

3.

A warm (25°C) air mass contains 80 percent of the total amount of water it can contain. The air mass warms to 30°C. a. b.

Does the volume of the air mass decrease or increase when the temperature goes up? Does the relative humidity of the air mass increase or decrease when the temperature goes up? (Assume that the amount of water vapor in the air mass stays the same.)

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Applying Your Knowledge Section 11.1

1.

Find out the atmospheric pressure for today. You can find this value by listening to a local TV weather report or by going to a weather Web site on the Internet. Convert this pressure reading so that you have the value in inches of mercury, atmospheres, and in millibars.

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Section 11.2

2.

3.

Read the following paragraph and then answer the question.

Study the following map showing population density and the Earth’s biomes map from the chapter. a. b. c.

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Warm, moist air crosses over the Pacific Ocean and reaches the Washington coast. At first, the air mass flows up the western side of a mountain, which has a lot of trees and plants. The air mass cools as it rises, reaches its dew point, and condenses to form a cloud and then rain droplets. As the air mass continues to move eastward, the now cool, dry air mass sinks down the eastern side of the mountain into warm temperatures. The land that this dry air passes over will have a dry climate.

CHAPTER 11

Which biomes have the most densely populated areas? Which biomes have the least densely populated areas? Propose an explanation as to why different biomes have such different population densities.

Section 11.3

Now, look at the illustration above. Which city would receive more rain per year—Olympia or Yakima? Explain your answer. Go to the Internet and find out what the average rainfall actually is for each of these cities. This data will help you determine if your answer is correct!

4.

Hurricane Katrina was a very strong hurricane that devastated the city of New Orleans. Use the Internet to research the development and path of Hurricane Katrina. What conditions caused the storm to become so intense?

5.

Use the Internet to research the National Weather Service’s recommendations for staying safe during a tornado. Write an action plan for your school or home that describes the safest place to seek shelter during a tornado in your area.

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Unit 4 Matter and Its Changes FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

CHAPTER 12 Atoms and the

Periodic Table

CHAPTER 13  Compounds CHAPTER 14 Changes in Matter CHAPTER 15 Chemical Cycles

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and Climate Change

‹ Try this at home Old pennies are darker in color than newer ones because of a chemical change between copper and oxygen in the air (oxidation). It also takes a chemical reaction to “undo” the oxidation. Try to clean some pennies in tomato sauce, ketchup, taco sauce, Tabasco sauce, and chili sauce. Be consistent in testing the “cleaners” (same amount of liquid, exposure time, etc.). Which “cleans” pennies the best? Compare ingredients lists to determine what might be causing the chemical reaction. (Ignore long names—they are just preservatives.) Once you have found what you think are the “agents of clean,” try them individually, then mixed together. Which works best? Why do you think so? Then look online for tips on cleaning copper pots. How do the suggestions compare with your results? Safety tip: Remember to wash your hands after handling the “cleaners," or wear latex gloves.

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12

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There is something more to wintergreen-flavored candy (the kind with a hole in the middle) than its refreshing taste. When you crush one of these candies with your teeth, blue sparks jump out of your mouth! You can only see the sparks if you hold a mirror up to your mouth in a very dark place, like a closet. You will be able to see the sparks even better if you crush one of the candies with a pair of pliers (no mirror required). In order to understand why the blue sparks appear, you must know what an atom is and what it is made of. After reading this chapter on atoms, you can do an Internet search on the term triboluminescence to find out why this candy sparks when you crush it.

4 What are atoms and what are they made of? 4 What does light have to do with atoms? 4 What is the periodic table and why does it have a specific shape?

4 What do electrons have to do with the chemical properties of atoms?

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12.1 The Structure of the Atom Scientists once believed atoms were the smallest particles of matter. With the advancement of technology, it became clear that atoms themselves are made of even smaller particles. Today, we believe atoms are made of three basic particles: the proton, electron, and neutron. It’s amazing that the incredible variety of matter around us can all be built from just three subatomic particles!

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Electric charge

electric charge - a fundamental property of matter that can be either positive or negative. elementary charge - the smallest unit of electric charge that is possible in ordinary matter; represented by the lowercase letter e.

Electric charge In order to understand atoms, we need to understand the idea of electric is a property of charge. Electric charge is a fundamental property of matter that can be matter either positive or negative. One of the two forces that holds atoms together

comes from electric charge. Positive and There are two different kinds of electric charge—positive and negative. negative Because there are two kinds of charge, the force between electric charges can

be either attractive or repulsive.

• A positive and a negative charge will attract each other. • Two positive charges will repel each other. • Two negative charges will also repel each other.

The elementary Scientists use the letter e to represent the elementary charge. At the size of charge atoms, electric charge always comes in units of +e or –e. It is only possible to

have charges that are multiples of e, such as +e, +2e, –e, –2e, –3e, and so on. Scientists believe it is impossible for ordinary matter to have charges that are fractions of e. For example, a charge of +0.5e is impossible in ordinary matter. Electric charge appears only in whole units of the elementary charge (Figure 12.1).

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Figure 12.1: Just as normal matter is divided into atoms, electric charge appears only in whole units of the elementary charge, e.

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Inside an atom: Solving the puzzle The electron The first strong evidence that something smaller than an atom existed was identified found in 1897. English physicist J. J. Thomson discovered that electricity

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passing through a gas caused the gas to give off particles that were too small to be atoms. The new particles had negative electric charge. Complete atoms have zero charge. Thomson’s particles are now known as electrons. Electrons were the first particles discovered that are smaller than atoms. An early model of an atom

electron - a particle with an electric charge (–e) found inside of atoms but outside the nucleus.

nucleus - the tiny core at the center of an atom containing most of the atom’s mass and all of its positive charge.

Thomson proposed that negative electrons were sprinkled inside atoms like raisins in a loaf of raisin bread. The “bread” was positively charged and the electrons were negatively charged. This was the first real model for the inside of an atom. As it soon turned out, it was not the right model, but it was a good place to start.

Testing the In 1911, Ernest Rutherford, Hans Geiger, and Ernest Marsden did an model with an experiment to test Thomson’s model of the atom. They launched positively experiment charged helium ions (a charged atom is an ion) at a very thin gold foil

(Figure 12.2). They expected most of the helium ions to be deflected a little as they plowed through the gold atoms. An unexpected They found something quite unexpected. Most of the helium ions passed right result! through the foil with no deflection at all. Even more surprising—a few

bounced back in the direction they came! This unexpected result prompted Rutherford to remark, “It was as if you fired a fifteen-inch (artillery) shell at a piece of tissue paper and it came back and hit you!” The nuclear The best way to explain the pass-through result was if a gold atom was mostly model of the empty space. If most of the helium ions hit nothing, they wouldn’t be atom deflected. The best way to explain the bounce-back result was if nearly all the

mass of a gold atom were concentrated in a tiny, dense core at the center. Remember, two positive charges will repel each other. This causes the deflection. Further experiments confirmed Rutherford’s idea about this dense core. We now know that every atom has a tiny nucleus, which contains more than 99 percent of the atom’s mass.

Figure 12.2: Rutherford’s famous experiment led to the discovery of the nucleus.

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Three particles make up all atoms Protons and Today, we know that the nucleus of an atom contains protons and neutrons. neutrons Protons have positive charge, opposite of electrons. The charge on a proton (+e) and an electron (–e) are exactly equal and opposite. Neutrons have

neutron - a particle found in the

zero electric charge.

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The nucleus contains most of the mass

Electron mass is 1 about that of 1,836 a proton Proton

Occurrence Electron

Found outside of nuclei

Proton

Found in all nuclei

Neutron

Found in almost all nuclei (exception: most H nuclei)

Protons and neutrons are much more massive than electrons. A proton has 1,836 times as much mass as an electron. A neutron has about the same mass as a proton. The table below compares electrons, protons, and neutrons in terms of charge and mass. Because protons and neutrons have so much more mass, more than 99 percent of an atom’s mass is in the nucleus. Charge -1 +1 0

Mass (g)

1

-24

1.673 × 10

1,836

1.675 × 10-24

1,839

9.109 × 10

more than 10,000 times larger than the nucleus. As a comparison, if an atom were the size of a football stadium, the nucleus would be the size of a pea, and the electrons would be equivalent to a small swarm of gnats buzzing around the stadium at an extremely high speed. Can you imagine how much empty space there would be in the stadium? An atom is mostly empty space!

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nucleus with mass similar to the proton but with zero electric charge.

Relative Mass

-28

Electrons define Electrons occupy the space outside the nucleus in a region called the electron the volume of an cloud. The diameter of an atom is really the diameter of the electron cloud atom (Figure 12.3). Compared to the tiny nucleus, the electron cloud is enormous,

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proton - a particle found in the nucleus with a positive charge exactly equal and opposite to the electron.

Figure 12.3: The overall size of an

atom is the size of its electron cloud. The nucleus is much, much smaller.

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Forces inside atoms Electromagnetic Electrons are bound to the nucleus by the attractive force between force electrons (–) and protons (+). The electrons don’t fall into the nucleus because

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they have kinetic energy, or momentum. The energy of an electron causes it to move around the nucleus instead of falling in (Figure 12.4). A good analogy is Earth orbiting the Sun. Gravity creates a force that pulls Earth toward the Sun. Earth’s kinetic energy causes it to orbit the Sun rather than fall straight in. While electrons don’t really move in orbits, the energy analogy is approximately right. Strong nuclear Because of electric force, all the positively-charged protons in the nucleus force repel each other. So, what holds the nucleus together? There is another force

that is even stronger than the electric force. We call it the strong nuclear force. The strong nuclear force is the strongest force known to science (Figure 12.5). This force attracts neutrons and protons to each other and works only at the extremely small distances inside the nucleus. If there are enough neutrons, the attraction from the strong nuclear force wins out over repulsion from the electromagnetic force and the nucleus stays together. In every atom heavier than helium, there is at least one neutron for every proton in the nucleus.

Figure 12.4: The negative electrons

are attracted to the positive protons in the nucleus, but their momentum keeps them from falling in.

Weak force There is another nuclear force called the weak force. The weak force is

weaker than both the electric force and the strong nuclear force. If you leave a single neutron outside the nucleus, the weak force eventually causes it to break down into a proton and an electron. The weak force does not play an important role in a stable atom, but it comes into action in certain special cases when atoms break apart. Gravity The force of gravity inside the atom is much weaker than even the weak force.

It takes a relatively large mass to create enough gravity to make a significant force. We know that particles inside an atom do not have enough mass for gravity to be an important force on the scale of atoms. But there are many unanswered questions. Understanding how gravity works inside atoms is an unsolved scientific mystery.

Figure 12.5: When enough neutrons

are present, the strong nuclear force wins out over the repulsion between positively charged protons and pulls the nucleus together tightly. The strong nuclear force is the strongest known force in the universe.

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How atoms of various elements are different The atomic number is the number of protons

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How is an atom of one element different from an atom of another element? The atoms of different elements contain varying numbers of protons in the nucleus. For example, all atoms of carbon have six protons in the nucleus and all atoms of hydrogen have one proton in the nucleus (Figure 12.6). Because the number of protons is so important, it is called the atomic number. The atomic number of an element is the number of protons in the nucleus of every atom of that element. Each element has a unique atomic number. On a periodic table of elements, the atomic number is usually written above or below the atomic symbol. An atom with only one proton in its nucleus is the element hydrogen, atomic number 1. An atom with six protons is the element carbon, atomic number 6. Atoms with seven protons are nitrogen, atoms with eight protons are oxygen, and so on.

Elements have unique atomic numbers

atomic number - the number of protons in the nucleus of an atom. The atomic number determines what element the atom represents.

All carbon atoms have 6 protons.

All hydrogen atoms have 1 proton.

Complete atoms Because protons and electrons attract each other with very large forces, the are electrically number of protons and electrons in a complete atom is always equal. For neutral example, hydrogen has one proton in its nucleus and one electron outside the

nucleus. The net electric charge of a hydrogen atom is zero because the negative charge of the electron cancels the positive charge of the proton. Each carbon atom has six electrons, one for each of carbon’s six protons. Like hydrogen, a complete carbon atom is electrically neutral. Ions Complete atoms have a net zero charge. Ions are atoms that have a

different number of protons than electrons and so have a net electric charge. Positively-charged ions have more protons than electrons. Negatively-charged ions have more electrons than protons.

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Figure 12.6: Atoms of the same

element always have the same number of protons in the nucleus.

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Isotopes Isotopes All atoms of the same element have the same number of protons in the

nucleus. However, atoms of the same element might have different numbers of neutrons in the nucleus. Isotopes are atoms of the same element that have different numbers of neutrons.

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The isotopes of Figure 12.7 shows three isotopes of carbon that exist in nature. Most carbon carbon atoms have six protons and six neutrons in the nucleus. However, some

isotopes - atoms of the same element that have different numbers of neutrons in the nucleus.

mass number - the number of protons plus the number of neutrons in the nucleus.

carbon atoms have seven or eight neutrons. They are all carbon atoms because they all contain six protons, but they are different isotopes of carbon. The isotopes of carbon are called carbon-12, carbon-13, and carbon-14. The number after the name is called the mass number. The mass number of an isotope tells you the number of protons plus the number of neutrons.

Solving Problems: Isotopes How many neutrons are present in an aluminum atom that has an atomic number of 13 and a mass number of 27? 1. Looking for:

You are asked to find the number of neutrons.

2. Given:

You are given the atomic number and the mass number.

3. Relationships:

Use the relationship: protons + neutrons = mass number.

4. Solution:

Plug in and solve: 13 + x = 27; x = 14 The aluminum atom has 14 neutrons.

Figure 12.7: The isotopes of carbon.

Your turn...

a. How many neutrons are present in a magnesium atom with a mass number of 24?

a. 12 b. 20

b. Find the number of neutrons in a calcium atom that has a mass number of 40.

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Section 12.1 Review

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1. Which of the following statements regarding electric charge is true? a. A positive charge repels a negative charge and attracts other positive charges. b. A positive charge attracts a negative charge and repels other positive charges. 2. Is electric charge a property of just electricity or is charge a property of all atoms? 3. Which of the drawings in Figure 12.8 is the most accurate model of the interior of an atom? 4. There are four forces in nature. Name the four forces and rank them from strongest to weakest. 5. There are three particles inside an atom. One of them has zero electric charge. Which one is it? 6. All atoms of the same element have (choose one): a. the same number of neutrons. b. the same number of protons. c. the same mass. 7. The atomic number is: a. the number of protons in the nucleus. b. the number of neutrons in the nucleus. c. the number of neutrons plus protons. 8. Use the diagram in Figure 12.9 to answer the following questions. a. Which atoms are isotopes of the same element? b. Give the mass number for each atom. 9. An atom has a mass number of 31 and 16 neutrons in its nucleus. What is its atomic number? What is the element?

Figure 12.8: Question 3.

Figure 12.9: Question 8.

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12.2 Electrons

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Atoms interact with one another through their electrons. This is why almost all the properties of the elements (except mass) are due to electrons. Chemical bonds involve only electrons, so electrons determine how atoms combine into compounds. We find a rich variety of matter because electrons inside atoms are organized in unusual and complex patterns. Exactly how electrons create the properties of matter was a puzzle that took bright scientists a long time to figure out!

The spectrum The spectrum is Almost all the light you see comes from atoms. For example, light is given off a pattern of when electricity passes through the gas in a fluorescent bulb or a neon sign. colors When scientists look carefully at the light given off by a pure element,

they find that the light does not include all colors. Instead, they see a few very specific colors, and the colors are different for different elements (Figure 12.10). Hydrogen has a red line, a green line, a blue line, and a violet line in a characteristic pattern. Helium and lithium have different colors and patterns. Each element has its own characteristic pattern of colors called a spectrum. The colors of clothes, paint, and everything else around you come from this property of elements that allows them to emit or absorb light of only certain colors. Spectrometers Each individual color in a spectrum is called a spectral line because each and spectral color appears as a line in a spectrometer. A spectrometer (also called a lines spectroscope) is a device that separates light into its different colors. The

illustration below shows a spectrometer made with a prism. The spectral lines appear on the screen at the far right.

spectrum - the characteristic colors of light given off or absorbed by an element. spectral line - a bright, colored line in a spectrometer. spectrometer - an instrument that separates light into a spectrum.

Hydrogen

Helium

Lithium

Figure 12.10: When light from

energized atoms is directed through a prism, spectral lines are observed. Each element has its own distinct pattern of spectral lines.

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The Bohr model of the atom Energy and Light is a form of pure energy that comes in tiny bundles called photons. color A photon is the smallest possible quantity of light energy. The amount of

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energy in a photon determines the color of the light. Red light has lower energy and blue light has higher energy. Green and yellow light have energy between red and blue. The fact that atoms only emit certain colors of light tells us that something inside an atom can only have certain values of energy.

energy level - one of the discrete allowed energies for electrons in an atom.

Neils Bohr Danish physicist Neils Bohr (1885–1962) proposed the concept of energy levels to explain the spectrum of hydrogen. In Bohr’s model, the electron in

a hydrogen atom must be in a specific energy level. You can think of energy levels like steps on a staircase. You can be on one step or another, but you cannot be between steps except in passing. Electrons must be in one energy level or another and cannot remain between energy levels. Electrons change energy levels by absorbing or emitting light (Figure 12.11). Explaining the When an electron moves from a higher energy level to a lower one, the atom spectrum gives up the energy difference between the two levels. The energy comes

out as different colors of light. The specific colors of the spectral lines correspond to the differences in energy between the energy levels. The diagram below shows how the spectral lines of hydrogen come from electrons falling from the 3rd, 4th, 5th, and 6th energy levels down to the 2nd energy level.

Figure 12.11: When the right

amount of energy is absorbed, an electron in a hydrogen atom jumps to a higher energy level. When the electron falls back to the lower energy level, the atom releases the same amount of energy it absorbed. The energy comes out as light of a specific color.

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The quantum theory Quantum versus Quantum theory says that when things get very small, like the size of an classical atom, matter and energy do not obey Newton’s laws or other laws of classical

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physics. That is, the classical laws are not obeyed in the same way as with a larger object, such as a baseball. According to the quantum theory, when a particle (such as an electron) is confined to a small space (such as inside an atom), the energy, momentum, and other variables of the particle become restricted to certain specific values.

quantum theory - the theory that describes matter and energy at very small (atomic) sizes.

Everything is A particle, such as a grain of sand, is small, but fuzzy in the you can easily imagine that it has a definite quantum world shape, size, position, and speed. According to

quantum theory, particles the size of electrons are fundamentally different. When you look closely, an electron is “smeared out” into a wave-like “cloud.” The uncertainty The work of German physicist Werner principle Heisenberg (1901–1976) led to Heisenberg’s uncertainty principle. According to the

uncertainty principle, a particle’s position, momentum, energy, and time in the quantum world can never be precisely known at the same time. For example, if you choose to measure the location of the electron, its momentum cannot be determined. Understanding The uncertainty principle arises because the quantum world is so small. To the uncertainty “see” an electron, you have to bounce a photon of light off it, or interact with principle it in some way (Figure 12.12). Because the electron is so small, even a single

photon moves it and changes its motion. That means the moment you use a photon to locate an electron, you push it, so you no longer know precisely how fast it was going. However, you know its position at that moment in time. In fact, any process of observing in the quantum world changes the very system you are trying to observe. The uncertainty principle exists because measuring any variable disturbs the others in an unpredictable way.

Figure 12.12: The act of observing

anything in the quantum world means disturbing in unpredictable ways the very thing you are trying to observe.

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Electrons and energy levels The energy levels are at different distances from the nucleus

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The positive nucleus attracts negative electrons the way gravity attracts a ball down a hill. The farther down the “hill” an electron slides, the less energy it has. Conversely, electrons have more energy farther up the hill, and away from the nucleus. The higher energy levels are farther from the nucleus and the lower energy levels are closer.

The electron While Bohr’s model of electron energy levels explained atomic spectra and cloud the periodic behavior of the elements, it was incomplete. Electrons are so

fast that their exact position within an atom cannot be defined. Remember, in the current model of the atom, we think of the electrons as moving around the nucleus in an area called an electron cloud. The energy levels occur because electrons in the cloud are at different average distances from the nucleus.

Orbitals

The energy levels in an atom are grouped into different shapes called orbitals.

The s-orbital is spherical and holds two electrons. The first two electrons in each energy level are in the s-orbital.

Rules for energy Inside an atom, electrons always obey the following rules. levels

• The energy of an electron must match one of the energy levels in the atom. • Each energy level can hold only a certain number of electrons, and no more. • As electrons are added to an atom, they settle into the lowest unfilled energy level. Quantum Energy levels are predicted by quantum mechanics, the branch of physics mechanics that deals with the microscopic world of atoms. While quantum mechanics is outside the scope of this book, you should know that it is a very accurate theory, and it explains the characteristics of the energy levels.

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The p-orbitals hold 6 electrons and are aligned along the three directions on a 3-D graph.

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The energy levels in an atom How electrons In the Bohr model of the atom, the first energy level can accept up to fill in the energy 2 electrons. The second and third energy levels hold up to 8 electrons each. levels The fourth and fifth energy levels hold up to 18 electrons each (Figure 12.13).

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A good analogy is to think of the electron cloud like a parking garage. The first level of the garage only has spaces for 2 cars, just as the first energy level only has spaces for 2 electrons. The second and third levels of the garage can hold 8 cars each, and the fourth and fifth levels can each hold 18 cars. Each new car that enters the garage parks in the lowest level with an unfilled space, just as each additional electron occupies the lowest unfilled energy level in the atom. How the energy The number of electrons in an atom depends on the atomic number because levels fill the number of electrons equals the number of protons. That means each

element has a different number of electrons and therefore fills the energy levels to a different point. For example, a helium atom (He) has two electrons (Figure 12.14). The two electrons completely fill up the first energy level (see the diagram below). The next element is lithium (Li) with three electrons. Since the first energy level only holds two electrons, the third electron must go into the second energy level. The diagram shows the first 10 elements, which fill the first and second energy levels.

Figure 12.13: Electrons occupy

energy levels around the nucleus. The farther away an electron is from the nucleus, the higher the energy it possesses.

Figure 12.14: A helium atom

has two protons in its nucleus and two electrons.

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Section 12.2 Review

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1. The pattern of colors given off by a particular atom is called: a. an orbital. b. an energy level. c. a spectrum. 2. Which of the diagrams in Figure 12.15 corresponds to the pelement lithium? 3. When an electron moves from a lower energy level to a higher energy level, the atom: a. absorbs light. b. gives off light. c. becomes a new isotope. 4. Two of the energy levels can hold eight electrons each. Which energy levels are they? 5. How many electrons can fit in the fourth energy level? 6. The element beryllium has four electrons. Which diagram in Figure 12.16 shows how beryllium’s electrons are arranged in the first four energy levels? 7. Which two elements have electrons only in the first energy level? a. hydrogen and lithium b. helium and neon c. hydrogen and helium d. carbon and oxygen 8. On average, electrons in the fourth energy level are: a. farther away from the nucleus than electrons in the second energy level. b. closer to the nucleus than electrons in the second energy level. c. about the same distance from the nucleus as electrons in the second energy level.

Figure 12.15: Question 2.

Figure 12.16: Question 6.

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12.3 The Periodic Table of the Elements

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How many elements make up the universe? The only way to tell if a substance is an element is to try and chemically break it down into other substances by any possible means. A substance that can be chemically broken apart cannot be an element. As of this writing, scientists have identified 117 confirmed elements. Only about 90 of these elements occur naturally. The others are made in laboratories.

The periodic table

periodic table - a chart that organizes the elements by their chemical properties and increasing atomic number. period - a row of the periodic table. group - a column of the periodic table.

The modern As chemists worked on identifying the true elements, they noticed that some periodic table elements acted like other elements. For example, the soft metals lithium,

sodium, and potassium always combine with oxygen in a ratio of two atoms of metal to one atom of oxygen (Figure 12.17). By keeping track of how each element combined with other elements, scientists began to recognize repeating patterns. From this data, they developed the first periodic table of the elements. The periodic table organizes the elements according to how they combine with other elements due to their chemical properties. Organization of the periodic table

The periodic table is organized in order of increasing atomic number. The lightest element (hydrogen) is at the upper left. The heaviest is on the lower right. Each element corresponds to one box in the periodic table, identified with the element symbol. The periodic table is further divided into periods and groups. Each horizontal row is called a period. Across any period, the properties of the elements gradually change. Each vertical column is called a group. Groups of elements have similar properties. The main group elements are Groups 1 and 2 and Groups 13 through 18 (the tall columns of the periodic table). Elements in Groups 3 through 12 are called the transition elements. The inner transition elements, called lanthanides and actinides, are often shown below the bottom row of the chart in order for the chart to fit on a page.

Lithium (Li)

Oxygen Lithium (Li)

Sodium (Na)

Oxygen Sodium (Na)

Potassium (K)

Oxygen

Potassium (K)

Figure 12.17: The metals lithium,

sodium, and potassium all form compounds with a ratio of two atoms of the metal to one atom of oxygen. All the elements in Group 1 of the periodic table form similar compounds.

12.3 THE PERIODIC TABLE OF THE ELEMENTS

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Reading the periodic table Metals, Most of the elements are metals. A metal is typically shiny, opaque, and a nonmetals, and good conductor of heat and electricity as a pure element. Metals are also metalloids ductile, which means they can be bent into different shapes without breaking. Nonmetals are poor conductors of heat and electricity. Solid nonmetals are

metals - elements that are typically shiny and good conductors of heat and electricity.

nonmetals - elements that are poor conductors of heat and electricity.

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brittle and appear dull. With the exception of hydrogen, the nonmetals are on the right side of the periodic table. The elements on the border between metals and nonmetals are called metalloids. Silicon is an example of a metalloid element with properties in between those of metals and nonmetals.

Periodic Table of the Elements

1 H 1

Main Group Elements

Li 3

4

5

lithium

beryllium

boron

Transition Elements

11 sodium

K 19 potassium

12

3 Ca Sc 20

21

calcium

scandium

Y

Rb Sr

5 V

22

23

6 Cr

40

41

strontium

yttrium

zirconium

niobium

Cs Ba

Hf

Ta

W

55

72

73

74

rubidium

56

lanthanum

cerium

Ac

Th

Pa

U

89

90

91

92

actinium

58

thorium

Pr 59

Ru Rh Pd Ag Cd 44

Br

Kr

bromine

krypton

Xe

16

gallium

32

33

34

germanium

arsenic

selenium

Te

I

52

53

54

iodine

xenon

Bi

Po At

Rn

83

84

Pt

Au Hg Tl

Pb

78

79

81

82

108 109

gold

61

111

neptunium

112

hassium meitnerium darmstadium roentgenium ununbium

62

63

94

64

europium gadolinium

95

plutonium americium

indium

thallium

Ds Rg Uub Uut

110

65

terbium

Np Pu Am Cm Bk 93

mercury

96

curium

97

113

ununtrium

tin

lead

antimony

bismuth

tellurium

polonium

astatine

86

radon

115

116

117

Tm Yb

Lu

thulium

lutetium

118

flerovium ununpentium livermorium ununseptium ununoctium

Er

dysprosium holmium

erbium

66

67

Cf

Es Fm Md No 99

85

Fl Uup Lv Uus Uuh

114

Dy Ho

98

36

51

Ir

platinum

18

50

77

rhenium

35

10

Sn Sb

75

80

17

Ne

In

Re Os

cadmium

9

helium

49

palladium

silver

48

31

rhodium

praseodymium neodymium promethium samarium

protactinium uranium

argon

47

76

45

Nd Pm Sm Eu Gd Tb 60

chlorine

46

seaborgium bohrium

Ce

Ar

P

15

zinc

Mt

57

Cl

Si

14

copper

molybdenum technetium ruthenium

La

S

13

nickel

Rf Db Sg Bh Hs rutherfordium dubnium

neon

cobalt

104 105 106 107

radium

fluorine

iron

43

tungsten

oxygen

30

88

87

tantalum

nitrogen

8

29

Ra

Fr

hafnium

carbon

7

6

27

iridium

barium

17 F

26

osmium

cesium

francium

42

16 O

11 12 aluminum silicon phosphorus sulfur Cu Zn Ga Ge As Se

Zr Nb Mo Tc

39

15 N

10 Ni

vanadium chromium manganese

titanium

14 C

Al

28

2

13 B

7 8 9 Mn Fe Co 25

24

38

37

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4 Ti

magnesium

Metals

COLUMNS = GROUPS

ROWS = PERIODS

Na Mg

292

Non metals

2 Be

hydrogen

18 He

68

100

berkelium californium einsteinium fermium

69

101

70

ytterbium

102

71

Lr

103

mendelevium nobelium lawrencium

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Atomic mass Atomic mass The mass of individual atoms is so small that the numbers are difficult to units work with. To make calculations easier, scientists came up with the atomic mass unit (amu). One atomic mass unit is about the mass of a single proton

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(or neutron). In laboratory units, 1 amu is 1.66 × 0.00000000000000000000000166 grams!

10–24

grams. That’s

atomic mass unit - a unit of mass equal to 1.66 × 10–24 grams. atomic mass - the average mass of all the known isotopes of an element, expressed in amu.

Atomic mass The atomic mass is the average mass (in amu) of an atom of each element. and isotopes Atomic masses differ from mass numbers because most elements in nature

contain more than one isotope (see chart below). For example, the atomic mass of lithium is 6.94 amu. That does not mean there are 3 protons and 3.94 neutrons in a lithium atom! On average, out of every 100 atoms of lithium, 6 atoms are Li-6 and 94 atoms are Li-7 (Figure 12.18). The average atomic mass of lithium is 6.94 because of the mixture of isotopes. Atomic number As you learned earlier, the atomic number is the number of protons all atoms review of that element have in their nuclei. If the atom is neutral, it will have the

same number of electrons as well.

Figure 12.18: Naturally-occurring elements have a mixture of isotopes.

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Groups of the periodic table Alkali metals All of the elements in the different groups of the periodic table have similar chemical properties. The first group is known as the alkali metals. Some

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examples of this group are the elements lithium (Li), sodium (Na), and potassium (K). The alkali metals are soft and silvery in their pure form and are highly reactive. Each of them combines in a ratio of two to one with oxygen. For example, lithium oxide has two atoms of lithium per atom of oxygen. Group 2 metals Some examples of Group 2 metals are beryllium (Be), magnesium (Mg),

alkali metals - elements in the first group of the periodic table.

halogens - elements in the group containing fluorine, chlorine, and bromine, among others.

noble gases - elements in the group containing helium, neon, and argon, among others.

and calcium (Ca). These metals also form oxides, however, they combine one-to-one with oxygen. For example, beryllium oxide has one beryllium atom per each oxygen atom. Halogens The halogens are on the right-hand side of the periodic table. These elements

tend to be toxic in their pure form. Some examples are fluorine (F), chlorine (Cl), and bromine (Br). The halogens are also very reactive and are rarely found in pure form. When combined with alkali metals, they form salts, such as sodium chloride (NaCl) and potassium chloride (KCl). Noble gases On the far right of the periodic table are the noble gases. Some examples

of this group are the elements helium (He), neon (Ne), and argon (Ar). These elements do not naturally form chemical bonds with other atoms and are almost always found in their pure state. They are sometimes called inert gases for this reason. Transition In the middle of the periodic table are the transition metals, including

titanium (Ti), iron (Fe), and copper (Cu). These elements are usually good conductors of heat and electricity. For example, the wires that carry electricity in your school are made of copper. Figure 12.19 shows the location of the groups of elements on the periodic table.

Figure 12.19: Groups of the periodic

table.

metals

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Energy levels and the periodic table Period 1 is the The periods (rows) of the periodic table correspond to the energy levels in the first energy level Bohr model of the atom (Figure 12.20). The first energy level can accept up to

two electrons. Hydrogen (H) has one electron and helium (He) has two. These two elements complete the first period.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

Period 2 is the The next element, lithium (Li), has three electrons. Lithium begins the second second energy period because the third electron goes into the second energy level. The level second energy level can hold eight electrons, so there are eight elements

in the second row of the periodic table, ending with neon (Ne). Neon has 10 electrons, which completely fill the second energy level. Period 3 is the Sodium (Na) has 11 electrons, and starts the third period because the eleventh third energy electron goes into the third energy level. We know of elements with up to level 118 electrons. These elements have their outermost electrons in the seventh

energy level. Outer electrons As we will see in the next chapter, the outermost electrons in an atom are the

ones that interact with other atoms. The outer electrons are the ones in the highest energy level. Electrons in the completely filled inner energy levels do not participate in forming chemical bonds.

Figure 12.20: The rows (periods) of the periodic table correspond to the energy levels for the electrons in an atom.

12.3 THE PERIODIC TABLE OF THE ELEMENTS

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Section 12.3 Review

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1. Groups of the periodic table correspond to elements with: a. the same mass number. b. the same atomic number. c. similar chemical properties. d. similar numbers of neutrons. 2. Which element is the atom shown in Figure 12.21? 3. Name three elements that have similar chemical properties to oxygen. 4. The atomic mass unit (amu) is: a. the mass of a single atom of carbon. b. one-millionth of a gram. c. approximately the mass of a proton. d. approximately the mass of an electron. 5. Which element belongs in the empty space in Figure 12.22? 6. The outermost electrons of the element vanadium (atomic No. 23) are in which energy level of the atom? How do you know? 7. The elements fluorine, chlorine, and bromine are in which group of the periodic table? a. the alkali metals b. the oxygen-like elements c. the halogens d. the noble gases 8. Which three metals are in the third period (row) of the periodic table?

Figure 12.21: Question 2.

Figure 12.22: Question 5.

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12.4 Properties of the Elements

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Elements have a wide variety of physical and chemical properties. Physical properties include their state, temperatures of melting or boiling, solubility, and whether or not they conduct electricity or heat. Chemical properties include how elements react to form new compounds. In this section, you will learn about some of the properties of elements and how the periodic table helps you predict the properties of elements. You will also learn interesting facts about specific elements.

State of matter at room temperature Most elements Most of the pure elements are solid at room temperature. Only 11 of the 92 are solid at room naturally occurring elements are a gas, and 10 of the 11 are found on the far temperature right of the periodic table. Only two elements (Br and Hg) are liquid at room

temperature. What this tells us about intermolecular forces

An element is solid when intermolecular forces are strong enough to overcome the thermal motion of atoms. At room temperature, this is true for most of the elements. The noble gases and elements to the far right of the periodic table are the exceptions. These elements have completely filled or nearly-filled energy levels (Figure 12.23). When an energy level is completely-filled, the electrons do not interact strongly with electrons in other atoms, reducing intermolecular forces.

Figure 12.23: The noble gases have

completely filled energy levels. All of the elements that are a gas at room temperature have filled or nearly filled energy levels.

12.4 PROPERTIES OF THE ELEMENTS

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Periodic properties of the elements The pattern in We said earlier that the periodic table arranges elements with common melting and properties into groups (columns). The diagram below shows the melting and boiling points boiling points for the first 36 elements. The first element in each row (Li,

periodicity - the repeating pattern of chemical and physical properties of the elements.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

Na, and K) always has a low melting point. The melting (and boiling) points rise toward the center of each row and then decrease again. Periodicity The pattern of melting and boiling points is an example of periodicity.

Periodicity means the pattern or trend in properties repeats for each period (row) of the periodic table (Figure 12.24). Periodicity tells us a property is strongly related to the filling of electron energy levels. Melting points reflect the strength of intermolecular forces. The diagram below shows that intermolecular forces are strongest when energy levels are about half full (or half empty). Elements with half-filled energy levels have the greatest number of electrons that can participate in bonding.

Figure 12.24: One of these graphs

shows periodicity and the other does not. Can you tell which one is periodic? The top graph shows the energy it takes to remove an electron. The bottom graph shows the atomic weight.

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Thermal and electrical conductivity Metals are good electrical conductors

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Electricity is something we often take for granted because we use it every day. Fundamentally, electricity is the movement of electric charge, usually electrons. Some materials allow electrons to flow easily through them. If you connected a battery and a light bulb through one of these materials, the bulb would light. We call these materials electrical conductors. Copper and aluminum are excellent electrical conductors. Both belong to the family of metals, which are elements in the center and left-hand side of the periodic table (Figure 12.25). Copper and aluminum are used for almost all electrical wiring.

Metals are good conductors of heat

If you hold one end of a piece of copper wire and put the other end in hot water, the wire will quickly become warmer. This is because copper is a good conductor of heat as well as of electricity. Like copper, most metals are good thermal conductors. That is one reason pots and pans are made of metal. Heat from a stove can pass easily through the metal walls of a pot to transfer energy (heat) to the food inside.

Nonmetals are typically insulators

Elements to the far right of the periodic table are not good conductors of electricity or heat, especially since many of them are gases. Because they are so different from metals, these elements are called nonmetals. Nonmetals make good insulators. An insulator is a material that slows down or stops the flow of either heat or electricity. Air is a good insulator. Air is made of oxygen, nitrogen, and argon.

electrical conductor - a material that allows electricity to flow through it easily. thermal conductor - a material that allows heat to flow through it easily. insulator - a material that slows down or stops the flow of either heat or electricity.

Figure 12.25: Dividing the

periodic table into metals, metalloids, and nonmetals.

12.4 PROPERTIES OF THE ELEMENTS

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Metals and metal alloys Steel is an alloy When asked for an example of a metal, many people immediately think of of iron and steel. Steel is made from iron, which is the fourth most abundant element in carbon Earth’s crust. However, steel is not pure iron. Steel is an alloy. An alloy is a

steel - an alloy of iron and carbon.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

solid mixture of two or more elements. Most metals are used as alloys and not in their pure elemental form. Common steel contains mostly iron with a small percentage of carbon. Stainless steel and high-strength steel alloys also contain small percentages of other elements such as chromium, manganese, and vanadium. More than 500 different types of steel are in everyday use (Figure 12.26). Aluminum is Aluminum is a metal widely used for structural applications. Aluminum light alloys are not quite as strong as steel, but aluminum has one-third the density

of steel. Aluminum alloys are used when the product, such as an airplane, needs to be lightweight. The frames and skins of airplanes are built of aluminum alloys (Figure 12.27). Titanium is both strong and light

Titanium combines the strength and hardness of steel with the light weight of aluminum. Titanium alloys are used for military aircraft, racing bicycles, and other high-performance machines. Titanium is expensive because it is somewhat rare and difficult to work with.

Brass

Brass is a hard, gold-colored metal alloy. Ordinary (yellow) brass is an alloy of 72 percent copper, 24 percent zinc, 3 percent lead, and 1 percent tin. Hinges, door knobs, keys, and decorative objects are made of brass because brass is easy to work with. Because it contains lead, however, you should never eat or drink from anything made of ordinary (yellow) brass.

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Figure 12.26: Nails are made of

steel that contains 95 percent iron and 5 percent carbon. Kitchen knives are made of stainless steel that is an alloy containing vanadium and other metals.

Figure 12.27: This aircraft is made

mostly from aluminum alloys. Aluminum combines high strength and light weight.

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Carbon and carbon-like elements Carbon is an Carbon represents less than 1/100th of a percent of Earth’s crust by mass, yet important it is the element most essential for life on our planet. Virtually all the element for life molecules that make up plants and animals are constructed around carbon.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

The chemistry of carbon is so important, it has its own name: organic chemistry (Figure 12.28). Diamond and graphite

Pure carbon is found in nature in two very different forms. Graphite is a black solid made of carbon that becomes a slippery powder when ground up. Graphite is used for lubricating locks and keys. Diamond (shown left) is also pure carbon. Diamond is the hardest natural substance known and also has the highest thermal conductivity of any material. Diamond is so strong because every carbon atom is bonded to four neighboring atoms in a tetrahedral crystal.

Figure 12.28: Organic chemistry is

the chemistry of living organisms and is based on the element carbon.

Silicon Directly under carbon on the periodic table is the element silicon. Silicon is

the second most abundant element in Earth’s crust, second only to oxygen. Like carbon, silicon has four electrons in its outermost energy level. This means silicon can also make bonds with four other atoms. Sand, rocks, and minerals are predominantly made of silicon and oxygen (Figure 12.29). Most gemstones, such as rubies and emeralds, are compounds of silicon and oxygen with traces of other elements. In fact, when you see a glass window, you are looking at (or through) pure silica (SiO2). Silicon and semiconductors

Perhaps silicon’s most famous application today is for making semiconductors. Virtually every computer chip and electronic device uses crystals of very pure silicon. The area around San Jose, California, is known as Silicon Valley because of the electronics companies located there. Germanium, the element just below silicon on the periodic table, is also used to make semiconductors.

Figure 12.29: Sand and glass are

two common materials made of silicon.

12.4 PROPERTIES OF THE ELEMENTS

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Nitrogen, oxygen, and phosphorus Nitrogen and oxygen make up most of the atmosphere

Nitrogen is a colorless, tasteless, and odorless gas that makes up about 77 percent of Earth’s atmosphere. Oxygen makes up 21 percent of the atmosphere (Figure 12.30). Both oxygen and nitrogen gas consist of molecules with two atoms (N2, O2).

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

Oxygen in rocks Oxygen makes up only 21 percent of the atmosphere, however, oxygen is by and minerals far the most abundant element in Earth’s crust. Almost 46 percent of Earth’s

crust is oxygen (Figure 12.31). Because it is so reactive, all of this oxygen is bonded to other elements in rocks and minerals in the form of oxides. Silicon dioxide (SiO2), calcium oxide (CaO), aluminum oxide (Al2O3), and magnesium oxide (MgO) are common mineral compounds. Hematite (Fe2O3), an oxide of iron, is a common ore from which iron is extracted.

Composition of Earth’s atmosphere Water vapor 1%

Argon, carbon dioxide, and other gases 1.8%

Oxygen 20.60%

Nitrogen 76.6%

Liquid nitrogen With a boiling point of –196°C, liquid nitrogen is used for rapid freezing in

medical and industrial applications. A common treatment for skin warts is to freeze them with liquid nitrogen. Oxygen and Oxygen and nitrogen are crucial to living animals and plants. For example, nitrogen in proteins and DNA both contain nitrogen. Nitrogen is part of a key ecological living organisms cycle. Bacteria in soil convert nitrogen dioxide (NO2) in the soil into

Percentages by weight at 70% relative humidity

Figure 12.30: Earth’s atmosphere

is predominantly made up of nitrogen and oxygen.

complex proteins and amino acids. These nutrients are taken up by the roots of plants and later eaten by animals. Waste and dead tissue from animals are recycled by the soil bacteria that return the nitrogen to begin a new cycle.

Phosphorus

Directly below nitrogen in the periodic table is phosphorus. Phosphorus is a key ingredient of DNA, the molecule responsible for carrying the genetic code in all living creatures. By far, the most common use of phosphorus is in fertilizers. Ammonium phosphate is a common fertilizer made from ores that contain phosphorus. Figure 12.31: Oxygen makes up

46 percent of the mass of Earth’s crust. This enormous quantity of oxygen is bound up in rocks and minerals.

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Section 12.4 Review One of the elements with an atomic number less than 54 has the honor of being the first man-made element. Which element is this, and how was it discovered?

1. Name two elements that are liquid at room temperature.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

2. Which of the following is not true about the noble gases? a. They have completely filled energy levels. b. They have weak intermolecular forces. c. They do not bond with other elements in nature. d. They have boiling points above room temperature. 3. Describe what it means if a chemical or physical property is periodic. 4. Name three elements that are good conductors of electricity. 5. Name three elements that are good conductors of heat. 6. A metalloid is an element that: a. has properties between those of a metal and a nonmetal. b. is a good thermal conductor but a poor electrical conductor. c. is a good electrical conductor but a poor thermal conductor. d. belongs to the same group as carbon in the periodic table. 7. Steel is a metallic-like material but is not a pure element. What is steel?

Figure 12.32: Questions 11 and 12.

8. Almost all of the oxygen on the planet Earth is found in the atmosphere. Is this statement true or false? 9. This element is abundant in Earth’s crust and combines with oxygen to form rocks and minerals. Which element is it? 10. An element that has strong intermolecular forces is most likely to have: a. a boiling point below room temperature. b. a melting point below room temperature. c. a boiling point very close to its melting point. d. a very high melting point. 11. Which element in Figure 12.32 is likely to be the best conductor of electricity? 12. Which element in Figure 12.32 is likely to be the best insulator? 12.4 PROPERTIES OF THE ELEMENTS

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Chapter 12 Assessment

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

Vocabulary

Section 12.2

Select the correct term to complete the sentences.

8.

One of the allowed energies for electrons in an atom is known as a(n) ____.

9.

A(n) ____ shows the characteristic colors of light given off or absorbed by an element.

atomic number

electron

alkali metals

metals

atomic mass

mass number

energy level

spectrum

noble gases

thermal conductor

proton

spectrometer

conductors

periodicity

periodic table

10. An instrument that is used to separate light into spectral lines is a(n) ____.

halogens

electric charge

nonmetals

Section 12.3

neutron

isotopes

atomic mass unit

insulator

electrical conductor

11. The elements are organized into a chart known as the ____.

Section 12.1

1.

The sum of protons plus neutrons in the nucleus of an atom is known as the ____.

2.

_____ is a fundamental property of matter that can be either positive or negative.

3.

A very low mass particle with a negative charge, found in atoms, is called a(n) ____.

4.

A neutral particle with nearly the same mass as the proton is the ____.

5.

A particle with a positive charge is called a(n) ____.

6.

The number of protons in an atom, unique to each element, is known as the ____.

7.

Atoms of the same element containing different numbers of neutrons are called ____.

12. ____ are good conductors of heat and electricity. 13. ____ are poor conductors of heat and electricity. 14. The ____ is a unit scientists use to measure the mass of individual atoms. 15. The average mass of all of the known isotopes of an element is known as its ____. 16. Elements in the first group of the periodic table are called ____. 17. The ____ include fluorine, chlorine, and bromine. 18. The ____ do not naturally form chemical bonds with other elements. Section 12.4

19. The repeating pattern of chemical and physical properties of the elements is called ____. 20. A(n) ____ is a material that allows electricity to flow through it easily. 21. A(n) ____ is a material that allows heat to flow through it easily. 22. A(n) ____ is a material that slows down or stops the flow of either heat or electricity.

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Concepts

CHAPTER 12

11. Describe the difference between a period and a group on the periodic table.

Section 12.1

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

1.

How did Rutherford’s Thomson’s model?

from

12. Describe the difference between the mass number and the atomic mass of an element.

2.

What do the atomic number and mass number tell you about an atom?

3.

Summarize the characteristics of the electron, proton, and neutron, comparing their relative mass, charge, and location within the atom by completing the table below.

13. How does the energy level of an element on the periodic table compare to its period number?

model

of

the

atom

differ

Section 12.4

14. Name two properties that display periodicity across the periodic table.

Location in Atom

Charge

Relative Mass

15. Name three elements that are good conductors of both heat and electricity.

electron

?

?

1

proton

?

+1

?

16. Name three elements that are poor conductors but are good insulators of both heat and electricity.

neutron

?

?

?

Particle

Problems

Section 12.2

4.

Which particle in chemical properties?

an

atom

is

most

responsible

for

its

5.

Cite evidence that electrons are restricted to having only certain amounts of energy.

6.

How did Neils Bohr explain spectral lines?

7.

What is the difference between an electron in ground state and one in an excited state?

8.

What would occur if an electron were to move from a certain energy level to a lower energy level?

9.

Why can’t the position of an electron be determined with certainty?

Section 12.3

10. How might a substance be tested to determine whether it is an element?

Section 12.1

1.

For each of the nuclei shown below, do the following. a. b. c.

2.

Name the element. Give the atomic number. Give the mass number.

A neutral atom has seven protons and eight neutrons. Determine its: a. b. c.

mass number. atomic number. number of electrons. CHAPTER 12 ASSESSMENT

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Applying Your Knowledge

Section 12.2

3.

Which diagram below represents neon?

Section 12.1

1.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

4.

An atom has an atomic number of 6. Sketch a diagram that correctly represents the electron arrangement in energy levels around the nucleus. What is the name of this atom?

Section 12.2

2.

Section 12.3

5.

Identify each of the following as a metal (M), nonmetal (N), or metalloid (T). a. b. c. d. e.

includes most of the elements as solids they are dull, poor conductors, and brittle generally located on the right side of the periodic table ductile share properties between metals and nonmetals

Section 12.4

6.

b. 7.

Name the two elements that are found as liquids at room temperature. Name 5 elements (out of 11) that are found as gases at room temperature.

Name the following. a. b.

The element helium is a light gas that is very rare on Earth. In fact, helium was not discovered on this planet, but in the Sun. Astronomers saw a series of spectral lines in sunlight that did not match any known element on Earth. Researchers were then able to locate helium on Earth because they knew what its spectrum looked like. Research and draw the visible spectrum for helium, labeling the wavelength of each spectral line. Rank the spectral lines from highest energy to lowest energy. Also, find out where its name comes from.

Section 12.3

3.

Create a pie graph showing the elements classified as nonmetals, metalloids, and metals.

4.

List the elements of the periodic table for which the symbol does not match the name. For example, the symbol for lead is Pb. Choose any three of those elements and find out where the symbols come from.

Most elements occur as solids at room temperature. a.

Make a poster illustrating the different models of the atom that scientists have proposed since the 1800s. Explain how each model reflects the new knowledge that scientists gained through their experiments. When possible, comment on what scientists learned about charge, mass, and location of subatomic particles.

Section 12.4

5.

Suppose the periodic table arranged periods 1 to 4 in order of increasing average atomic mass instead of increasing atomic number. Would this arrangement show periodicity? Explain your answer.

The two most abundant gases and their approximate percentage of occurrence in Earth’s atmosphere. The most abundant element in Earth’s crust and its percentage of occurrence.

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CHAPTER

13

CHAPTER 13

Compounds FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

What does the word chemical mean to you? Does it make you think of strange, bubbling concoctions in test tubes, mixed by a scientist in a white lab coat? You might have heard or read about a hazardous chemical spill, or you might have experimented with chemicals in a science lab. Would it surprise you to know that you are a mixture of chemicals? So are a block of wood and a glass of orange juice. The scientific term for a chemical is compound. The word compound is used to describe any substance that is composed of atoms bonded together. Water (H2O) and sodium chloride (NaCl) are compounds. Your body contains thousands of different compounds. While some compounds are hazardous to your health, many—such as proteins and carbohydrates—are necessary for growth and survival. All of the millions upon millions of different compounds are made of only 92 elements combined in different ways. Just as you can spell thousands of words with the same 26 letters, you can make all the compounds from 92 elements.

4 What does the chemical formula H2O mean? 4 Why do elements tend to combine to form compounds?

4 What compounds is your body made of?

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CHAPTER 13

COMPOUNDS

13.1 Chemical Bonds and Electrons

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Most matter exists as compounds, not as pure elements. That’s because most pure elements are chemically unstable. They quickly form chemical bonds with other elements to make compounds. For example, water (H2O) is a compound of hydrogen and oxygen. The salt used in food is a compound that contains two elements, sodium and chlorine, that are poisonous by themselves. In this section, you will learn why and how the atoms of elements form compounds.

chemical bond - a bond that

Covalent bonds

chemical formula - a

Electrons form A chemical bond forms when atoms transfer or share electrons. Almost all chemical bonds elements form chemical bonds easily. This is why most of the matter you

experience is in the form of compounds.

forms when atoms transfer or share electrons.

covalent bond - a chemical bond formed by atoms that are sharing one or more electrons. representation of a compound that includes the symbols and ratios of atoms of each element in the compound.

Covalent bonds A covalent bond forms when atoms share electrons. A group of atoms held

together by covalent bonds is called a molecule. The bonds between oxygen and hydrogen in a water molecule are covalent bonds (Figure 13.1). There are two covalent bonds in a water molecule, between the oxygen and each of the hydrogen atoms. Each bond represents a shared electron pair. Chemical A molecule’s chemical formula tells you the ratio of atoms of each element formulas in the compound. For example, the chemical formula for water is H2O. The

subscript 2 indicates there are two hydrogen atoms in a water molecule. No subscript after the O indicates there is only one oxygen atom for every two hydrogen atoms in the molecule. Reading a chemical formula Element symbol indicates hydrogen

H2 O

Subscript means there are two hydrogen atoms in each molecule Water molecule

Element symbol indicates oxygen

Figure 13.1: In a covalent bond,

electrons are shared between atoms.

No subscript means there is one oxygen atom in each molecule

Ratio of two hydrogen atoms to one oxygen atom in the compound

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Ionic bonds An ion is a Not all compounds are made of molecules. For example, sodium chloride charged atom (NaCl) is a compound of sodium (Na) and chlorine (Cl) in a ratio of one

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sodium atom per chlorine atom. The difference is that in sodium chloride, the electron is transferred (instead of shared) from the sodium atom to the chlorine atom. When atoms gain or lose an electron, they become ions. An ion is a charged atom. By losing an electron, the sodium atom becomes a sodium ion with a charge of +1. By gaining an electron, the chlorine atom becomes a chloride ion with a charge of –1. (Note that when chlorine becomes an ion, the name changes to chloride.)

ion - an atom (or group of atoms) that has an electric charge other than zero, created when an atom (or group of atoms) gains or loses electrons. ionic bond - a bond that transfers one or more electrons from one atom to another, resulting in attraction between oppositely-charged ions.

Ionic bonds Sodium and chlorine form an ionic bond because the positive sodium ion is

attracted to the negative chloride ion. Ionic bonds are bonds in which one or more electrons are transferred from one atom to another. Ionic compounds do not form molecules

Unlike covalent bonds, ionic bonds are not limited to a single pair of atoms. In sodium chloride, each positive sodium ion is attracted to all of the neighboring chloride ions (Figure 13.2). Likewise, each chloride ion is attracted to all the neighboring sodium ions. Because the bonds are not just between pairs of atoms, ionic compounds do not form molecules. In an ionic compound, each atom bonds with all of its neighbors through attraction between positive and negative charges.

Sodium and Chlorine form an ionic compound Chloride ion

Sodium ion

The chemical Like covalent compounds, ionic compounds have fixed ratios of elements. formula for ionic For example, there is one sodium ion per chloride ion in sodium chloride compounds (NaCl). This means we can use chemical formulas for ionic compounds just

like we do for covalent compounds. Ions might be Sodium chloride involves the transfer of one electron. However, ionic multiply charged compounds may also be formed by the transfer of two or more electrons.

A good example is magnesium chloride (MgCl2). The magnesium atom gives up two electrons to become a magnesium ion with a charge of +2. Each chlorine atom gains one electron to become a chloride ion with a charge of –1. The ion charge is written as a superscript after the element symbol (Mg2+, Cl–, Fe3+, etc.).

Figure 13.2: Sodium chloride is an ionic compound in which each positive sodium ion is attracted to all of its negative–chloride ion neighbors and vice versa.

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Why chemical bonds form Atoms form bonds to reach a lower energy state

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It takes energy to pull tape off of a surface. Similarly, it also takes energy to separate atoms that are bonded together. If it takes energy to separate bonded atoms, then the same amount of energy must be released when the bond forms. Energy is released when chemical bonds form. Energy is released because atoms that have bonded together have less total energy than the same atoms separately. Like a ball rolling downhill, atoms form compounds because the atoms have lower energy when they are together in compounds. For example, one carbon atom and four hydrogen atoms have more total energy apart than they do when combined in a methane molecule (Figure 13.3).

Chemical All elements, except the noble gases, form chemical bonds. However, some reactivity elements are much more reactive than others. In chemistry, reactive means

an element easily forms chemical bonds, often releasing energy. For example, sodium is a highly-reactive metal. Chlorine is a highly-reactive gas. If pure sodium and pure chlorine are placed together, a violent explosion occurs as the sodium and chlorine combine. The energy of the explosion is the energy given off by the formation of the chemical bonds.

Figure 13.3: The methane (CH4)

molecule has lower total energy than four separate hydrogen atoms and one separate carbon atom.

The noble gases (He, Ne, Ar, etc.) are called inert because they do not ordinarily react with anything. You can put sodium in an atmosphere of pure helium and nothing will happen. However, scientists have found that a few noble gases do form compounds in very special circumstances. Research this topic and see if you can find a compound involving a noble gas.

Some elements are more reactive than others

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The closer an element is to having the same number of electrons as a noble gas, the more reactive the element is. The alkali metals are very reactive because they are just one electron away from the noble gases. The halogens are also very reactive because they are also one electron away from the noble gases. The beryllium group and the oxygen group are less reactive because each element in these groups is two electrons away from a noble gas.

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Valence electrons Compounds contain particular ratios of elements

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The discovery of energy levels in the atom solved a 2,000-year-old mystery. Why do elements combine with other elements only in particular ratios (or not at all)? For example, why do two hydrogen atoms bond with one oxygen atom to make water? Why isn’t there a molecule with three (H3O) or even four (H4O) hydrogen atoms? Why does sodium chloride have a precise ratio of one sodium ion to one chloride ion? Why don’t helium, neon, and argon form compounds with any other elements? The answers have to do with the electrons in the outermost energy levels.

valence electrons - the electrons in the highest unfilled energy level of an atom.

What are Chemical bonds are formed only between the electrons in the highest unfilled valence energy level. These electrons are called valence electrons. You can think of electrons? valence electrons as the outer “skin” of an atom. Electrons in the inner (filled)

energy levels do not interact with other atoms because they are shielded by the valence electrons. For example, chlorine has seven valence electrons. The first 10 of chlorine’s 17 electrons are in the inner (filled) energy levels (Figure 13.4). Most elements bond to reach eight valence electrons

It turns out that eight is the stable number for chemical bonding. All the elements heavier than boron form chemical bonds to acquire a configuration with eight valence electrons. For example, sodium and chlorine form an ionic bond so each can have a configuration of eight valence electrons (Figure 13.5). Eight is a stable number because eight electrons completely fill a part of the outermost energy level. The noble gases already have a stable number of eight valence electrons. They don’t form chemical bonds because they don’t need to react to achieve this stable number.

Light elements bond to reach two valence electrons

For elements with an atomic number of five (boron) or less, the stable number is two instead of eight. For these light elements, two valence electrons completely fill the first energy level. The elements H, He, Li, Be, and B form bonds to reach the stable number of two valence electrons.

Hydrogen is Because of its single electron, hydrogen can also have zero valence electrons. special Zero is a stable number for hydrogen, as well as two. This flexibility makes

hydrogen a very “friendly” element; hydrogen can bond with almost any other element.

Figure 13.4: Chlorine has 7 valence electrons. The other 10 electrons are in filled (inner) energy levels.

Figure 13.5: Chlorine and sodium

bond so each can reach a configuration with eight valence electrons.

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Valence electrons and the periodic table Period 2 The illustration below shows how the electrons in the elements in the second elements period (lithium to neon) fill the energy levels. Two of lithium’s three

electrons go in the first energy level. Lithium has one valence electron because its third electron is the only one in the second energy level.

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Each successive element has one more valence electron

Going from left to right across a period, each successive element has one more valence electron. Beryllium has two valence electrons, boron has three, and carbon has four. Each element in the second period adds one more electron until all eight spots in the second energy level are full at atomic number 10, which is neon, a noble gas. Neon has eight valence electrons.

Figure 13.6: Oxygen has six valence electrons and hydrogen has two. In a water molecule, each hydrogen supplies one electron to make a total of eight valence electrons.

Bonding Oxygen has six valence electrons. To get to the magic number of eight,

oxygen needs to add two electrons. Oxygen forms chemical bonds that provide these two extra electrons. For example, a single oxygen atom combines with two hydrogen atoms because each hydrogen can supply only one electron (Figure 13.6). Double bonds Carbon has four valence electrons. That means two oxygen atoms can bond share two with a single carbon atom, with each oxygen sharing two of carbon’s four electrons valence electrons. The bonds in carbon dioxide (CO2) are double bonds

because each bond involves four electrons (Figure 13.7), two from carbon and two from oxygen. Each oxygen has two lone pairs of electrons (see the in-text diagram on the next page).

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Figure 13.7: Carbon forms two double bonds with oxygen to make carbon dioxide.

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Lewis dot diagrams Dot diagrams of A Lewis dot diagram is a way to represent an atom’s valence electrons. the elements A dot diagram shows the element symbol surrounded by one to eight dots

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representing its valence electrons. Each dot represents one electron. Lithium has one dot, beryllium has two, boron has three, etc. Figure 13.8 shows dot diagrams for some of the elements.

Lewis dot diagram - a method for representing an atom’s valence electrons using dots around the element symbol.

Dot diagrams of Each element forms bonds to reach one of the stable numbers of valence molecules electrons: two or eight. In dot diagrams of a complete molecule, each element

symbol has either two or eight dots around it. Both configurations correspond to completely filled (or empty) energy levels.

Example dot Carbon has four dots and hydrogen has one. One carbon atom bonds with four diagrams hydrogen atoms because this allows the carbon atom to have eight valence

electrons (eight dots)—four of its own and four shared with four hydrogen atoms. The picture above shows dot diagrams for carbon dioxide (CO2), ammonia (NH3), methane (CH4), and carbon tetrachloride (CCl4). The formation of A sodium atom is neutral with 11 positively charged protons and 11 negatively an ionic bond charged electrons. When sodium loses one electron, it has 11 protons (+) and

10 electrons (–) and becomes an ion with a net charge of +1. This is because it now has one more positive charge than its negative charges. A chlorine atom is neutral with 17 protons and 17 electrons. When chlorine gains one electron to have a stable eight electrons, it has 17 protons (+) and 18 electrons (–) and becomes an ion with a charge of –1. This is because it has gained one negative charge. When sodium and chlorine form an ionic bond, the resulting compound is neutral (+1) + (–1) = 0.

Figure 13.8: Dot diagrams for some of the elements.

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Section 13.1 Review

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1. Molecules are held together by: a. ionic bonds. b. covalent bonds. c. both a and b. 2. How many atoms of chlorine (Cl) are in the carbon tetrachloride molecule (CCl4)? 3. Which of the compounds below has a chemical formula of C3H8?

Figure 13.9: Question 6.

4. True or false: Ionic compounds do not form molecules. 5. Atoms form chemical bonds using: a. electrons in the innermost energy level. b. electrons in the outermost energy level. c. protons and electrons. 6. Which of the diagrams in Figure 13.9 shows an element with three valence electrons? What is the name of this element? 7. Name two elements that have the Lewis dot diagram shown in Figure 13.10. 8. Draw dot diagrams for the following. a. silicon b. xenon c. calcium d. H2O

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Figure 13.10: Question 7.

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13.2 Chemical Formulas In the previous section, you learned how and why atoms form chemical bonds with one another. You also learned that atoms combine in certain ratios with other atoms. These ratios determine the chemical formula for a compound. In this section, you will learn how to write the chemical formulas for compounds. You will also learn how to name compounds based on their chemical formulas.

oxidation number - a quantity that indicates the charge on an atom when it gains, loses, or shares electrons during bond formation.

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Chemical formulas and oxidation numbers Ionic Recall that the chemical formula for sodium chloride is NaCl. This formula compounds indicates that every formula unit of sodium chloride contains one atom of

sodium and one atom of chlorine; it’s a 1:1 ratio. Why do sodium and chlorine combine in a 1:1 ratio? When sodium loses an electron, it becomes an ion with a charge of +1. When chlorine gains an electron, it becomes an ion with a charge of –1. When these two ions combine to form an ionic bond, the net electrical charge is zero (Figure 13.11). This is because (+1) + (–1) = 0.

All compounds have an electrical charge of zero. This means they are neutral. Oxidation A sodium atom always ionizes to become Na+ (a charge of +1) when it numbers combines with other atoms to make a compound. Therefore, we say that sodium has an oxidation number of 1+. An oxidation number indicates the

electric charge on an atom when electrons are lost, gained, or shared during chemical bond formation. Notice that the convention for writing oxidation numbers is the opposite of the convention for writing the charge. When writing the oxidation number, the positive (or negative) symbol is written after the number, not before it. What is chlorine’s oxidation number? If you think it is 1–, you are right. This is because chlorine gains one electron, one negative charge, when it bonds with other atoms. Figure 13.12 shows the oxidation numbers for some of the elements.

Figure 13.11: Sodium and chlorine combine in a 1:1 ratio.

Atom

Electrons gained or lost

Oxidation number

K

loses 1

1+

Mg

loses 2

2+

Al

loses 3

3+

P

gains 3

3–

Se

gains 2

2–

Br

gains 1

1–

Figure 13.12: Oxidation numbers of some common elements.

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Predicting oxidation numbers from the periodic table Valence electrons and oxidation numbers

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In the last section, you learned that you can tell how many valence electrons an element has by its location on the periodic table. If you can determine how many valence electrons an element has, you can predict its oxidation number. An oxidation number corresponds to the need of an atom to gain or lose electrons (Figure 13.13).

Beryllium has an For example, locate beryllium (Be) on the periodic table below. It is in the oxidation second column, or Group 2, which means beryllium has two valence number of 2+ electrons. Will beryllium get rid of two electrons, or gain six in order to

obtain a stable number? Of course, it is easier to lose two electrons. When these two electrons are lost, beryllium becomes an ion with a charge of +2. Therefore, the most common oxidation number for beryllium is 2+. In fact, the most common oxidation number for all elements in Group 2 is 2+. The periodic The periodic table below shows the most common oxidation numbers of table most of the elements. The elements known as transition metals (in the

Oxidation number of 1+ (need to lose 1 electron)

K

H

19

1

Li 3

Oxidation number of 2+ (need to lose 2 electrons)

Be 4

middle of the table) have variable oxidation numbers.

Mg 12

Ca 20

Oxidation number of 2– (need to gain 2 electrons)

O 8

S

16

Se 34

Oxidation number of 1– (need to gain 1 electron)

Cl 17

F 9

Br 35

Figure 13.13: Oxidation numbers correspond to the need to gain or lose electrons.

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Predicting ionic and covalent bonds Why bonds are Whether a compound is ionic or covalently bonded depends on how much ionic or covalent each element “needs” an electron to get to a magic number (two or eight).

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Elements that are very close to the noble gases tend to give or take electrons rather than share them. These elements often form ionic bonds rather than covalent bonds. Sodium chloride As an example, sodium has one electron more than the noble gas neon. is ionic Sodium has a very strong tendency to give up that electron and become a

positive ion. Chlorine has one electron less than argon. Therefore, chlorine has a very strong tendency to accept an electron and become a negative ion. Sodium chloride is an ionic compound because sodium has a strong tendency to give up an electron, and chlorine has a strong tendency to accept an electron. Forming ionic On the periodic table, strong electron donors are on the left side (alkali compounds metals). Strong electron acceptors are on the right side (halogens). The farther

separated two elements are on the periodic table, the more likely they are to form an ionic compound. Forming Covalent compounds form when elements have roughly equal tendency to covalent accept electrons. Elements that are nonmetals and therefore close together on compounds the periodic table tend to form covalent compounds with each other because

You can use the periodic table to predict whether two elements will form ionic or covalent compounds. For example, potassium combines with bromine to make potassium bromide (KBr). Are the chemical bonds in this compound likely to be ionic or covalent? To solve this problem, look at the periodic table at the left. K is a strong electron donor and Br is a strong electron acceptor. KBr is an ionic compound because K and Br are from opposite sides of the periodic table. Now you try the following. 1. Are the chemical bonds in silica (SiO2) likely to be ionic or covalent? 2. Are the chemical bonds in calcium fluoride (CaF2) likely to be ionic or covalent?

they have approximately equal tendency to accept electrons. Compounds involving carbon, silicon, nitrogen, and oxygen are often covalent.

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Oxidation numbers and chemical formulas Oxidation numbers in a compound add up to zero

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When elements combine in molecules and ionic compounds, the total electric charge is always zero. This is because any electron donated by one atom is accepted by another. The rule of zero charge is easiest to apply using oxidation numbers. The total of all the oxidation numbers for all the atoms in a compound must be zero. This important rule allows you to predict many chemical formulas.

The oxidation numbers for all the atoms in a compound must add up to zero. Example: To see how this works, consider the compound carbon tetrachloride (CCl4). carbon Carbon has an oxidation number of 4+. Chlorine has an oxidation number of tetrachloride 1–. It takes four chlorine atoms to cancel carbon’s 4+ oxidation number.

Element

Oxidation number

Copper (I)

Cu+

Copper (II)

Cu2+

Iron (II)

Fe2+

Iron (III)

Fe3+

Chromium (II)

Cr2+

Chromium (III)

Cr3+

Lead (II)

Pb2+

Lead (IV)

Pb4+

Figure 13.14: In some cases, roman numerals are used to distinguish the oxidation number for an element with multiple numbers.

Most elements have more than one possible oxidation number

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Some periodic tables list multiple oxidation numbers for most elements. This is because more complex bonding is possible. When multiple oxidation numbers are shown, the most common one is usually in bold type. For example, nitrogen has possible oxidation numbers of 5+, 4+, 3+, 2+, and 3–, even though 3– is the most common (shown at the right). In some reference materials, roman numerals are used to distinguish the oxidation number. Figure 13.14 shows a few of these elements.

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Predicting chemical formulas for binary compounds Rules for predicting chemical formulas

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Once you know how to find the oxidation numbers of the elements, you can predict the chemical formulas of binary compounds (Figure 13.15). A binary compound is a compound that consists of two elements. Sodium chloride (NaCl) is a binary compound. To predict and write the chemical formula of a binary compound, use the following rules. 1. Write the symbol for the element that has a positive oxidation number first. Do not write the oxidation number. 2. Write the symbol for the element that has a negative oxidation number second. Do not write the oxidation number. 3. Find the least common multiple between the oxidation numbers to make the sum of their charges equal zero. Use the numbers you multiply the oxidation numbers by as subscripts.

binary compound - a chemical compound that consists of two elements.

Solving Problems: Binary Compounds

1. Looking for: 2. Given: 3. Relationships: 4. Solution:

Iron (III) (3+) and oxygen (2–) combine to form a compound. Predict the chemical formula of this compound. Chemical formula for a binary compound Elements and oxidation numbers: Fe (III) = 3+ and O = 2– Write the subscripts so that the sum of the oxidation numbers equals zero. The least common multiple between 3 and 2 is 6. For iron (III): 2 × (3+) = 6+. For oxygen: 3 × (2–) = 6 – (6+) + (6–) = 0. The chemical formula is Fe2O3 because it took 2 Fe atoms and 3 O atoms to make a neutral compound.

Figure 13.15: The steps to predict the chemical formula of a binary compound.

Your turn...

a. Predict the chemical formula of the compound containing beryllium (2+) and fluorine (1–). b. Predict the chemical formula of the compound containing lead (IV) and sulfur (2–).

a. BeF2 b. PbS2

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Compounds with more than two elements Not all compounds are made of only two types of atoms

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Have you ever taken an antacid for an upset stomach? Many antacids contain calcium carbonate, or CaCO3. How many types of atoms does this compound contain? You are right if you said three: calcium, carbon, and oxygen. Some compounds contain more than two elements. Some of these types of compounds contain polyatomic ions. A polyatomic ion contains more than one atom. The prefix poly- means “many.” Figure 13.16 lists some common polyatomic ions. The example below illustrates how to write chemical formulas for these types of compounds.

Solving Problems: More Chemical Formulas Aluminum (3+) combines with sulfate (SO42– ) or the sulfate ion to make aluminum sulfate. Write the chemical formula for aluminum sulfate.

polyatomic ion - an ion that contains more than one atom. Oxidation number

Name of ion

Formula

1+

Ammonium

NH4+

1–

Acetate

C2H3O2–

2–

Carbonate

CO32–

2–

Chromate

CrO42–

1–

Hydrogen carbonate

HCO3–

1+

Hydronium

H3O+

1–

Hydroxide

OH–

1–

Nitrate

NO3–

1. Looking for:

Chemical formula for a compound containing more than two elements

2–

Peroxide

O22–

2. Given:

Al 3+ and SO42–

3–

Phosphate

PO43–

2–

Sulfate

3. Relationships:

The oxidation numbers for all of the atoms in the compound must add up to zero.

SO42–

2–

Sulfite

SO32–

4. Solution:

Two aluminum ions have a charge of 6+. It takes three sulfate ions to get a charge of 6–. To write the chemical formula, parentheses must be placed around the polyatomic ion. The subscript is placed on the outside of the parentheses. The formula is: Al2(SO4)3

Figure 13.16: Oxidation numbers of some common polyatomic ions.

a. H2O2 Your turn...

b. Ca3(PO4)2

a. Write the chemical formula for hydrogen (1+) peroxide (O22– ). b. Write the chemical formula for calcium (2+) phosphate (PO43– ).

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Naming compounds Naming binary By using the following rules, you can name a binary ionic compound if you ionic are given its chemical formula. A binary ionic compound is held together compounds by ionic bonds. Binary molecular compounds consist of covalently-bonded

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atoms. Naming binary molecular compounds is discussed in the Solve It! on the next page. To name a binary ionic compound: 1. Write the name of the first element. 2. Write the root name of the second element. 3. Add the suffix -ide to the root name. What is the MgBr2 is magnesium (name of first element) plus -brom (root name of second name of MgBr2? element) plus -ide = magnesium bromide (Figure 13.17, top). If the positive element has more than one oxidation number, you must first figure out that number. Then, use a roman numeral to indicate the oxidation number. For example, FeCl3 = iron (III) chloride because iron (III) has a charge of 3+. It would take three chloride ions (oxidation number = 1–) to make the sum of the oxidation numbers equal zero. Naming Naming compounds with polyatomic ions is easy. compounds with polyatomic ions 1. Write the name of the first element or polyatomic ion first. Use the

periodic table or ion chart (Figure 13.16, previous page) to find its name. 2. Write the name of the second element or polyatomic ion second. Use the periodic table or ion chart (Figure 13.16, previous page) to find its name. If the second one is an element, use the root name of the element with the suffix -ide. What is the NH4Cl is ammonium (the name of the polyatomic ion from Figure 13.16) plus name of NH4Cl? -chlor (root name of the second element) plus -ide = ammonium chloride (Figure 13.17, bottom). Again, if an element has more than one oxidation number, you must figure out that number. For example, Cu2SO3 would be named copper (I) sulfite and CuSO3 would be copper (II) sulfite.

Figure 13.17: Naming compounds. 13.2 CHEMICAL FORMULAS

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Section 13.2 Review

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1. The oxidation number is: a. the number of oxygen atoms an element bonds with. b. the positive or negative charge acquired by an atom in a chemical bond. c. the number of electrons involved in a chemical bond. 2. Name three elements that have an oxidation number of 3+. 3. What is the oxidation number for the elements in Group 17? 4. When elements form a molecule, what is true about the oxidation numbers of the atoms in the molecule? a. The sum of the oxidation numbers must equal zero. b. All oxidation numbers from the same molecule must be positive. 5. True or false: All oxidation numbers from the same molecule must be negative. 6. Which of the following elements will bond with oxygen, resulting in a 1:1 ratio of oxygen and the element? a. lithium b. boron c. beryllium d. nitrogen 7. Name the following compounds. a. NaHCO3 b. BaCl2 c. LiF d. Al(OH)3 e. SrI 8. Would a bond between potassium and iodine most likely be covalent or ionic? Explain your answer.

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Naming Binary Molecular Compounds Naming binary molecular compounds is similar to the methods used in naming binary ionic compounds described on the previous page. However, in this case, the number of each type of atom (the subscript) is also specified in the name of the compound. From 1 to 10, the Greek prefixes are: mono, di, tri, tetra, penta, hexa, hepta, octa, nona, deca. To name a binary molecular compound, specify the number of each type of atom using the Greek prefix. As with binary ionic compounds, the ending of the name of the second element in the compound is modified by adding the suffix -ide as shown in the example below.

If the first element in the compound does not have a subscript, do not use a Greek prefix for that element, but use one for the second element. For example, CO2 is carbon dioxide. Name the following binary molecular compounds. (a) CCl4

(b) N4O6

(c) S2F10

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13.3 Molecules and Carbon Compounds

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Do you know which compounds you are made of? Excluding water, 91 percent of your body mass consists of compounds that are made up of only four elements: carbon, oxygen, nitrogen, and hydrogen. Of those four, carbon is the largest part at 53 percent. The molecules of some of those compounds are large and complex. In this section, you will learn more about molecules and why carbon is such an important element in the molecules of living things.

Structural diagrams of molecules Molecules are represented using structural diagrams

In addition to the elements that it is made of, the shape of a molecule is also important to its function and properties. For this reason, we use structural diagrams to show the shape and arrangement of atoms in a molecule. Single bonds between atoms are shown with solid lines connecting the element symbols. Double and triple bonds are shown with double and triple lines. Figure 13.18 shows the chemical formula and structural diagram for some compounds.

Properties come Both the chemical formula and the structure of the molecules determine the from the properties of a compound. For example, aspirin, a pain reducer, is a molecule molecule made of carbon, hydrogen, and oxygen according to the chemical formula

C9H8O4. The same 21 atoms in aspirin can be combined in other structures with the same chemical formula. But the resulting molecules do not have the pain-relieving properties of aspirin. Figure 13.18: Chemical formulas and structural diagrams.

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Carbon molecules Many Most of the compounds you are made of contain the element carbon. compounds Organic chemistry is the branch of chemistry that specializes in carbon contain carbon compounds, also known as organic molecules. But carbon compounds are

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not only found in living things. Plastic, rubber, and gasoline are carbon compounds. In fact, there are over 12 million known carbon compounds! Carbon is unique among the elements because a carbon atom can form chemical bonds with other carbon atoms in long chains or rings. Some carbon compounds contain several thousand carbon atoms.

organic chemistry - a branch of chemistry that specializes in the study of carbon compounds, also known as organic molecules. polymer - a compound that is composed of long chains of smaller molecules.

Carbon forms Carbon atoms have four valence electrons and can share one or more of these ring and chain electrons to make covalent bonds with other carbon atoms or as many as four molecules other elements. Carbon molecules come in three basic forms: straight chains,

branching chains, and rings. The three basic shapes can be combined in the same molecule. Ring

Chain

Branched

H H

C C

C

C H

H H

C C

H

H

H

H

H

C

C

C

C

H

H

H

H

H

N H

Benzene

C6H6

C

C

C

H

O H

H

C

Butane

C4H10

O

H H

H

H

H

C H

H

H

Valine

C5H11NO2 Polymers A polymer is a compound that is composed of long chains of smaller,

repeating molecules. Plastic (polyethylene) is a polymer that is composed of long chains of a smaller molecule called ethylene. You can think of a plastic molecule as a chain of paperclips. Each paperclip represents an ethylene molecule (Figure 13.19).

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Figure 13.19: Plastic is a polymer made of long chains of ethylene molecules.

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Carbohydrates The four types Scientists classify the organic molecules in living things into four basic of biological groups: carbohydrates, proteins, fats, and nucleic acids. All living things molecules contain all four types of molecules. And each type of molecule includes

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thousands of different compounds, some specific to plants, some to animals. In the past few decades, biotechnology has revealed much more about the rich chemistry of living things. What are Carbohydrates are energy-rich compounds made of carbon, hydrogen, and carbohydrates? oxygen. Carbohydrates are classified as sugars and starches. Sugars are

smaller molecules. Glucose is a simple sugar made of 6 carbon, 12 hydrogen, and 6 oxygen atoms (Figure 13.20). The sugar you use to sweeten food is called sucrose. A sucrose molecule is made of two simple sugars. Starches are Starches are long chains of glucose molecules joined together to make natural chains of sugar polymers. Because starches are larger molecules, they are slower to break

down in the body and therefore can provide energy for a longer period than sugars. Corn, potatoes, and wheat contain substantial amounts of starches. Cellulose Cellulose is the primary molecule in plant fibers, including wood. The long-

carbohydrates - a group of energyrich compounds that are made of carbon, hydrogen, and oxygen; they include sugars and starches. Glucose molecule H

H

H

C C

C H

H

H

C

H

H

C

O

C O

O H

H

H

Figure 13.20: A glucose molecule.

chain molecules of cellulose are what give wood its strength. Like starch, cellulose is a polymer made of thousands of glucose molecules. However, in a starch, all the glucose units are the same orientation. In cellulose, alternate glucose units are inverted. This difference makes cellulose difficult for animals to digest. Trees grow so large partly because so few animals can digest wood. 13.3 MOLECULES AND CARBON COMPOUNDS

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H O

O

O

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Lipids Lipids Like carbohydrates, lipids are energy-rich compounds made of carbon,

lipids - a group of energy-rich

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hydrogen, and oxygen (Figure 13.21). Lipids include fats, oils, and waxes. Lipids are made by cells to store energy for long periods of time. Animals that hibernate (sleep through the winter) live off of the fat stored in their cells. Polar bears have a layer of fat beneath their skin to insulate them from very cold temperatures. Can you name some foods that contain lipids? Cholesterol is a Like fat, cholesterol is listed on food labels. Cholesterol is a lipid that makes lipid up part of the outer membrane of your cells. Your liver normally produces

enough cholesterol for your cells to use. Too much cholesterol in some people’s diet might cause fat deposits on their blood vessels. This might lead to coronary artery disease. Foods that come from animals are often high in cholesterol. Saturated fats A lipid molecule has a two-part structure. The first part is called glycerol.

Attached to the glycerol are three carbon chains. In a saturated fat, the carbon atoms are surrounded by as many hydrogens as possible. (See graphic below, left.) Unsaturated fats An unsaturated fat has fewer hydrogen atoms than it could have, because

double bonds exist between some of the carbon atoms. (See graphic below, right.) Chemical processing of food adds some hydrogen to unsaturated fats in a process called hydrogenation. While partially hydrogenated fats have a longer shelf life, research is showing that consuming them might be unhealthy. Double bond O C O

Saturated fat

H

H

H

H

H

H

H

H

H

C

C

C

C

C

C

C

C

C

H

H

H

H

H

H

H

H

H

O C

H

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unsaturated fat - a fat that has fewer hydrogen atoms because double bonds exist among some of the carbon atoms.

Lipid molecule H H

H

H O H C H C H C C H C H C H H C O H C H C H H

H

H H H C

C

H C H H C

H

H H C H C H

H

C H H H C H C H H

Unsaturated fat

Double bond D

O

saturated fat - a fat in which the carbon atoms are surrounded by as many hydrogen atoms as possible.

Figure 13.21: A lipid molecule.

H

H

compounds that are made of carbon, hydrogen, and oxygen; they include fats, waxes, and oils.

H

H

H

H

H

H

C

C

C

C

C

C

H

H

H

H

H

H

H

C

H

C

C

H

H

Double bond

H

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Proteins Proteins Proteins are very large molecules made of carbon, hydrogen, oxygen,

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nitrogen, and sometimes sulfur. Many animal parts such as hair, fingernails, muscle, and skin contain proteins. Hemoglobin is a protein in your blood that carries oxygen to your cells. Enzymes are also proteins. An enzyme is a type of protein that cells use to speed up chemical reactions in living things. Proteins are Protein molecules are made of smaller molecules called amino acids. Your made of amino cells combine different amino acids in various ways to make different acids proteins. There are 20 amino acids used by cells to make proteins. You can

compare amino acids to letters in the alphabet. Just as you can spell thousands of words with just 26 letters, you can make thousands of different proteins from just 20 amino acids (Figure 13.22).

proteins - a group of very large molecules made of carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur.

enzyme - a type of protein used to speed up chemical reactions in living things. amino acids - a group of smaller molecules that are the building blocks of proteins.

Shape and Only certain parts of a protein are function chemically active. The shape of a

protein determines which active sites are exposed. Many proteins work together by fitting into each other like a lock and key. This is one reason why proteins that perform a function in one organism cannot perform the same function in another organism. For example, a skin protein from an animal cannot replace a skin protein from a human. Amino acids from food are used to build proteins

Food supplies new proteins that a body needs to live and grow. However, proteins from one organism cannot be directly used by another. Fortunately, the same 20 amino acids are found in proteins from almost all living things. In your body, digestion breaks down food protein into its component amino acids. Cells reassemble the amino acids into new proteins suitable for your body’s needs.

Figure 13.22: Proteins are made of smaller molecules called amino acids.

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DNA and nucleic acids What are nucleic Nucleic acids are compounds made of long, repeating chains called acids? nucleotides. Nucleotides are made of carbon, hydrogen, oxygen, nitrogen,

and phosphorus. Each nucleotide contains a sugar molecule, a phosphate molecule, and a base molecule, as shown in the graphic below.

nucleic acids - compounds made of long, repeating chains of smaller molecules called nucleotides.

DNA - a type of nucleic acid that

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contains the genetic code for an organism.

DNA base-pairing A pairs with T G pairs with C

Sugar

T

A

T

A

DNA DNA (deoxyribonucleic acid) is a nucleic acid that contains the information

cells need to make all of their proteins. A DNA molecule is put together like a twisted ladder, or double helix. Each rung of the DNA ladder consists of a base pair. A base on one side of the molecule always matches up with a certain base on the other side (Figure 13.23). The base adenine (A) only pairs with thymine (T), and cytosine (C) only pairs with guanine (G). This base pairing is very important to the function of DNA. A single DNA molecule contains more than 1 million atoms!

A

T

Phosphate

C

G G

Bases

T

C

A

The four bases H H H

N C

N C N

H C C

Adenine

A

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N H

N C

H O

N C

O C N

H

H H C C H C

H

Thymine

T

H H N H

N C

O C N

H C C

Guanine

G

N H

N C

O

N C

N C

H

N

Figure 13.23: The DNA molecule.

C C

H

Cytosine

C

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Section 13.3 Review Counting Calories

1. Explain why life is often referred to as “carbon based.” 2. What are the four groups of carbon compounds found in living things?

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3. You might have heard the saying, “You are what you eat.” Use the information you learned in this section to explain what this statement means. 4. Classify each substance as either sugar, starch, protein, or nucleic acid. a. the major compound that makes up the skin b. glucose c. the major compound in potatoes d. DNA 5. Complete the table below. Carbon compound

Elements it is made of

Importance to living things

A food calorie (kilocalorie) tells you how much energy is in different foods. Each type of carbon compound has a certain number of food calories per gram. Fat contains 9 food calories per gram. Carbohydrate and protein each contain 4 food calories per gram. Based on this information, answer the following questions.

Example

Carbohydrate Lipid Protein Nucleic acid

6. What is the difference between saturated and unsaturated fat? Why are partially hydrogenated fats useful for making potato chips but not particularly healthy for humans to eat? 7. Simple sugars are the building blocks of carbohydrates. What are the simple units that make up proteins? 8. How many amino acids are used by cells to make proteins? How many different kinds of proteins can be made by this number of amino acids? 9. What type of biological molecule is an enzyme, and why are enzymes so important to living things?

1. How many food calories in the product above come from fat? 2. How many food calories come from carbohydrates? 3. How many food calories come from protein? 4. According to the nutrition label, one serving contains 130 food calories (130 kilocalories). Does this number sound reasonable to you? Explain.

13.3 MOLECULES AND CARBON COMPOUNDS

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Chapter 13 Assessment Vocabulary

Section 13.3

Select the correct term to complete the sentences.

11. Fats, oils, and waxes are examples of _____.

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12. ____ are molecules composed of long chains of smaller, repeating molecules.

polyatomic ion

organic chemistry

Lewis dot diagram

nucleic acids

binary compound

saturated fat

chemical formula

amino acids

enzyme

13. Sugars and starches are examples of _____.

proteins

valence electrons

ion

14. The building blocks of proteins are called _____.

ionic bond

carbohydrates

covalent bond

oxidation number

unsaturated fat

polymer

lipids

chemical bond

DNA

Section 13.1

1.

H2O is the ____ of water.

2.

A(n) ____ is formed when atoms share one or more electrons.

3.

A(n) ____ is formed when atoms transfer or share electrons.

4.

A(n) ____ is formed when atoms transfer electrons.

5.

You can use a(n) _____ to represent the valence electrons of an atom.

6.

A charged atom is called a(n) _____.

7.

The electrons involved in chemical bonds are called _____.

15. A branch of chemistry that specializes in the study of carbon compounds is _____. 16. A fat that has fewer hydrogen atoms because double bonds exist among some of the carbon atoms is called a(n) _____. 17. A fat in which the carbon atoms are surrounded by as many hydrogen atoms as possible is called a(n) _____. 18. Very large molecules composed of carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur are called _____. 19. A type of protein that speeds up a chemical reaction in living things is called a(n) _____. 20. Compounds made of many repeating nucleotides are known as _____. 21. _____ is a nucleic acid that contains the genetic code for an organism.

Section 13.2

8.

A(n) _____ indicates the electric charge on an atom when it gains, loses, or shares electrons during chemical bond formation.

Concepts

9.

A compound consisting of two elements is called a(n) _____.

Section 13.1

10. The type of ion that contains more than one atom is called a(n) _____.

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1.

What is the chemical formula for water? What atoms make up this compound?

2.

Why do atoms form compounds instead of existing as single atoms?

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16. Elements that are close together on the periodic table tend to form ____ compounds.

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3.

What type of bond holds a water molecule together?

4.

What does the subscript 2 in H2O mean?

5.

Name the two most important factors in determining the properties of a compound.

6.

Summarize the differences between a covalent compound and an ionic compound.

Section 13.3

When atoms form chemical bonds, which of their electrons are involved in the bonds?

19. What makes carbon uniquely suited to being the basis for biological molecules?

7.

Section 13.2

8.

Name a very reactive group of metals and a very reactive group of nonmetals. Why do they behave this way?

9.

Noble gases usually don’t form chemical bonds. Why?

10. Fill in the blank: Each successive element on the periodic table going from left to right across a period has an additional _____.

17. Strong electron donors are on the ____ side of the periodic table, while strong electron acceptors are on the ____ side. 18. What do all organic molecules have in common?

20. An organic compound contains carbon, hydrogen, oxygen, and nitrogen. Is this compound likely to be a lipid, carbohydrate, or protein? Explain. 21. Describe the four types of biological molecules. Give an example for each type. a. b.

11. How does the oxidation number indicate if an electron will be lost or gained by the bonding atom? 12. Using the periodic table, what is the oxidation number of: a. b. c.

calcium? aluminum? fluoride?

15. Elements that are widely separated on the periodic table tend to form ____ compounds.

c. d.

protein nucleic acid

Problems Section 13.1

1.

13. What is the total electric charge on a compound? 14. When elements in groups 1 and 17 combine, what type of compounds do they tend to form, covalent or ionic?

carbohydrate fat

For each of the chemical formulas listed below, name each element and tell how many atoms of each element are in that compound. a. b.

2.

C6H12O6 CaCO3

c. d.

Al2O3 B(OH)3

Draw Lewis dot diagrams for the following. a. b.

Bi Ge

c. d.

Ne SrI2

CHAPTER 13 ASSESSMENT

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Applying Your Knowledge

Section 13.2

3.

4.

Predict the formula for a molecule containing carbon (C) with an oxidation number of 4+ and oxygen (O) with an oxidation number of 2–.

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determine the oxidation number of Ca and Cl. write the chemical formula for calcium chloride.

sodium iodide aluminum hydroxide

c. d.

2.

KI SrCl2

b. c.

c. d.

KNO3 Al2O3

The diagram below shows an enzyme and three different molecules. Which of the three molecules would this enzyme target for a reaction?

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Ammonium sulfate is often used as a chemical fertilizer. What is its chemical formula? Calcium carbonate is a main ingredient in some antacids. What is its chemical formula? Kidney stones, a painful ailment, are partially made of a compound whose chemical formula is Ca3(PO4)2. What is the name of this compound?

Section 13.3

3.

Suppose that there are only three amino acids called 1, 2, and 3. If all three are needed to make a protein, how many different proteins could be made? Each amino acid may only appear in each protein once. Also, the position of the amino acid is important—123 is not the same as 321. Show your number arrangements to support your answer.

4.

You are entering a contest to design a new advertising campaign for National Nutrition Awareness Week. Create a slogan and a written advertisement that encourages teens to eat the right amounts of carbohydrates, lipids, and proteins. Use at least three facts to make your advertisement convincing.

Section 13.3

8.

Answer each of the following questions about compounds. a.

magnesium sulfide ammonium nitrate

Name the following compounds. a. b.

The noble gases used to be called inert gases until 1962, when scientists were able to cause them to react and form compounds. Using a search engine and keywords “noble gas compound,” conduct research on this topic. Find the names of some noble gas compounds, who discovered them, their chemical formulas, and how they are used.

Section 13.2

Write the chemical formulas for the following compounds. Consult Figure 13.16 on page 320 if necessary. a. b.

7.

HNO3 H3N6 NH3

Using the periodic table: a. b.

6.

1.

Which of the following would be a correct chemical formula for a molecule of N3– and H+? a. b. c.

5.

Section 13.1

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CHAPTER

14

CHAPTER 14

Changes in Matter

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When studying science, it is common to be told, “Look around!” However, in chemistry, the objects of study aren’t cars or people in motion, which are easy to see. The objects of study are atoms and molecules, which are extremely small. Nonetheless, these tiny particles are all around you. In fact, some scientists describe the space around them as “chemical space.” They think that the number of possible arrangements of atoms in the universe might be as many as 1060 compounds. That is a huge number! To date, only about 27 million compounds are known to occur naturally on Earth or to have been made by scientists. For a new compound to be made, a chemical change has to occur. This means the atoms in the starting materials are rearranged to make different or even new compounds. What might the motivation be for making a new compound? New compounds can mean new medicines, new materials to make lighter cars or airplanes, and even new fuels. Being able to predict the outcome of chemical changes is important when making new compounds. You are going to learn the basics of doing that in this chapter.

4 What is a chemical reaction and how do you show what happens during one?

4 How are chemical reactions classified? 4 What does energy have to do with chemical reactions?

4 What is a nuclear reaction and how is it different from a chemical reaction?

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14.1 Chemical Reactions

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Atoms and molecules are all around us and so are chemical reactions. How do you know a chemical reaction is occurring? When you make pizza, for example, some of your work involves physical changes and some involves chemical changes (Figure 14.1). You know a chemical reaction has occurred if a chemical change has occurred as well. In this section, you will learn about chemical reactions.

Chemical reactions involve chemical changes A review of Earlier, you learned that matter undergoes chemical changes and physical changes changes. Recall that a physical change is a change that affects only the

physical properties of a substance. Examples of physical changes include chopping pizza toppings (such as vegetables) into smaller pieces and melting an ice cube into liquid water. Both of these changes involve a change in size, shape, or state of matter. A chemical change is a change in a substance that involves the breaking and reforming of chemical bonds to make one or more different substances. Physical and chemical changes in making pizza

The process of making pizza involves some physical changes (such as chopping vegetables) and chemical changes. Pizza dough is made of flour, oil, salt, and yeast (a type of fungus). As pizza dough is made, the yeast produces carbon dioxide gas in a process called cellular respiration. The carbon dioxide causes the dough to rise. This gas, the result of a chemical change, is responsible for the small holes you see in any kind of bread made with yeast. The action of the yeast and heat from an oven cause chemical changes that transform the sticky pizza dough into a tasty crust.

Energy and Both physical and chemical changes involve energy. For example, you need changes energy to chop a green pepper into smaller pieces. Energy is also required for

a substance to change its state from a solid to a liquid to a gas. Because chemical changes involve breaking and forming bonds, energy is also involved in these changes. Heat or light—forms of energy—are produced or used during a chemical change. The chemical changes in making pizza require the yeast to use and release energy and the heat of an oven to cook the pizza.

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Figure 14.1: This woman is making pizza from scratch. Here, she is preparing the dough. What part of making a pizza involves physical changes? What part of the process involves chemical changes?

Science in Your Mouth Place a saltine cracker in your mouth. How does it taste? Hold it there for about 3 to 5 minutes. Now how does it taste? Is this evidence of a chemical or a physical change? Write down what you observe and think.

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CHAPTER 14

What is a chemical reaction? Chemical You have just learned something about the physical and chemical changes reaction defined involved in making pizza. Any time there is a chemical change, a chemical reaction has occurred. A chemical reaction is the process of breaking

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chemical bonds in one or more substances and reforming new bonds to create new substances. The process of cellular respiration performed by yeast in making pizza dough is a chemical reaction. The process used to generate heat in a gas stove to bake the pizza is also a chemical reaction and is illustrated below. When methane gas (a fuel) and oxygen react, the bonds in these molecules are broken to form the compounds carbon dioxide and water. Substances that change

+

of breaking chemical bonds in one or more substances and the reforming of new bonds to create new substances.

precipitate - a solid that forms and does not dissolve in a reaction mixture.

Substances that are formed

+ CH4

chemical reaction - the process

+ O2

Methane (gas) + Oxygen (gas)

CO2

+

H2O

Carbon dioxide (gas) + Water (gas)

Evidence of a When you combine two or more compounds, how do you know whether or chemical not a chemical reaction has occurred? You can’t see atoms and molecules reaction actually breaking and forming bonds, but you can observe other events that

indicate a chemical reaction. Figure 14.2 illustrates the type of evidence you can expect. For example, if you see a newly formed substance, such as a gas or a solid, you can suspect a chemical reaction. If a gas is a product in the reaction, you might see bubbles. If a new solid is produced, you might see powder forming in the reaction mixture so that it turns cloudy. A solid that forms and does not dissolve in the reaction mixture is called a precipitate. Similarly, if you see a color change in the reaction mixture, a new substance might have been formed. Finally, evidence of a chemical reaction includes a temperature change. Keep in mind that any heat added to the reaction to get it started is not part of the evidence of a chemical reaction.

Figure 14.2: These are all different kinds of evidence that a chemical reaction is occurring.

14.1 CHEMICAL REACTIONS

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Reactants and products Parts of a You can think of a chemical reaction as a kind of recipe. A recipe calls for chemical specific amounts of ingredients to make a food—such as a cake. A reactant reaction is a starting ingredient in a chemical reaction. The resulting substances formed in a chemical reaction are called the products. A product is a

reactant - a starting ingredient in a chemical reaction. product - a new substance formed in a chemical reaction.

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compound that results from new chemical bonds formed when a chemical reaction occurs. Reactants are chemically changed to form products

On the previous page, you saw a reaction involving methane and oxygen. Below is that reaction presented again so that you can see what happens when reactants are chemically changed to become products. In the reaction, methane (a natural gas) is burned, or combusted. Some energy is added to get the reaction started. Once this happens, a carbon atom from the methane molecule reacts with oxygen in the air to form carbon dioxide. Single oxygen atoms and hydrogen atoms also combine to form water. This reaction is particularly useful in making gas stoves work because it releases a large amount of heat.

States of matter You know that the reactants in the reaction below are gases because of the in chemical symbol (g) listed next to the molecules (Figure 14.3). Likewise, you know reactions that the products are gases—carbon dioxide gas and water vapor.

Chemical reaction Reactants

Products

+

+

CH4 (g)

+

O2 (g)

Energy added to start the reaction

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CO2 (g) Bonds broken

+

Symbol

Meaning

(s)

Substance is a solid

(l)

Substance is a liquid

(g)

Substance is a gas

(aq)

Substance is dissolved in water (aqueous)

Figure 14.3: Symbols used for states of matter.

For the methane reaction, does the number of atoms of the reactants equal the number of atoms of the products? Count and see. How could you make the numbers match? (Note: In the next section, you’ll find out!)

H2O (g)

New bonds formed Energy released

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CHAPTER 14

The law of conservation of mass Burning wood is Have you ever wondered what happens to wood in a fireplace or campfire as a chemical it is burned? The burning of wood is a chemical reaction. By writing this reaction reaction as a chemical equation, you can figure out what happened to the

wood. It doesn’t just disappear!

law of conservation of mass - a principle that states that the total mass of the reactants equals the total mass of the products in a chemical reaction.

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The law of In the 18th century, chemical reactions were still a mystery. A French conservation of scientist, Antoine Laurent Lavoisier established an important principal based mass on his experiments with chemical reactions. He stated that the total mass of

the reactants of a reaction is equal to the total mass of the products. This statement, which relates reactants and products, is known as the law of conservation of mass. Investigating a To understand the law of conservation of mass, let’s look at the reaction of reaction burning wood. It is easy to find the mass of a piece of wood you want to burn.

But, what happens to the mass of the wood after it burns (Figure 14.4)? To find out, look at the reaction below. The combined mass of the burning wood and oxygen is converted into carbon dioxide and water.

Figure 14.4: What happens to wood when it is burned?

Using a closed How can you prove that the mass of the reactants is equal to the mass of the system to study products in the reaction of burning wood? Lavoisier showed that a closed a reaction system must be used when studying chemical reactions. When chemicals are

reacted in a closed container, you can show that the mass before and after the reaction is the same (Figure 14.5).

For a chemical reaction, the total mass of reactants always equals the total mass of the products.

Figure 14.5: A closed system

illustrates the law of conservation of mass.

14.1 CHEMICAL REACTIONS

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How are chemical reactions written? The chemical So far you have seen how a chemical reaction—such as the methane reaction equation below—is written. When a chemical reaction is written using chemical formulas and symbols, it is called a chemical equation. Chemical

chemical equation - an expression of a chemical reaction using chemical formulas and symbols.

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equations are a convenient way to describe chemical reactions. Here you see the methane reaction written as a chemical equation and as a sentence. What advantages do you see for writing the reaction as an equation?

Parts of a In Chapter 13, you learned how to write chemical formulas (Figure 14.6). chemical Recall that the symbols for elements are used along with subscripts. equation Additional parts of a chemical equation are symbols that indicate the state of

matter for each reactant and product. An arrow is always included between reactants and products. The arrow means “to produce” or “to yield.” Accounting for You know that a chemical reaction involves breaking and reforming the atoms chemical bonds. See if you can account for how atoms are distributed on the

Figure 14.6: The parts of a chemical formula.

reactant side versus the product side in the methane reaction above. What’s wrong? Notice that there are only two oxygen atoms on the reactant side, but there are three on the product side. You might also notice that you have four hydrogen atoms on the reactant side and only two on the product side (Figure 14.7). This means that the chemical equation above is not completely correct. Numbers and The law of conservation of mass is always applied to chemical equations. types of atoms The law is applied by balancing the number and type of atoms on either side must balance of the equation. When balancing a chemical equation, you consider whole

atoms rather than fractions of an atom because only whole atoms react. Also, you are not allowed to change the chemical composition of any of the compounds on the reactant or product side. To learn how to balance chemical equations, let’s take another look at the methane reaction.

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Figure 14.7: This graphic illustrates

that the number of oxygen and hydrogen atoms are not balanced for the methane reaction.

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Balancing a chemical equation Begin by counting the number of atoms

The first step in balancing a chemical equation involves counting the number of each type of atom on both sides of the reaction. Recall that the subscripts in a chemical formula tell you the number of each type of atom. The table below summarizes this information for the methane reaction (Figure 14.8).

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Type of atom in methane reaction

Total on reactant side

Total on product side

Balanced?

C

1

1

yes

H

4

2

no

O

2

3

no

When an As you can see, the chemical equation for the methane reaction is not equation is balanced. The number of hydrogen and oxygen atoms is different on each side unbalanced of the equation. To make the number of atoms equal and balance the equation,

coefficient - a whole number placed in front of a chemical formula in a chemical equation.

Figure 14.8: Graphic of the unbalanced methane reaction.

you must figure out what number to multiply each compound by in order to make the numbers add up. Remember, you cannot change the number of individual atoms in a compound. That would change its chemical formula and you would have a different compound. Adding To change the number of molecules of a compound, you can write a whole coefficients number coefficient in front of the chemical formula (Figure 14.9). When you

do this, all of the types of atoms in that formula are multiplied by that number. When there is no coefficient in front of a chemical formula, you assume that one molecule of that compound is sufficient. Figure 14.9: What do coefficients and subscripts mean?

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Checking your Figuring out where to place coefficients to multiply the numbers of atoms in work a chemical formula is largely a process of trial and error. Let’s look at the

methane reaction after the correct coefficients have been added.

When balancing a chemical equation... 1. Make sure you have written the correct chemical formula for each reactant and product.

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Counting the atoms on both sides again, we see that the equation is balanced. Type of atom in methane reaction

Total on reactant side

Total on product side

Balanced?

C

1

1

yes

H

4

2(× 2) = 4

yes

O

2(× 2) = 4

2 + 1(× 2) = 4

yes

Reading a Now that the equation is balanced, it can be read as follows: “One molecule balanced of methane reacts with two molecules of oxygen to produce one molecule of equation carbon dioxide and two molecules of water.” Figure 14.10 reviews key

points to remember when balancing chemical equations.

2. The subscripts in the chemical formulas of the reactants and products cannot be changed during the process of balancing the equation. Changing the subscripts will change the chemical makeup of the compounds. 3. Numbers called coefficients are placed in front of the formulas to make the number of atoms on each side of the equation equal.

Figure 14.10: Key points for balancing a chemical equation.

a. balanced Your turn... balanced or unbalanced?

Identify which of the following equations are balanced. Count the number of each type of atom on both sides. a. 2H2 + O2 → 2H2O b. MgO + H2O → Mg(OH)2

b. balanced c. unbalanced d. unbalanced e. balanced

c. Ca + O2 → CaO d. Na2O + H2O → NaOH e. 2HCl + Ca(OH)2 → CaCl2 + 2H2O

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First try:

Cu2S + 2O2 → 2Cu2O + SO2

Solving Problems: Balancing Equations

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In this reaction, chalcocite (a mineral) reacts with oxygen in the presence of heat. The products are a type of copper oxide and sulfur dioxide. Balance this equation (Figure 14.11): Cu2S + O2 → Cu2O + SO2 . 1. Looking for:

Coefficients that will balance the chemical equation.

2. Given:

The following information is based on the chemical equation.

3. Relationships:

4. Solution:

Atom

Reactants

Products

Cu

2

2(× 2) = 4

S

1

1

O

2(× 2) = 4

1(× 2) + 2 = 4

Second try:

2Cu2S + 2O2 → 2Cu2O + SO2

Type of atom

Reactants

Products

Balanced?

Cu S O

2 1 2

2 1 3

yes yes no

Coefficients can be added in front of any chemical formula in a chemical equation. When a coefficient is added in front of a chemical formula, all atoms in that formula are multiplied by that number. First try: Add a 2 in front of O2 and in front of Cu2O so that there are four O atoms on each side. However, this changes the number of Cu atoms. Second try: Add a 2 in front of Cu2S so that there are four Cu atoms on each side. However, this changes the number of S atoms. Third try: Add a 2 in front of the SO2. Change the 2 in front of O2 to a 3. Now there are two S atoms and six O atoms on each side and the equation is balanced: 2Cu2S + 3O2 → 2Cu2O + 2SO2

Atom

Reactants

Products

Cu

2(× 2) = 4

2(× 2) = 4

S

1(× 2) = 2

1

O

2(× 2) = 4

1(× 2) + 2 = 4

Third try:

2Cu2S + 3O2 → 2Cu2O + 2SO2 Atom Reactants

Products

Cu

2(× 2) = 4

2(× 2) = 4

S

1(× 2) = 2

1(× 2) = 2

O

2(× 3) = 6

1(× 2) + 2(× 2) = 6

Figure 14.11: Balancing the equation.

Your turn...

a. KClO3 → KCl + O2 b. Al2S3 + H2O → Al(OH)3 + H2S

a. 2KClO3 → 2KCl + 3O2 b. Al2S3 + 6H2O → 2Al(OH)3 + 3H2S 14.1 CHEMICAL REACTIONS

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Section 14.1 Review

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1. Is the formation of rust on an iron nail a chemical change or a physical change? Explain your answer. 2. List the kinds of evidence that indicate that a chemical reaction has occurred. 3. Identify the reactants and products in this chemical reaction. Identify each compound as a gas, a solid, a liquid, or a solution.

Some chemical formulas

Barium peroxide

BaO2

Barium oxide

BaO

Oxygen

O2

Figure 14.12: Question 9.

STUDY SKILLS 4. What is the law of conservation of mass? How is it related to balancing chemical equations? 5. Why is it important to study chemical reactions in closed containers? 6. In one of his experiments, Lavoisier placed 10.0 grams of mercury (II) oxide into a sealed container and heated it. The mercury (II) oxide then reacted in the presence of heat to produce 9.3 grams of mercury. Oxygen gas was another product in the reaction. According to the law of conservation of mass, how much oxygen gas would have been produced? 7. What is the difference between a subscript and a coefficient in a chemical equation? 8. Are the following chemical equations balanced or unbalanced? Balance any unbalanced equations. a. 2KClO3 → KCl + 3O2 b. Fe + O2 → FeO c. 2Li + Cl2 → 2LiCl d. NH3 + HCl → NH4Cl 9. BaO2 (s) → BaO (s) + O2 (g) a. Balance the chemical equation above. b. Use the information in Figure 14.12 to write the equation in words. Be sure to describe the state of matter for each compound.

Look for Chemistry Everywhere This chapter is all about chemistry. How can you improve your understanding? One way is to practice seeing objects and events in terms of chemistry. Here are some simple examples. (1) When you see a glass of water think of the chemical formula for water—H2O. (2) When you breathe, think about the oxygen (O2) coming in and the carbon dioxide (CO2) going out of your nose or mouth. (3) Identify events as causing a physical change or a chemical change. For example, when you write with a pencil, you are causing a physical change in the pencil lead by wearing it down. If you cook food, you are probably causing chemical changes. (4) Read the ingredients on labels. Can you write the chemical formula for any of the ingredients?

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14.2 Types of Reactions

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Most of the products you use every day are the result of one or more chemical reactions. As you might imagine, there are many possible chemical reactions. This section provides you with information on how to classify the different types of chemical reactions.

synthesis reaction - a chemical reaction in which two or more substances combine to form a new compound.

Synthesis reactions

polymerization - the formation of polymers by a series of synthesis reactions.

Making In a synthesis reaction, two or more substances combine to form a new compounds compound. A good example of a synthesis reaction is the formation of rust.

From this example, how might you describe the reaction in general terms? The answer to this question is below. In this general equation for a synthesis reaction and the other reactions in this section, A and B represent ions, atoms, or molecules.

A+B

AB

Polymerization Recall that a polymer is a large molecule made up of repeating segments. Polymerization, or the formation of polymers, is a series of synthesis

reactions taking place to produce a very large molecule. Polymers are made by joining smaller molecules called monomers.

+

+

monomers

polymer

Synthesis Reactions and Acid Rain Some fossil fuels, such as coal, contain sulfur. When these fuels are burned, the sulfur reacts with oxygen in the air to form sulfur dioxide in the following synthesis reaction: S (s) + O2 (g) → SO2 (g) In air polluted with sulfur dioxide, acid rain is produced in the reaction below: SO2 (g) + H2O2 (g) → H2SO4 (aq)

monomer

larger polymer

Table 14.1: Polymers Common polymers

Polymer products

Polystyrene

Foam containers

Polyethylene

Food packaging

Polyester

Clothing

Polyvinyl chloride

Plumbing (PVC pipes)

Polyvinyl acetate

Chewing gum

H2O2 is hydrogen peroxide, a substance that is produced in clouds in a reaction between oxygen and water. H2SO4 is sulfuric acid.

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Decomposition reactions Breaking down As you might suspect, chemical reactions are used to make compounds. compounds However, a chemical reaction is also used to break down compounds. A

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chemical reaction in which a single compound is broken down to produce two or more smaller compounds is called a decomposition reaction. The general equation for decomposition is:

decomposition reaction - a chemical reaction in which a compound is broken down into two or more smaller substances.

Energy is In most cases, energy is required to get a decomposition reaction going. The required most common form of energy used in these chemical reactions is heat. For

example, the reaction below was involved in the discovery of oxygen. Heat was used in the decomposition of mercury (II) oxide.

For the decomposition of water into hydrogen and oxygen, the energy source is electricity. In fact, this particular reaction, illustrated in Figure 14.13, is called electrolysis.

The number of The simplest kind of decomposition is the breakdown of a binary compound products formed into its elements. However, larger compounds can also decompose to

produce other compounds. The number of compounds that form as products in a decomposition reaction depends on the number of elements in the reactant compound. For example, baking soda (NaHCO3) has four elements. When it undergoes a decomposition reaction with heat, three products form.

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Figure 14.13: A diagram of the

experimental setup for performing the electrolysis of water. Why do you think the balloon for hydrogen gas is twice as big as the one for oxygen gas?

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Displacement reactions Single- In a single-displacement reaction, one element replaces a similar element displacement in a compound. For example, if you place an iron nail into a beaker of reactions copper (II) chloride, you will begin to see reddish copper forming on the iron

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nail. In this reaction, iron replaces copper in the solution and the copper falls out of the solution onto the nail as a metal.

The general equation for a single-displacement reaction is:

single-displacement reaction a chemical reaction in which one element replaces a similar element in a compound. double-displacement reaction - a chemical reaction in which ions from two compounds in solution exchange places to produce two new compounds.

In this equation, A and B are elements, and AX and BX are compounds. Double- In a double-displacement reaction, ions from two compounds in a displacement solution exchange places to produce two new compounds. One of the reactions compounds formed is usually a precipitate that settles out of the solution,

a gas that bubbles out of the solution, or a molecular compound such as water. The other compound formed often remains dissolved in the solution. Precipitates are first recognizable by the cloudy appearance they give to a solution. A precipitate is the result of one of the products in a double-displacement reaction being insoluble in water (Figure 14.14). The term insoluble means that it does not dissolve. Depending on the compound formed, the precipitate can be many different colors from white to fluorescent yellow, as in the reaction between lead (II) nitrate and potassium iodide. Figure 14.14: The formation of a The general formula for a double-displacement reaction is give below. Each pairing of letters—AB and CD, and AD and CB—are ionic compounds in a solution.

cloudy precipitate is evidence that a double-displacement reaction has occurred. If left undisturbed in a beaker, a precipitate will settle to the bottom. The precipitate in the image is potassium iodide.

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Combustion reactions In a combustion A combustion reaction, also called burning, occurs when a substance, reaction, energy such as wood, natural gas, or propane, combines with oxygen and releases a is released large amount of energy in the form of light and heat. The products of this

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kind of combustion reaction are carbon dioxide and water. What do reactants such as wood, natural gas, and propane have in common? The answer is that they are all carbon compounds. Following is the general equation for a combustion reaction.

Carbon compound + O2 (g)

CO2 (g) + H2O (g)

Carbon The methane reaction, which you have seen before, is a good example of a compounds combustion reaction. As you can see, a carbon compound is a mixture of

carbon and hydrogen atoms. The general formula for a carbon compound is CxHy where x and y represent different subscripts. Examples of carbon compounds can be found in Figure 14.15.

Another kind of Not all combustion reactions use carbon compounds as a reactant. These combustion types of combustion reactions do not produce carbon dioxide. For example, reaction when hydrogen gas is burned in oxygen, water is the only product.

The value of an alternative combustion reaction

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Perhaps in the future some of our cars will run by the reaction above. Instead of using gasoline, which is a mixture of carbon compounds, cars might run on hydrogen. Currently, automobile manufacturers are developing technologies that utilize hydrogen combustion in the internal combustion engines of cars. Another way hydrogen can be used to power cars is in an electrochemical process that uses a fuel cell. In either case, the use of hydrogen fuel could help reduce the amount of carbon dioxide emissions related to transportation. However, it would still take energy, sometimes in the form of fossil fuels, to make the hydrogen fuel. What do you think? Should hydrogen technologies be developed for cars?

combustion reaction - a chemical reaction that results in a large amount of energy being released when a carbon compound combines with oxygen. Carbon compound

Chemical formula

Methane

CH4

Ethane

C 2H 6

Propane

C 3H 8

Butane

C4H10

Pentane

C5H12

Hexane

C6H14

Heptane

C7H16

Octane

C8H18

Figure 14.15: Examples of carbon compounds.

Hydrogen Technology In the text, you learned about two forms of hydrogen technology used for running an automobile. Find out more about each one. Is hydrogen fuel a viable alternative to fossil fuels?

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Section 14.2 Review 1. Why is polymerization a type of synthesis reaction?

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2. You have learned about the different kinds of chemical reactions. Come up with a set of simple rules that you can use to help you identify each kind of chemical reaction. There are no right or wrong answers. Write rules that make sense to you. 3. The graphic at the right shows the electrolysis of water. a. Come up with an explanation for why oxygen forms near the positively-charged metal and hydrogen forms near the negatively-charged metal. b. Why is a greater amount of hydrogen gas collected in this reaction? c. Is this reaction occurring in a closed container? Justify your answer. 4. How does the involvement of energy in a decomposition reaction compare to how energy is involved in a combustion reaction? 5. Compare and contrast single-displacement and double-displacement reactions. 6. Identify the following reactions as synthesis, decomposition, single or double displacement, or combustion. a. N2 (g) + 3H2 (g) → 2NH3 (g) b. NH4NO3 (s) → N2O (g) + 2H2O (g) c. AgNO3 (aq) + NaCl (aq) → AgCl (s) + NaNO3 (aq) d. Fe (s) +H2SO4 (aq) → H2 (g) + FeSO4 (aq)

George Washington Carver George Washington Carver was born around 1864 in Missouri toward the end of the Civil War. George and his mother, a slave for Moses and Susan Carver, were kidnapped when he was an infant. Only George was found and returned to the Carvers who then raised him. Due to frail health, he spent a lot of time exploring nature and developed his talent for studying plants. He pursued plant studies in school and earned an agricultural degree from Iowa State College. He became the first African American faculty member at the college and earned his master's degree two years later. Soon afterward, Booker T. Washington, founder of Tuskegee Institute in Alabama, recruited Carver to lead the agricultural department. There, Carver taught students and local farmers to rotate crops annually to enrich the soil. Benefits included improving the cotton crop and adding new cash crops such as peanuts and sweet potatoes. Carver is especially known for compiling a list of products and recipes that utilized the peanut plant. His many achievements include conducting research on soy as a possible biofuel, displaying artwork at the 1893 World’s Fair, and meeting with three American presidents.

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14.3 Energy and Chemical Reactions All chemical reactions involve energy. If you have ever sat near a campfire, you have experienced this energy as heat and light. In addition to producing energy, chemical reactions also use energy. For example, plants perform photosynthesis, which is a chemical reaction that uses energy from sunlight.

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Exothermic and endothermic reactions

exothermic - describes a chemical reaction that releases more energy than it uses. endothermic - describes a chemical reaction that uses more energy than it releases.

Energy is Energy is involved in chemical reactions in two ways: (1) At the start of a involved in two chemical reaction, energy is used to break some (or all) bonds between ways atoms in the reactants so that the atoms are available to form new bonds; and

(2) Energy is released when new bonds form as the atoms recombine into the new compounds of the products. We classify chemical reactions based on how the energy used in (1) compares to the energy released in (2). Exothermic If forming new bonds releases more energy than it takes to break the old reactions bonds, the reaction is exothermic (Figure 14.16, top). Once started,

exothermic reactions tend to keep going because each reaction releases enough energy to start the reaction in neighboring molecules. A good example is the reaction of hydrogen with oxygen. If we include energy, the balanced reaction looks like this:

Endothermic If forming new bonds in the products releases less energy than it took to reactions break the original bonds in the reactants, the reaction is endothermic

(Figure 14.16, bottom). Endothermic reactions absorb energy. In fact, endothermic reactions need more energy to keep going. An example of an important endothermic reaction is photosynthesis. In photosynthesis, plants use energy from sunlight to make glucose and oxygen from carbon dioxide and water. If we include energy, the balance formula looks like this:

Figure 14.16: Exothermic and endothermic reactions.

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Activation energy An interesting Exothermic reactions occur because the atoms arranged as compounds of the question products have lower energy and are more stable than they are when arranged as

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compounds of the reactants. Chemical reactions—like other systems—move toward more stable circumstances. If this is true, why don’t all the elements combine into the molecules that have the lowest possible energy?

activation energy - energy needed to break chemical bonds in the reactants to start a reaction.

Activation The answer has to do with activation energy, which is the energy needed to energy begin a reaction and break chemical bonds in the reactants. Without enough

activation energy, a reaction will not happen even if it is exothermic. That is why a flammable material such as gasoline does not burn without a spark or flame. The spark supplies the activation energy to start the reaction.

An example of The diagram above shows how the energy flows in the reaction of hydrogen a reaction and oxygen. The activation energy must be supplied to break the molecules of

hydrogen and oxygen apart. Energy is then released when the four free hydrogen and two free oxygen atoms combine to form two water molecules. The reaction is exothermic because the energy released by forming water is greater than the activation energy. Once the reaction starts, it supplies its own activation energy and quickly grows (Figure 14.17). Reactions occur only when conditions are right

A reaction begins by itself when thermal energy is greater than the activation energy. However, any reaction that could start by itself probably already has! The compounds and molecules in substances around you need more activation energy to change into anything else. For example, table salt in a dish will remain table salt for a long time unless the conditions change to cause a chemical reaction between the salt and another compound.

Figure 14.17: Because energy

released by one reaction supplies activation energy for new reactions, exothermic reactions can grow quickly once activation energy has been supplied.

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Examples of endothermic reactions Endothermic It’s certainly useful when chemical reactions produce more energy than they reactions in use. But how do we benefit from reactions that use more energy than they industry produce? It turns out that most of the reactions used in industry to produce

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useful materials require more energy than they produce. This is one of the reasons sources of energy are so important to industry. In other words, exothermic reactions are needed to cause endothermic reactions to run. One example of an industry process that frequently uses endothermic reactions is the refining of ores to produce useful metals. Here is a specific example, the refinement of aluminum ore from aluminum oxide.

dissolution reaction - an endothermic reaction that occurs when an ionic compound dissolves in water to make an ionic solution.

This reaction requires the input of energy because it takes more energy to break the bonds in the aluminum oxide than is released when the products are formed. Cold packs Have you ever used an instant cold pack as a treatment for a twisted ankle or

a bruise? These products, found in your local drugstore, work by using an endothermic chemical reaction. The fact that more energy is used than produced is what makes the cold pack cold. The reaction, shown below, works as follows. The product usually comes in a plastic bag. Inside of the bag is a sealed packet of water surrounded by crystals of ammonium nitrate. To activate the cold pack, you squeeze the plastic bag to break the packet of water. When the water contacts the ammonium nitrate crystals, a reaction occurs and the pack becomes icy cold (Figure 14.18).

Dissolution The ice pack gets very cold because it takes energy to dissolve the ionic reactions bonds in the ammonium nitrate. Besides being endothermic, this reaction is also a dissolution reaction. A dissolution reaction occurs when an ionic

Figure 14.18: A cold pack works because of an endothermic reaction.

compound, such as ammonium nitrate, dissolves in water to make an ionic solution. In the cold pack reaction, the ions are ammonium (NH4+ ) and nitrate (NO3– ).

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Reaction rate Kinetic In all phases of matter, atoms and molecules exhibit random motion. This molecular concept is part of the kinetic molecular theory. The speed at which atoms or theory molecules move depends on the state of matter and the temperature. As you

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know, gas molecules move faster than molecules in a solid, and warmer substances have greater molecular motion than cold ones. What is reaction The reaction rate for a chemical reaction is the change in concentration of rate? reactants or products over time. For a reaction involving two or more

reactants, the reaction only works if the molecules collide. If we want the reaction to go faster, what kinds of things could we do to increase the motion and number of collisions among the reactants?

reaction rate - the change in concentration of reactants or products in a chemical reaction over time. catalyst - a molecule added to a chemical reaction that increases the reaction rate without getting used up in the process.

inhibitor - a molecule that slows down a chemical reaction.

Increasing For starters, you can add heat to a reaction to increase molecular motion. For collisions example, to dissolve salt faster in water in a dissolution reaction, you increase

the temperature of the water. Other ways to increase collisions include stirring the reaction mixture and using powdered reactants. Fine particles in powders have more available surface area for reacting. Increasing Another way to increase collisions among atoms or molecules is to increase concentration of the concentration of the reactants. When you increase the concentration of a reactants reactant, it is like adding an extra team member to complete a project. If the

project involved many calculations, the team could complete them more quickly with six people than with five. As you know, doing calculations by hand takes a while. What if the team had a computer or calculator?

A

B

Catalysts and A catalyst is a molecule that can be added to a reaction to speed it up, but it inhibitors doesn’t get used up. A catalyst is a little like using a computer or a calculator

to help you speed up the job of making calculations. Catalysts work by increasing the chances that two molecules will be positioned in the right way for a reaction to occur. Because a catalyst ensures the correct orientation of colliding molecules, less energy is needed in the collision for the reaction to occur. In effect, a catalyst provides a “shortcut” because a lower activation energy is needed for a reaction to proceed (Figure 14.19). Reactions can also be slowed down by molecules called inhibitors. Inhibitors bind with reactant molecules and effectively block them from combining to form products.

Figure 14.19: By bringing together reactants, a catalyst lowers the activation energy needed.

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Chemical equilibrium The direction of Up until now, we have thought about chemical reactions as going in only a chemical one direction. Reactants react to make products. This has been shown in reaction chemical equations with a right-pointing arrow that points toward the

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products of the reaction. Therefore, chemical reactions are commonly described as proceeding to the right. In some cases, once a reaction goes to the right, the reaction reverses and goes to the left. The products become reactants and the reactants become products (Figure 14.20). Chemical Eventually, a reaction might reach chemical equilibrium, the state in equilibrium which the rate of the forward reaction equals the rate of the reverse reaction.

When we talk about chemical equilibrium, we acknowledge that the reaction can go left and right simultaneously. Chemical equilibrium is represented by arrows going both ways, or a double-headed arrow (Figure 14.20). Characteristics Because chemical reactions are often open systems, the reactants and of chemical products can easily react with other compounds. If this happens, the products equilibrium cannot revert back to reactants because they are unavailable. A gas that is a

product, for example, easily leaves the reaction system. Therefore, for chemical equilibrium to be established, the chemical reaction has to occur in a closed system. When a chemical reaction occurs in a closed system at a constant temperature, the forward and reverse reactions occur at the same rate, and the amounts of reactants and products are constant. An advanced topic: Le Chatelier’s principle

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Let’s say you have a chemical reaction at chemical equilibrium in a closed container in your laboratory. You leave the system alone but someone turns up the heat by accident and the room you are in gets hotter and hotter. What happens to the chemical reaction in the container? A change in temperature is considered to be a stress on the system. In response to this stress, the system reacts until chemical equilibrium is reestablished. This phenomenon is called Le Chatelier’s principle. This principle states that a chemical reaction at chemical equilibrium reacts to any stress on the system until equilibrium is re-established. A stress could include increasing the concentration of a reactant or product, or changing the temperature or pressure conditions of the reaction.

chemical equilibrium - the state in a chemical reaction at which the rate of the forward reaction equals the rate of the reverse reaction.

A reaction going to the right

Reactants A+B

Products AB

A reaction going to the left

Products A+B

Reactants AB

Chemical equilibrium

Products A+B

Reactants AB

Figure 14.20: The direction of a

reaction is indicated with an arrow. When a reaction is in chemical equilibrium, a double-headed arrow is used.

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Section 14.3 Review Many reactions in the human body require enzymes, a kind of catalyst, to get reactions going. Not surprisingly, the temperature of the human body, 37°C or 98°F, is ideal for enzymes to work well.

1. List the two ways that energy is involved in chemical reactions.

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2. Identify the following statements as describing either an exothermic or an endothermic reaction. a. more energy is released than is used by the reaction b. the chemical reaction involved in burning wood c. less energy is released than is used by the reaction 3. Why is a spark of energy required to begin the chemical reaction of burning a fossil fuel? What is another name for this spark of energy? 4. The reaction below is an exothermic reaction. K2O (s) + CO2 (g) → K2CO3 (s) a. Rewrite this reaction and add “+ energy” in the correct location. b. Describe how the energy level of the reactants compares to the energy level of the products. 5. The reaction below is an endothermic reaction. 2HgO (s) → 2Hg (l) + O2 (g) a. Rewrite this reaction and add “+ energy” in the correct location. b. Describe how the energy level of the reactants compares to the energy level of the products. Table 14.2: A Review of the Factors Affecting Reaction Rate Action Stirring Increasing temperature Increasing surface area Increasing concentration Adding a catalyst Adding an inhibitor

Do collisions increase?

Does the energy of the collisions increase?

Yes No Yes Yes Yes No Yes No Improves the effectiveness of collisions so less energy is needed for a reaction Prevents or diminishes the effectiveness of collisions so more energy is needed for a reaction

Getting a mild fever indicates that you might be sick. However, you are dangerously ill if you have a high fever for too long. Based on the information above, what might be a consequence of having a high fever in terms of how your body works?

Table 14.2 organizes information related to the factors affecting reaction rate. (1) List the two most effective factors in increasing reaction rate. Explain your choices. (2) What is the most effective way to slow down a reaction rate? Explain your choice. (3) Would stirring affect a chemical reaction that has chemical equilibrium? Explain your answer.

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14.4 Nuclear Reactions

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What do you think of when you hear the terms nuclear reactions or nuclear science? You might think that anything involving nuclear reactions is considered controversial. Why might that be? For starters, a great deal of energy can be produced by nuclear reactions, and humans need energy constantly. You were introduced to the structure of the atom and the forces that hold atoms together in Chapter 12. In this section, you will learn about reactions that occur within the nuclei of atoms.

nuclear reaction - a reaction in which the number of protons and/or neutrons is altered in one or more atoms.

Chemical vs. nuclear reactions Chemical When you mix two compounds such as calcium carbonate (CaCO3) and reactions hydrochloric acid (HCl), something happens (Figure 14.21). In this case, you

get calcium chloride (CaCl), carbon dioxide (CO2), and water (H2O). In the transition between the reactants and the products of a chemical reaction, either energy is mostly released (as in an exothermic reaction) or used (as in an endothermic reaction). The involvement of energy in chemical reactions has to do with the breaking and forming of chemical bonds. As you have learned, these bonds involve the outermost electrons of atoms.

Figure 14.21: A chemical reaction.

Size and structure of the atom

Introducing In the case of nuclear reactions, the main events and source of energy occur nuclear in the nuclei of the atoms involved. A nuclear reaction involves altering reactions the number of protons and/or neutrons in an atom. Recall from Chapter 12

that protons have a positive charge, the opposite of electrons. The charge on a proton (+e) and an electron (–e) are exactly equal and opposite. Neutrons have zero electric charge (Figure 14.22). Energy and A great deal of energy is needed to begin a nuclear reaction. However, a reactions great deal of energy is also released by this kind of reaction. Although they

can produce a lot of energy, chemical reactions fall short of producing as much energy as nuclear reactions. For example, a coal power plant uses chemical reactions to produce energy and a nuclear plant uses nuclear reactions. The fuel for a nuclear power plant, uranium-235, can produce 3.7 million times as much energy as an equivalent amount of coal!

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-

Atom Diameter = 10–10m

+

+

-

+ -

+

Proton

+

Neutron

Nucleus

Electron

Diameter = 10–15m

Figure 14.22: Electrons are

involved in chemical reactions. Protons and neutrons are involved in nuclear reactions.

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Radioactivity What if there are Almost all elements have one or more isotopes that are stable. Stable means too many the nucleus stays together. For complex reasons, the nucleus of an atom neutrons? becomes unstable if it contains too many or too few neutrons relative to the

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number of protons. If the nucleus is unstable, it breaks apart. Carbon has two stable isotopes, carbon-12 and carbon-13. Carbon-14 is radioactive because it has an unstable nucleus. An atom of carbon-14 eventually changes into an atom of nitrogen-14.

stable - a term that describes an atomic nucleus that stays together.

radioactive - a nucleus is radioactive if it spontaneously breaks up, emitting particles or energy in the process.

Radioactivity If an atomic nucleus is unstable for any reason, the atom eventually changes

into a more stable form. Radioactivity (also called radioactive decay) is a process in which the nucleus spontaneously emits particles or energy as it changes into a more stable isotope. Radioactivity can change one element into a completely different element.

Alpha decay Nucleus ejects a helium-4 nucleus Protons Neutrons Atomic number Mass number

Alpha decay When alpha decay occurs, the nucleus ejects two protons and two neutrons

(Figure 14.23, top). Check the periodic table and you can quickly find that two protons and two neutrons are the nucleus of a helium-4 (He-4) atom. Alpha radiation is actually fast-moving He-4 nuclei. When alpha decay occurs, the atomic number is reduced by two because two protons are removed. The atomic mass is reduced by four because two neutrons go along with the two protons. For example, uranium-238 undergoes alpha decay to become thorium-234.

Beta decay Nucleus converts a neutron to a proton and an electron, ejecting the electron. Protons Neutrons Atomic number Mass number

Beta decay Beta decay occurs when a neutron in the nucleus splits into a proton and an

electron (Figure 14.23, middle). The proton stays in the nucleus, but the high-energy electron is ejected (this is called beta radiation). During beta decay, the atomic number increases by one because one new proton is created. The atomic mass stays the same because the atom lost a neutron but gained a proton. Gamma decay Gamma decay is how the nucleus gets rid of excess energy. In gamma decay,

the nucleus emits pure energy in the form of gamma rays (Figure 14.23, bottom). The number of protons and neutrons stays the same.

Increase by 1 Decrease by 1 Increases by 1 Stays the same

Gamma decay Nucleus emits gamma radiation and lowers its energy. Gamma ray

Protons Neutrons Atomic number Mass number

Stays the same Stays the same Stays the same Stays the same

Figure 14.23: Comparing three radioactive decay reactions.

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Decrease by 2 Decrease by 2 Decreases by 2 Decreases by 4

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Two types of nuclear reactions

nuclear fission - a nuclear reaction in which the nuclei of heavier atoms are split to make lighter atoms.

make heavier atoms. This process is occurring all the time in a very familiar object—the Sun. What exactly happens in nuclear fusion? The process that occurs matches its name. Two nuclei are “fused” together, a particle is emitted, and a lot of energy is released. The reaction below shows the fusion of hydrogen-3 (1 proton + 2 neutrons) with hydrogen-2 (1 proton + 1 neutron) to produce a helium nucleus, a neutron, and energy. This process occurs in the Sun and the resulting energy released provides Earth with heat and light.

er

gy

Nuclear fission

C #2

At

om

B At

om

A

Nuclear fusion

Helium nucleus

Energy

Emitted particle

om

B C

gy

er

#3

En

om

At

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Atom #1 Atom #1

#3

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Atom #1

om

number of atoms can be made in this way at one time. Fission, and the resulting energy production in nuclear reactors, is controlled by releasing neutrons to start a chain reaction or by capturing neutrons to slow or stop a chain reaction. As you have just learned, the largest nuclear reactor in our solar system is the Sun.

Energy

At

Performing Both fusion and fission reactions can be performed in a special machine fusion and called a particle accelerator. The particle accelerator bombards particles and fission reactions atoms in order to achieve these reactions. However, only a very small

C

#3

reaction can be started when a neutron bombards a nucleus. A chain reaction results. A free neutron bombards a nucleus and the nucleus splits, releasing more neutrons. These neutrons then bombard other nuclei (Figure 14.24).

B

om

Fission Nuclear fission is the process of splitting the nucleus of an atom. A fission

A

A

Nuclei fuse

+

At

+

#2

Hydrogen-3 nucleus

Hydrogen-2 nucleus

En

Fusion Nuclear fusion is the process of combining the nuclei of lighter atoms to

in which the nuclei of lighter atoms are combined to make heavier atoms.

At

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useful in nuclear reactions. There are two kinds of nuclear reactions: fusion and fission.

nuclear fusion - a nuclear reaction

#2

Getting to the As you have just learned, the nucleus of an atom can change. All by itself, an nucleus of the unstable isotope can experience radioactive decay and become a new, more matter stable isotope. Atoms that are unstable and prone to radioactive decay are

Figure 14.24: Nuclear fission can be started when a free neutron (blue ball, step A) bombards a nucleus (step B). A chain reaction results as the nucleus splits, releasing more neutrons, which bombard other nuclei (step C).

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Using nuclear reactions in medicine and science Half-life On this page, you will learn about why radioactive waste is harmful, but also

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how radioactivity is useful. Let’s begin by looking at nuclear waste. The atoms that are a part of nuclear waste from nuclear reactors have long half-lives ranging from thousands (as in the case of plutonium-239) to millions of years. A half-life is a certain length of time after which half of the amount of radioactive element has decayed. For example, the half-life of carbon-14 (one of the radioactive isotopes of carbon) is 5,730 years. This means that if you start out with 100 atoms of carbon-14, 5,730 years from now, only 50 atoms will still be carbon-14. The rest of the carbon will have decayed to nitrogen-14 (a stable isotope). As a radioactive element decays, it emits harmful radiation such as alpha and beta particles and gamma rays. By breaking chemical bonds, radiation can damage cells and DNA. Exposure to radiation is particularly harmful if it is intense or for a long period of time.

half-life - a certain length of time after which half the amount of a radioactive element has undergone radioactive decay.

Radioactive Radioactive dating is a process that is used to figure out the age of objects by dating measuring the amount of radioactive material in a substance and by knowing

the half-life of that substance. For example, carbon dating is used to date material made from plants or animals. Much of the carbon absorbed by plants and animals is carbon-12 and carbon-13 because these are the most abundant carbon isotopes. However, some carbon-14 is also absorbed. By measuring the amount of carbon-14 remaining in a plant or animal fossil, the age of the fossils that are between 50,000 and a few thousand years old can be estimated. For older material, the amount of uranium-238 can be measured. It takes 4.5 billion years for one-half of the uranium-238 atoms in a sample to turn into lead (Figure 14.25). If a rock contains uranium-238, scientists can determine the rock’s age by the ratio of uranium-238 to lead atoms in the sample. Understanding radioactive decay of uranium-238 has allowed scientists to determine that the age of Earth is 4.6 billion years old. Radioisotopes Radioisotopes (also called radioactive isotopes) are commonly used as tracers detect problems in medicine and science. By adding a radioactive isotope into a system (such in systems as the human body or an underground water supply), problems can be

detected. The tracer’s radiation allows it to be detected using a Geiger counter or other machine and followed as it travels through the system.

Figure 14.25: The radioactive decay of uranium to lead. Radioactive decay is measured in half-lives. After one half-life, 50 percent of the uranium-238 atoms have decayed.

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Nuclear vs. chemical reactions A summary of the differences between chemical and nuclear reactions is listed in the table below.

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Chemical reactions

Nuclear reactions

Outermost electrons

Protons and neutrons in the nucleus

How is the reaction started?

Atoms are brought close together with high temperature or pressure, or catalysts, or by increasing concentrations of reactants

High temperature is required or atoms are bombarded with high-speed particles

What is the outcome of the reaction?

Atoms form ionic or covalent bonds

The number of protons and neutrons in an atom usually changes and/or energy is released

What part of the atom is involved?

How much energy is absorbed or released?

What are some examples?

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A small amount

A huge amount

Burning fossil fuels, digesting food, making medicines and commercial products

Generating nuclear energy, treating cancer, irradiating food to sterilize it, the Sun generating heat and light

Radiation Is All Around Because you cannot see or feel radiation, you might not be aware that it is all around you. Many common objects contain radioactive isotopes. Exposure to radiation can come from space (radiation entering Earth’s atmosphere), an X-ray, brick or stone buildings, or even Brazil nuts! Fortunately, exposure to radiation from these sources is very low.

STUDY SKILLS Isotope Notation Isotope notation is a way to write the atomic mass number and atomic number of the isotope of an element. This particular notation is useful for tracking whether a radioactive isotope has undergone alpha, beta, or gamma decay.

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Section 14.4 Review

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1. Why is so much energy required and released in a nuclear reaction?

Irene Joliot-Curie

2. Gold-185 decays to iridium-181. Is this an example of alpha or beta decay?

Irene Joliot-Curie was a remarkable woman. She was the oldest daughter of Marie and Pierre Curie. Irene studied both mathematics (her forte) and physics at the University of Sorbonne in Paris. However, her education was interrupted by World War I. Irene joined her mother in military hospitals and on the battlefield. Marie had developed portable X-ray machines that she set up and used to treat wounded soldiers. For her service, Irene was awarded France’s Military Medal. By 1925, Irene had earned her Ph.D., studying alpha rays of the element polonium, which was discovered by her parents. Around this time, she also met her future husband and scientific collaborator, Frederic Joliot. Frederic and Irene were both passionate about science and also shared interests in politics, art, and sports. The couple married in 1926 and had two children. They earned the Nobel Prize in 1935 for discovering that nonradioactive elements could be turned into radioactive isotopes using alpha particles.

3. What has to happen, in terms of radioactive decay, for carbon-14 to decay to nitrogen-14? 4. How is gamma decay different from alpha or beta decay? 5. In your own words, describe the difference between fusion and fission. Why do certain elements undergo fusion or fission? 6. Which type of nuclear reaction is used in modern-day nuclear reactors? Why is the other type of nuclear reaction not used in modern-day energy production? 7. When an atom of beryllium-9 is bombarded by an alpha particle, an atom of carbon-12 is produced and a neutron is emitted. What kind of nuclear reaction has just occurred? 8. What is the half-life of each of these radioactive isotopes? a. A radioactive isotope decreased to one-half its original amount in 18 months. b. A radioactive isotope decreased to one-fourth its original amount in 100 years. 9. For each scenario below, indicate whether a chemical reaction or a nuclear reaction is occurring. a. When two compounds are combined, heat is released. b. A sample of galium-68 is reduced to one-half of its original amount in 68.3 minutes. c. Radium-226 decays to radon-222. d. A spark of energy is used to begin the combustion of methane gas. e. Hydrogen nuclei are fused in the Sun to make helium atoms.

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Chapter 14 Assessment Vocabulary

9.

Select the correct term to complete the sentences.

____ is the formation of large, repeating molecules by a series of synthesis reactions.

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10. When a compound is broken down into two or more smaller substances, it is called a(n) ____ reaction.

reactant

product

catalyst

precipitate

radioactive

chemical reaction

nuclear fission

synthesis reaction

exothermic

stable

chemical equilibrium

nuclear fusion

activation energy

polymerization

chemical equation

Section 14.3

coefficient

law of conservation of

decomposition

12. A reaction that releases more energy than it uses is called ____.

combustion reaction endothermic

mass dissolution reaction

nuclear reaction reaction rate

half-life Section 14.1

11. A(n) ____ results in a large amount of energy being produced when a carbon compound combines with oxygen.

13. A reaction that uses more energy than it releases is called ____. 14. The energy required to start a reaction is called ____. 15. The change in concentration of reactants or products in a chemical reaction over time is called ____.

1.

A(n) ____ is a process that involves reactants and products.

2.

A starting ingredient in a chemical reaction is called a(n) ____.

16. For a given chemical reaction, ____ is the state at which the forward reaction equals the reverse reaction.

3.

A substance that is the result of the forming of new bonds in a chemical reaction is called a(n) ____.

Section 14.4

4.

An insoluble product in a double-displacement reaction is called a(n) ____.

5.

A(n) ____ is the written form of a chemical reaction.

6.

The ____ states that the mass of reactants always equals the mass of the products.

7.

You can change the number of atoms in a chemical equation by placing a(n) ____ in front of a chemical formula.

Section 14.2

8.

A(n) ____ is a chemical reaction in which two or more substances combine to form a new compound.

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17. A(n) ____ occurs when the number of protons and/or neutrons is altered in one or more atoms. 18. When an atomic nucleus stays together it is called ____. 19. A nucleus that spontaneously falls apart is called ____. 20. When the nuclei of lighter atoms combine to make heavier atoms, a(n) ____ has occurred. 21. When the nuclei of heavier atoms are split to make lighter atoms, a(n) ____ has occurred. 22. The time it takes for half the amount of a radioactive element to undergo radioactive decay is called ____.

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Concepts Section 14.1

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

1.

Your body produces heat and maintains a stable, warm body temperature of about 98°F (37°C). Is this evidence that your body is undergoing chemical changes or physical changes?

2.

In your chemistry lab, you mix baking soda and vinegar in a beaker. You carefully find the mass of the baking soda and vinegar you use in the reaction. However, after you are done with the reaction, you find that the product of the reaction has much less mass than the combined mass of the reactants. Evaluate your results. Are they correct? How might you perform this reaction again to make sure?

3.

Answer the following for the reaction below. You should be able to recognize three of the compounds. The compound C6H12O6 is a molecule of glucose, a sugar. C6H12O6 (s) + 6O2 (g) → 6CO2(g) + 6H2O(l)

CHAPTER 14

Section 14.3

6.

Write a general equation that illustrates the difference between an exothermic reaction and an endothermic reaction. You only need to use the following items in your general equation: reactants, products, and energy. Be sure to include an arrow in your equation.

7.

Your teacher asks you to mix two compounds to find out if the reaction is endothermic or exothermic. What will you do to determine which type of reaction is occurring?

Section 14.4

8.

Describe two ways that nuclear reactions are different from chemical reactions.

9.

Say you know a certain fossil is more than 1 million years old. Can you use carbon dating to date it? Why or why not?

Problems Section 14.1

a.

What are the reactants and products in this reaction? Give the state of matter for each.

b.

What does the arrow in a chemical equation mean?

c.

Is this equation balanced? Justify your answer.

Section 14.2

4.

Write the general equations for each type of reaction.

5.

You perform a reaction with two substances. One of the reactants is an oxygen-containing compound. The products are oxygen gas and another binary compound. What kind of reaction is this? Justify your answer. Illustrate this reaction with symbols and a diagram.

1.

Which of the following equations is balanced? a. b. c. d.

2.

Al + Br2 → 2AlBr3 2Al + 2Br2 → 3AlBr3 2Al + 3Br2 → 2AlBr3 Al + Br2 → AlBr3

Balance the following equations. If an equation is already balanced, say so in your answer. a. b. c. d. e. f.

Cl2 + Br → Cl + Br2 CaO + H2O → Ca(OH)2 Na2SO4 + BaCl2 → BaSO4 + NaCl ZnS + O2 → ZnO + SO2 Cl2 + KBr → KCl + Br2 H2SO4 + NaOH → Na2SO4 + H2O

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Applying Your Knowledge

Section 14.2

3.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

When your body burns food for energy, carbon dioxide and water are released. This process is called respiration and it is exactly like the respiration process performed by yeast in making pizza dough. Oxygen is needed for respiration to occur. Answer these questions:

a.

Where do the carbon dioxide and water come from in this reaction?

b.

Classify this reaction. Justify your answer.

Section 14.1

1.

Section 14.2

2.

c.

The graph below illustrates the change in energy for an exothermic reaction. a. b.

Label A and B on the graph. Make a sketch that would show the change of energy that occurs for an endothermic reaction.

5. The half-life of cesium-137 is 30 years. Make a graph that shows its radioactive decay over a period of 300 years. Show time on the x-axis of the graph and number of atoms on the y-axis. The starting amount of cesium-137 is 100 atoms. Be sure to give the graph a title and label the axes.

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What kind of reaction is this? Pure silicon is very useful in the electronics industry. How is it used? Oxygen is the most abundant element in Earth’s crust. How does silicon compare in abundance?

Section 14.3

3.

The U.S. Army developed a Meal, Ready to Eat (or MRE) for the 1991 Gulf War. These meals have a special sleeve placed around the food, which is wrapped in aluminum foil. When water is added to the sleeve, the resulting chemical reaction produces enough heat to cook the food inside the foil. The sleeve contains a pad with suspended particles of magnesium metal. When the magnesium reacts with the water to produce magnesium hydroxide, heat is released. Write the balanced chemical equation for this reaction. What kind of reaction is this? How do you know?

Section 14.4

Section 14.4

362

Balance this equation and then answer the questions. SiI4 (g) + heat → Si (s) + I2 (g) a. b.

Section 14.3

4.

Look for situations that demonstrate chemical change. List each situation and describe the evidence of chemical change that you observe. Try to identify the reactants and products.

4.

For every atom heavier than helium, there needs to be at least as many neutrons as protons to hold the nucleus together. For example, calcium-40 has 20 protons and 20 neutrons. For heavier atoms, more neutrons are needed than protons. For atoms with more than 83 protons, even the added strong nuclear force from neutrons is not enough to hold the nucleus together. How would you describe the elements that have more than 83 protons?

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CHAPTER 15

Chemical Cycles and Climate Change FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

In this chapter, you will learn why chemistry is important in understanding key components of our planet—chemical cycles and Earth’s climate. A place to begin learning about chemical cycles is the atmosphere. Earth’s atmosphere is full of atoms and molecules. You can’t see them, but as parts of chemical cycles they get incorporated into substances—like the wood of trees—that you can see. Carbon dioxide in the atmosphere, trees, nearly all of the food you eat, and human beings are all part of an important cycle called the carbon cycle. Since all of these things, including you, are made up of carbon atoms, it is extremely important that these atoms get recycled by the carbon cycle. You will also learn about the water, oxygen, nitrogen, and phosphorus cycles. Special attention will be given to the carbon cycle and global climate change. Currently, Earth’s climate is changing because of our use of fossil fuels as a source of energy. Finding alternative energy resources is one way to address climate change. In addition, you can address climate change by reducing the size of your “carbon footprint.” Since you can’t make your shoe size smaller, what can you do to reduce such a footprint? Read on to find out!

4 How are chemical cycles interconnected? 4 How is the greenhouse effect related to global climate change?

4 What can you do to address global climate change and make a difference?



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CHEMICAL CYCLES AND CLIMATE CHANGE

15.1 Chemical Cycles

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With a diameter of more than 12,000 kilometers, Earth is a huge ball of matter. Living things on Earth’s surface use this matter to grow and survive. For example, a single tree in its lifetime takes up and stores a small mass of elements. Now consider that billions of trees are growing on Earth and that the world has been around for many tree lifetimes. If every tree that ever lived held on to its stored matter, there would be shortages of several key elements and new life might stop developing. Why haven’t Earth’s elements been used up by living things by now? The answer to this question is chemical cycles.

chemical cycles - sets of processes that recycle elements on Earth.

Chemical cycles recycle elements Elements are Some of Earth’s many elements are essential for all living things; they are recycled by called nutrients. Living things need macronutrients in large quantities. living things Micronutrients are needed in small quantities. Nutrients can be found in soil

and rocks; in oceans, rivers, and lakes; in the atmosphere; and in biomass (the matter of living things), as seen in Figure 15.1. In time, elements are transported through the living and nonliving parts of our planet in sets of processes called chemical cycles. Examples of these cycles include the oxygen cycle, the carbon cycle, the nitrogen cycle, and the phosphorus cycle.

Elements are recycled by physical processes

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Macronutrients

Some micronutrients

carbon, hydrogen, oxygen, nitrogen, phosphorus

calcium, potassium, chlorine, sodium, magnesium

Even before life appeared on Earth millions of years ago, elements were recycled by chemical cycles as well as by physical processes. For example, the recycling of water by evaporation of oceans and lakes, cloud formation, and rain happened in the ancient past and continues today. Dissolved elements move around Earth via these water processes and travel long distances with flowing water as it moves from mountaintops, to rivers, to oceans. The presence of biological processes in the world complicates, but also enhances, the recycling of elements. On the next page, you will learn how living things affect and depend on chemical cycles.

Figure 15.1: Locations of essential elements on Earth.

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CHAPTER 15

How living organisms affect cycles

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Ecosystems How living things affect chemical cycles is understood by first learning about ecosystems. An ecosystem consists of a group of living things and their

ecosystem - a group of living things and their physical surroundings.

physical surroundings. A tropical rain forest, for example, is an ecosystem that is made up of the plants and animals that live there, plus nonliving things such as soil, air, water, sunlight, and nutrients. The living and nonliving parts of an ecosystem work together like a team.

photosynthesis - the process that plants use to convert sunlight energy into chemical energy.

Energy from the The Sun is the main energy source for ecosystems. Green plants capture Sun energy from sunlight and convert it into chemical energy. This chemical

energy is then used for growth and reproduction. When an animal in an ecosystem eats a plant, it gains nutrients as well as energy that came first from the Sun. Photosynthesis Photosynthesis is the process by which plants and some other organisms

convert the Sun’s energy to chemical energy. In this process, a plant uses the Sun’s energy to turn water and carbon dioxide into energy-rich carbon molecules such as sugars and starches. Oxygen is another important by-product of photosynthesis.

Figure 15.2: A tropical rain forest

ecosystem includes all the living parts of the system, such as plants and animals, and the nonliving parts such as sunlight, water, soil, and nutrients.

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Living parts of an ecosystem Producers and Plants and other living things that can take the Sun’s energy and turn it into consumers chemical energy in the form of sugars and starches are called producers.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

Producers are crucial to an ecosystem because other living organisms depend on them for food. Animals are called consumers because they feed on other living things to get food and energy. Some consumers, called herbivores, eat only plant material, and some, called carnivores, eat only other animals. A consumer that eats both plants and animals is called an omnivore. There are many consumers in a tropical rain forest ecosystem. For example, insects, caterpillars, and monkeys feed on the plants and trees. These herbivores are eaten by carnivores such as ocelots and pumas. What about you? Are you an herbivore, a carnivore, or an omnivore?

food chain - shows how each member of an ecosystem community gets its food.

Decomposers Producers and consumers in an ecosystem create waste and both eventually

die. If waste and dead organisms are not somehow broken down, the nutrients they contain would not become available for other living organisms in that ecosystem. The waste would pile up and potentially harm living things. Imagine what it would be like in your neighborhood if the trash were not taken away—you would not be able to stay there for very long without getting sick. A decomposer takes care of waste by consuming it and dead organisms to get energy. By breaking down material from waste and dead organisms, decomposers return nutrients to the ecosystem. For this reason, decomposers can be called nature’s recyclers. Bacteria and fungi are decomposers (Figure 15.3).

Figure 15.3: Mushrooms are fungi that help decompose fallen branches and leaves on the forest floor.

Food chains In effect, decomposers are like chemical laboratories that convert unusable

forms of many elements into forms that plants and animals (through food chains) can use. What is a food chain? A food chain shows how each member of an ecosystem gets its food. A simple food chain links a producer, an herbivore, and one or more carnivores. Figure 15.4 illustrates a simple food chain for a field ecosystem. You might be familiar with this kind of ecosystem. Food chains within ecosystems and the work of decomposers ensure that essential elements are constantly moving through living systems, whether they be in a tropical rain forest or an open field near your town.

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Figure 15.4: A food chain.

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CHAPTER 15

Pollution in ecosystems Human activities Sometimes non-essential elements are involved in food chains. For example, sometimes human activities may create toxic pollutants (toxins). High concentrations of create toxins toxins may impact living things. Toxins can cause slowed growth, decreased

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reproduction, and even death. When toxins enter ecosystems, they often spread out and become less concentrated. Some toxins end up in lakes and oceans (Figure 15.5). Food chains can However, food chains may concentrate some toxins, like mercury, into the concentrate tissues of animals like fish. Mercury is an element that can be found naturally toxins in an ecosystem. Human activities like industry also cause the release of

mercury into the environment. Because mercury is stored up in the fatty tissues of the fish over its entire lifetime, the level of the mercury in the fish may be thousands of times higher than the level of the mercury in the water. To understand how this happens, let’s look at a marine food chain.

Figure 15.5: Some power plants

send mercury into the air. This eventually falls to Earth with the rain and ends up in lakes and oceans.

Concentration of Toxins like mercury are concentrated at each link in a food chain. As producers toxins make food, they absorb particles of mercury from the water. Next, herbivores

eat large numbers of producers. Mercury dissolves in fat, not water and is stored in the fatty tissues of herbivores and is not passed out of their bodies. Toxins can be When carnivores eat many herbivores, they accumulate even higher levels of passed on to mercury in their fatty tissues. Secondary carnivores, who prey on other offspring carnivores, can accumulate dangerous levels of mercury or other toxins.

These toxins can sometimes be passed on to their young. Figure 15.6 shows how the amount of a toxin can multiply as it travels up the food chain.

Figure 15.6: The pyramid shows

how toxins are concentrated at each link in a food chain.

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The water and oxygen cycles Living things Water and oxygen are two essential substances that living things need. Most need water plants obtain water by absorbing it through their roots. Humans and other

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animals obtain water by drinking it. Water is essential because living organisms are mostly water. Water provides the medium in which nutrients flow in blood and in which food digests. Additionally, each cell in a living organism contains a watery solution.

respiration - the process by which living organisms use oxygen to obtain energy from food.

The water cycle Although most of Earth’s water is contained in the oceans, water does get

from place to place via the water cycle. Heat from the Sun causes water to evaporate, pass into the atmosphere as vapor, condense into droplets, and then fall as rain (precipitation). Along the way, the water enters the ground, finds its way into streams and rivers, and eventually returns to the oceans. At any point along this journey, water might evaporate and start over in the atmosphere (Figure 15.7). You have learned that plants participate in the water cycle during photosynthesis. The water used in photosynthesis might return to the atmosphere when the plant dies and decomposes. If an animal eats the plant, the animal will return the water by respiration, elimination, or decay upon its death. You will learn about the water cycle from a global point of view in Chapter 22. The oxygen Like water, oxygen is essential for living things. During photosynthesis, plants cycle release oxygen into the atmosphere and make sugars and starches that are used

as stored food and structural material. To break down stored food, plants use the process of respiration. In fact, all living organisms use respiration to break down food. During respiration, plants or animals use oxygen from the atmosphere to obtain energy from their food. Carbon dioxide is released in this process (Figure 15.8). Sources of Most of Earth’s oxygen is contained in the atmosphere. This oxygen is oxygen supplied by photosynthesis taking place in plants and other organisms such

as phytoplankton (microscopic algae) in oceans. The rest of Earth’s oxygen is combined with other elements in rocks and soil. The iron ore mined from the ground for steel production is a combination of iron atoms and oxygen atoms.

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Figure 15.7: The water cycle. Oxygen cycle Sunlight

Oxygen Photosynthesis

Carbon dioxide

Respiration

Oxygen in soil and rocks Respiration by decomposers

Figure 15.8: The oxygen cycle.

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The carbon cycle Carbon is Carbon ranks as the fourth most abundant element in the universe. Carbon is abundant found in Earth’s atmosphere as carbon dioxide and in rivers, lakes, and oceans

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as carbonate and bicarbonate ions. Carbon is also found in the ground in the form of fossil fuels, such as coal, oil, and natural gas. The many tons of biomass on Earth also contain mostly carbon. You might be wondering how carbon gets from place to place in the carbon cycle. The diagram below shows the pathways through which carbon is released and absorbed. Because carbon is so abundant, carbon is never in short supply in the carbon cycle. This means that carbon is not a limiting factor. A limiting factor is one that is in short supply and so “limits” processes. Carbon is an When carbon forms bonds, energy is stored for later use. In this way, carbon energy carrier is a powerful energy carrier. For example, during photosynthesis plants store

sunlight energy in the bonds between carbon atoms of simple sugars. During respiration, animals use oxygen to break those bonds and capture the energy stored by the plants. In this way, respiration is similar to burning gasoline in a car engine or burning wood for a campfire. All of these processes are performed in the presence of oxygen to obtain energy, with the products being water vapor and carbon dioxide gas.

Carbon Dioxide Emissions by Country Emissions are air pollution released into the air as tiny particles and gases. Air pollution is a negative component of the atmosphere since it can result in harm to living things. The following chart lists CO2 emissions data for the world and the five countries that produce the most emissions. This information was collected in 2011 by the Carbon Dioxide Information Analysis Center, which is part of the United States Department of Energy. Make a pie chart that represents the data for the top five countries and all the other countries. Then, write a paragraph that expresses what you think about this information. Country

Annual CO2 emissions (in thousands of metric tons)

World

33,600,095

100%

China (Mainland)

9,019,518

26%

United States

5,305,569

16%

India

2,074,345

6%

Russia

1,808,073

5%

Japan

1,187,657

4%

All other countries

14,204,933

43%

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Percentage of total emissions

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The nitrogen and phosphorus cycles Nitrogen in the Nitrogen is important to living things because it is used to make amino acids, atmosphere the building blocks of proteins. Approximately 78 percent of Earth’s

Nitrogen cycle Nitrogen in atmosphere (N2)

atmosphere is nitrogen gas (N2).

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The nitrogen The nitrogen cycle moves nitrogen through living systems (Figure 15.9). cycle Although it is abundant, nitrogen is a limiting factor for plant growth. To be

useful to plants, nitrogen must be combined with hydrogen or oxygen to make ammonium (NH4+) or nitrate (NO3–). This process, called nitrogen fixation, can be done by certain bacteria and to a smaller extent by lightning. Although nitrogen is released when plants and animals die, it is not readily available to living things. Rainwater washes the easily dissolved nitrogen compounds deep into the soil where plant roots can’t reach them. For this reason, nitrogen-fixing bacteria are essential to plants, and nitrogen compounds are a common ingredient in plant fertilizers.

Decomposers (bacteria and fungi)

Plants Denitrifying bacteria Assimilation Nitrates (NO3–)

Nitrogen-fixing bacteria

Nitrifying bacteria

Ammonium (NH4+)

Figure 15.9: The nitrogen cycle.

Sources of Phosphorus is important to living things because phosphorus is essential for phosphorus cell replication, metabolism, and structures. Phosphorus occurs in nature as

phosphate (PO43–), a phosphorus atom bound to oxygen atoms. Most phosphate is found as minerals in ocean sediment or in rocks. Plant roots produce weak organic acids that release small amounts of phosphorus from rocks and minerals. Once released from rocks and minerals, the phosphorus is absorbed by the roots for use by the plant. Animals obtain phosphorus by eating plants.

The phosphorus The phosphorus cycle keeps phosphorus available for living things cycle (Figure 15.10). Phosphate does not enter the atmosphere, and it is often a

limiting factor in aquatic environments. When phosphorus becomes abundant through runoff from animal waste, the resulting plant growth might overwhelm a river or lake. In a marine environment, abundant phosphate can increase phytoplankton growth and enhance food chains that include phytoplankton. After organisms die, their phosphorus is released by decay and becomes incorporated into marine sediment.

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Figure 15.10: The phosphorus cycle.

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The water, oxygen, and carbon cycles interconnect

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The diagram below shows that the water, oxygen, and carbon cycles interconnect. Cycles do not have beginning or ending points. See if you can trace the path of oxygen through all three cycles. Remember that oxygen changes form and appears in the environment in oxygen gas, O2; as water, H2O; as carbon dioxide, CO2, and as glucose (a simple sugar), C6H12O6.

The Flow of Energy and Nutrients All living things must complete three tasks. These are (1) gathering materials and energy, (2) growing, and (3) reproducing. The diagram below illustrates the flow of energy and nutrients that happens for living things to perform these tasks. Because organisms are not 100% efficient at using what they consume, they release heat energy as they metabolize nutrients. With the exception of water and oxygen, consumers obtain their essential elements and energy by eating plants (producers) or by eating animals that have consumed plants. Decomposers obtain essential elements when they act as nature’s recyclers for nutrients.

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Section 15.1 Review

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1. Macro- and micronutrients are essential for life. Where are nutrients found? 2. Give an example of a macronutrient. Why is this particular nutrient essential for living organisms? 3. Sally visits an apple farm to pick apples. After picking one apple from an apple tree, she eats it. Explain how the energy Sally gains from the apple is related to the Sun’s energy. 4. Which of the following would be described as biomass? a. rocks b. bacteria and fungi 5. 6. 7. 8.

9. 10. 11. 12. 13. 14.

c. minerals d. the atmosphere

What is the difference between a macronutrient and a micronutrient? What role does the Sun play in ecosystems? Compare and contrast photosynthesis and respiration. In the text, you were given an example of a food chain. Give another example of a food chain that includes a producer, an herbivore, and one carnivore. You might need to do some research. Why are decomposers such important parts of all ecosystems? Once consumed by animals, mercury is not eliminated as a waste product. Why? What is the main source of oxygen in the atmosphere? What percent of Earth’s atmosphere is oxygen? Explain why the carbon, nitrogen, and phosphorus cycles are important for living things. Give one reason for each cycle. What is nitrogen fixation? Why is it important for the nitrogen cycle to work? True or False Challenge: The DNA in your cells is part of the phosphorus cycle. If this statement is true, explain why it is true. If this statement is false, rewrite it to make it true.

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Micronutrients Micronutrients are required in very small quantities by living organisms. Nevertheless, without them a living organism might be unable to perform key metabolic functions. Find out more about the micronutrients that are important for human health. Make a list of five of these micronutrients and how they can best be obtained in one’s diet.

The Phosphorus Cycle In the text, you saw a diagram that shows how the water, oxygen, and carbon cycles are interconnected. Is the phosphorus cycle interconnected with these cycles? Write a paragraph that explains what you think. You can draw a diagram that illustrates how the phosphorus cycle is interconnected. Extend your ability to answer this question by doing some research about the phosphorus cycle.

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15.2 Global Climate Change global climate change - any

Looking at climate change

greenhouse gases - atmospheric gases that trap heat from the Sun so that Earth stays warm.

decades. Global climate change can be caused by natural processes and human activity. Since the Sun and the oceans affect weather patterns, changes in the Sun’s intensity or in ocean circulation can cause climate change. Human activities that affect our climate include burning fossil fuels and altering the land. For example, through photosynthesis, trees contribute to the oxygen and carbon cycles. Cutting down large areas of trees or burning trees affects these cycles. What are Greenhouse gases “blanket” our planet by trapping heat from the Sun greenhouse so that Earth’s average temperature is hospitable for living things. About gases? 99 percent of Earth’s atmosphere contains nitrogen and oxygen gases.

global warming - the increase of Earth’s average temperature due to increased concentrations of greenhouse gases in the atmosphere.

Carbon dioxide emissions and carbon dioxide concentrations (1751-2004)

35 30

Greenhouse gases represent a small portion of the atmosphere, but they are very important. The greenhouse gases are water vapor, carbon dioxide, methane, nitrous oxide, ozone, and carbon compounds produced by industry.

Increasing concentrations of greenhouse gases in our atmosphere are causing global climate change. What is global In the past 200 years, the concentrations and types of greenhouse gases in our warming? atmosphere have increased. The most significant cause of this increase is the

burning of fossil fuels (Figure 15.11) and deforestation (the removal of forests). The increase of greenhouse gases in the atmosphere leads to the greenhouse effect that is causing global warming. Global warming is the increase of Earth’s average temperature as a result of increased concentrations of greenhouse gases in the atmosphere.

400

Concentration in parts per million

300

20

250 200

15 10

150

Emissions in billion metric tons

100

5 0 1751

50 1800

1850

1900

1950

0 2000

Years Source: Oak Ridge National Laboratory, Carbon Dioxide Information Analysis Center

Figure 15.11: This graph shows

that an increase in carbon dioxide (CO2) produced by human activity (green line) coincides with an increase in atmospheric carbon dioxide concentration (blue line). In the last 100 years, the increase has accelerated.

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350

25

Parts per million

Causes of Global climate change refers to changes in the factors used to describe a climate change climate (such as temperature, precipitation, or wind) that last for two or more

significant change in Earth’s climate for an extended time period that happens naturally or is humancaused.

Billion metric tons CO2

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Global climate change is happening now. It’s happening because an increase in greenhouse gases in our atmosphere is causing global warming. A majority of scientists believe that the increase of greenhouse gases is related to human activities such as the burning of fossil fuels. In this section, you will learn more about climate change and its effects on our planet.

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How greenhouse gases work Trapping heat A greenhouse full of plants is a warm place, even on a cold day. Why is that? The

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glass walls and ceiling of a greenhouse allow sunlight that is needed for photosynthesis. The glass also traps heat from the Sun so the greenhouse stays warm. Like glass, greenhouse gases allow the Sun’s radiation to reach Earth’s surface. Some of the Sun’s radiation is emitted by Earth’s surface as infrared radiation (or heat). This form of radiation cannot escape into space easily or quickly. Instead, it gets trapped by greenhouse gases. The greenhouse effect and Earth’s energy balance

What makes a gas a greenhouse gas?

The greenhouse effect is the warming of Earth that results when greenhouse gases trap heat emitted from the planet’s surface (Figure 15.12). This effect happens in spite of the fact that for every 100 units of radiation that enter Earth’s atmosphere, 100 units exit. Here’s why. Radiation that reaches Earth’s surface is mostly in the form of visible and ultraviolet light. These light waves have a higher frequency and shorter wavelength than the infrared waves. The higher frequency waves also pass through the atmosphere faster than the infrared rays. The time lag between incoming and outgoing radiation means energy is available in the atmosphere to keep Earth warm. What makes carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and water vapor (H2O) greenhouse gases? Notice that all of these molecules have at least three atoms joined together. They are larger than the nitrogen (N2) and oxygen (O2) molecules that make up most of Earth’s atmosphere. The larger size of greenhouse gas molecules makes them good absorbers of infrared radiation. As a result, they are most responsible for increasing the time that the Sun’s energy remains in the atmosphere and for making Earth’s average surface temperature comfortably warm, on average about 15°C (59°F).

Global warming The greenhouse gases mentioned above occur in nature. Why then is global is a serious warming a serious concern? The answer to this question is two-fold. First, concern greenhouse gases are dramatically increasing because of fossil fuel use and

deforestation. More greenhouse gases in the atmosphere will trap more heat and cause our planet’s average temperature to increase. Second, an increased average temperature or one that continues to rise will mean global climate change with known and unknown consequences for all living things.

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greenhouse effect - the warming of Earth that results when greenhouse gases trap heat reflecting from the planet’s surface.

The greenhouse effect Sun

Heat escapes after a lag time

N2O

H2O

Visible and ultraviolet light pass through the atmosphere (100 units)

CO

2

CH 4 O3 N O2 2 t trapped by Hea house gases n e e gr

CH4 N2O

O2 N2

CH4 H2O

Infrared radiation (100 units)

Earth Figure 15.12: The greenhouse effect. Without greenhouse gases, Earth’s average temperature would be about 16°C less!

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Upsetting the balance in our atmosphere The Industrial The Industrial Revolution, which lasted from the late 1700s to the mid-1800s, Revolution was a period in which many manual tasks in agriculture and manufacturing

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were replaced by machines. Over time, our world has become full of useful machines. Think of the machines that you use each day. Each of these devices requires an energy source. In our modern world, fossil fuels are used the most as energy sources because they are easily available and affordable. Combustion Using fossil fuels as an energy source requires the process of combustion,

which is very similar to the process of respiration. A combustion reaction, also called burning, takes place when a carbon-based substance, such as wood, oil, or natural gas, combines with oxygen and releases a large amount of energy in the form of light and heat. The products of a combustion reaction are carbon dioxide and water. The general equation for a combustion reaction is as follows:

Greenhouse Gases Carbon dioxide (CO2): 82% of emissions; from burning fossil fuels, respiration, and volcanic activity. Methane (CH4): 9% of emissions, from landfills, the petroleum industry, and agriculture. Nitrous oxide (N2O): 5% of emissions; from fertilizer, burning fossil fuels, and industrial and waste management processes. Ozone (O3): formed when sunlight reacts with air pollutants. Chlorofluorocarbons (CFCs): used as refrigerants. Because these humanmade gases also deplete the ozone layer, their production has been banned in many countries. This table lists the levels of greenhouse gases for the time before the Industrial Revolution and today.

The atmospheric Carbon dioxide, produced by many combustion reactions since the Industrial balance Revolution, is one of the main causes of global warming. Carbon dioxide also

enters the atmosphere whenever respiration takes place. With about one million species of living organisms on our planet, that’s a lot of respiration! Balancing respiration, plants turn carbon dioxide into biomass during photosynthesis. Global warming is happening because of the extra amount of carbon dioxide and other greenhouse gases added to the atmosphere above the natural balance for Earth. Greenhouse gases produced by human activity include carbon dioxide, methane, nitrous oxide, and carbon compounds such as chlorofluorocarbons (CFCs) from industry. Other greenhouse gases include ozone and water vapor, which is the most abundant greenhouse gas. See the sidebar for more information about these gases.

Greenhouse gases Gas

Before the Industrial Revolution

Current level

Carbon dioxide

280 ppm

387 ppm

Methane

700 ppb

1,745 ppb

Nitrous oxide

270 ppb

314 ppb

ppm = parts per million ppb = parts per billion

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Understanding global climate change Svante Svante Arrhenius was a Swedish chemist who won the Nobel Prize in 1903 Arrhenius for his work on acid and base chemistry. Arrhenius is also known for

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recognizing that carbon dioxide (CO2) results from burning fossil fuels and is a greenhouse gas. He calculated that doubling the CO2 in the atmosphere would increase Earth’s temperature by 4–5°C. Arrhenius’s prediction is close to current estimates obtained using computers and modern equipment! Roger Revelle In the 1950s, American oceanographer Roger Revelle noted that the addition and Charles of CO2 to our atmosphere by burning fossil fuels was a giant experiment. Keeling Revelle did not know the consequences of adding more CO2 to Earth’s

atmosphere, so he decided to monitor the effects with fellow scientist Charles Keeling. These two scientists began their now-famous recording of atmospheric levels of CO2 at Mauna Loa Observatory (MLO) in Hawaii. The MLO record showed an increase in CO2 over about a 30-year period. To find out about CO2 levels in the distant past, other scientists have analyzed gas bubbles trapped in glacial ice (Figure 15.13). These records have helped make graphs like the one shown in Figure 15.11.

Al Gore In 1967, Roger Revelle taught a class at Harvard University that was

attended by former Vice President Al Gore. Gore has stated that Revelle’s class inspired him to raise public awareness about global warming. Al Gore starred in An Inconvenient Truth, the Academy Award-winning documentary about global climate change. For his environmental activism, Al Gore, along with the Intergovernmental Panel on Climate Change (IPCC), won the Nobel Peace Prize in 2007.

Kyoto Treaty Between 1997 and 2006, leaders of nations met to discuss the problem of global climate change. Ultimately, it was decided to reduce greenhouse gas emissions by 55 percent, based on 1990 levels. This guideline and others are part of the Kyoto Treaty (commonly referred to as the Kyoto Protocol). In 2001, the United States refused to ratify (approve) the treaty because it feared the guidelines would negatively affect the United States’ economy. However, certain U.S. states and cities that were inspired by the treaty are actively working to reduce greenhouse gas emissions in accord with the Kyoto Treaty. What is happening with the Kyoto Treaty now? Do some research and find out.

IPCC: Many In 1988, the United Nations Environment Program (UNEP) established the scientists in IPCC to address global climate change. The members of the IPCC include action government-nominated scientists who review scientific evidence for climate

change. Members are selected so that there is a balance of points of view, gender, age, and nationality. IPCC reports are produced by three working groups that focus on climate-change issues. The most recent report was published in 2014. This report and all reports by the IPCC are extensively reviewed by hundreds of other scientists before publication.

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Figure 15.13: Ice cores are studied to understand the composition of Earth’s atmosphere in the past.

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Today and the future The current Currently, the amount of carbon dioxide in our atmosphere is 35 percent more state than it was 200 years ago. Below are other indicators that global climate

change is happening. See the sidebar box for the source of this information.

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• Warming temperatures: Ten of the warmest years on record have occurred between 1998 and 2014. A number of warm years in a row indicates that the cause is probably global warming rather than random chance. There is an overall global warming trend from 1906 forward. • Rising sea level: The change in sea level from 1993 to 2003 was approximately 3 millimeters per year for a total rise of about 33 millimeters. The rise is due to (1) oceans absorbing more heat and water expands when it is heated, and (2) more water entering the ocean as glaciers and ice sheets melt. • Decreasing ice coverage: There have been reductions in Arctic Ocean sea ice since 1978 and reductions in the size of glaciers. • Increasing water vapor in the atmosphere: As temperatures rise, more evaporation takes place, leading to more water vapor in the atmosphere. Water vapor is actually the most abundant and effective greenhouse gas. As a result of increased water vapor in the atmosphere, more precipitation and more severe weather have occurred in certain regions of the world. The future The IPCC states that even if greenhouse gases were to stabilize at their current levels, climate change would continue for centuries. This is partly due to the fact that our oceans have a high specific-heat capacity, meaning that they hold heat for a long time. Predictions for the 21st century include:

What can be done about global climate change?

How Do Scientists Know That Human Activities Cause Global Warming? (1) Some greenhouse gases that are accumulating in our atmosphere only come from human sources (e.g., CFCs). (2) Concentrations of greenhouse gases differ from place to place. The highest greenhouse gas concentrations are over the Northern Hemisphere, which has a higher human population. (3) A study of carbon isotopes reveals that the increased levels of carbon dioxide in our atmosphere come directly from the burning of fossil fuels. Isotopes can be traced back to their carbon source.

• An increase in global temperatures ranging from 1.8 to 4.0°C; • A rise in sea level ranging from 30 to 40 centimeters; and • Effects on the oceans, ice cover, and cloud cover that could cause as yet unknown effects on other systems. Global climate change is a serious concern for all people. At present, governments and other organizations are looking at ways to reduce greenhouse gas emissions. What can you do to make a difference? Think about it. Answers to this question will be explored on the next page. 15.2 GLOBAL CLIMATE CHANGE

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Global climate change and you Fingerprints and The IPCC has identified “fingerprints,” which are indicators that global climate harbingers change is happening. The IPCC has also identified “harbingers,” which are

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indicators of events that will increase if greenhouse gas emissions aren’t reduced and if Earth’s average temperature continues to increase. See Figure 15.14 for a list of fingerprints and harbingers.

Global climate change FINGERPRINTS FINGERPRINTS • Heat waves and unusually warm periods • Oceans warming, sea level rising, and coastal flooding • Glaciers and sea ice melting • Warming of the Arctic and Antarctica

! !

What With growing evidence that global climate change is happening due to human governments activities, more governments worldwide are taking action. Here’s what some can do governments are doing: enacting laws that force the reduction of greenhouse gas

emissions; developing alternative, nonpolluting energy resources; and working with other governments to address global climate change. You will learn more about alternative energy resources for generating electricity in Chapter 17. What you can do Most of the energy used in the United States comes from fossil fuels, and most of

the greenhouse gas emissions (such as carbon dioxide) come from the use of fossil fuels. What can you do to help reduce greenhouse gas emissions? To start, you can reduce your carbon footprint. Your carbon footprint is how much greenhouse gas emissions are produced as a result of your activities, both directly and indirectly. Here are suggestions for reducing your carbon footprint: • Reduce your use of electricity. For example, turn off lights when you leave rooms and use efficient lighting sources (like compact fluorescent lamps). • Use less hot water when you take showers and wash your clothes. Heating water takes a lot of energy. • Use less energy to heat or cool your house. Wear a sweater in the winter to stay warm. Close curtains or blinds to keep your house cooler during the summer and warmer in the winter. • Use your own energy for transportation. Walk more or use your bicycle to get from place to place. Or use public transportation to cut down on using fossil fuels for your transportation needs. • Use fewer products made from petrochemicals. For example, reduce your need for plastic bags by taking your own bags to the grocery store. • Grow plants. Plant a tree or a garden. • Educate yourself about global climate change.

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HARBINGERS HARBIN NGERS

• Diseases spreading • Spring arriving earlier than usual around the world (flowers blooming earlier) • Northern migrations and changing population sizes of plants and animals • The bleaching of coral reefs • Heavy rains, snows, and flooding • Droughts and wildfires

Figure 15.14: Fingerprints and

harbingers for global climate change.

Emissions Trading One way to reduce greenhouse gases is by “emissions trading.” Emissions trading depends on businesses having credits to match the amount of emissions they produce. A business that produces less greenhouse emissions than allowed by law can sell credits to a business that produces more. Emissions trading is controversial. Find out why.

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Section 15.2 Review

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1. What is global climate change? Does an unusually warm winter provide evidence for global climate change? Why or why not? 2. Why are greenhouse gases such an important component of our atmosphere? What might Earth be like without greenhouse gases? 3. What are the two main human activities that scientists believe have caused our current condition of global climate change? Explain why each of these activities has led to global climate change. 4. The Industrial Revolution was a revolution in using machines to do more work, more efficiently. How did this revolution affect our global climate? 5. What are the reactants and products of a combustion reaction? 6. How is combustion like respiration? 7. If greenhouse gases are a natural part of Earth’s atmosphere, why are increasing concentrations of these gases a worldwide concern? 8. Who was Svante Arrhenius? 9. Describe the roles played by Roger Revelle and Charles Keating in raising awareness of global climate change. 10. What is the Kyoto Treaty? 11. What does IPCC stand for? Who is involved with the IPCC? 12. Is the work of the IPCC consistent with following the scientific method? Justify your answer. 13. Do you think the reports by the IPCC are trustworthy? Why or why not? 14. List two effects of global climate change that are happening today. 15. List two effects of global climate change that might happen in the future. 16. What is a carbon footprint? 17. Can an infant have a carbon footprint? Explain your answer. 18. The image on the first page of the chapter includes a student who is recycling. How might recycling be a way to reduce your carbon footprint? 19. List five ways that you can reduce the size of your carbon footprint. Which of these do you think will have the greatest impact on reducing greenhouse gas emissions?

Chlorofluorocarbons Chlorofluorocarbons (CFCs) are the only greenhouse gases that come entirely from human sources. All of the other greenhouse gases have natural sources as well as human sources. For example, natural sources of nitrous oxide (N2O) cause 70% of this gas in the atmosphere. Because CFCs were causing the depletion of the ozone layer (which provides Earth with some protection from ultraviolet light), the manufacture of these chemicals in industry has been greatly reduced or banned. However, CFCs are still a problem. Find out why. Write a short paragraph that explains your findings.

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Chapter 15 Assessment Vocabulary

5.

Select the correct term to complete the sentences.

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food chain

respiration

global climate change

ecosystem

global warming

photosynthesis

chemical cycles

greenhouse gases

Section 15.1

1.

An example of a(n) _____ is a tropical rainforest or a field.

2.

The oxygen and carbon cycles are interconnected _____.

3.

A simple _____ consists of a producer, herbivore, and omnivore.

4.

_____ and _____ are two chemical processes that involve carbon dioxide.

Section 15.2

5.

Methane is one of a number of _____.

6.

_____, the increase of Earth’s average temperature due to an increase in greenhouse gases, is an example of _____.

Concepts 1.

Why are chemical cycles important for living organisms?

2.

What does the term biomass mean? Why is biomass mentioned in Section 15.1?

3.

What happens to the carbon in carbon dioxide once it is used by a plant in photosynthesis?

4.

Use the terms producer, consumer, and decomposer to label each member of a meadow ecosystem: dandelions, rabbit, snake, owl, and bacteria.

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a. b. c. d.

Tropical rainforest School gymnasium Rotting log and surroundings A rock

e. f. g. h.

Desert Sun A bean plant A human being

6.

Describe how photosynthesis and respiration are parts of both the water cycle and the oxygen cycle.

7.

Does it make sense to describe the carbon cycle as an energy cycle? Why or why not?

8.

Nitrogen is the most abundant gas in Earth’s atmosphere. However, it is often a limiting factor. Why?

9.

What is the main source of phosphorus? Why is phosphorus important for living organisms?

10. Give three reasons that justify this statement: The water, oxygen, and carbon cycles are interconnected. 11. Why is heat produced as energy and nutrients flow from producers to consumers to decomposers to producers? Section 15.2

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Which of the following would be considered an ecosystem? (You may choose more than one.) Justify your answer.

12. True or false? If a statement is false, rewrite it so that it is true. a. b. c. d.

Greenhouse gases are a natural part of Earth’s atmosphere. Only increased concentrations of carbon dioxide are causing global warming. Global climate change can be caused only by human activity. Greenhouse gas emissions have been increasing in Earth’s atmosphere since the Industrial Revolution.

13. Explain the greenhouse effect in your own words.

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14. How are chloroflurocarbons different from other greenhouse gases?

3.

15. Why was the work of Revelle and Keeling important for stating the case that global climate change is happening?

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17. What are governments doing to address global climate change?

Problems Section 15.1

1.

A food web is a combination of many food chains. For the food web below: a. b.

Name two producers, three herbivores, four carnivores, and two omnivores. Identify two decomposers (“nature’s recyclers”) that could be involved in the ecosystem shown below.

The following “to do” list was suggested in this chapter as a way to reduce greenhouse gas emissions and your carbon footprint. Explain why doing each item will help you achieve your goal. a. b. c. d. e. f.

16. Give two reasons that indicate that human activity is causing global climate change.

CHAPTER 15

Reduce your use of electricity. Use less hot water when you wash your clothes. Use less energy to heat or cool your house. Ride a bicycle instead of using a car. Use fewer products made from petrochemicals. Grow plants. Plant a tree or plant a garden.

Applying Your Knowledge Section 15.1

1.

Research the term chemosynthesis on the Internet. Explain chemosynthesis and then provide an explanation for why the statement “All living things require energy from the Sun” is not true.

2.

The white cliffs of Dover along the British coastline are an impressive site to see. Find out how these white cliffs represent part of the carbon cycle.

Section 15.2

3.

For each of the following, research the topic and write a short essay about it. a.

Section 15.2

2.

How are these events related? (a) Heat is released when fossil fuels are burned. (b) A pile of decomposing grass clippings releases heat.

b. c.

One of the responses to global climate change is to develop new technology to “vacuum” carbon dioxide from the air rather than focus on reducing greenhouse gas emissions. Research the pros and cons of developing this new technology to solve global warming. Find out more about existing technology focused on carbon capture and storage. What are your ideas for addressing global climate change? What do you think people and governments should do?

CHAPTER 15 ASSESSMENT

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Unit 5 Electricity and Magnetism FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

CHAPTER 16 Electricity CHAPTER 17  Magnetism

‹ Try this at home Find a strong magnet and some breakfast cereal that is advertised as “iron fortified.” Place a small amount of cereal in a freezer-type zip top bag and gently crush the cereal into a fine powder. Spread some of the powder out into a thin layer inside the bag. Hold the magnet over the thin layer (outside the bag) and move it around. You will see pieces of the cereal moving with the magnet! Iron-fortified cereal actually has bits of iron metal in it, and the iron is attracted to the magnet.

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16

CHAPTER 16

Electricity

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Suppose you had a stationary bicycle that was connected to a light bulb so that when you pedaled the bicycle, the energy from the turning wheels lit the bulb. How fast would you have to pedal to generate enough electrical energy to light the bulb? You might be surprised at how fast you would have to pedal to do something that seems so simple. Some science museums have interactive exhibits like this bicyclepowered light bulb to help people see how much energy is needed to accomplish everyday tasks. What would your life be like without electricity? You can probably name at least a dozen aspects of your morning routine alone that would change if you didn’t have electricity. Do you know how electrical circuits work? Do you know what voltage and current mean? This chapter will give you the opportunity to explore electricity, electrical circuits, and the nature of electrical energy. Electricity can be powerful and dangerous, but when you know the basic facts about how electricity works, you can use electricity safely and with confidence.

4 What is inside an AA battery, and how does a battery work?

4 Why is the shock from a household outlet more dangerous if your skin is wet?

4 Are there electrical circuits in the human body? In an electric eel?

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16.1 Charge and Electric Circuits Like mass, charge is a fundamental property of all matter, but one that can easily be overlooked. All matter has electrical properties because the atoms that make up matter contain protons and electrons. In this chapter, you will learn about charge and electric circuits. Many of the devices that we rely on, such as televisions and computers, exist because of electric charge and circuits.

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Positive and negative charge Two kinds of Virtually all of the matter around you has electric charge because all atoms electric charge contain electrons (–) and protons (+). However, unlike mass, electric charge

is usually hidden inside atoms. Charge is hidden because atoms are made with equal amounts of positive and negative charges. The forces from positive charges are canceled by negative charges, the same way that +1 and –1 add up to 0. Because ordinary matter has zero net (total) charge, most matter acts as if there is no electric charge at all, and is said to be electrically neutral.

positive, negative - the two kinds of electric charge.

electrically neutral - describes an object that has equal amounts of positive and negative charges. coulomb - the unit for electric charge.

charged - describes an object whose net charge is not zero.

static electricity - caused by a tiny imbalance between positive and negative charge on an object.

Like charges Whether two charges attract or repel depends on whether they are the same or repel and unlike opposite. A positive and a negative charge will attract each other. Two charges attract positive charges will repel each other. Two negative charges will also repel each other. The unit of charge is the coulomb (C). The name was chosen in

honor of Charles Augustin de Coulomb (1736–1806), a French physicist who performed the first accurate measurements of the force between charges. Charged objects An object is charged when its net charge is not zero. If you have ever felt a

shock when you have touched a doorknob (Figure 16.1) or removed clothes from a dryer, you have had contact with a charged object. An object with more negative than positive charge has a negative net charge. If it has more positive than negative charge, the object has a positive net charge. The net charge is also sometimes called excess charge because a charged object has an excess of either positive or negative charges.

Figure 16.1: The shock you get from

touching a doorknob on a dry day comes from a tiny imbalance of charge.

Static electricity A tiny imbalance in either positive or negative charge on an object is the and charge cause of static electricity. The static electricity you feel when taking

clothes from a dryer or scuffing your socks on a carpet typically results from an excess charge of less than one-millionth of a coulomb.

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Electricity and electric circuits What is You just learned that static electricity is caused by a charge imbalance. The electricity? word static in this case refers to lack of movement. The charge builds up and

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it might discharge, but it does not always flow in a controlled pathway. The regular electricity that we use on a daily basis, on the other hand, occurs when there is a complete pathway for moving charges. The use of electricity has become so routine that most of us never stop to think about what happens when we switch on a light. Circuits usually consist of wires that carry electricity and devices that use the electricity. Electricity refers to the flow of electric current in wires, motors, light bulbs, and other objects. Electric current is almost always invisible and comes from the motion of electrons or other charged particles.

electricity - the science of electric charge and current. electric current - the flow of electric charge.

electric circuit - a complete path through which electric charge flows.

Electricity An electric circuit is a complete path through which electricity travels. A travels in good example of a circuit is the one in an electric toaster. Bread is toasted by circuits heaters that convert electrical energy to heat. The circuit has a switch that

turns on when the lever on the side of the toaster is pushed down. With the switch on, electric current enters through one prong of the plug from the socket in the wall, and goes through the toaster and out the other prong. Wires are like Wires in electric circuits are similar in some ways to pipes and hoses that pipes for carry water (Figure 16.2). Wires act like pipes for electric current. Current electricity enters the house on the supply wire and leaves on the return wire. The big

difference between wires and water pipes is that you can’t get electricity to leave a wire the way you can get water to leave a pipe. Examples of Circuits are not confined to appliances, wires, and devices built by people. circuits in The first experience humans had with electricity was in the natural world. nature Following are some examples of natural circuits.

• The tail of an electric eel makes a circuit when it stuns a fish with a jolt of electricity. • The Earth makes a gigantic circuit when lightning carries electric current between the clouds and the ground. • The nerves in your body form an electric circuit that carries messages from your brain to your muscles.

Figure 16.2: Comparing “circuits” for water and electricity.

16.1 CHARGE AND ELECTRIC CIRCUITS

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Circuit diagrams and electrical symbols Circuit diagrams Circuits are made up of wires and electrical parts such as batteries, light bulbs,

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motors, and switches. When designing a circuit, drawings are made to show how the parts are connected. These drawings are called circuit diagrams. In a circuit diagram, symbols are used to represent each part of the circuit. Using these electrical symbols makes drawing circuits quicker and easier than drawing realistic pictures of each part of the circuit.

resistor - a device that uses energy carried by electric current; resistors are often used to control current in a circuit.

Electrical A circuit diagram is a shorthand method of describing a working circuit. The symbols electrical symbols used in circuit diagrams are standard so that anyone

familiar with electricity can build the circuit by looking at the diagram. Figure 16.3 shows some common parts of a circuit and their electrical symbols. The picture below shows an actual circuit on the left and its circuit diagram on the right. Can you identify the real parts with their symbols? Note that the switch is open in the circuit diagram, but closed in the actual circuit. Closing the switch completes the circuit so the light bulb lights.

Resistors A resistor is an electrical device that uses or controls the energy carried by

electric current. In many circuit diagrams, any electrical device that uses energy is shown with a resistor symbol. A light bulb, heating element, speaker, or motor can be drawn with a resistor symbol. Later in this chapter you will learn how resistors are used in electric circuits.

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Figure 16.3: These electrical

symbols are used when drawing circuit diagrams.

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Open and closed circuits Batteries All electric circuits must have a source of energy. Circuits in your home get

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their energy from power plants that generate electricity. Circuits in flashlights, cell phones, cameras, and portable radios get their energy from batteries. Some calculators have solar cells that convert energy from the Sun or other sources of light into electrical energy. Of all the types of circuits, those with batteries are the easiest to understand. We will focus on battery circuits for now and will eventually learn how circuits in buildings work.

closed circuit - a circuit with no breaks so charge can flow. open circuit - a circuit with a break so charge cannot flow.

switch - a device that controls the flow of electricity in a circuit.

Open and We want to be able to turn light bulbs, radios, and other devices used in closed circuits circuits on and off. One way to turn off a device is to stop the current by

“breaking” the circuit. Electric current can only flow when there is a complete and unbroken path from one end of the circuit to the other. A circuit with no breaks is called a closed circuit. A light bulb will light only when it is part of a closed circuit. Opening a switch or disconnecting a wire creates a break in the circuit and stops the current. A circuit with any break in it is called an open circuit (Figure 16.4). Switches Switches are used to turn electricity on and off. Flipping a switch to the off

position creates an open circuit by making a break in the wire. The break stops the current because electricity cannot normally travel through air. Flipping a switch to the on position closes the break and allows the current to flow again, supplying energy to the bulb, radio, or other device. Breaks in A switch is not the only way to make a break in a circuit. An incandescent circuits light bulb burns out when the thin wire that glows inside it breaks. This

creates an open circuit and explains why a burned-out bulb cannot light. Today, incandescent bulbs are being replaced with compact fluorescent light bulbs (CFLs), which use less electrical energy to put out the same amount of light. CFLs work differently than incandescent bulbs. Instead of having a thin wire inside that gets heated, a CFL is a coiled glass tube that contains a gas. When the circuit is closed, electricity passes through the gas-filled tube and causes the atoms in the gas to emit light. Just like incandescent bulbs however, when a CFL bulb does finally quit working, the circuit will be broken and the CFL will need to be replaced.

Figure 16.4: There is current in a

closed circuit but not in an open circuit.

16.1 CHARGE AND ELECTRIC CIRCUITS

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Section 16.1 Review

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1. Explain the difference between an electrically charged object and a neutral object. Does a neutral object contain any electric charge at all?

Lightning and Charged Particles

2. If you rub an air-filled balloon on your hair, you can make it stick to a wall. When the balloon and your hair are rubbed together, electrons are transferred from your hair to the balloon.

Lightning is caused by a giant buildup of static charge. Before a lightning strike, particles in a cloud collide, and charges are transferred from one particle to another. The forces of gravity and wind cause the different particles to separate. Positively charged particles accumulate near the top of the cloud and negatively charged particles fall toward the bottom. These negatively charged cloud particles repel negative charges in the ground, causing the ground to become positively charged. The negative charges in the cloud are attracted to the positively charged ground. The cloud, air, and ground can act like a giant circuit. All the accumulated negative charges flow from the cloud to the ground, heating the air along the path (to as much as 20,000°C) so that the air glows like a bright streak of light.

a. Is the net charge on the balloon after it is rubbed on your hair positive, negative, or zero? b. What do you think happens to the atoms near a wall’s surface when the charged balloon is brought near the wall? (Hint: The balloon will stick to the wall.) c. What happens when you try to stick a charged balloon to a metal object, such as a doorknob? Try it or do some research to find the answer and explain. Don’t forget to include website and/or book citations. 3. How are electric circuits and systems for carrying water in buildings similar? 4. Give one example of a circuit found in nature and one example of a fabricated circuit. 5. What is the difference between an open circuit and a closed circuit? 6. How does a resistor function in a circuit? Give an example. 7. Use the circuit diagram at the right to answer the following questions. a. b. c. d. e.

How many bulbs are there in this circuit? How many batteries? How many resistors? How many switches? Is this circuit open or closed? Justify your answer.

8. When you turn a light switch to the on position, does this open or close the circuit? Explain.

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16.2 Current and Voltage Current is what carries energy in a circuit. Like water current, electric current only flows when there is a difference in energy between two locations that are connected. Water flows downhill from higher gravitational potential energy to lower energy. Electric current flows “downhill” from higher electrical potential energy to lower electrical potential energy.

ampere - the unit of electric current.

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Current Measuring Electric current is measured in units called amperes (A), or amps for short. electric current The unit is named in honor of Andre-Marie Ampere (1775–1836), a French

physicist who studied electricity and magnetism. A small battery-powered flashlight bulb uses about 1/2 amp of electric current. Conventional current flows from positive to negative

Examine a battery and you will find a positive and a negative end. The positive end on an AA, C, or D battery has a raised bump, and the negative end is flat. In a circuit diagram, a battery’s electrical symbol uses a long line to show the positive end and a short line to show the negative end.

Current in Electric current from a battery flows out of the positive end and returns back equals current in at the negative end. An arrow can be used to show the direction of current out on a circuit diagram (Figure 16.5). In most electric circuits, negative charge

flows, so you would think the correct direction would be negative to positive. It is practical and conventional, however, to describe current as flowing from positive to negative, or from high voltage to low voltage. The amount of electric current coming out of the positive end of the battery must always be the same as the amount of current flowing into the negative end. You can picture this by imagining steel balls flowing through a tube. When you push one ball into the tube, one ball comes out the other end. The rate at which the balls flow in equals the rate at which they flow out.

Figure 16.5: Direction of electric

current (Conventional diagrams show flow from positive to negative.)

Either positive or negative charges can create an electric current, depending on the circuit materials. In the human body, current is the movement of both positive and negative charges. In ordinary electric circuits, current is the movement of negative charge in metal conductors.

16.2 CURRENT AND VOLTAGE

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Voltage Energy and Voltage is a measure of electric potential energy, just like height is an voltage indicator of gravitational potential energy. Voltage is measured in volts (V).

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Like other forms of potential energy, a voltage difference means there is energy that can be used to do work. Current is what actually flows and does work. A difference in voltage provides the energy that causes current to flow (Figure 16.6). What voltage A voltage difference of 1 volt means 1 amp of current does 1 joule of work in 1 means second. Since 1 joule per second is a watt (power), voltage is the power per

amp of current that flows. Every amp of current flowing out of a 1.5-volt battery carries 1.5 watts of power. The voltage in your home’s electrical system is 120 volts, which means each amp of current carries 120 watts of power.

voltage - a measure of electric potential energy.

volt - the unit for voltage. multimeter - a measuring instrument for current, voltage, and resistance.

battery - a device that transforms chemical energy to electrical energy, and provides electrical force in a circuit.

Using a meter to A voltmeter measures voltage. A more useful meter is a multimeter, which measure voltage can measure voltage or current, and sometimes also resistance. To measure

voltage, the meter’s probes are touched to two places in a circuit or across a battery. The meter shows the difference in voltage between the two places.

Batteries A battery uses chemical energy to create a voltage difference between its

two terminals. When current leaves a battery, it carries energy. The current gives up its energy as it passes through an electrical device such as a light bulb. When a bulb is lit, the electrical energy is taken from the current and is transformed into light and heat energy. The current returns to the battery, where it gets more energy.

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Figure 16.6: A change in height

causes water to flow through a pipe. Current flows in this circuit because a battery creates a voltage difference.

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Measuring current in a circuit Measuring Electric current can be measured with a multimeter. However, if you want to current with a measure current you must force the current to pass through the meter. That meter usually means you must break the circuit somewhere and rearrange wires so

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that the current flows through the meter. For example, Figure 16.7 shows a circuit with a battery and bulb. The meter has been inserted into the circuit to measure current. If you trace the wires, the current comes out of the positive end of the battery, through the light bulb, through the meter, and back to the battery. The meter in the diagram measures 0.37 amps of current. Some electrical meters, called ammeters, are designed specifically to measure only current. Setting up the If you use a multimeter, you must remember to set its dial to measure the type meter of current in your circuit. Multimeters can measure two types of electric

current, called alternating current (AC) and direct current (DC). You will learn about the difference between alternating and direct current in the next chapter. For circuits with light bulbs and batteries, you must set your meter to read direct current, or DC. The symbols for AC and DC are shown in Figure 16.8. Protecting the A meter can be damaged if too much current passes through it. Always be meter sure there is a light bulb or some other resistor in the circuit when you use the

meter. Without a bulb or other resistor to use some of the current, the circuit’s current might become too high for the meter and can cause an overload.

Figure 16.7: Current must pass through the meter when it is being measured.

To protect its delicate electronics, most meters contain a circuit breaker or fuse. Circuit breakers and fuses are fast-acting, automatic switches that open a circuit if they sense too much current. A circuit breaker can be reset the way a switch can be flipped. A broken fuse, however, is similar to a burned out light bulb and must be replaced for the meter to work again. The meter you use in your electric circuit investigations has a fuse inside. To replace the fuse, you will need a replacement fuse and a small screwdriver to open up the back of the meter. Your teacher can show you how this is done. To make your investigations easier, be careful when measuring current and you won’t have to replace the fuse!

Figure 16.8: A multimeter often uses these symbols for AC and DC settings.

16.2 CURRENT AND VOLTAGE

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Section 16.2 Review 1. List the units for measuring current and voltage. 2. What is the difference between current and voltage, besides their units of measurement?

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3. Why does a multimeter display a reading of zero when both of its probes are touched to the same end of a battery? 4. The direction of electric current is away from the _____ end of the battery and toward the _____end. 5. What voltage would the electrical meter show in each of the diagrams below? Figure 16.9: Question 7.

6. Which of the following diagrams shows the correct way to measure current in a circuit?

7. A flashlight needs three C batteries. How many volts of electricity does it need (Figure 16.9)?

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16.3 Resistance and Ohm’s Law You can apply the same voltage to different circuits and different amounts of current will flow. For example, when you plug in a desk lamp, the current through it is 1 amp. If a hair dryer is plugged into the same outlet (with the same voltage) the current is 10 amps. For a given voltage, the amount of current that flows depends on the resistance of the circuit.

resistance - determines how much current flows for a given voltage. Higher resistance means less current.

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Electrical resistance Current and Resistance is the measure of how strongly a wire or other object resists resistance current flowing through it. A device with low resistance, such as a copper

wire, can easily carry a large current. An object with a high resistance, such as a rubber band, can only carry a current so tiny it can hardly be measured. A water analogy The relationship between electric current and resistance can be compared

with water flowing from the open end of a bottle (Figure 16.10). If the opening is large, the resistance is low and lots of water flows out quickly. If the opening is small, the resistance is greater and the water flow is slow. Circuits The total amount of resistance in a circuit determines the amount of current in

the circuit for a given voltage. Every device that uses electrical energy adds resistance to a circuit. The more resistance the circuit has, the less the current. For example, if you string several light bulbs together in a circuit, the resistance in the circuit increases and the current decreases, making each bulb dimmer than a single bulb in the same circuit would be. Figure 16.10: The current is less when the resistance is greater.

16.3 RESISTANCE AND OHM’S LAW

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Measuring resistance The ohm Electrical resistance is measured in units called ohms. This unit is abbreviated with the Greek letter omega (Ω). When you see Ω in a sentence, think or read

ohm - the unit of measurement for resistance.

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“ohms.” For a given voltage, the greater the resistance, the less the current. If a circuit has a resistance of 1 ohm, then a voltage of 1 volt causes a current of 1 amp to flow.

Figure 16.11: A multimeter can be used to measure resistance of a device.

How Resistance Is Measured

Resistance of The wires used to connect circuits are made of metals that have low resistance wires such as copper or aluminum. The resistance of wires is usually so low

compared with other devices in a circuit that you can ignore wire resistances when measuring or calculating the total resistance. The exception is when there are large currents. If the current is large, the resistance of wires might be important. Measuring You can use a multimeter to measure the resistance of wires, light bulbs, resistance and other devices (Figure 16.11). You must first remove the device from the

circuit. Then set the dial on the multimeter to the resistance setting and touch the probes to each end of the device. The meter will display the resistance in ohms (Ω), kilo-ohms (× 1,000 Ω), or mega-ohms (× 1,000,000 Ω).

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A multimeter contains a battery with a fixed voltage. When the fixed voltage is applied to the device, the meter measures the resulting current and calculates the resistance. For example, if you want to measure the resistance of a light bulb, you would remove it from the circuit so the meter can apply a precise amount of voltage to the bulb and give an accurate resistance value. If you left the bulb in the circuit, other circuit current might interfere with the operation of the meter.

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Ohm’s law Ohm’s law The current in a circuit depends on the battery’s voltage and the circuit’s

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resistance. Voltage and current are directly related. Doubling the voltage doubles the current. Resistance and current are inversely related. Doubling the resistance cuts the current in half. These two relationships form Ohm’s law. The law relates current, voltage, and resistance with one formula. If you know two of the three quantities, you can use Ohm’s law to find the third. You might think it seems strange to use I as the variable symbol for current, rather than C. This is a convention that started many years ago and is still used today.

Applying Ohm’s Ohm’s law shows how resistance is used to control the current. If the law resistance is low, then a given voltage will result in a large amount of current.

Devices that need a large amount of current typically have lower resistance, to allow the device to get the large amount of current it needs. For example, a small electric motor might have a resistance of only 1 ohm. When connected in a circuit with a 1.5-volt battery, the motor draws 1.5 amps of current. By comparison, a small light bulb with a resistance of 2.5 ohms in the same type of circuit would draw only 0.6 amps. Equation

Gives you...

If you know...

I = V/R

current (I)

voltage and resistance

V = IR

voltage (V)

current and resistance

R = V/I

resistance (R)

voltage and current

Ohm’s law - states that the current is directly related to the voltage and inversely related to the resistance.

Why does a meter show no voltage when the leads are placed on the same point in a closed circuit? Placing multimeter leads on only one side of a component in a circuit is like trying to measure the height difference of a tipped water pipe by placing both ends of the measuring tape at the same point—it simply doesn’t work! The pipe’s height difference is what allows the water to move. Likewise, the charge separation, or voltage, in a circuit, is what allows charge to flow. To measure how much voltage there is at different places in a circuit, you must place the multimeter leads across a component. Similarly, if you want to measure the height difference of the water pipe, you must place the measuring tape across the distance, not just at the raised end.

16.3 RESISTANCE AND OHM’S LAW

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Solving Problems: Using Ohm’s Law A toaster oven has a resistance of 12 Ω and is plugged into a 120-V outlet. How much current does it draw?

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1. Looking for:

You are asked for the current in amperes.

2. Given:

You are given the resistance in ohms and voltage in volts.

3. Relationships:

Ohm’s law: I =

4. Solution:

Plug in the values for V and R: I =

Superconductivity A superconductor allows current to flow without losing any energy as heat or light. Do some research. What kinds of technology have been developed on the principles of superconductivity? What future technologies are being explored?

V R 120 V =10 A 12 Ω

Your turn...

a. A laptop computer runs on a 24-V battery. If the resistance of the circuit inside is 16 Ω, how much current does it use? b. A motor in a toy car needs 2 A of current to work properly. If the car runs on four 1.5-V batteries (in series), what is the motor’s resistance? c. What is the current in the circuit below?

The levitated dipole experiment (LDX) at the Massachusetts Institute of Technology (MIT) uses a superconducting coil to explore fusion technology.

a. 1.5 A b. 3 Ω c. 3 A

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The resistance of common objects Resistance matches operating voltage

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The resistance of electrical devices ranges from small (0.001 ohms) to large (10 × 106 ohms). Every electrical device is designed with a resistance that causes the right amount of current to flow when the device is connected to the proper voltage. For example, a 100-watt light bulb has a resistance of 144 ohms. When connected to 120 volts from a wall socket, the current is 0.83 amps and the bulb lights (Figure 16.12). If you connect the same light bulb to a 1.5-volt battery it will not light. According to Ohm’s law, the current is only 0.01 amps when 1.5 volts is applied to a resistance of 144 ohms. This amount of current will not light the bulb. All electrical devices draw the right amount of power only when connected to the voltage they were designed for.

The resistance Electrical outlets are dangerous because you can get a fatal shock by touching of skin the wires inside. So, why can you safely handle a 9-volt battery? The reason is

Ohm’s law. The typical resistance of dry skin is 100,000 ohms or more. According to Ohm’s law, 9 V ÷ 100,000 Ω is only 0.00009 A. This is not enough current to be harmful. On average, nerves in the skin can feel a current of around 0.0005 amps. You can get a dangerous shock from 120 volts from a wall socket because that is enough voltage to force 0.0012 amps (120 V ÷ 100,000 Ω) through your skin, and you certainly can feel that!

Figure 16.12: A light bulb designed for use in a 120-volt household circuit does not light when connected to a 1.5-volt battery.

Water lowers Wet skin has much lower resistance than dry skin. Because of the lower skin’s resistance, the same voltage will cause more current to pass through your resistance body when your skin is wet. The combination of water and 120-volt

electricity is especially dangerous because the high voltage and lower resistance make it possible for large (possibly fatal) currents to flow. Changing The resistance of many electrical devices varies with temperature. For example, resistance the amount of resistance a light bulb contributes to a circuit increases as its

temperature increases (due to the current running through it). Devices that have a variable resistance like this are referred to as non-ohmic, because you can’t use Ohm’s law to predict the current when there is an ever-changing resistance (Figure 16.13). The small light bulbs in your circuit kit are non-ohmic, so you will use fixed resistors to apply Ohm’s law to your simple circuits.

Figure 16.13: The resistance of

many materials, including those in light bulbs, increases as their temperature increases. A light bulb is said to be non-ohmic for this reason.

16.3 RESISTANCE AND OHM’S LAW

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Conductors and insulators Conductors Current passes easily through some materials, such as copper, which are called conductors. A conductor can conduct, or carry, electric current. The

electrical resistance of wires made from conductors is low. Most metals are good conductors.

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Insulators Other materials, such as rubber, glass, and wood, do not allow current to easily pass through them. These materials are called insulators because

they insulate against, or block, the flow of current. Semiconductors Some materials are in between conductors and insulators. These materials are called semiconductors because their ability to carry current is higher

conductor - a material with low electrical resistance. Metals such as copper and aluminum are conductors. insulator - a material with high electrical resistance. Plastic and rubber are good insulators. semiconductor - a material between conductor and insulator in its ability to carry current.

than an insulator but lower than a conductor. Computer chips, televisions, and portable radios are among the many devices that use semiconductors. You might have heard of a region in California called Silicon Valley. Silicon is a semiconductor commonly used in computer chips. This area south of San Francisco is called Silicon Valley because many semiconductor and computer companies are located there. Comparing No material is a perfect conductor or insulator. Some amount of current materials will always flow through any material if a voltage is applied, and even

copper (a good conductor) has some resistance. Figure 16.14 shows how the resistances of various conductors, semiconductors, and insulators compare. Applications of Both conductors and insulators are conductors and necessary materials in technology. insulators For example, a wire has one or more

conductors on the inside and an insulator on the outside. An electrical cable might have twenty or more conductors, each separated from the others by a thin layer of insulator. The insulating layer prevents the other wires or other objects from being exposed to the current and voltage carried by the conducting core of the wire.

Figure 16.14: Comparing the resistance of materials.

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Resistors Resistors are As you have learned, resistors are used to control the current in circuits. They used to control are found in many common electronic devices such as computers, televisions, current telephones, and stereos.

potentiometer - a type of variable resistor that can be adjusted to give resistance within a certain range.

Fixed resistors There are two main types of resistors: fixed and variable. Fixed resistors have

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a resistance that cannot be changed. If you have ever looked at a circuit board inside a computer or other electrical device, you have seen fixed resistors. They are small, skinny cylinders or rectangles with colored stripes on them. Because resistors are so tiny, it is impossible to label each one with the value of its resistance in numbers. Instead, the colored stripes are a code that tells you the resistance (see below).

Variable Variable resistors, also called potentiometers, can be adjusted to have resistors a resistance within a certain range. If you have ever turned a dimmer switch

or volume control, you have used a potentiometer. When the resistance of a dimmer switch increases, the current decreases, and the bulb gets dimmer. Inside a potentiometer is a circular resistor and a little sliding contact called a wiper (Figure 16.15). If the circuit is connected at A and C, the resistance is always 100 ohms. But if the circuit is connected at A and B, the resistance can vary from 0 ohms to 100 ohms. Turning the dial changes the resistance between A and B and also changes either the current or the voltage in the circuit.

Figure 16.15: The resistance of this potentiometer can vary from 0 ohms to 100 ohms.

16.3 RESISTANCE AND OHM’S LAW

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Section 16.3 Review 1. List the units and their abbreviations for resistance, voltage, and current.

Extension Cord Safety

2. What happens to the current if a circuit’s resistance increases?

The label on an extension cord will tell you how many amps of current it can safely carry. The length and wire thickness are both important. Always check to see if the extension cord can carry at least as much current as the device you plug in will require. Many fires have been caused by using the wrong extension cord!

3. What happens to the current if a circuit’s voltage increases?

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4. A circuit contains one light bulb and a battery. What happens to the total resistance in the circuit if you replace the one light bulb with a string of four identical bulbs? Why? 5. Why can you safely handle a 1.5-V battery without being electrocuted? 6. A flashlight bulb has a resistance of about 6 Ω. It works in a flashlight with two AA alkaline batteries. About how much current does the bulb draw? 7. What voltage produces a 6-A current in a circuit that has a total resistance of 3 Ω? 8. What is a circuit’s resistance if 12 V produces 2 A of current? 9. If you plug a device that has a resistance of 15 Ω into a 120-V outlet, how much current does the device draw? 10. What is the difference between a conductor and an insulator? Give an example of each. 11. Do some research to find out why semiconductors are so important to computer technology. Don’t forget to include website and/or book citations. 12. What is a fixed resistor, and where could you find fixed resistors in your home? 13. What is a variable resistor, and where could you find variable resistors in your home? 14. Look on the back or underside of different appliances and devices in your home. Find two that list the current and voltage each uses. Calculate the resistance of each.

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16.4 Types of Circuits We use electric circuits for thousands of things, from flashlights to computers, cars, and satellites. There are two basic ways circuits can be built to connect different devices. These two types of circuits are called series and parallel. Series circuits have only one path for the current. Parallel circuits have branching points and multiple paths for the current.

series circuit - an electric circuit that has only one path for current.

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What is a series circuit? A series circuit has one path

A series circuit contains only one path for electric current to flow. This means the current is the same at all points in the circuit. All the circuits you have studied so far have been series circuits. For example, two D-cells and three identical + – bulbs connected in a loop form a series circuit because there is only one path through the circuit (Figure 16.16). The current is the same in each bulb, so they are equally bright.

Figure 16.16: A series circuit.

A series circuit has only one path for the current, so the current is the same at any point in the circuit. Series circuit in If there is a break at any point in a series circuit, the current will stop holiday lights everywhere in the circuit. Inexpensive strings of holiday lights are wired with

the bulbs in series. The bulbs are rated for 2.5 volts each, and with 50 of them wired in series, the string runs well when plugged into a 120-volt outlet. Manufacturers and marketing specialists like to work with nice round numbers. With 50 bulbs in a strand that is plugged into a 120-volt outlet, each bulb will get (120/50) 2.4 volts. This works just fine, even though the bulbs are rated at 2.5 volts each. If you remove one of the bulbs from its socket, the whole string of mini bulbs will go out. However, if a bulb’s filament burns out, but the bulb is still in the socket, the string will stay lighted. How does this work? Modern 2.5-volt mini bulbs have a special backup wire to carry the current when a filament breaks (Figure 16.17). As long as the burned-out bulb is still in the socket, the series circuit will not be broken because the current can travel through the backup wire (often called a shunt).

Figure 16.17: A strand of 50 mini bulbs has a backup wire inside. If the filament burns out, current can flow through the backup wire, and the rest of the bulbs in the strand can stay lit.

16.4 TYPES OF CIRCUITS

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Current and resistance in a series circuit Using Ohm’s law You can use Ohm’s law to calculate the current in a circuit if you know the

voltage and resistance. If you are using a battery, you know the voltage from the battery. If you know the resistance of each device, you can find the total resistance of the circuit by adding up the resistance of each device.

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Adding Adding resistances is like adding pinches to a hose (Figure 16.18). Each resistances pinch adds some resistance. The total resistance is the sum of the resistance

from each pinch. To find the total resistance in a series circuit, you add the individual resistances.

Figure 16.18: Adding resistance in a circuit is like adding pinches in a hose. Why aren’t birds electrocuted?

Ignoring resistance from wires in simple circuits

Everything has some resistance, even wires. However, the resistance of a wire is usually so small compared with the resistance of light bulbs and other devices that we can ignore the resistance of the wire in the simple circuits we build and analyze.

If high-voltage wires are so dangerous, how can birds sit on them without being instantly electrocuted? First, the bird’s body has a higher resistance than the electrical wire. The current tends to stay in the wire because the wire is an easier path. The most important reason, however, is that the bird has both feet on the same wire. That means the voltage is the same on both feet, and no current flows through the bird.

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Solving Problems: Current in a Series Circuit A series circuit contains a 12-V battery and three bulbs with resistances of 1 Ω, 2 Ω, and 3 Ω. What is the current in the circuit (Figure 16.19)?

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1. Looking for:

You are asked for the current in amps.

2. Given:

You are given the voltage in volts and resistances in ohms.

3. Relationships:

Rtot = R1 + R2 + R3 Ohm’s law: I = V/R

4. Solution:

Rtot = 1 Ω + 2 Ω + 3 Ω = 6 Ω

Figure 16.19: What is the current in the circuit?

I = (12 V)/(6 Ω) = 2 A Your turn...

a. A string of five lights runs on a 9-V battery. If each bulb has a resistance of 2 Ω, what is the current? b. A series circuit operates on a 6-V battery and has two 1-Ω resistors. What is the current?

a. 0.9 A

c. A string of 50 mini-bulbs is wired in series. Each bulb has a resistance of 7 Ω. The string is plugged into a 120-V outlet. How much current does the string of lights draw?

c. 0.3 A

b. 3 A

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Energy and voltage in a series circuit Energy changes Energy cannot be created or destroyed. The devices in a circuit convert forms electrical energy into other forms of energy. The rate of energy transfer that

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takes place is called power, measured in watts. Each device requires power to work properly, so the power carried by the current is reduced. As a result, the voltage in the circuit is lower after each device that uses power. This is known as the voltage drop. The voltage drop is a reduction of electrical potential across an electrical device that has current flowing through it. Charges lose Consider a circuit with three bulbs and two batteries (illustration C below). their energy The voltage is 3 volts, which means that each amp of current leaves the

battery carrying 3 watts. Each bulb changes one third of the power into light and heat. Because the first bulb uses 1 watt, the voltage drops from 3 volts to 2 volts as the current flows through the first bulb. Remember, the current in a series circuit is the same everywhere! As power gets used, voltage drops. Voltage If the three bulbs are identical, each gives off the same amount of light and heat. Each uses the same amount of power. A meter will show the voltage drop from 3 volts to 2 volts to 1 volt, and finally down to 0 volts after the last bulb. After passing through the last bulb, the current returns to the battery where it is given more power and the cycle starts over.

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voltage drop - the reduction of electrical potential across an electrical device that has current flowing through it.

STUDY SKILLS Voltage in a Series Circuit To remember how voltage works in a series circuit, think of the word share (series/share). If circuit components are wired in series, the components share the total voltage available.

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Voltage drops and Ohm’s law Voltage drops Each separate bulb or resistor creates a voltage drop. The voltage drop across

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Ohm’s law

Energy conservation

Applying Kirchhoff’s law

a bulb is measured by connecting an electrical meter’s leads at each side of the bulb (Figure 16.20). The greater the voltage drop, the greater the amount of power being used per amp of current flowing through the bulb. The voltage drop across a resistance is determined by Ohm’s law in the form V = IR. The voltage drop (V) equals the current (I) multiplied by the resistance (R) of the device. In a series circuit, the current is the same at all points, but devices might have different resistances. In the circuit below, each bulb has a resistance of 1 ohm, so each has a voltage drop of 1 volt when 1 amp flows through the circuit. The law of conservation of energy applies to a circuit. Over the entire circuit, the power used by all the bulbs must equal the power supplied by the battery. This means the total of all the voltage drops must add up to the battery’s voltage. This rule is known as Kirchhoff’s voltage law, named after German physicist Gustav Robert Kirchhoff (1824–1887). In the circuit below, three identical bulbs are connected in series to two 1.5-volt batteries. The total resistance of the circuit is 3 ohms. The current flowing in the circuit is 1 amp (I = 3 V ÷ 3 Ω). Each bulb creates a voltage drop of 1 volt (V = IR = 1 A × 1 Ω). The total of all the voltage drops is 3 volts, which is the same as the voltage of the battery.

Kirchhoff’s voltage law - the total of all voltage drops in a series circuit must equal the voltage supplied by the battery.

Figure 16.20: A multimeter can be

used to measure the voltage drop across a bulb in a circuit.

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Finding voltage Ohm’s law is especially useful in series circuits where the devices do not drops have the same resistance. A device with a larger resistance has a greater

voltage drop. However, the sum of all the voltage drops must still add up to the battery’s voltage. The example below shows how to find the voltage drops in a circuit with two different light bulbs.

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Solving Problems: Voltage in a Series Circuit The circuit shown at the right (Figure 16.21) contains a 9-V battery, a 1-Ω bulb, and a 2-Ω bulb. Calculate the circuit’s total resistance and current. Then find each bulb’s voltage drop. 1. Looking for:

You are asked for the total resistance, current, and voltage drops.

2. Given:

You are given the battery’s voltage and the resistance of each bulb.

3. Relationships:

Total resistance in a series circuit: Rtot = R1 + R2 Ohm’s law: I=V/R or V=IR

4. Solution:

Figure 16.21: What is the circuit’s total resistance and current? What is each bulb’s voltage drop?

Calculate the total resistance: Rtot = 1 Ω + 2 Ω = 3 Ω Use Ohm’s law to calculate the current: I = (9 V)/(3 Ω) = 3 A Use Ohm’s law to find the voltage drop across the 1 Ω bulb: V = (3 A)(1 Ω) = 3 V Use Ohm’s law to find the voltage drop across the 2 Ω bulb: V = (3 A)(2 Ω) = 6 V Your turn...

a. The battery in Figure 16.21 is replaced with a 12-V battery. Calculate the new current and the voltage drops across the bulbs.

a. 4 A, 4 V drop across the 1-Ω bulb, 8 V drop across the 2-Ω bulb b. 2 V, 10 V

b. A 12-V battery is connected in series to a 1-Ω bulb and a 5-Ω bulb. What is the voltage drop across each bulb?

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What is a parallel circuit?

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Parallel It would be a big problem if your refrigerator shut off whenever you switched branches off the overhead kitchen light! This is why houses are wired with parallel

parallel circuit - an electric circuit

circuits instead of series circuits. Parallel circuits provide each device with a separate path back to the power source. This means each device can be turned on and off independently from the others. A parallel circuit is a circuit with more than one path for the current. Each path in the circuit is sometimes called a branch. The current through a branch is also called the branch current. The current supplied by the battery in a parallel circuit splits at one or more branch points.

Kirchhoff’s current law - states

Example: Three All of the current entering a branch point must exit again. This rule is known bulbs in parallel as Kirchhoff’s current law (Figure 16.22). For example, suppose you have

three identical light bulbs connected in parallel as shown below. The circuit has two branch points where the current splits (green dots). There are also two branch points where the current comes back together (black dots). You measure the branch currents and find each to be 1 amp. The current supplied by the battery is the sum of the three branch currents, or 3 amps. At each branch point, the current entering is the same as the current leaving.

with more than one path or branch. that all of the current entering a circuit branch must exit again.

Kirchhoff's current law All current flowing into a branch point must flow out again.

I2 I1 I3

I 1 = I2 + I3 Figure 16.22: All the current

entering a branch point in a circuit must also exit the branch.

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Voltage and current in a parallel circuit Each branch has The voltage in a circuit is the same anywhere along the same wire. This is the same true as long as the resistance of the wire itself is very small compared to the voltage rest of the circuit. If the voltage is the same along a wire, then the same

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voltage appears across each branch of a parallel circuit. In other words, each branch of a parallel circuit sees the total voltage available for the circuit. This is true even when the branches have different resistances (Figure 16.23). Both bulbs in this circuit get 3 volts from the battery since each is connected back to the battery by wires without any other electrical devices in the way. Advantages of Parallel circuits have two big advantages over series circuits. parallel circuits

1.

Each device in the circuit has a voltage drop equal to the full battery voltage.

2.

Each device in the circuit can be turned off independently without stopping the current in the other devices in the circuit. Parallel circuits Parallel circuits need more wires to connect, but are used for most of the in homes wiring in homes and other buildings. Parallel circuits allow you to turn off one lamp without all of the other lights in your home going out. They also allow you to use many appliances at once, each at full power.

Figure 16.23: The voltage across

each branch of a parallel circuit is the same.

Current in Because each branch in a parallel circuit has the same voltage, the current in branches a branch is determined by the branch resistance and Ohm’s law, I = V/R

(Figure 16.24). The greater the resistance of a branch, the smaller the current. Each branch works independently, so the current in one branch does not depend on what happens in other branches. Total current The total current in a parallel circuit is the sum of the currents in each

branch. The only time branches have an effect on each other is when the total current is more than the battery or wall outlet can supply. A battery has a maximum amount of current it can supply at one time. If the branches in a circuit try to draw too much current, the battery voltage will drop and less current will flow.

Figure 16.24: The current in each branch might be different.

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Calculating current and resistance in a parallel circuit More branches With parallel circuits, adding a resistor in parallel provides another independent mean less path for current. More current flows for the same voltage so the total resistance resistance is less.

short circuit - a branch in a circuit with zero or very low resistance.

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Example of a Compare the series and parallel circuits in Figure 16.25. All bulbs are parallel circuit identical and have a resistance of 2 ohms. In the series circuit, the current is

6 amps (I = V/R = 12 V ÷ 2 Ω = 6 Α). In the parallel circuit, the current is 6 amps in each branch. The total current, therefore, is 12 amps. So what is the total resistance of the parallel circuit? Ohm’s law solved for resistance is R = V ÷ I. The total resistance of the parallel circuit is the voltage (12 volts) divided by the total current (12 amps), which equals 1 ohm. The resistance of the parallel circuit is half that of the series circuit!

Short circuits

Total resi resistance sist stan ance c =2ȉ

6A

+ 12 V

If too much current flows through too small a wire, the wire will overheat and might melt or start a fire. A short circuit is a parallel path in a circuit with very low resistance. A short circuit can be created accidentally by making a parallel branch with a wire. A plain wire might have a resistance as low as 0.001 ohm. Ohm’s law tells us that with a resistance this low, 1.5 volts from a battery results in a (theoretical) current of 1,500 amps! A short circuit is dangerous because currents this large can melt wires.

Circuit safety in Appliances and electrical outlets in homes are connected in many parallel homes circuits. Each circuit has its own fuse or circuit breaker that stops the current

if it exceeds the safe amount, usually 15 or 20 amps. If you turn on too many appliances in one circuit at the same time, the circuit breaker or fuse cuts off the current. To restore the current, you must first disconnect some or all of the appliances. Then, either flip the tripped circuit breaker (in newer homes) or replace the blown fuse (in older homes). Fuses are also used in car electrical systems and in electrical devices such as televisions.

6A 6A

ist stan ance = 1 ȉ Total resi resistance

6A

12 A

6A

+ 12 V

Figure 16.25: The parallel circuit

has twice the current and half the total resistance of the series circuit.

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12 A

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Solving Problems: Current in a Parallel Circuit

What if you plug in too many things?

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All of the electrical outlets in Jonah’s living room are on one parallel circuit. The circuit breaker cuts off the current if it exceeds 15 A. Will the breaker trip if he uses a light (240 Ω), a radio (150 Ω), and an air conditioner (10 Ω)? 1. Looking for:

You are asked whether the current will exceed 15 A.

2. Given:

You are given the resistance of each branch and the circuit breaker’s maximum current.

3. Relationships:

Ohm’s law: I=V/R

4. Solution:

Because the devices are plugged into electrical outlets, the voltage is 120 V for each. Ilight = (120 V)/(240 Ω) = 0.5 A Istereo = (120 V)/(150 Ω) = 0.8 A IAC = (120 V)/(10 Ω) = 12 A The total is 13.3 A, so the circuit breaker will not trip. Your turn...

a. Will the circuit breaker trip if Jonah also turns on a computer (60 Ω)? b. What is the total current in a parallel circuit containing a 12-V battery, a 2-Ω resistor, and a 4-Ω resistor?

In a parallel circuit, each connection uses as much current as it needs. If you plug in a coffee maker that uses 10 amps and a toaster oven that uses 10 amps, a total of 20 amps needs to come through the wire. If you plug too many appliances into the same outlet, you will eventually use more current than the wires can carry without overheating. On the previous page, you learned how circuit breakers prevent this.

a. Yes. The additional current is 2 A, so the total is 15.3 A. b. 9 A

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Section 16.4 Review 1. What do you know about the current in a series circuit? 2. Three bulbs are connected in series with a battery and a switch. Do all of the bulbs go out when the switch is opened? Explain.

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3. What happens to a circuit’s resistance as resistors are added in series? 4. A series circuit contains a 9-V battery and three identical bulbs. What is the voltage drop across each bulb? 5. A student builds a series circuit with four 1.5-V batteries, a 5-Ω resistor, and two 1-Ω resistors. a. What is the total resistance in the circuit? b. Use Ohm’s law to find the value of the current in the circuit. 6. What happens to the total current in a parallel circuit as more branches are added? Why? 7. What is the total resistance of two 12-Ω resistors in parallel? What is the total for three 12-Ω resistors in parallel? 8. For each diagram below, label the circuit series, parallel, or short circuit. The arrows show the flow of current. One circuit type is not shown.

9. A circuit breaker in your house is set for 15 A. You have plugged in a coffee maker that uses 10 A. Plugging which of the four items into the same circuit will cause the circuit breaker to trip (because the current is too high)? a. a light that uses 1 A b. a can opener that uses 2 A c. a mixer that uses 6 A d. an electric knife that uses 1.5 A

Lewis Latimer Lewis Latimer was born in Chelsea, Massachusetts, in 1848, six years after his parents escaped from slavery in Virginia. As a child, Lewis loved to read and draw. When he was sixteen, Lewis joined the U.S. Navy, fighting for the Union in the Civil War. Afterward, he worked in a law office in Boston that specialized in helping people patent their inventions. There he taught himself how to use draftsmen’s tools to make scale drawings of machines. Latimer met Alexander Graham Bell at that office. Working late, Latimer made blueprints and helped Bell file the papers for his telephone patent—just hours before a rival. A new job as a mechanical draftsman for U.S. Electric Lighting helped Latimer learn about incandescent lighting. Four years later, Thomas Edison hired Latimer as an electrical engineer and patent advisor. Latimer was later invited to join the prestigious research team known as Edison’s pioneers. Latimer improved incandescent bulb design by replacing a paper filament with a carbon one. He also wrote the first engineer’s handbook on electric lighting.

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Chapter 16 Assessment Vocabulary

11. A circuit diagram uses electrical symbols to represent a(n) ____.

Select the correct term to complete the sentences.

12. ____ is the science of electric current and charge.

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ampere

insulator

potentiometer

13. When a light switch is in the off position, you have a(n) ____.

battery

Kirchoff’s current law

resistance

Section 16.2

charged

Kirchoff’s voltage law

resistor

closed circuit

multimeter

semiconductor

conductor

negative

series circuit

15. A(n) ____ provides voltage for a circuit.

coulomb

ohm

short circuit

16. ____ is a measure of electric potential energy.

electric circuit

Ohm’s law

static electricity

17. Use a(n) ____ to measure current or voltage in a circuit.

electric current

open circuit

switch

electrically neutral

parallel circuit

volt

electricity

positive

voltage

Section 16.3

voltage drop

19. The ____ is the unit for measuring resistance.

14. The unit for current is the ____.

18. The ____ is the unit for measuring voltage.

1.

The unit in which charge is measured is the ____.

20. ____ explains the relationship between current, voltage, and resistance in a circuit.

2.

An object is ____ when it has an equal number of positive and negative charges.

21. Wires in a circuit are made of a material that is a(n) ____, such as copper.

3.

All atoms have protons, which carry a(n) ____ charge.

22. ____ is the measure of how strongly a material resists current.

4.

All atoms have electrons, which carry a(n) ____ charge.

23. A(n) ____ such as rubber or plastic has high electrical resistance.

5.

____ is caused by a tiny imbalance of charge.

24. Silicon is an example of a(n) ____.

6.

A(n) ____ object is not electrically neutral.

25. A(n) ____ is a type of variable resistor.

7.

____ is what flows and carries energy in a circuit.

Section 16.4

8.

A(n) ____ is used to create a break in a circuit.

9.

A(n) ____ has a complete path for the current.

26. In a(n) ____, there is one path for current and the value for current is the same everywhere.

Section 16.1

10. A light bulb, motor, or speaker can act as a(n) ____ in a circuit.

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27. ____ states that the sum of the voltage drops in a circuit must equal the battery voltage.

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28. The ____ is the difference in voltage across an electrical device that has current flowing through it.

8.

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30. In a(n) ____, there is more than one path or branch for current, and the voltage is the same everywhere.

Why are symbols used in circuit diagrams? Draw the electrical symbol for each of the following devices. a. b.

29. ____ states that all current entering a branch point in a circuit must exit.

CHAPTER 16

battery resistor

c. switch d. wire

Section 16.2

9.

How does voltage cause current to do work?

31. A branch in a circuit with zero or very low resistance is a(n) ____.

10. Explain how a battery in a circuit is similar to a water pump.

Concepts

11. What are the differences between a multimeter, an ammeter, and a voltmeter?

Section 16.1

1.

Like charges ____ and opposite charges ____.

2.

What does it mean to say an object is electrically neutral?

3.

Is an object’s net charge positive or negative if it loses electrons?

4.

Why don’t you usually notice electric forces between objects?

5.

What unit is used for measuring charge, and where did the name come from?

6. 7.

Why do clothes sometimes stick together when you pull them out of a clothes dryer? Use the illustrations (below) to answer the following questions.

12. Suppose you have a closed circuit containing a battery that is lighting a bulb. a. b.

Explain how you would use a multimeter to measure the voltage across the bulb. Explain how you would use a multimeter to measure the current in the circuit.

13. What should you do to protect the multimeter when you measure current? Section 16.3

14. What does it mean to say that current and resistance in a circuit are inversely related? 15. What does it mean to say that current and voltage in a circuit are directly related? 16. According to Ohm’s law, the current in a circuit increases if the ____ increases. The current decreases if the ____ increases.

a. b. c.

Which of the circuit(s) is/are closed? Which circuit(s) will not light a bulb? For any open circuits shown, explain why the circuit is open.

17. A battery is connected to a light bulb, creating a simple circuit. Explain what will happen to the current in the circuit if a. b.

the bulb is replaced with a bulb having a higher resistance. the battery is replaced with a battery having a greater voltage.

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18. Explain why electrical wires are made of copper covered in a layer of plastic. Use the terms insulator and conductor in your answer.

Section 16.2

3.

Section 16.4

What voltage would the multimeter show in each of the diagrams below?

19. Draw a circuit diagram for a circuit containing a battery and two bulbs in series.

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20. As more bulbs are added to a series circuit, what happens to the resistance of the circuit? What happens to the current? What happens to the brightness of the bulbs? 21. How is Kirchhoff’s voltage law useful for analyzing series circuits? 22. A parallel circuit contains two bulbs in parallel. Why do the bulbs have the same voltage?

Section 16.3

23. Draw the circuit diagram for a circuit containing two bulbs in parallel.

4.

What happens to the current in a circuit if the resistance triples? If the voltage triples?

5.

A hair dryer draws a current of 10 A when plugged into a 120-V outlet. What is the resistance of the hair dryer?

6.

A digital camera uses one 6-V battery. The circuit that runs the flash and takes the pictures has a resistance of 3 Ω. What is the current in the circuit?

24. List two advantages of parallel circuits over series circuits. 25. What happens to the total resistance of a parallel circuit as more branches are added? Why? 26. What is a short circuit, and why can it be dangerous?

Problems Section 16.1

Section 16.4

1.

7.

A circuit contains a 5-Ω, a 3-Ω, and an 8-Ω resistor in series. What is the total resistance of the circuit?

8.

A circuit contains a 9-V battery and two identical bulbs. What is the voltage drop across each bulb?

9.

A circuit contains a 12-V battery and two 3-Ω bulbs in series. Draw a circuit diagram and use it to find the current in the circuit and the voltage drop across each bulb.

2.

Describe the forces between the positive and negative electric charges in each pair below.

Draw a circuit diagram of a circuit containing a battery, three wires, a light bulb, and a switch.

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10. A circuit contains a 12-V battery and three 1-Ω bulbs in series. Draw the circuit diagram and find the current in the circuit.

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CHAPTER 16

11. Calculate the total resistance of each circuit shown below and calculate the current in each.

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16. Do the following for each of the three circuits shown above. 12. A circuit contains two 1-Ω bulbs in series. The current in the circuit is 1.5 A. What is the voltage provided by the batteries? 13. A circuit contains two identical resistors in series. The current is 3 A, and the batteries have a total voltage of 24 V. What is the total resistance of the circuit? What is the resistance of each resistor? 14. Find the amount and direction of the current through point P in each of the circuits shown below.

a. b. c. d.

Find the voltage drop across each resistor. Use Ohm’s law to find the current through each resistor. Find the total current in the circuit. Find the total resistance of the circuit.

17. Find the unknown quantity in each of the circuits below.

Applying Your Knowledge 15. A parallel circuit contains a 24-V battery, a 4-Ω bulb and a 12-Ω bulb. a. b. c. d.

Draw the circuit diagram for this circuit. Calculate the current through each branch. Calculate the total current in the circuit. Use Ohm’s law to calculate the total resistance of the circuit.

Section 16.1

1.

On very dry days, when you use a comb or a brush, your hair sometimes stands on end and maybe even sticks to the comb or brush. Explain why this happens in terms of electric charge.

2.

A wire carrying an electric current is often likened to a pipe carrying water. What part of this analogy is incorrect?

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Section 16.2

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3.

Study the illustration below. Name the parts of the circuit that are analogous to the parts of the water system.

4.

Design an experiment to determine whether more expensive household batteries last longer than cheaper ones. Don’t forget to carefully select your controls! With your teacher’s approval, try your experiment and report your findings.

5.

Standard voltage for electrical circuits in the United States is 120 volts. Is this the standard voltage in other countries? Do some research and report your findings.

Section 16.3

6.

Why can’t you use an electric blender purchased in the U.S. in another country, such as Spain or China?

Section 16.4

7.

Some appliances contain devices that are connected in series. For example, many microwave ovens have a light that turns on while the microwave is running. List appliances in your house that use series circuits.

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17

CHAPTER 17

Magnetism

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Electricity and magnetism may not seem to be related. You don’t get a shock from picking up a magnet. However, you can create magnetism with electric current in an electromagnet. Why does electric current create magnetism? In 1819, a teacher named Hans Christian Oersted (1777–1851) tried an experiment in front of his students for the first time. He passed electric current through a wire near a compass. To his surprise, the compass needle moved! A few years later, Michael Faraday (1791–1867) built the first electric motor. Today, we know electricity and magnetism are two faces of the same basic force: the force between charges. In this chapter, you will see how our knowledge of electricity and magnetism allows us to build electric motors and generators. It would be hard to imagine today’s world without either of these important inventions. As you read this chapter, you will see that our study of the atom, electricity, and magnetism has come full circle. You will come to understand exactly how the electricity that we use in our homes, schools, and offices is generated. It is actually all about magnets!

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17.1 Properties of Magnets

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Magnetism has fascinated people since the earliest times. We know that magnets stick to refrigerators and pick up paper clips and pins. They are also found in electric motors, computer disk drives, alarm systems, and many other common devices. This chapter explains some of the properties of magnets and magnetic materials. What is the source of Earth’s magnetism? How does a compass work? Read on to find out.

magnetic - describes a material that can respond to forces from magnets.

permanent magnet - a material that retains its magnetic properties, can attract or repel other magnets, and can attract magnetic materials.

What is a magnet? Magnets and Magnets are usually made of the elements iron, cobalt, or nickel, or of some magnetic combinations that include them, such as steel (a mixture of iron and carbon). materials A magnet has an invisible force field that can attract or repel other magnets. A magnetic material, such as the steel in a paperclip, can be attracted to a

magnet, but is never repelled. Thus, magnetic materials are affected by magnets but do not actively create their own magnetic field. Permanent A permanent magnet is a material that keeps its magnetic properties, even magnets when it is not close to other magnets. Bar magnets, refrigerator magnets, and

horseshoe magnets are good examples of permanent magnets.

Figure 17.1: If a magnet is cut in

half, each half will have both a north pole and a south pole.

Poles All magnets have two opposite magnetic poles, called the north pole and the

south pole. If a magnet is cut in half, each half will have its own north and south poles (Figure 17.1). It is impossible to have only a north or south pole by itself. The north and south poles are like the two sides of a coin. You cannot have a one-sided coin, and you cannot have a magnetic north pole without a south pole.

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The magnetic force Attraction and When they are near each other, magnets exert forces. Two magnets can either repulsion attract or repel. Whether the force between two magnets is attractive or

Most materials are transparent to magnetic forces

Figure 17.2: Many materials, such

N S

S N

S N

N S

S N

The three interactions between two magnets

S N

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repulsive depends on which poles face each other. If two opposite poles face each other, the magnets attract. If two of the same poles face each other, the magnets repel.

N-S

S-S

N-N

Attract

Repel

Repel

as wood, are transparent to magnetic forces.

Magnetic forces can pass through many materials with no apparent decrease in strength. For example, one magnet can drag another magnet even when there is a piece of wood between them (Figure 17.2). Plastic, wood, and most insulating materials are transparent to magnetic forces. Conducting metals, such as aluminum, also allow magnetic forces to pass through, but might change the nature of the force, since aluminum and other materials like it are weakly magnetic. Iron and a few metals near it on the periodic table have strong magnetic properties. Iron and iron-like metals can either block or concentrate magnetic forces. They are discussed later in this chapter.

Using magnetic Magnetic forces are used for many applications because they are relatively forces easy to create and can be very strong. There are large magnets that create

forces strong enough to lift a car or even a moving train (Figure 17.3). Small magnets are everywhere; for example, some doors are sealed with magnetic weather-stripping that blocks out drafts. There are several patents pending for magnetic zippers, and many handbags, briefcases, and cabinet doors close with magnetic latches. Magnetic repulsion is the principle behind how Magnetic Resonance Imaging (MRI) works. MRI is a process that uses magnetism and radio waves to scan the body for disease or injury.

Figure 17.3: Powerful magnets are used to lift cars in a junkyard.

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The magnetic field How to describe How does the force from one magnet get to another magnet? Does it happen magnetic forces instantly? How far does the force reach? These questions puzzled scientists

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for a long time. Eventually, they realized that the force between magnets acts in two steps. First, a magnet fills the space around itself with a kind of potential energy called a magnetic field. Then the magnetic field makes forces that act on other nearby magnets (and act on the original magnet, too).

magnetic field - the influence created by a magnet that exerts forces on other magnets and magnetic materials.

The speed of When you move a magnet, the magnetic field spreads out around the magnet magnetic forces at the speed of light. The speed of light is nearly 300 million meters per

second. That means the force from one magnet reaches a nearby magnet so fast it seems like it happens instantly. However, it actually takes a tiny fraction of a second. Magnetic forces The force from a magnet gets weaker as it gets farther away. You can feel get weaker with this when you hold two magnets close together, then compare the force when distance you hold them far apart (Figure 17.4). Try this, and you will find that the

force loses strength very rapidly with increasing distance. Separating a pair of magnets by twice the distance reduces the force by eight times or more. The magnetic field

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All magnets create a magnetic field in the space around them, and the magnetic field creates forces on other magnets. Imagine you have a small test magnet that you are moving around another magnet (Figure 17.5). The north pole of your test magnet feels a force everywhere in the space around the source magnet. To keep track of the force, imagine drawing an arrow in the direction in which the north pole of your test magnet is pulled or pushed as you move it around the source magnet. The arrows that you draw show you the magnetic field. If you connect all the arrows, you get lines called magnetic field lines. You can actually see the pattern of the magnetic field by sprinkling magnetic iron filings on cardboard with a magnet underneath (shown at left).

Figure 17.4: The force between two magnets quickly gets weaker as the magnets are separated.

Figure 17.5: The magnetic field lines show the force exerted by one magnet on the north pole of another magnet.

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Earth’s magnetic field and compasses A compass A compass needle is a freely spinning magnet. If you bring the south pole of a needle is a permanent magnet near the compass needle, the needle’s north pole magnet (identified by a red-painted tip) will spin around and point toward the south

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pole of the permanent magnet (Figure 17.6). This is because opposite poles attract. North and south The planet Earth itself has a magnetic field that comes from the core of the poles planet. A compass needle spins around until the north-seeking pole of the

needle points toward Earth’s North Pole. This action has been helpful to explorers for centuries. But doesn’t this contradict Figure 17.6? Yes, it is contradictory to say that the north end of the compass needle points north, when you know that, scientifically, the north pole of the needle is always attracted (and points toward) a south magnetic pole. This is an example of an old naming convention that was decided long before people understood how a compass needle really worked. It is customary to say that the north pole of a compass needle points to Earth’s North Pole, but technically, it does this because it is attracted to a south magnetic pole. Geographic and magnetic poles

The true geographic North and South Poles are where the Earth’s axis of rotation intersects its surface. The North Pole is the northernmost point on Earth’s surface. However, as you can see in the illustration at the left, Earth’s internal magnetic field poles are actually the opposite of the geographic poles. Now, here is one more interesting point of confusion. Scientists still stick to the old naming convention, and refer to the magnetic pole that is near the geographic North Pole as the magnetic north pole (even though, technically, it’s a south pole). Read on to find out why we make a distinction between Earth’s geographic and magnetic poles.

Figure 17.6: This diagram

illustrates how a compass needle interacts with a magnet. Remember, the compass needle is a magnet itself, and the red-painted end of the needle is a north pole.

Some Animals Have Biological Compasses Many organisms, including some species of birds, frogs, fish, turtles, and bacteria, can sense the planet’s magnetic field. Migratory birds are the best known examples. Magnetite, a magnetic mineral made of iron oxide, has been found in bacteria and in the brains of birds. Tiny crystals of magnetite may act like compasses and allow these organisms to sense the small magnetic field of Earth. You can find more information about this topic by using your favorite search engine and the keywords “magnetite in birds.”

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Magnetic declination and true north Magnetic Earth’s geographic North Pole (true north) and magnetic north pole are not declination located at the same place, so a compass needle will not point directly to the

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geographic North Pole. Depending on where you are, a compass needle will point slightly east or west of true north. The difference between the direction a compass needle points and the direction of true north is called magnetic declination. Magnetic declination is measured in degrees and is indicated on topographical maps.

magnetic declination - the difference between true north and the direction a compass needle points.

Finding true Most orienteering compasses contain an adjustable ring with a degree scale north with a and an arrow that can be turned to point toward a destination on a map compass (Figure 17.7). The ring is turned the appropriate number of degrees to

compensate for the declination. Suppose you are using a compass and the map shown below, and you want to travel true north. You would not simply walk in the direction that the compass needle points to. To go true north, you must walk in a direction 16 degrees west of the way the needle points.

Figure 17.7: An orienteering compass.

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The source of the Earth’s magnetism Earth’s While Earth’s core is magnetic, we know it is not a solid permanent magnet. magnetic core Studies of earthquake waves reveal that Earth’s core is made of hot, dense,

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molten iron, nickel, and possibly other metals that slowly circulate around a solid metal core (Figure 17.8). Huge electric currents flowing in the molten iron produce Earth’s magnetic field, much like a giant electromagnet. The strength of The magnetic field of Earth is weak compared to the magnetic field of the Earth’s ceramic magnets you have in your classroom. For this reason, you cannot magnetic field trust a compass to point north if any other magnets are close by. The gauss is

a unit used to measure the strength of a magnetic field. A small ceramic permanent magnet has a field between 300 and 1,000 gauss at its surface. By contrast, Earth’s magnetic field averages only about 0.5 gauss at the surface. Reversing poles Historical data shows that both the strength of Earth’s magnetic field and the

location of the north and south magnetic poles change over time. Studies of magnetized rocks in Earth’s crust provide evidence that the poles have reversed many times over the last tens of millions of years. The reversal has happened every 500,000 years on average. The last field reversal occurred roughly 750,000 years ago, so Earth is overdue for a pole reversal.

Figure 17.8: Scientists believe

moving charges in the molten core create Earth’s magnetic field.

The next Earth’s magnetic field is currently losing approximately seven percent of its reversal strength every 100 years. We do not know whether this trend will continue, but

if it does, the magnetic poles could reverse sometime in the next 2,000 years. During a reversal, Earth’s magnetic field would not completely disappear. However, the main magnetic field that we use for navigation would be replaced by several smaller fields with poles in different locations. Movements of The location of Earth’s magnetic poles is always changing—slowly—even the magnetic between full reversals. Currently, the magnetic north pole is located about poles 1,000 kilometers from the geographic North Pole. During the last century,

the magnetic north pole has moved over 1,000 km (Figure 17.9). Just remember—if you are using a handheld compass, and the red tip of the compass needle lines up with the north direction on the compass housing, you must adjust the compass to compensate for the fact that Earth’s magnetic north and geographic north are in different places!

Figure 17.9: The location of the

magnetic north pole is moving approximately northwest at about 40 km per year, according to the Canadian Geological Survey.

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Using a Suppose you want to find a windowsill in your house that faces east and compass would provide good light for growing African violets. Here’s how to use a

handheld compass to find an east-facing window.

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• Turn the moveable ring so east is lined up with the direction arrow, as in Figure 17.10. • Walk up to a window in your house. • With the compass flat on your hand, turn your body until the red end of the compass needle is lined up with north on the compass housing. • The direction arrow now points directly east. Is this pointing toward the window? If not, keep checking different windows in your house until you find one that faces east, in the direction of the arrow on the compass base. You don’t need to adjust for magnetic declination because you are looking for an approximate easterly direction. Figure 17.10: Using a compass.

Section 17.1 Review 1. Suppose you put a magnet on a refrigerator door. Is the magnet a magnetic material, or is it a permanent magnet? Is the door a magnetic material or is it a permanent magnet? Explain. 2. Describe three common uses of magnets. 3. What happens to a magnet if it is cut in half? 4. Is it possible to have a magnetic south pole without a north pole? Explain. 5. What happens to the strength of a magnetic field as you move away from a magnet?

Antigravity Magnets! You can “float” a tethered magnet by attracting it to another magnet that has been glued to the bottom of a shelf or table. See if you can do it! How far apart can you get the two magnets before the lower one falls?

6. Why does a compass point north? 7. How does the strength of Earth’s magnetic field compare to the strength of the field of a typical ceramic magnet like the kind in your classroom? 8. What is the cause of Earth’s magnetism? 9. Is Earth’s magnetic north pole at the same location as the geographic North Pole? Explain.

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17.2 Electromagnets In the last section, you learned about permanent magnets and magnetism. There is another type of magnet, one that is created by electric current. This type of magnet is called an electromagnet. What is an electromagnet? Why do magnets and electromagnets act the same way? In this section, you’ll learn about electromagnets and how they helped scientists explain how magnetism works.

electromagnet - a magnet created by a wire carrying electric current.

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What is an electromagnet? Searching for a For a long time, people thought about electricity and magnetism as different connection and unrelated topics. Around the beginning of the nineteenth century, scientists

started to suspect that the two were related. As scientists began to understand electricity better, they searched for relationships between electricity and magnetism. The principle In 1819, Hans Christian Øersted, a Danish physicist and chemist, noticed that of an a current in a wire caused a compass needle to deflect. He had discovered that electromagnet moving electric charges create a magnetic field! A dedicated teacher, he made

this discovery while teaching his students at the University of Copenhagen. He suspected there might be an effect and did the experiment for the very first time in front of his class. With his discovery, Øersted was the first to identify the principle of an electromagnet. How to make an Electromagnets are magnets that are created when there is electric current electromagnet flowing in a wire. The simplest electromagnet uses a coil of wire, often

wrapped around a piece of iron (Figure 17.11). Because iron is magnetic, it concentrates the magnetic field created by the current in the coil. The north and south poles of an electromagnet

The north and south poles of an electromagnet are located at the ends of the coil (Figure 17.11). Which end is the north pole depends on the direction of the electric current. If you curl the fingers of your right hand in the direction of the current, your thumb will point toward the magnet’s north pole. This method of finding the magnetic poles is called the right-hand rule. You can switch the north and south poles of an electromagnet by reversing the direction of the current. This is a great advantage over permanent magnets. You can’t easily change the poles of a permanent magnet.

Figure 17.11: A simple

electromagnet uses a coil of wire, often wrapped around a piece of iron or steel. If you curl the fingers of your right hand in the direction of the current, your thumb will point toward the north pole of the electromagnet.

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Applications of electromagnets Current controls By changing the amount of current, you can easily change the strength of an electromagnets electromagnet or even turn its magnetism on and off. Electromagnets can

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also be much stronger than permanent magnets because the electric current can be large. For these reasons, electromagnets are preferable to permanent magnets in many applications. Magnetically Magnetically levitated (maglev) train technology uses electromagnetic levitated trains force to lift a train a few inches above its track (Figure 17.12). By “floating”

the train on a powerful magnetic field, the friction between wheels and rails is eliminated. Maglev trains can achieve high speeds using less power than normal trains. In 2003, in Japan, a three-car maglev train carrying 12 passengers reached a world-record speed of 581 kilometers (360 miles) per hour. Maglev trains are now being developed and tested in Germany, Japan, and the United States. Electromagnets The sliding switch on a toaster does several things. First, it turns the heating and toasters circuit on. Second, it activates an electromagnet that then attracts a spring-

Figure 17.12: A maglev train track has electromagnets in it that both lift the train and pull it forward.

loaded metal tray to the bottom of the toaster (Figure 17.13). When a timing device signals that the bread has been toasting long enough, current to the electromagnet is cut off. This releases the spring-loaded tray that then pushes up on the bread so that it pops out of the toaster. Electromagnets and doorbells

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A doorbell contains an electromagnet. When the button of the doorbell is pushed, current is sent through the electromagnet. The electromagnet attracts a piece of metal called the striker. The striker moves towards the electromagnet but hits a bell that is in the way. The movement of the striker away from the contact breaks the circuit after it hits the bell. A spring pulls the striker back and reconnects the circuit. If a finger is still pressing on the button, the cycle starts over again and the bell keeps ringing.

Figure 17.13: A toaster tray is

pulled down by an electromagnet while bread is toasting. When the toast is done, current is cut off and the tray pops up. The cutaway shows the heating element—nichrome wires wrapped around a sheet of mica.

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Making an electromagnet from wire and a nail

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You can easily build an electromagnet from wire and a piece of iron, such as a nail. Wrap the wire in many turns around the nail and connect a battery as shown in Figure 17.14. When current flows in the wire, the nail becomes a magnet. Use the right-hand rule to figure out which end of the nail is the north pole and which is the south pole. To reverse north and south, reverse the connection to the battery, making the current flow the opposite way.

Increasing the As you read on the previous page, increasing the current makes an strength of an electromagnet stronger. There are two ways to increase the current: electromagnet

1.

apply more voltage by adding a second battery; or

2. add more turns of wire around the nail. Why adding The second method works because the magnetism in your electromagnet turns works comes from the total amount of current flowing around the nail. If there is 1 amp of current in the wire, each loop of wire adds 1 amp to the total amount that flows around the nail. Ten loops of 1 amp each make 10 total amps flowing around. By adding more turns, you use the same current over and over to get stronger magnetism (Figure 17.15).

A simple electromagnet Nail

Wire Switch +

1.5 V

Building an electromagnet

CHAPTER 17

Battery

Figure 17.14: Making an

electromagnet from a nail and wire.

More turns also Of course, nothing comes for free. By adding more turns, you also increase mean more the resistance of your coil. Increasing the resistance makes the current a little resistance lower and generates more heat. A good electromagnet has enough turns to get

a strong enough magnet without too much resistance. Factors The magnetic force exerted by a simple electromagnet depends on three affecting the factors: force

1.

the amount of electric current in the wire;

2.

the amount of iron or steel in the electromagnet’s core; and,

3.

the number of turns in the coil.

In more sophisticated electromagnets, the shape, size, material in the core, and winding pattern of the coil also have an effect on the strength of the magnetic field produced.

Figure 17.15: Adding turns of wire increases the total current flowing around the electromagnet. The total current in all the turns is what determines the strength of the electromagnet.

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Similarities between permanent magnets and electromagnets Electric Why do permanent magnets and electromagnets act the same way? The currents cause discovery of electromagnets helped scientists to determine why magnetism all magnetism exists. Electric current through loops of wire creates an electromagnet.

Atomic-scale electric currents create a permanent magnet.

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Electrons move, Atoms contain two types of charged particles, protons (positive) and electrons creating small (negative). The charged electrons in atoms behave like small loops of current. loops of current These small loops of current mean that atoms themselves act like tiny

How permanent magnets work

Why iron always attracts magnets and never repels them

electromagnets with north and south poles! We don’t usually notice the magnetism from atoms for the following two reasons. 1. Atoms are very tiny, and the magnetism from a single atom is far too small to detect without very sensitive instruments. 2. The alignment of the atomic north and south poles changes from one atom to the next. On average, the atomic magnets cancel each other out. If all the atomic magnets are lined up in a similar direction, the magnetism of each atom adds to that of its neighbors, and we observe magnetic properties on a large scale. This is what makes a permanent magnet. Permanent magnets have the magnetic fields of individual atoms aligned in the same direction (Figure 17.16). In magnetic materials (such as iron), the atoms are free to rotate and align their individual north and south poles. If you bring the north pole of a magnet near iron, the south poles of all the iron atoms are attracted. Because they are free to move, the iron near your magnet becomes a south pole and it attracts your magnet. If you bring a south pole near iron, the opposite happens. The iron atoms nearest your magnet align themselves to make a north pole, which also attracts your magnet. This is why magnetic materials such as iron always attract your magnet, and never repel, regardless of whether your test magnet approaches with its north or south pole.

Nonmagnetic The atoms in nonmagnetic materials, such as plastic, are not free to move materials and change their magnetic orientation. This is why most objects are not

affected by magnets.

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Figure 17.16: Atoms act like tiny

magnets. Permanent magnets have their atoms partially aligned, creating the magnetic forces we observe. The magnetic properties of iron occur because iron atoms can easily adjust their orientation in response to an outside magnetic field.

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Section 17.2 Review

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1. Which of the following will NOT increase the strength of an electromagnet made by wrapping a wire around an iron nail? a. increasing the number of turns of the wire b. increasing the current in the electromagnet c. removing the nail from the center of the electromagnet 2. Explain why an electromagnet usually has a core of iron or steel. 3. Name two devices that use electromagnets. Explain the purpose of the electromagnet in each device.

Magnetism in Materials Materials can have different magnetic classifications based on their atomic structure. Do a keyword search on the following classifications. Explain how the atoms of each type of material behave, and give examples of each. • • •

diamagnetic paramagnetic ferromagnetic

4. In your own words, explain how atoms give rise to magnetic properties in certain materials. 5. Which picture shows the correct location of the north and south poles of the electromagnet? Choose A or B and explain how you arrived at your choice.

6. The north pole of a magnet is brought near a refrigerator door, and the magnet sticks. If the magnet is removed and the south pole is brought near the door instead, will it also stick? Explain. 7. What would happen if you placed a compass near an electromagnet when there is an electric current in the coil of the electromagnet? Why would this happen? What if you flipped the electromagnet around so the end that was closest to the compass is now farthest away?

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17.3 Electric Motors and Generators

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Permanent magnets and electromagnets work together to make electric motors and generators. In this section, you will learn how an electric motor works. The secret is in the ability of an electromagnet to reverse its north and south poles. By changing the direction of electric current, the electromagnet attracts and repels other magnets in the motor, causing the motor to spin. Electric motors convert electrical energy into mechanical energy.

electric motor - a device that converts electrical energy into mechanical energy. rotor - the rotating disk of an electric motor or generator.

Using magnets to spin a disk Imagine a Imagine you have a disk that can spin on an axis at its center. Around the edge spinning disk of the disk are several magnets. You have cleverly arranged the magnets so with magnets they have alternating north and south poles facing out. Figure 17.17 shows a

picture of your disk. Making the disk Imagine you also have another magnet which is not attached to the disk. You spin bring this loose magnet close to the disk’s edge. The loose magnet attracts

one of the magnets on the disk while at the same time repelling an adjacent magnet on the disk. These attract-and-repel forces make the disk spin a little way around (Figure 17.17). Reversing the To keep the disk spinning, you need to reverse the magnet in your fingers as magnet is the soon as the magnet that was attracted passes by. This way, you first attract key the magnet on the disk, and then reverse the loose magnet to repel that same

magnet on the disk and attract the next one in line on the disk. You make the disk spin by using the loose magnet to alternately attract and repel the magnets on the disk. Knowing when The disk is called a rotor because it can rotate. The key to making the rotor to reverse the spin smoothly is to reverse your magnet when the disk is at just the right magnet place. You want the reversal to happen just as each magnet in the rotor passes

Figure 17.17: Using a single magnet to spin a disk of magnets. Reversing the magnet in your fingers attracts and repels the magnets in the rotor, making it spin.

by. If you reverse too early, you will repel the magnet on the rotor backward before it reaches the loose magnet. If you reverse too late, you will attract the magnet backward after it has passed. For the best results, you need to change your magnet from north to south just as each magnet on the rotor passes by.

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How the electromagnets in a motor operate How electromagnets are used in electric motors

In a working electric motor, an electromagnet replaces the magnet you reversed with your fingers. The switch from north to south is done by reversing the electric current in the electromagnet. The diagrams below show how an electromagnet switches its poles to make the rotor keep turning.

commutator - a device that switches the direction of electrical current in the electromagnet of an electric motor.

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The three main parts of an electric motor 1

Rotor

Electromagnet

N Current

The commutator Just like with the magnet you flipped with your fingers, the electromagnet is a kind of must switch from north to south as each rotor magnet passes by to keep the switch rotor turning. The device that makes this happen is called a commutator. As

the rotor spins, the commutator reverses the direction of the current in the electromagnet. This makes the electromagnet’s pole that faces the disk change from north to south, and then back again. The electromagnet attracts and repels the magnets in the rotor, and the motor turns. Three things All types of electric motors must have three parts (Figure 17.18). They are: you need to make a motor • a rotating part (rotor) with magnets that have alternating polarity;

3

2

Fixed magnets on a rotor

Commutator

Switches the direction of current in the electromotor at the right time

Figure 17.18: An electric motor has three main parts.

• one or more electromagnets; and, • a commutator that switches the direction of current in the electromagnets back and forth in the correct sequence to keep the rotor spinning.

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How a battery-powered electric motor works Inside a small If you take apart an electric motor that runs on batteries, it doesn’t look like electric motor the spinning disk motor illustrated on the previous page. However, the same

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three mechanisms are still there. The difference is in the arrangement of the electromagnets and permanent magnets. The illustration below shows a small, battery-powered electric motor and what it looks like inside with one end of the motor case removed. The permanent magnets surround the rotor, and they stay fixed in place on the inside surface of the metal housing.

Electromagnets The electromagnets are in the rotor, and they turn. The rotating part of the and the motor, including the electromagnet coils, is called the armature. The armature armature in the illustration above has three electromagnets. Figure 17.19

shows the same motor, with the essential parts labeled. How the The wires from each of the three coils are attached to three metal plates (the switching commutator) at the end of the armature. As the rotor spins, the three plates happens come into contact with positive and negative brushes. Electric current flows

Figure 17.19: A simple battery-

powered motor. Refer to this labeled photograph as you read how the parts work together to make the shaft spin.

through the brushes into the coils. As the motor turns, the plates rotate past the brushes, reversing the positive and negative connections to the coils. As you know, when you change the direction of current through a coil, the electromagnet’s magnetic poles switch positions. The turning electromagnets with alternating poles are thus attracted and repelled by the permanent magnets, and the motor turns. AC motors Motors that run on AC electricity are easier to make because the current

switches direction all by itself. Almost all household, industrial, and power tool motors are AC motors. These motors use electromagnets for both the rotating and fixed magnets.

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Electromagnetic induction Motors and Motors transform electrical energy into mechanical energy. Electric generators generators do the opposite. They transform mechanical energy into electrical

energy. Generators are used to create the electricity that powers all of the appliances in your home.

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Magnetism and An electric current in a wire creates a magnetic field. The reverse is also true. electricity If you move a magnet near a coil of wire, an electric current is induced in the

generator - a device that converts kinetic energy into electrical energy using the law of induction.

electromagnetic induction - the process of using a moving magnet to create an electric current.

coil. The word induce means “to cause to happen.” The process of using a moving magnet to create electric current is called electromagnetic induction. A moving magnet induces electric current to flow in a circuit. Symmetry in Many laws of physics display symmetry. In physics, symmetry means a physics process works in both directions. Earlier in this chapter, you learned that

moving electric charges create magnetism. The symmetry is that changing magnetic fields also causes electric charges to move. Nearly all physical laws display symmetry in one form or another. Making current Figure 17.20 shows an experiment demonstrating electromagnetic induction. flow In the experiment, a magnet can move in and out of a coil of wire. The coil is

attached to a meter that measures the electric current. When the magnet moves into the coil of wire, electric current is induced in the coil as the magnet is moving, and the meter swings to the left. The current stops if the magnet stops moving. Reversing the When the magnet is pulled back out again, current is induced in the opposite current direction as the magnet is moving. The meter swings to the right as the

magnet moves out. Again, if the magnet stops moving, the current also stops. Current flows only when the magnet is moving

Current is produced only if the magnet is moving, because a changing magnetic field is what creates current. Moving magnets induce current because they create changing magnetic fields. If the magnetic field is not changing, such as when the magnet is stationary, the current is zero.

Figure 17.20: A moving magnet

produces an electric current in a coil of wire.

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Generating electricity A simple A generator converts mechanical energy into electrical energy using the law generator of induction. Most large generators use some form of rotating coil in a

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magnetic field (Figure 17.21). You can also make a generator by rotating magnets past a stationary coil (see the diagram below). As the disk rotates, first a north pole and then a south pole passes the coil. When a north pole is approaching, the current is in one direction. After the north pole passes and a south pole approaches, the current is in the other direction. As long as the disk is spinning, there is a changing magnetic field through the coil and electric current is created. Figure 17.21: Current is created when a coil rotates in a magnetic field.

Electrical energy Mechanical energy

Alternating The generator shown above makes alternating current or AC electricity. The current direction of current is one way when the magnetic field is becoming “more

north” and the opposite way when the field is becoming “less north.” It is impossible to make a situation where the magnetic field keeps increasing (becoming more north) forever. Eventually the field must stop increasing and start decreasing. Therefore, the current always alternates. The electricity in your home is produced by AC generators. The current from a battery, on the other hand, is always in the same direction, from the positive to the negative end of the battery. This type of current is called direct current or DC. Energy for The electrical energy produced by a generator must have a source. Energy generators must continually be supplied to keep the rotating coil (or magnetic disk)

Generator

Turbine

Figure 17.22: A power plant

generator contains a turbine that turns magnets inside loops of wire, generating electricity. Some other form of energy must be continually supplied to turn the turbine.

turning. In the next section, you will explore energy sources that can be used to produce electricity (Figure 17.22).

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Section 17.3 Review Electrical Wiring

1. A(n) _____ is used to convert mechanical energy into electrical energy. 2. A(n)_____ is used to convert electrical energy into mechanical energy. 3. Using a magnet to create electric current in a wire is called _____.

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4. Why is it necessary to use at least one electromagnet in a motor instead of only permanent magnets? 5. At the instant shown below, the electromagnet in the motor has its north pole facing the rotor that holds the permanent magnets. In which direction is the rotor spinning?

N

6. The rotor in the motor below is spinning clockwise. Is the direction of the current in the electromagnet from A to B or from B to A?

There is a magnetic field around all the wires that carry current, but you don’t notice magnetic fields created by electrical wiring in your house. Why not? The wires in your home are actually made of two parallel wires. If you look at an appliance cord, you will notice the two wires inside the plastic covering. At any instant, the current in one wire is opposite the other. Each creates a magnetic field, but the fields are in opposite directions so they mostly cancel each other out. Because the wires are not at exactly the same location, and field strength depends on distance, the fields do not completely cancel each other right at the wire, but quickly fall off to nothing a short distance away.

7. In most electric power plants, the energy stored in gas, coal, oil, or nuclear energy is transformed into the movement of a turning turbine. Why is the turning turbine necessary in a power plant?

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17.4 Generating Electricity Hoover Dam, near Las Vegas, Nevada, towers more than 200 meters above the raging Colorado River. This gigantic concrete structure is known as one of the greatest engineering projects in the world. Hoover Dam is called a hydroelectric plant because it turns the energy of falling water into electricity. In this section, you will learn more about ways to generate electricity.

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Making and transporting electricity

Do some research and find out how far the nearest power plant is from your house. What is the name of the power plant? What energy source is used to make electricity at this power plant? How is the power transported to your house?

Starting at the To find out how electricity is made and transported, let’s trace the energy power plant pathway. Electricity is made in a power plant (see below). Most power plants

burn coal, oil, or natural gas to produce heat (later in this section, you will learn about alternative ways to produce heat). Next, this heat is used to boil water. The steam from the boiling water turns a turbine. The turbine turns a generator which produces electricity. Electricity is Electricity leaves the power plant and is carried to buildings by wires. The carried by wires fuel energy from the coal, oil, or natural gas changes its form several times

on the way to the buildings. With each change, some energy is converted to heat. In fact, most of the energy that is transferred from fuels such as coal, oil, and natural gas will eventually become heat energy. Some will be used, but most will be unusable.

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Electricity from fossil fuels What is a A nonrenewable resource is not replaced as it is used. Fossil fuels are nonrenewable good examples of nonrenewable resources. Fossil fuels are found within the resource? rocks of Earth’s surface. They are called fossil fuels because they were

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formed hundreds of millions of years ago by processes acting on dead plants and animals. The three major fossil fuels are coal, petroleum, and natural gas. Fossil fuels

Downsides of using fossil fuels to generate electricity

Earth’s coal, petroleum, and natural gas deposits took hundreds of millions of years to form. Because it takes so long for these resources to form, they are not replaced as they are used and are considered nonrenewable resources. Natural gas is pumped out of gas pockets both onshore and offshore. Coal is a solid fossil fuel that is mined from the ground. Petroleum (oil) is drilled out of natural deposits both onshore and offshore. Petroleum deposits are located in many parts of the world, including the United States. Petroleum, coal, and natural gas can all be used to make electricity.

nonrenewable resource - a natural resource that is not replaced as it is used.

fossil fuel - substance found in Earth’s crust that was formed over millions of years from the remains of dead organisms.

Study the pie chart at the left and answer the following questions. 1. Which fossil fuel is used the most to make electricity? 2. Which fossil fuel do you think is found in the largest amount in the United States? 3. What resources do you think make up the “other” category? (Hint: Read ahead to learn about renewable resources that can be used to make electricity.)

Since nonrenewable resources are not replaced as they are used, someday we will not have enough fossil fuels to produce the electricity we need. Besides being nonrenewable, fossil fuels pose additional problems. Burning fossil fuels produces sulfur oxide emissions that reduce air quality. Carbon dioxide is also produced when fossil fuels are burned. The amount of carbon dioxide in the atmosphere has increased by about 30 percent since the 1800s, and Earth’s average surface temperature has increased 0.6 to 1.2°F over that same time period. These increases are not huge, but they are enough to have warmed the North Pole and caused the sea level to rise 4 to 10 inches. These consequences, and the possibility of global climate change, are causing scientists to look for alternative ways to produce electricity. 17.4 GENERATING ELECTRICITY

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Electricity from nuclear energy What is nuclear The United States gets about 19 percent of its electricity production from energy? nuclear power plants. As an interesting comparison, France leads the world

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with 75 percent of its electricity coming from nuclear energy. According to the U.S. Nuclear Energy Institute, as of 2015, there were 61 operating commerical nuclear power plants in the U.S. The fuel used in nuclear power plants is uranium, an extremely high-energy source of heat. Uranium atoms split apart in the nuclear reactor and the energy released is used to heat water and make steam. The steam drives a turbine, which spins a generator to produce electricity.

Uranium is an element, and you can find it listed on the periodic table of elements. Elements are the most basic substances. Uranium has characteristics that make it very useful as a fuel for nuclear reactors. Uranium is naturally radioactive, and it releases particles from its atoms that have a lot of energy. Do some research on uranium. 1. How is uranium used to produce electricity? (Hint: If you can describe the process shown in the picture to the left, you will have your answer!)

Advantages and disadvantages of nuclear energy

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The main advantage of using nuclear energy to produce electricity is that it doesn’t pollute the air like fossil fuel power plants do. Interestingly, there has not been a single nuclear power plant built in the United States since 1973. This slowdown in progress is due to two major disadvantages of nuclear energy. One disadvantage is that used uranium fuel from a reactor stays dangerously radioactive for a long time. Also, storage of nuclear waste has always been a major disadvantage of nuclear power plants.

2. Nuclear power plants do not pollute the air like fossil fuel plants do. However, there are some big drawbacks to nuclear power plants. Discuss these drawbacks.

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Electricity from renewable resources renewable resource - a natural

Renewable A renewable resource can be replaced naturally in a relatively short resources period of time. Falling water, energy from the Sun, and wind energy are

resource that can be replaced.

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examples of renewable resources that can be used to make electricity. The Energy Information Administration (EIA) predicts that by 2020, 30 percent of the electricity generated in the United States will be from renewable resources (as compared to 9.4 percent in 2006). Figure 17.23 shows how the 30 percent renewable resource contribution in 2020 will be allocated. Hydroelectric: impoundment and pumped storage

A hydroelectric (or hydropower) plant uses energy from falling water to generate electricity. The two most common types of hydroelectric power plants are impoundment (a dam is used), and pumped storage. An impoundment facility (see photo at the left) dams up river water and stores it in a reservoir. The water falls from the reservoir and turns a turbine, which spins a generator and produces electricity. Instead of holding back river water in a reservoir, a pumped storage facility actively pumps water from a lower reservoir to a higher reservoir (during off-peak or low-demand hours) and then releases it back to the lower reservoir during high-demand hours. Again, the energy of the falling water is used to generate electricity. Hydroelectric power generation has advantages and disadvantages, like any other energy resource. This method of generating electricity does not pollute the air, it is considered renewable (the Sun constantly drives the water cycle), and it is sufficiently available in the United States (as opposed to fossil fuels which require some imports). However, hydroelectric plants are known to negatively impact fish populations, they can be vulnerable to drought, and they can directly impact the flow and quality of water in the surrounding area. Researchers must continue to find ways to offset these disadvantages in order to make hydroelectric a more viable solution to long-term energy needs.

hydroelectric - a type of power plant that generates electricity from the energy of falling water.

Projected renewable resource contributions, 2020

Wind 37%

Hydroelectric 47%

Solar 5% Biomass Solid 4% waste 3%

Geothermal 4%

Source: Energy Information Administration

Figure 17.23: The EIA predicts that

30% of U.S. electricity generation will be from renewable resources in 2020. This graph shows how each resource will contribute to this projection.

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Geothermal and biomass Geothermal Iceland is a country of contrasts. Glaciers cover 11 percent of Iceland, yet reservoirs there are also many places where molten rock is close to the surface. At these

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hot spots, where geothermal reservoirs are located, wells have been drilled to tap into the hot water. Geothermal power plants use Earth’s internal heat energy, in the form of water or steam, to produce electricity. Iceland produces most of its electricity from geothermal energy. Geothermal power plants can be found all over the world, including Alaska, Hawaii, and some western parts of the United States. Heat pump Geothermal energy can even be used to heat homes in places that are not systems geologically as active as Hawaii or Iceland. A geothermal heat pump system takes advantage of the relatively constant temperature of Earth’s

shallow ground. In winter, heat from the relatively warmer ground goes through a heat exchanger into the house. In summer, warmer air from the house is pulled through the heat exchanger into the cooler ground. This heat can even be used to heat water in the summer. Geothermal power plants and heat pump systems are clean, and Earth’s heat energy is almost unlimited. However, in the United States, geothermal power plants are limited to a relatively small number of geologically active sites. Biomass Biomass is organic material from plants or animals. For thousands of years,

people have used wood, a type of biomass, for space and water heating. Now, new technology allows farmers to grow crops, such as corn, specifically to be used for biomass energy. Biomass can also come from municipal waste, industrial waste, or agricultural and forestry leftovers. But how is biomass used to produce electricity? In waste-to-energy plants, renewable solid waste is burned to produce steam, which is used to generate electricity. This creates some air pollution, but not as much sulfur oxide as fossil fuels produce (sulfur oxides contribute to acid rain). Biomass, such as harvested corn, can even produce liquid transportation fuels (biofuels) such as ethanol and biodiesel. Plants used to make biomass can be grown over and over, so biomass is considered a renewable resource. Burning biomass does produce carbon dioxide (a greenhouse gas), but as living plants, the biomass originally consumed carbon dioxide during its growth process.

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geothermal - describes energy from Earth’s internal heat.

heat pump system - takes advantage of Earth’s constant shallow ground temperature for seasonal heating and cooling of buildings and homes.

biomass - organic material from plants and animals.

From Biomass to Electricity The McNeil generating station in Burlington, Vermont, uses waste wood from forestry and used wood shipping pallets to produce electricity. In 1989, a natural-gas-burning system was added to the plant. The heat energy from the combustion of both wood and gas is fed into the same boiler. This unique power plant has been fully operational since 2000. Some interesting McNeil station facts: • • • • •

turbine spins at 3,600 rpm steam temperature is 950°F uses 76 tons of wood per hour uses 550,000 cubic feet of gas per hour generates enough electricity for almost the entire city of Burlington; 50 megawatts at full capacity

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Wind and solar energy wind farm - a collection of wind

Wind energy A wind energy system captures the energy of motion from moving air and

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turns the energy into electricity. California was the first U.S. state to build large wind farms. Today, Texas produces more electricity from wind energy than any other state, followed by Iowa and California. Wind is the world’s fastest-growing energy source used to make electricity. According to the National Renewable Energy Laboratory, as of 2015, China has the largest wind energy production capacity in the world, followed by the United States (who was the leader until 2011).

turbines.

solar energy - energy from the Sun.

Wind energy Wind is a clean, plentiful fuel source, but what disadvantages are there to challenges using wind as an energy source? The wind does not always blow when

electricity is needed, and right now, the cost of building a wind farm is greater than the cost of building a power plant that uses fossil fuel to make electricity. Also, some argue that wind farms can have a negative effect on the environment. Wind farms can disturb natural habitats, and can perhaps scar a large area of scenery (although some see wind farms as majestic, welcome sights in the landscape). Scientists, engineers, and policy-makers are addressing these challenges to make wind energy more widely accepted, cost effective, and useful. Solar energy The Sun is our biggest source of light and heat. In fact, 99 percent of the

energy used to heat Earth and all of our buildings comes from the Sun. The Sun’s energy is often called solar energy. A solar cell (also known as a photovoltaic cell) can convert solar energy to electricity (Figure 17.24). Solar energy A big challenge to using solar energy for electricity production is that a challenges backup energy source must be used on cloudy days. Also, solar energy is very

spread out, so it must be collected from a huge area to be used to generate electricity for a power grid. Currently, solar technology is very expensive, much more so than even wind technology. The Solar America Initiative (SAI) is a partnership between the U.S. Department of Energy (DOE) and industry; universities; federal, state, and local government; and nongovernmental agencies. The goal of SAI is to develop lower-cost solar technologies to produce large amounts of electricity in the future.

Figure 17.24: A photovoltaic (PV)

cell (sometimes called a solar cell) like this one from a solar calculator can convert light energy into a small amount of electrical energy. When light energy strikes the PV cell, electrons from specially treated silicon atoms become free to flow within the electric field set up by the differently charged silicon layers. As you know, a flow of charge like this produces current, which can be directed in a circuit to do work, such as operating a simple calculator.

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Electricity and power A watt is a unit Electrical power is measured in watts, just like mechanical power. of power Electrical power is the rate at which electrical energy is changed into other

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forms of energy such as heat, sound, or light. Anything that “uses” electricity is actually converting electrical energy into some other type of energy. The watt is an abbreviation for one joule per second. A 100-watt light bulb uses 100 joules of energy every second. Figure 17.25 shows some typical power ratings for common devices.

electrical power - the rate at which electrical energy is changed into other forms of energy.

kilowatt-hour - a unit of energy equal to one kilowatt of power used for one hour. One kilowatt-hour equals 3.6 million joules.

Kilowatt-hours Utility companies charge customers for the

number of kilowatt-hours (kWh) used each month. One kilowatt-hour means that a kilowatt of power has been used for one hour. A kilowatt-hour is not a unit of power but a unit of energy, like a joule. A kilowatthour is a relatively large amount of energy, equal to 3.6 million joules. If you leave a 1,000-watt hair dryer on for 1 hour, you have used 1 kilowatt-hour of energy. You could also use one kilowatt-hour by using a 100-watt light bulb for 10 hours. The number of kilowatt-hours used equals the number of kilowatts multiplied by the number of hours the appliance was turned on. Electric companies charge for kilowatt-hours used monthly. Your home is connected to a meter that keeps track of the kilowatt-hours used. Save money on How can you save money on your household’s electric bill? Use less electricity electricity, of course! There are many simple things you can do to use less

Appliance

Power (watts)

Electric stove

3,000

Electric heater

1,500

Toaster

1,200

Hair dryer

1,000

Iron

800

Washing machine

750

Television

300

Light

100

Small fan

50

Clock radio

10

Figure 17.25: Typical power usage of some common appliances.

electricity. When added up, these simple things can mean many dollars of savings each month, which adds up to a large amount of money over a oneyear period. What can you do? Make sure your windows are locked so they seal properly. Turn off lights when you are not using them. Switch off electronic equipment that uses standby power. Electric utility companies will send an energy consultant to your home to give suggestions on how to conserve electricity. Conserving electricity means lower bills and a cleaner environment.

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Section 17.4 Review 1. Some of the energy that comes from burning a fossil fuel can be turned into electricity, but most of the energy is lost. Explain why this is a true statement and identify the unusable or lost energy.

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2. Define the terms nonrenewable resource and renewable resource and give three examples of each. 3. Create a table like the one started below. Include a row for each of these energy sources: fossil fuels, nuclear, hydroelectric, geothermal, biomass, wind, and solar List the advantages and disadvantages for each one. Advantages and disadvantages of energy sources Energy source

Advantages

Predict the Future Study the pie graph below. Redraw your own version of this graph as it will most likely look 50 years from now. Information from the Energy Information Administration's web site will be helpful. You can also get information from the United States Department of Energy. Explain the reasoning behind your graph, and don’t forget to list your sources.

Disadvantages

Fossil fuels Nuclear

4. How much energy does a 1,500-watt hair dryer use every second? 5. Which of the following does the electric utility company charge for each month? a. electrical power used b. electrical energy used c. electrical current used 6. A student used three appliances in her dormitory room: a 1,200-watt iron, which she uses 3.5 hours per month; a lamp with a 100-watt bulb, which she uses 125 hours per month; and a 700-watt coffee maker, which she uses 15 hours per month. a. How many kWh of electrical energy are consumed in one month by each appliance? b. If the local utility company charges $0.15 cents per kWh of electrical energy consumed, how much does it cost per month to operate each appliance?

17.4 GENERATING ELECTRICITY

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Chapter 17 Assessment Vocabulary Select the correct term to complete the sentences.

8.

A(n) ____ is a device that converts electrical energy into mechanical energy.

9.

A(n)____ is the rotating disk of an electric motor.

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biomass

generator

nonrenewable resource

commutator

geothermal

permanent magnets

electric motor

heat pump system

renewable resource

10. A(n) ____ can switch the direction of electrical current in the electromagnet of an electric motor.

electrical power

hydroelectric

rotor

Section 17.4

electromagnet

kilowatt-hour

solar energy

11. A(n) ____ such as coal, petroleum, or natural gas is a ____ used to generate electricity.

electromagnetic induction magnetic fossil fuel

wind farm

magnetic declination magnetic field

Section 17.1

1.

A(n) ____ material can create or respond to forces from magnets.

2.

A magnet fills the space around itself with a kind of potential energy called a(n) ____.

12. A waste-to-energy plant uses ____ to generate electricity. 13. ____ power plants use Earth’s internal heat energy to generate electricity. 14. A collection of wind turbines, called a(n) ____, is an example of using a(n) ____ to generate electricity. 15. A photovoltaic cell can convert ____ to electricity.

3.

The difference between the direction a compass needle points and the direction of true north is called ____.

16. A(n) ____ takes advantage of Earth’s constant shallow ground temperature for seasonal heating and cooling of buildings.

4.

Bar magnets, refrigerator magnets, and horseshoe magnets are all good examples of ____.

17. ____ plants will contribute over 50 percent of the renewable resource electricity generation in 2010.

Section 17.2 5.

A simple ____ uses a coil of wire, often wrapped around an iron or steel object.

Section 17.3 6.

The process by which a moving magnet creates voltage and current in a loop of wire is called ____.

7.

A device that uses electromagnetic induction to make electricity is called a ____.

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18. ____ is the rate at which electrical energy is changed into other forms of energy. 19. A ____ is a relatively large amount of energy, equal to 3.6 million joules.

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Concepts Section 17.1

1.

Name a metal that has strong magnetic properties.

2.

Describe the types of forces that magnetic poles exert on each other.

3.

Earth’s magnetic north pole is:

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a. b. c. d.

aligned with the North Star. near Earth’s geographic North Pole. near Earth’s geographic South Pole. at the equator.

Section 17.2

4.

If you reverse the direction of electrical current in an electromagnet, what happens to the electromagnet?

5.

What are three ways you can increase the strength of an electromagnet?

6.

Explain why an electromagnet usually has a core of iron or steel.

7.

Relatively few materials show magnetic properties because: a. b. c. d.

8. 9.

their atomic magnets must line up with Earth’s geographic South and North Poles, and this is rare. they contain a rare substance. their atomic magnets are much stronger than the atomic magnets of other materials. we see magnetic properties only if atomic magnets line up in the same direction throughout a material.

Name two examples of machines that use electromagnets. Explain the purpose of the electromagnet in each machine. Plastic and wood are not magnetic materials. Explain, in terms of their atoms, why they are not magnetic.

Section 17.3

CHAPTER 17

11. You can say that the battery used to power a DC motor is not directly responsible for making the rotor spin. What, then, is the battery directly responsible for? What actually causes the rotor to spin? 12. What is the purpose of a commutator in an electric motor? Section 17.4

13. Why is nuclear energy considered a nonrenewable resource? 14. Less than 15 percent of the United States’ electric power generation in 2014 came from renewable resources. What is the main reason for this low percentage? 15. Why is hydroelectric the most widely used renewable resource for electricity generation in the United States?

Problems Section 17.1

1.

A student places two magnets with their north poles facing each other, 50.0 cm apart. When she moves one magnet toward the other, the first magnet repels the second at a distance of 26.0 cm. She repeats the procedure, but, now she places the magnets so the south pole of one faces the north pole of the other (see below).

a. b.

What is she likely to observe? Next, she put one of the magnets on her wooden desk with the north pole down. If the desk top is 2.5 cm thick, do you think she could move the magnet by placing another magnet under the desk? Explain.

10. What are the key parts of an electric motor? CHAPTER 17 ASSESSMENT

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2.

MAGNETISM

The graph below shows the force between two magnets when they are at various distances from each other.

c. d. 6.

An even number of magnets, never an odd number. A stationary element with magnets.

The diagram represents the rotor of an electric motor. In order for the rotor to turn in a counterclockwise direction, the north pole of a magnet should be placed at which position (A, B, C, or D)?

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Section 17.4

a. b.

What does this graph show about the force between magnets that are very close together? What can you do to two magnets to decrease the force between them?

7.

a. b. c.

Section 17.2

3.

4.

The atoms of a permanent magnet can’t move, and the electrons in the atoms are lined up so that a magnetic field is created around the magnet. The atoms in iron or steel can move. Describe what you think happens to the atoms of a steel paperclip when the paperclip is near a permanent magnet. Draw an electromagnet. Label all parts including the magnetic poles.

Section 17.3

5.

A working electric motor needs to have three things. Which of the following are the three? a. b.

A device to switch the polarity of the electromagnets at the right time. A moving element with magnets.

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Alex uses a 1,000-watt heater to heat his room. What is the heater’s power in kilowatts? How many kilowatt-hours of electricity does Alex use if he runs the heater for eight hours? If the utility company charges $0.15 per kilowatt-hour, how much does it cost to run the heater for 8 hours?

Applying Your Knowledge Section 17.1

1.

Would a magnetic screwdriver be useful? Why or why not?

2.

Neodymium magnets are very strong. Do an Internet search to find the answers to the following questions. a. b. c.

What materials does this type of magnet contain? Describe two uses for neodymium magnets. Why should someone use extreme caution when using these magnets?

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Section 17.2

3.

5.

Suppose you are walking in a wooded park and you want to use a hand-held compass to walk directly west from your current position. Describe, using numbered steps, exactly how you would use the compass to direct you.

CHAPTER 17

A bicycle light generator is a device that you place on the wheel of your bike. When the wheel turns, the generator powers a light. When you stop, the light goes out. Explain how the bike generator makes electricity.

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Section 17.3

4.

In 1996, NASA scientists worked with Italian scientists to carry out an interesting experiment. They made a special satellite and connected it to the space shuttle with over 20 km of insulated copper cable. As the shuttle orbited Earth, scientists released the tethered satellite and conducted 12 different experiments while dragging the cable through Earth’s magnetic field at speeds of over 15,000 mph! The satellite was equipped with many instruments to study the effects on the special copper cable. Based on your understanding of electromagnetic induction, what do you think happened to the copper cable?

Section 17.4

6.

Wind energy is a renewable resource used to produce electricity in the United States. a.

b.

Is wind energy being used at all in your state to generate electricity? Explain your answer and remember to cite your sources of information. Do you think wind energy will be used more than any other resource to generate electricity 50 years from now? Why or why not?

CHAPTER 17 ASSESSMENT

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Unit 6 Earth’s Structure FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

CHAPTER 18 Earth’s History

and Rocks

CHAPTER 19  Changing Earth CHAPTER 20 Earthquakes and

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Volcanoes

‹ Try this at home You may have heard of plate tectonics, but how does it work? To help you picture this process, try the following. Get a small hardcover book and some putty from the toy department. Set the book up so that it makes a “tent”. Make a rectangle out of the putty and lay it over the point of the tent. Next take an index card and cut it in half. Place each half touching, but on either side of the point. Let go of the cards and let them rest for 5-10 minutes. What happens to the two pieces of index card? What happens to the putty? Look through the pages of this unit to see if you can discover what layers of Earth the putty and the cards represent. How is this model similar to the process of plate tectonics? How is it different?

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18

CHAPTER 18

Earth’s History and Rocks

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If you wanted to learn about people and places that existed 50 years ago, what would you do? Maybe you would read a history book or talk to your grandparents to find out what things were like a long time ago. Fifty years is a long time for people, but not for planet Earth. Our planet is 4.6 billion years old and a lot has happened here on Earth since it formed. For example, life forms have evolved, and many—like the dinosaurs—have disappeared. How do you think scientists learn about Earth’s ancient past? For starters, they might look at the layers of rock underfoot. How a rock has been formed and shaped tells a story. Additional stories are told by fossils found inside rocks. Fortunately, there are places on Earth where layers and layers of rock are above ground for all to see and interpret. One such amazing place is the Grand Canyon. This chapter takes you back through Earth’s geologic history and gives you tools to interpret that history. And because Earth’s history is “written” in them, at the end of this chapter, you will learn about rocks.

4 How do we know Earth’s age?? 4 How do scientists “read” Earth’s history in rocks?

4 What is the rock cycle?

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18.1 Geologic Time The geologic time scale is a model of Earth’s history. You’ll find a colorful chart of the geologic time scale on the next page. What are the units of time on the geologic time scale? How do scientists use fossils to chart Earth’s history? Read on to find out.

geologic time scale - a model of Earth’s history.

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Earth’s earliest history Parts of The geologic time scale is divided into shorter and shorter lengths of time, geologic time from eons to eras to periods. This is similar to how a day is divided into

hours, and hours into minutes (Figure 18.1). However, time units on the geologic time scale are much longer. The geologic time scale units are based on tracking life forms within the layers of Earth’s crust. If a particular kind of fossil that has been dated is found in two locations some distances apart, this suggests that the life forms might have been deposited in the same layer. The The Precambrian can be divided into two eons (the Archean and the Precambrian Proterozoic) and represents 88 percent of Earth’s history. Early in the

Precambrian, Earth’s surface was molten rock. From this molten rock, the oceanic crust formed. Later, through partial melting of the oceanic crust, continental crust began to form. Earth’s atmosphere formed from volcanic outgassing and water vapor. Then, cooling of the atmosphere led to rain which collected in low areas and formed the oceans. The first primitive cells appeared in these oceans. With the appearance of photosynthesis in cells, oxygen began to build up in the atmosphere, and the early ozone layer began to act as a sun shield as more complex life forms evolved. Most of the life forms of the Precambrian did not have hard body parts and so left no easily found fossils.

Figure 18.1: A comparison of units of time.

Paleozoic Era The Paleozoic Era and the eras that followed represent the Phanerozoic Eon.

The word Paleozoic comes from Greek and means “ancient life.” Paleozoic rocks contain fossils of the first plants and animals, such as snails, clams, corals, and trilobites, that had hard parts. Trilobites were invertebrates, meaning they had no backbones (Figure 18.2). The Paleozoic Era lasted for nearly 300 million years. At the end of this era, the continents that existed during this time period collided to form a new supercontinent, Pangaea.

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Figure 18.2: A trilobite fossil.

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CHAPTER 18

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The Mesozoic Era to the present Mesozoic Era Animals with backbones began to appear during the Paleozoic Era. These

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new animals, called vertebrates, rose to dominance during the next era, the Mesozoic Era. The word Mesozoic means “middle life.” The Mesozoic Era lasted for nearly 200 million years and saw the rise and disappearance of the dinosaurs. Dinosaurs gave this era its common name, the Age of Reptiles. The Mesozoic was also the time during which flowering plants evolved. The breakup of Pangaea also marked this era. Cenozoic Era The first mammals began to appear during the Mesozoic Era, but they

became the dominant life form during the Cenozoic Era. Not surprisingly, the common name for the Cenozoic Era is the Age of Mammals (Figure 18.3). Cenozoic gets its name, which means “recent life,” from the fact that it is the most recent of the three eras. Today’s continents moved into their current positions during the Cenozoic. Patterns in the Do you notice any patterns in Earth’s geologic history? The positions and geologic time shapes of Earth’s landmasses have changed over time. Additionally, there scale has been a progression of life forms. Vertebrate animals have some

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United States

Outer rim diameter: 180 km

` Yucatan

Crater center

o ic

extinction. A new hypothesis is that ash from massive volcanic eruptions caused the extinction by blocking sunlight and causing a greenhouse effect. Scientists do not agree whether the asteroid impact, the volcanic eruptions, some other yet undiscovered factors, or some combinations of these events was the ultimate cause of the mass extinction. What do you think?

Chicxulub impact crater

ex

What if? Recent findings suggest this asteroid impacted 300,000 years before the mass

Cenozoic era.

M

advantages over invertebrates, and so the Age of Invertebrates gave way to the Age of Reptiles. Similarly, the Age of Reptiles gave way to the Age of Mammals because warm-blooded animals have some advantages over coldblooded reptiles. In addition to gradual changes in life forms during Earth’s history, there have been dramatic events that led to change. For example, scientists have accumulated evidence to indicate that a large asteroid crashed into Earth near Mexico’s Yucatan peninsula about 65 million years ago (Figure 18.4). The resulting climate change may have caused the extinction of the majority of Mesozoic Era reptiles, including the dinosaurs.

Figure 18.3: Mammals of the

`n Yucatan Peninsula ula

Chicxulub Crater

Figure 18.4: The Chicxulub crater

marks the spot where a large asteroid crashed into Earth 65 million years ago.

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CHAPTER 18

Absolute dating What is absolute Absolute dating is any process that provides the real age of a sample in dating? years. Radiometric dating is a form of absolute dating that measures the

change in naturally-occurring radioactive forms of certain elements in rocks, minerals, or fossils.

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Radioactive Radiometric dating relies on using isotopes of elements. For example, a isotopes hydrogen atom always has only one proton, but isotopes of hydrogen might

absolute dating - any process that provides the real age of a sample in years. radioactive isotope - an unstable isotope that loses energy and matter over time.

have one, two, or no neutrons. Some isotopes are unstable and break down, or decay, over time. An isotope that decays is called a radioactive isotope. When such a radioactive isotope decays, it loses energy and matter. After decay, the radioactive isotope becomes a daughter isotope of a different daughter element. This daughter isotope might be stable, or it might be unstable and decay again. Radiometric Uranium-238 is a radioactive isotope that has 92 protons and 146 neutrons. dating using Through radioactive decay, slightly unstable uranium-238 changes to become uranium another radioactive isotope, thorium-234. In 4.5 billion years, half of a sample

of uranium-238 will become thorium-234. This amount of time-the time it takes for half of the unstable atoms in uranium-238 to decay -is the half-life of uranium-238. After a series of additional decays, ordinary lead is produced. Scientists can determine the rock's age by the ratio of uranium-238 to lead atoms in the sample (Figure 18.5). Earth is approximately 4.6 billion years old

Why are Earth rocks only 4 billion years old?

Radiometric dating has been used to find the age of Earth. Interestingly, the oldest rocks on Earth have been dated with the uranium-lead system to be approximately 4 billion years old. But scientists have found moon rocks and meteorites that are approximately 4.6 billion years old. Since Earth was formed at the same time as the rest of the solar system, Earth must be approximately 4.6 billion years old too.

Figure 18.5: The radioactive decay

of uranium to lead. Radioactive decay is measured in half-lives. After one halflife, 50 percent of the uranium-238 atoms have decayed.

So why are the rocks found on Earth only 4 billion years old? Rocks that are as old as Earth are not found because our planet is geologically active and has been since it formed. Over time, rocks have been eroded away or buried deeply beneath other rocks. However, it is possible that rocks older than 4 billion years old exist on Earth and might one day be found. 18.1 GEOLOGIC TIME

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Trees and absolute dating What trees can You have just learned about radiometric dating as a way for gauging the tell us absolute age of something. Tree-ring dating or dendrochronology is another

absolute dating method that dates trees by studying tree rings.

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One tree ring You have seen tree rings if you have ever looked at the cross-section of a log. equals one year The concentric circular layers are formed as the tree grows. One tree ring

represents one year of growth. Often, a tree ring includes two bands—one light and one dark (Figure 18.6). Counting tree rings can tell you a tree’s age while the pattern of rings provides a record of the tree’s growth in varying environmental conditions. Tree coring Tree coring is a technique for finding the age of a tree without having to cut

it down. To get a tree core, a scientist uses a thin metal tube, called a borer, to drill to the center of the tree. When the scientist pulls the borer back out of the tree, a pencil-sized tree core is inside the tube. It looks like this.

Figure 18.6: A cross-section of a tree shows tree rings. The oldest rings are at the center of the tree and the youngest rings are around the edge.

Tree-ring dating Dendrochronology was founded and named by Andrew Douglass

(1867–1962), an American astronomer. Realizing that trees can be very old and being curious about Earth’s past climate, he hypothesized that trees might be excellent recorders of climate changes. He began to test his hypothesis by studying and recording tree ring patterns. By 1914, he had published his findings that trees within a similar area had matching tree ring patterns. He showed that wide tree rings indicated a year with a lot of rain and narrow rings indicated a dry year. Trees live a long Trees are good record-keepers because they tend to live a long time. The time oldest tree that we know about, a bristlecone pine called “Methuselah,” is

over 4,800 years old. This bristlecone pine and others live in California (Figure 18.7). Redwood trees, one of the world’s tallest species at about 300 feet tall, are also found in California and live as long as 2,000 years.

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Figure 18.7: A bristlecone pine growing in California.

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CHAPTER 18

Section 18.1 Review 1. Explain how Earth’s history is divided in the geologic time scale.

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2. Which answer is correct? During the Precambrian: a. human beings lived and thrived. b. dinosaurs became extinct. c. single-celled and soft-bodied organisms appeared. d. flowering plants evolved. 3. Compare and contrast the Paleozoic and Mesozoic Eras in terms of the length of each era, landmasses, and the life forms that evolved in each. What is interesting or surprising to you in each era?

Learn more about Earth’s geologic history by doing one of the following projects. (1) Create a time line for one era. (2) Create a colorful poster that illustrates the events in one period. (3) Write a short story about one period. Your story should include one or more major events that happened during that period.

4. Look at the chart of Earth’s geologic history on page 411. Were humans around when the supercontinent Pangaea broke up? 5. Compare and contrast the two methods of absolute dating you read about. 6. How much uranium-238 isotope is left in a pure sample after one half-life? 7. How have scientists determined the age of Earth? How old is Earth? 8. The half-life of uranium-238 is 4.5 billion years. The half-life of carbon-14, another radioactive element, is 5,730 years. You want to use absolute dating to determine the age of a rock that was about as old as Earth. Would you measure the radioactive decay of carbon-14 or uranium-238? Explain your answer. 9. If a tree has 25 rings, how old is it? 10. Figure 18.8 shows cross-sections from two trees that grew in different areas. a. The trees were the same age when they were cut. How old are these trees? b. Make a drawing of what a tree core would look like for each tree cross-section. c. Write a fictional history that explains the wet and dry conditions for each tree during each year of its lifetime.

Figure 18.8: Question 10. Note:

When counting rings, do not count the very center (called the pith).

18.1 GEOLOGIC TIME

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18.2 Relative Dating Earth science is a large field of science that includes geology, the study of the solid matter that constitutes Earth. By “solid matter,” we mean rocks. As you read in the chapter introduction, rocks and rock layers contain stories about Earth’s history. This section presents some of the scientific processes used to discover and understand these stories.

geology - the study of the solid matter that constitutes Earth.

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The beginnings of modern geology Shark’s teeth Nicolas Steno (1638–1686), a Danish anatomist, studied a shark’s head and

noticed that the shark’s teeth resembled mysterious stones called “tongue stones” that were found inside local rocks. At that time, some people believed that tonguestones had either fallen from the moon or that they grew inside the rocks. Steno thought that tongue stones looked like shark’s teeth because they were shark’s teeth that had been buried and became fossils! How did teeth Steno realized that when an animal dies it is eventually covered by layers of get inside a sediment. The animal’s soft parts decay quickly, but bones and teeth do not. rock? Over a long period of time, the sediment around the dead animal becomes

rock, with the bones and teeth inside.

The girl in this image is climbing some of the “solid matter” found on Earth. Study the image and answer the following geology questions. 1. How do you think the features of this canyon were made? 2. Which was made first—each layer of rock or the holes and indentations in the rock? Explain your answer.

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Relative dating Steno’s ideas Steno’s observations helped him develop ideas about how rocks and fossils

form. His ideas, which are described on the next page, are still used today in the study of geology as a technique called relative dating. Relative dating is the process of putting events in the order in which they happened.

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How is relative Relative dating is used to determine the order of events that affected a rock dating used? formation, including the order of its layers. Unlike absolute dating, relative

dating does not try to determine the exact age of an object, but instead uses clues to figure out the order of events over time.

relative dating - the process of putting events in the order in which they happened.

fossil - the remains or traces of a dead animal or plant that has been preserved for a long time.

paleontologist - a scientist who studies and identifies fossils.

Fossils are A fossil is the remains or traces of a dead animal or plant that has been clues preserved for a long time. Found within a layer of rock, a fossil can be used to

identify the general age of that layer of rock, especially if it is a fossil of a known life form that has been dated using absolute dating. For example, if you found a trilobite fossil within a rock layer, in what era might this layer have been formed? If you said the Paleozoic era, you are correct. A question like this can be answered by a paleontologist, a scientist who studies fossils. The present Like Steno, Scottish geologist James Hutton (1726–1797) was an important explains the figure in the development of modern geology. Hutton is credited with past identifying one of the most important clues for deciphering Earth’s history.

Hutton realized that if you understand processes that are happening now, you can use that knowledge to explain what happened a long time ago. The short form of his idea is: The present is the key to the past.

The present is the key to the past. —James Hutton Comparing the You see geologic processes in action on a regular basis. For example, when it present and past rains hard you might see flowing water washing away or eroding sediment

(Figure 18.9). When the rain stops, you might observe that grooves were left behind by the flowing water. Observations of common, small-scale events in the present like this are helpful for understanding how large land features formed. For example, the Grand Canyon was eroded by the Colorado River (see the next page).

Figure 18.9: The way water erodes the land is seen every time it rains.

18.2 RELATIVE DATING

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Identifying clues using relative dating Superposition Steno identified the law of superposition, which states that the bottom layer

of a rock formation is older than the layer on top, because the bottom layer formed first. A stack of newspapers is a good illustration of superposition (Figure 18.10).

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Original Steno also identified the law of original horizontality which refers to how horizontality sediment particles settle to the bottom of a body of water, such as a lake, in

response to gravity. The result is horizontal layers of sediment. Over time, these layers can become layers of rock. As you see in the graphic below, sometimes horizontal layers of rock might become tilted or folded by a geological event, such as an earthquake. Layers might be tilted at any angle and can even be upside down. Original horizontality Sediment is deposited horizontally.

Geological event

Geological event

Layers of sediment become layers of rock.

Horizontal layers may become tilted or folded.

Figure 18.10: A stack of newspapers illustrates superposition. The oldest newspaper is on the bottom of the stack and the more recent newspapers are piled on, with the most recent on top.

Lateral Steno’s third contribution to the technique of relative dating and modern continuity geology is the law of lateral continuity. Lateral continuity refers to how

layers of sediment extend in all directions horizontally. Later, a separation might be caused by a geological event such as erosion (the breaking down of rock as it is moved by water) or movement during an earthquake. The Colorado River created the gap that is now the Grand Canyon. If you were to compare rock layers in the Grand Canyon, you would find that the layers on one side of the canyon match up with the layers on the other side (Figure 18.11).

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Figure 18.11: Layers of rock are

continuous unless a river erodes the layers or an earthquake moves them.

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CHAPTER 18

Identifying the relative age of a rock or fossil Cross-cutting The principle of cross-cutting relationships relationships states that a vein of rock or a break (called

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a fault) that cuts across a rock’s layers is younger (more recent) than the layers. The graphic at the right shows a rock formation with three layers and a cross-cutting vein. The rock layers formed first. The vein formed when molten rock oozed into a crack in the original rock, cutting across the layers. The bottom layer is the oldest part of the rock formation and the vein is the youngest. The middle and top layers formed after the bottom layer, but before the vein. Similarly, a fault that cuts across layers of rock will always be younger than the layers. Inclusions Sometimes inclusions or pieces of one rock

are found inside another rock. During the formation of a rock with inclusions, sediments or melted rock surrounded the inclusions and then solidified. Therefore, the inclusions are older than the surrounding rock. A rock with inclusions is like a chocolate chip cookie. The chocolate chips (inclusions) are made first. Then they are added to the batter (melted rock or sediment) before being baked (hardened) into a cookie (rock). Fossil The principle of fossil succession means that succession fossils can be used to identify the relative age of

the layers of a rock formation. For example, dinosaur fossils are found in rock that is about 200 to 65 million years old because these animals lived that long ago. The fossils of modern human beings (Homo sapiens) are only found in rock that is younger than 200,000 years old.

Hutton, Lyell, and Darwin A few of the important storytellers of Earth’s history are James Hutton (1726–1797), Charles Lyell (1797–1875), and Charles Darwin (1808–1882). Hutton recognized that present events explain how past events occurred, and he understood that the processes that shape Earth take a long time. His ideas were eventually referred to as “uniformitarianism.” Between 1830 and 1833, Lyell published Principles of Geology, a threevolume book that was extremely popular. In his book, Lyell supported uniformitarianism with evidence from his own extensive travels, particularly in North America. A young Darwin sailed as the ship naturalist on the HMS Beagle. On his journey, he found geological and fossil evidence that supported Lyell’s ideas in Principles of Geology and uniformitarianism. Darwin used his findings to develop his theory of natural selection that said organisms arise from a common ancestor and evolve over a long period of time. His ideas were published in 1859 in On the Origin of the Species.

18.2 RELATIVE DATING

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Fossils and Earth’s changing surface One large Fossils provide evidence for how Earth’s surface has changed over time. At landmass the beginning of the Mesozoic Era (250 mya), the land on Earth existed as a

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supercontinent called Pangaea. In the graphic below, find the part of Pangaea that would eventually become South America. How does South America’s present day climate compare to what it would have been 250 million years ago? Earth today Eventually, pieces of Pangaea separated and moved away from the South

Pole. The right side of the graphic shows the way land is distributed today. The colors show where you would find the fossils of the organisms featured in Figure 18.12. The black dotted line marks where glaciers used to be. Where organisms lived on Pangaea

Pa

Where fossils are found today

Ancient continents

a ae ng

South Pole

Modern continents

Pacific Ocean

Indian Ocean Atlantic Ocean

Glacial limit

Range of organisms

Cynognathus

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Glossopteris

Lystrosaurus

Mesosaurus

Figure 18.12: These organisms lived on Earth when the land was connected as one large landmass, Pangaea.

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Section 18.2 Review 1. Describe Nicolas Steno’s contribution to modern geology. 2. James Hutton recognized that the present explains the past. Why is this idea so important in modern geology?

Use classroom resources, home resources, or the Internet to research the geology of the Grand Canyon. Then, answer the following questions.

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3. How are a vein of rock and an inclusion similar? How are they different? Describe a vein and an inclusion in your answer.

When was the Grand Canyon formed?

4. Use the graphic at the right to answer the following questions. Justify your answers using relative dating principles. a. Assuming that the layers are still in the position in which they were laid down, what idea is represented? b. Which organism is oldest? c. Which is youngest?

What are the different rock layers found in the Grand Canyon?

How was it formed?

How old is the oldest rock layer? How is the Grand Canyon changing today? Why is it changing?

5. True or false: Superposition states that rock layers near the surface of Earth are younger than rock layers further from the surface. Explain your reasoning. 6. A geologist sees a series of vertical layers of rock. Does this observation disprove the law of original horizontality? Why or why not? 7. Study Figure 18.13 to answer the following questions. Justify your answers using relative dating principles. a. Which horizontal layer of rock is the oldest? The youngest? b. Which event occurred more recently—H or G? c. Are the inclusions in layer B older or younger than layer B? d. Form a hypothesis: What is the source of the inclusions in layer B? e. List the layers and events in the chronological order in which they occurred. 8. How are layers of rock like a history book?

Figure 18.13: Question 7.

Unconformity In Figure 18.13 you can see that the vein (G) is cut off by a rock layer (B). An interruption like this in the geologic record is called an unconformity. How do you think an unconformity forms?

9. Why is there evidence of glaciers in Africa? 10. Why do some fossils in South America match some fossils in Africa? 18.2 RELATIVE DATING

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18.3 The Rock Cycle You have read that rocks and layers tell stories about Earth’s history. A rock is a naturally formed solid made of one or more minerals. In this section, you will first learn about the minerals that make up a rock, and then about a special set of processes called the rock cycle.

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Rocks are made of minerals

rock - a naturally formed solid made of one or more minerals. mineral - a solid, naturally occurring, crystalline object with a defined chemical composition.

What is a A mineral is a solid, naturally occurring, inorganic object with a defined mineral? chemical composition. Minerals have a crystal structure, which means they

have an orderly arrangement of atoms. Minerals can be made of one or more elements. Graphite and diamonds, both made only of carbon, have different properties because they have different crystalline structures (Figure 18.14). Minerals in There are more than 4,000 minerals on Earth. Eight of these minerals make Earth’s crust up about 98 percent of Earth’s continental crust by weight. Feldspar and

quartz are the two most abundant minerals. As silicate minerals, feldspar and quartz mostly contain silicon and oxygen, the two most abundant elements in Earth’s crust (Figure 18.15). Minerals are made by geologic processes. One process is the cooling of molten rock inside Earth. Granite, for example, is a rock that forms underground as molten rock cools. As cooling takes place, different minerals crystallize. You can see these individual mineral crystals in the photo of a piece of granite at the left. Another process that allows minerals to form or crystallize is when water containing dissolved minerals evaporates.

How are minerals made?

Minerals help The crystalline structure and chemical composition of a mineral is tell the story determined by the conditions under which it forms. Additionally, existing

minerals can change due to heat, pressure, or chemical reactions. When the minerals change, the rock that is made up of the minerals also changes.

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Figure 18.14: Diamonds and

graphite are minerals that are made of carbon. Approximate percentage by weight of elements in Earth’s crust Oxygen

46.6%

Silicon

27.7%

Other minerals

25.7%

Figure 18.15: Oxygen and silicon

are the two most abundant elements in Earth’s crust.

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Common minerals and cleavage planes Mica Mica is composed of silicon and oxygen along

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with iron, magnesium, and sodium. A piece of mica has layers, like a stack of pages in a book. Each single layer of mica is described as having one direction of cleavage or one set of cleavage planes. A cleavage plane is a surface along which a mineral cleanly splits. The placement of a cleavage plane occurs where there are weak bonds between the molecules in the mineral (Figure 18.16).

cleavage plane - a surface along which a mineral cleanly splits.

Feldspar and Feldspar is the most abundant mineral in hornblende Earth’s crust. Feldspar is composed of

silicon and oxygen along with sodium, calcium, and potassium. Feldspar has two cleavage planes at right angles to each other. Hornblende, also found in granite, is a dark mineral made of a mixture of elements including silicon, oxygen, and calcium along with iron, magnesium, or aluminum. Like feldspar, hornblende has two cleavage planes, but not at right angles. Quartz Quartz is the second most abundant mineral in Earth’s crust. Quartz crystals

can appear to shine like glass. Unlike feldspar, quartz lacks cleavage planes (Figure 18.17). When quartz breaks, it does not split along planes. Quartz is made of silica and is used in making glass. Many gemstones are simply quartz with trace amounts of other elements or compounds mixed in. For example, onyx, agate, and amethyst are gemstones formed in this way.

Figure 18.16: Mica has one

direction of cleavage and breaks into sheets. The mineral halite has three directions of cleavage and breaks into cubes.

Figure 18.17: Quartz is a mineral in granite. It lacks cleavage planes. 18.3 THE ROCK CYCLE

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Mohs hardness scale Identifying Mohs hardness scale was developed in 1812 by Friedrick Mohs minerals (1773–1839), an Austrian mineral expert, as a method to identify minerals

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(Figure 18.18). This scale uses 10 minerals to represent variations in hardness. Here, the word hardness means resistance to being scratched. You can identify a mineral’s place on the scale by whether it can scratch another mineral. For example, gypsum (hardness = 2) scratches talc (hardness = 1). The hardest mineral, diamond, can scratch all other minerals. Minerals of the same hardness (and without impurities) scratch each other. Common items You can use common items to test the hardness of a mineral. For example, test hardness your fingernail, a penny, a steel nail, or glass can be used. The following

scenarios illustrate how to use Mohs hardness scale.

Mohs hardness scale - a scale used to identify minerals based on their hardness or resistance to being scratched.

Mineral

Hardness

Talc

1

Gypsum

2

Calcite

3

Fluorite

4

Apatite

5

Orthoclase (feldspar)

6

Quartz

7

Topaz

8

Corundum

9

Diamond

10

Figure 18.18: Mohs hardness scale.

Streak plate test Sets of minerals often come with a white, unglazed, ceramic streak plate or

tile. You can identify certain minerals by scratching them on the streak plate. The color of the streak they leave behind can help you identify the mineral. For example, both pure gold and pyrite (also called Fool’s Gold) are goldcolored minerals (Figure 18.19). Gold is rare and valuable. It leaves a golden-yellow streak. Pyrite is shiny, brassy, and a common mineral. It could be mistaken for gold, but it leaves a gray or black streak on a streak plate! Figure 18.19: Gold and pyrite.

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Rock groups Three groups Now, that we have learned about minerals, let’s learn about rocks. All rocks

on or below Earth’s surface belong to one of three groups, depending on how the rock formed.

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Rock group

Igneous

rock cycle - the formation and recycling of rocks by geologic processes.

Formation These rocks form when molten rock (lava or magma) cools and crystallizes.

Use the definition of a mineral to answer the following questions. 1. Is ice a mineral? Why or why not?

Sedimentary

Metamorphic

Particles of other rocks and minerals or once-living things are moved by water, wind, ice, or gravity and eventually settle in layers. The layers are compacted and cemented to form a new rock.

2. Is coal a mineral? Why or why not?

These rocks form from other rocks that are changed by heat and pressure.

Rocks are made Like the other planets, Earth was formed from the gas and dust that of old material surrounded the Sun when it formed. Earth has gone through many changes

since it formed 4.6 billion years ago. The rocks that are currently on our planet’s surface are made of material that formed long ago. The oldest rocks found on Earth so far are approximately 4 billion years old. However, some rocks are “young.” A young rock might be a million years old! The presence of young rocks on Earth suggests that old rocks have been recycled. The original Earth has been recycling material for billions of years and the rock cycle is recycling plan the original recycling plan. The rock cycle (or geologic cycle) describes how

rocks are formed and recycled by geologic processes. Igneous, sedimentary, and metamorphic rocks are all part of this cycle.

18.3 THE ROCK CYCLE

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Rocks keep moving

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The processes that keep rock material moving through the rock cycle include weathering, erosion, deposition, compaction and cementation, metamorphism, and melting and crystallizing. Weathering and erosion are ways in which rock is broken down and the pieces are moved from place to place. Compaction and cementation are processes which cause pieces of rock to become a sedimentary rock. You will learn more about the processes involved in forming sedimentary rocks in Chapter 23. When lava or magma cools, it forms crystals in a process called crystallization. Processes involving igneous rocks are explained in Chapter 20. Additionally, an important and fascinating geologic process—plate tectonics— plays an important role in the rock cycle. Rocks melt or metamorphose when subjected to heat and/or pressure. For example, the pressure between two pieces of Earth’s crust that are coming together can create mountains of folded rock. If new mountains weren’t always being built, the weathering and erosion of rocks over time would leave the continents smooth and flattened. You will learn about plate tectonics and metamorphic rocks in Chapter 19.

A Cycle with Many Pathways

The rock cycle does not always follow a simple path with igneous rocks forming first followed by sedimentary then metamorphic rocks. An igneous rock could become a metamorphic rock or a metamorphic rock could melt and crystallize to become igneous. All rocks will break down over time and might become part of a sedimentary rock. The important thing to remember is that the rock cycle allows material to keep changing form and moving from place to place on Earth.

The rock cycle Weathering and erosion of all rocks (sedimentary, igneous, metamorphic) IGNEOUS ROCK

Deposition of sediment

Lava

Compaction and cementation

Crystallizing SEDIMENTARY ROCK

Melting magma IGNEOUS ROCK Metamorphism (heat and pressure)

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Metamorphism (heat and pressure) METAMORPHIC ROCK

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Section 18.3 Review 1. Describe the difference between an element, a mineral, and a rock. 2. Is a diamond a rock or a mineral? Explain your answer.

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3. List the two most abundant elements and the two most abundant minerals in Earth’s crust. 4. Why are minerals an important part of the story of a rock? 5. The mineral halite naturally forms cubes. How many directions of cleavage does it have? 6. What does the word hardness mean in reference to the Mohs hardness scale? 7. Use Mohs hardness scale (Figure 18.18) to answer the following questions. a. A mineral scratches talc and gypsum. This mineral does not scratch fluorite. What is the Mohs hardness of this mineral? b. A mineral scratches topaz and quartz, and is scratched by diamond. What is the Mohs hardness of this mineral? c. A steel nail scratches apatite but not quartz. What might be the hardness of a steel nail? d. Which mineral scratches all other minerals?

More Mineral Tests You can identify a mineral using cleavage planes, a streak test, and the Mohs hardness scale. Following are some additional tests that geologists use to identify minerals. Density: The density of the mineral is measured in g/cm3. Some minerals are dense and heavy for their size. Others are less dense and light weight for their size. Luster: Luster is how a mineral reflects light. Metallic minerals (like pyrite) are shiny. Nonmetallic minerals can appear dull or glassy (reflect light the way glass does). Magnetism: Some minerals (like magnetite) are magnetic. Acid test: Some minerals bubble and produce gas by reacting with dilute hydrochloric acid.

8. How does a streak plate test help identify a mineral? 9. Based on the reading, list one feature that you could use to identify each of the three groups of rocks. 10. What kind of rock is granite? Justify your answer. 11. Does the rock cycle have a beginning point and an ending point? Explain your answer. 12. True or false: Metamorphic rocks could be made from sedimentary and igneous rocks, but not from other metamorphic rocks? 13. A rock is 500,000 years old. Would you classify this rock as young or old? Explain your answer. 18.3 THE ROCK CYCLE

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Chapter 18 Assessment Vocabulary

11. A surface along which a mineral cleanly splits is a(n) _____.

Select the correct term to complete the sentences.

12. A(n) _____ is a naturally formed solid composed of one or more minerals.

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geology

relative dating

radioactive isotope

fossil

paleontologist

absolute dating

geologic time scale

cleavage plane

half-life

mineral

rock

rock cycle

Mohs hardness scale

13. Quartz is a(n) _____ found in granite.

Concepts Section 18.1

Section 18.1

1.

Which time period in geologic history lasted the longest time?

1.

The _____ is divided into blocks of time called eons, eras, and periods.

2.

2.

The _____ of uranium is 4.5 billion years.

3.

_____ is a way of determining the age of something in years.

4.

An unstable isotope that experiences radioactive decay is called a(n) _____.

Name the era or time period during which each of the following organisms or events first appeared. a. dinosaurs e. modern climate b. invertebrates f. Pangaea c. humans g. ferns d. single-celled organisms h. fishes

3.

Uranium ultimately decays into a stable element called: a. lead c. carbon b. nitrogen d. phosphorous

Section 18.2

5.

Through their observations of rock formations, Nicholas Steno and James Hutton helped develop the field of modern _____.

6.

_____ is a method that involves putting events in the order in which they happened.

4.

How might a tree fossil help a scientist understand the climate of certain places millions of years ago?

7.

An ancient, preserved shark tooth is an example of a(n) _____.

5.

8.

A scientist who studies fossils is called a(n) _____.

You notice that a tree cross-section has a very wide tree ring that occurred in 1985 and a very narrow tree ring that occurred in 1992. From this information, what can you infer about the tree’s environment in 1985? In 1992?

6.

How do scientists know which plants and animals lived at the same time as the dinosaurs?

Section 18.3

9.

The resistance to scratching that a mineral exhibits is identified using the _____.

10. The _____ represents the formation and recycling of rocks by geologic processes.

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7. 8.

Lystrosaurus fossils are found in Antarctica and Africa. How it is possible for fossils of this organism to be found in both places? Is measuring the amount of uranium-238 in a fossil to determine its age relative dating or absolute dating?

Section 18.3

16. Name one similarity and one difference between graphite and diamond. 17. Answer the following questions about pyrite (fool’s gold) and gold. a.

Section 18.2

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9.

CHAPTER 18

If you had a question about where to find trilobite fossils, would you ask a geologist or a paleontologist? Explain your answer.

b.

What is one characteristic that can be used to tell pyrite and gold apart? Are pyrite and gold rocks or minerals? Explain your answer.

10. Why are superposition and lateral continuity useful ideas in interpreting how the rocks of the Grand Canyon formed?

18. How are minerals distinguished on the Mohs hardness scale? What mineral represents the “bottom” of this scale?

11. Use relative dating to identify the order in which each line was drawn. Which line was drawn first? Which line was drawn last?

19. What is the rock cycle? List the three groups of rocks that are formed by the rock cycle.

12. An inclusion is: a. b. c.

younger than surrounding rock. the same age as surrounding rock. older than surrounding rock.

13. Due to original horizontality, layers of sediment form in horizontal layers. However, sometimes these layers (once they become rock) are found in other positions. What kinds of events might cause layers of rock to change positions? 14. Put the rock bodies (A, B, C, and D) illustrated at the right in order from oldest to youngest. 15. How do scientists use the ideas of fossil succession to identify how long ago different animals lived?

20. Peat and bituminous coal are rocks that are formed from ancient plant remains. What kind of rocks are peat and bituminous coal? Justify your answer.

Problems Section 18.1

1.

A fossil is determined to be about 280 million years old. a. b.

2.

A rock that is 100% uranium goes through three half-lives. a. b.

3.

How do scientists determine the age, in years, of a fossil? To which era and period does the fossil belong? What are some organisms that lived during that time? How many years is three uranium half-lives? How much uranium is left after three half-lives: 6.25%, 12.5%, 25%, or 50%?

The amount of carbon-14 in a fossil has undergone four half- lives. What is this length of time in years? If the sample contained 10 grams of carbon-14, how much is left now?

CHAPTER 18 ASSESSMENT

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EARTH’S HISTORY AND ROCKS

Use this tree core diagram to answer the questions. Do not count the bark or pith when determining the age of the tree. One tree ring equals a white area and one dark line.

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a. b. c. d.

How old is the tree? What year was this core sample taken? Give an example of a year that was probably warm with a lot of rainfall. Name a year that was probably cool and dry.

Applying Your Knowledge Section 18.1

1.

Imagine that you could go back in time and visit any period of Earth’s geologic history. Describe which period would you visit and why you would visit it.

2.

You learned that geologic time is divided into eons, eras, and periods. The Precambrian is divided into the Archean and Proterozoic Eons, and the Phanerozoic Eon is divided into the Paleozoic, the Mesozoic, and the Cenozoic Eras. Research each eon. List one fact about each.

Section 18.2

3.

Nicolas Steno and James Hutton contributed to the development of modern geology. Through research, find a fact about each of these scientists that was not mentioned in the chapter.

4.

You want to explain superposition to a group of second graders. Think of a creative model you could use that would help them understand this concept. Describe your model and explain how you would teach superposition.

5.

Explain in a short paragraph how the shell of an ocean creature could become a fossil.

Section 18.2

5.

While out on a geology field trip, you find a rock formation that has five layers of rock. A crack goes across all the layers. Answer the following questions using relative dating principles. a. b. c.

Make a diagram of this rock formation. When did the crack occur—before or after the rock layers formed? How did this rock formation form?

Section 18.3

Section 18.3

6.

Make a pie graph based on the information provided in Figure 18.15 of the text.

7.

You are looking for a birdbath for your garden in a catalog. You see a granite birdbath that costs $100. You see another birdbath made of limestone that costs $75. Granite is made of quartz and feldspar. Limestone is mostly made of the mineral calcite. Write a paragraph describing the birdbath you will purchase and why you will purchase it.

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6.

Use the rock cycle diagram on page 426 to write a story about what might happen to a small amount of hot rock in the mantle as it experiences the rock cycle. Write the story from the point of view of this piece of hot rock. You have not read much about how sedimentary, igneous, and metamorphic rocks are formed at this point, so do your best to write a story based on your reading, but you may also use your imagination.

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CHAPTER

19

CHAPTER 19

Changing Earth FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

Earth is changing all the time, but some changes occur so slowly we don’t even notice. Right now, the ground under our feet is moving as a separate layer over the interior of Earth. The theory of plate tectonics explains how and why the ground moves. By the end of this chapter, you will know more about the evidence for this theory than any scientist knew only forty years ago. Wow! The continents of South America and Africa appear to fit together like puzzle pieces. Were they ever connected? If so, how did they get separated? These questions were asked by scientists for a long time before enough scientific evidence established the theory of plate tectonics. Plate tectonics explains how and why Earth’s surface has changed over millions and millions of years. The changes are due to the flow of solid rock, under great heat and pressure, deep within our planet. The motion of pieces of Earth’s lithosphere caused by this flow leads to earthquakes and volcanoes; the building of mountain ranges, such as the Himalayas; the creation of trenches; and the melting of rocks as well as the formation of new ones.

4 What does the interior of Earth look like? 4 Why do South America and Africa seem to fit together like puzzle pieces?

4 How are rocks made from other rocks?

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CHANGING EARTH

19.1 Inside Earth

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The center of Earth is about 6,400 kilometers below the surface. The deepest anyone has ever drilled is 13 kilometers—not even close to the center! Yet scientists know a lot about Earth’s interior. This section is about the inside of Earth and how we know what it looks like.

seismic waves - vibrations that

Waves inside Earth

seismologist - a scientist who

Special Special vibrations that travel through Earth, called seismic waves, have vibrations revealed the structure of Earth’s interior. Seismic waves, which are caused

by events like earthquakes and human-made blasts, pass along the surface and through Earth. A seismologist is a scientist who studies earthquakes by detecting and interpreting seismic waves using sensors at different places on Earth’s surface. Wave motion Wave motion is the way that energy is transmitted though Earth as a result of

a disturbance. Seismic waves transmit energy released by earthquakes, meteorite impacts, or human activities to other locations. Wave motion is a series of movements that progress through materials while the material remains in place. This is how waves transfer the energy from a disturbance from one location to a very distant location. P-waves and Two types of seismic waves that are important for studying Earth’s interior S-waves are primary and secondary waves, or P-waves and S-waves. P-waves travel

faster than S-waves and move with a forward-and-backward motion. Slower S-waves travel with a side-to-side motion. S-waves cannot pass through liquids, but P-waves can pass through both solids and liquids.

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travel through Earth and are caused by events like earthquakes or humanmade blasts. studies earthquakes.

P-waves - seismic waves that move with a forward-and-backward motion. They are faster than S-waves and can travel through both solids and liquids.

S-waves - seismic waves that move with a side-to-side motion, are slower than P-waves, and can only travel through solids.

Richter Magnitude Scale You have probably heard of the Richter scale which is used to identify the magnitude (size) of earthquakes. It was first presented to the world in 1936, in a publication by Charles F. Richter, a California seismologist and physicist. At first, Richter’s scale only applied to Southern California. With the help of Dr. Beno Gutenberg, the scale was developed to apply worldwide to various types of instruments that measure and record seismic waves.

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CHAPTER 19

Seeing Earth’s interior with waves Waves tell us P-waves and S-waves might be bent, reflected, sped up, slowed down, or about Earth’s stopped depending on the nature of the material they encounter. By studying interior what happens to the waves as they travel through Earth, scientists are able to

make a detailed model of Earth’s interior (see below).

S-waves on one side of Earth, there was a large area on the other side where the waves couldn’t be detected (Figure 19.1). They called this area the S-wave shadow zone. Since secondary waves cannot pass through liquids, scientists realized that the outer core of Earth must be liquid, blocking the path of the S-waves through Earth.

Detailed view Crust

Mantl

e

Upper e mantl

STUDY SKILLS

here enosp

Use flash cards to help you practice using new terms.

Asth

Inner core

Mantle

5,100 km

Outer core

2,900 km

Lower mantle

660 km

Lower mantle

Figure 19.1: S-waves are unable to

penetrate the liquid outer core of Earth. An S-wave shadow zone occurs on the side of Earth opposite the earthquake.

Crust

410 km

Lithosphere

Simplified view

Average depth 15 km

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A clue from The discovery that Earth has a liquid outer core was determined by following S-waves the path of S-waves. Scientists observed that when an earthquake produced

Core 6,400 km

Depths are not shown to scale.

19.1 INSIDE EARTH

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Layers inside Earth Crust Earth’s outermost layer is called the crust. Oceanic crust is made of basalt,

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lies under the oceans, and is about 7 to 10 kilometers thick. Continental crust is made of granite, forms continents, and has an average thickness of 35 to 40 kilometers (Figure 19.2). The rock in the crust is brittle because it is cool. The crust breaks easily—like a cracker— when forces are applied to it. Mantle Earth’s crust floats on the mantle, which lies between the crust and Earth’s

core. The mantle is the thickest layer and makes up almost half of Earth’s diameter. Temperature and pressure increase with depth in the mantle. Due to high heat and pressure, the rock of the mantle is solid, but it flows in huge, heat-driven, slow currents that have been in motion for millions of years. Asthenosphere Earth’s mantle is divided into the upper and lower mantle. Just below the

upper mantle is a zone where the combination of high heat and pressure cause rock to be softest and weakest. This zone, called the asthenosphere, divides the upper mantle and the much larger lower mantle. Geologists compare the harder upper and lower mantle separated by the softer asthenosphere to a jelly sandwich, the asthenosphere being the jelly.

crust - the outermost layer of Earth. mantle - the hot, slow-flowing, solid layer of Earth between the crust and the core.

lithosphere - a layer of Earth that includes the crust and the upper mantle, above the asthenosphere. asthenosphere - a zone in the mantle below the lithosphere where the combination of heat and pressure cause the mantle rock to be softest and weakest. core - the center of Earth; it is divided into the solid inner core and the liquid outer core.

Lithosphere It is a common mistake to think that Earth’s lithosphere is the same as the crust. It’s not! The lithosphere is Earth’s outer shell that includes both the

crust and the upper mantle. Pieces of the lithosphere, called tectonic plates, move slowly around Earth’s surface over the softer asthenosphere and shape our oceans and continents. Each plate is like the top piece of bread of the geologists’ jelly sandwich. Core Earth’s core is divided into two layers, the outer and inner core. Both the

outer and inner layers are composed mostly of iron. The outer core is hot enough to melt and is liquid. You might think that the inner core would also be liquid, but the greater pressure at this depth prevents it from melting. The pressure causes the inner core to be solid. Rotation of the solid inner core and convection in the liquid outer core cause powerful electric currents that create Earth’s magnetic field. This magnetic field protects the atmosphere and planet from harmful solar radiation. For this reason, life on Earth would be in danger if core movement stopped.

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Figure 19.2: The continental crust and the oceanic crust.

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Density and Earth’s materials How Earth’s Earth formed from the gas and dust that surrounded our young Sun. At first, layers formed Earth’s surface was made of the same materials as its center. Later on, these

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materials melted. As the materials began to flow, less buoyant, denser materials settled toward the center, while more buoyant, less dense materials rose toward the surface. Aluminum and silicon, which have low densities, are common within Earth’s crust. Earth’s inner and outer cores are composed mostly of dense iron (Figure 19.3). Earth’s crust Earth’s crust is made of various types of rock that are less dense than the floats on the mantle. Oceanic crust is made of basalt and is slightly denser than continental mantle crust. The density of oceanic crust is 3.0 g/cm3, whereas continental crust is

Substance

Density (g/cm3)

Aluminum

2.7

Silicon

2.3

Iron

7.9

Water

1.0

Figure 19.3: Density values for substances that make up Earth.

made of andesite and granite and has a density of 2.7 g/cm3(Figure 19.4).

Convection in the lower mantle

Convection is the transfer of heat as material circulates. Inside Earth, convection takes place in the lower mantle. Most of the heat left over from the formation of Earth lies in the core. This heat is constantly being transferred to lower mantle material, causing it to expand. Since the mass doesn’t change but the volume increases, the heated material is less dense and rises from the core toward the lithosphere. Since less dense materials float on more dense materials, a convection current develops.

Convection cells As the convection current nears the lithosphere, it turns and runs along

underneath. Eventually the convection current loses its heat and sinks back toward the core, creating a convection cell. In the next section, you will learn how lower-mantle convection helps drive the tectonic plates across Earth’s surface.

Figure 19.4: The oceanic crust is

made mostly of basalt. The continental crust is made mostly of andesite and granite.

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Floating continents Rocks float on It’s hard to imagine rocks floating on other rocks, but it happens inside Earth. rocks The cold, brittle rock of the lithosphere floats on the hot, denser rock of the

mantle below.

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How is a Imagine stacking blocks on a toy boat floating in a pool. As you add blocks, continent like a the stack gets higher and heavier. The extra weight presses more of the boat boat? into the water to support the stack. The finished stack stands taller than the

Figure 19.5: How a mountain affects the crust.

original boat, but the boat is also deeper in the water.

Mountains on Earth’s crust floats on the mantle just like the boat. A mountain on land is continents just like the stack of blocks (Figure 19.5). Like the boat, the part of the crust

with a mountain on it sticks down into the mantle. The average thickness of continental crust is 35 to 40 kilometers, but the combination of a mountain and its bulge underneath might make the crust as thick as 70 kilometers. Glaciers on During an ice age, the weight of glacial ice presses the crust down just like a continents mountain. After the ice age ends and the glacier melts, the crust rises back up

again (Figure 19.6).

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Figure 19.6: How a glacier affects the crust. The effects have been exaggerated to show the changes.

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Section 19.1 Review 1. What are seismic waves and what causes them? What have they revealed about Earth’s interior?

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2. List the two most important types of seismic waves used for studying Earth’s interior. Give three facts about each type of wave. 3. Compare and contrast the two kinds of crust at Earth’s surface. 4. What is the asthenosphere and how is it related to the lithosphere? 5. What factors increase as you go deeper toward Earth’s core? Name two. 6. How is Earth’s magnetic field generated? What role does Earth’s magnetic field play in protecting our planet? 7. Explain how the young Earth separated into layers. Use the term density in your answer. 8. Using the density values in Figure 19.3, explain why water “floats” on Earth’s surface. 9. Describe how convection works in the mantle. What is the source of heat? 10. How is a piece of continental crust like a boat?

Science Fiction and Jules Verne Jules Verne wrote science-fiction books in the mid-1800s. Verne was popular among readers because he researched his topics and wrote stories that could have been true. In 1864, he wrote Journey to the Center of the Earth. The main characters were three adventurers who explored a hollow Earth and lived to tell their tale. Along the way, they entered Earth through an opening in a volcano in Iceland, climbed down through many strange chambers, crossed an ocean at the center of Earth, and escaped to the surface by riding a volcanic eruption. Wow! Are any parts of this story possible? Why or why not? Justify your answer.

11. What might happen to a mountain that would cause the crust to float higher in the mantle? What might happen to a glacier that would cause the crust to float higher in the mantle? 12. The table below lists details about the layers of Earth from its surface to its core. Imagine that you could travel to Earth’s core (an impossible feat). What would you experience along the way? Layers of Earth

Core

{ {

Appoximate temperature (ºC)

Crust

15

0

Upper mantle

410

870

Asthenosphere

660

Lower mantle

2900

3700

Outer core

5100

3700

Inner core

6400

5000

Temperature increases with depth

Lithosphere

Average depth (km)

Description The uppermost layer The lower part of the lithosphere Zone where mantle rock is most fluid Largest part of Earth’s interior Liquid iron Solid iron

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19.2 Plate Tectonics

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A map of the world illustrates that the continents look like pieces of a puzzle. In fact, if all the continents were moved closer together across the Atlantic Ocean, they would fit together to form a giant landmass. In the first part of this section, you will learn about Alfred Wegener, who collected evidence that the continents had once fit together. Based on this evidence, Wegener proposed that the continents formed a supercontinent long ago. Wegener’s idea eventually led to one of the most important discoveries of the twentieth century—plate tectonics.

Pangaea - an ancient, huge landmass composed of earlier forms of today’s continents; an ancient supercontinent.

continental drift - the idea that continents move around on Earth’s surface.

Movement of continents In 1915, Alfred Wegener, a German scientist and arctic explorer, published Origins of the Continents and Oceans. In this book, Wegener hypothesized that the continents we know today had once been part of an earlier supercontinent which he called Pangaea (Greek for “all land”). Calling his idea continental drift, Wegener proposed that Pangaea broke apart and the pieces moved to their present places, becoming today’s continents.

Pangaea and continental drift

Continental drift Continental drift was a scientific hypothesis based on observations and was rejected collected evidence (see next page). A key part of Wegener’s hypothesis was

that some unknown force had caused the continents to slide over, or push through, the rocky bottoms of the oceans. Yet, neither he nor anyone else could identify the source of the force needed to move continents. Continental drift helped explain issues in geology—like why South America and Africa seem to fit together. However, continental drift could not be accepted by scientists because there was no evidence to explain how the continents moved. For this reason, no one paid much attention to continental drift as a valid hypothesis until the 1950s and 1960s. The sidebar at the right illustrates our current understanding of the time line for the breakup of Pangaea.

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From Pangaea to Today

About 250 million years ago (mya), all land on Earth was part of the supercontinent Pangaea. About 180 mya, this huge landmass began to split apart into many sections. Seven of the largest sections form our continents. Before Pangaea existed, there were other earlier configurations of oceans and continents, and, over a very long period of time, forces related to plate tectonics brought them together to form Pangaea.

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Evidence on Earth’s surface Matching coal beds, Wegener was not the only scientist to suggest that continents move. His idea mountains, and stood out because of the evidence that he gathered to support his idea of fossils continental drift. Wegener’s evidence is presented in the graphic below and

listed in Figure 19.7.

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Undersea During World War II, the United States Navy needed to locate enemy mountains submarines hiding on the bottom of shallow seas. Because of this, large areas discovered of the ocean floor were mapped for the first time. American geophysicist and

naval officer Harry Hess did some of the mapping. The naval maps showed huge mountain ranges that formed a continuous chain along the ocean floors. These mountain ranges are now called mid-ocean ridges.

Wegener’s evidence for continental drift • Coal beds stretch across the eastern United States and continue across parts of Europe. • Matching plant fossils are found in South America, Africa, India, Australia, and Antarctica. • Matching reptile fossils are found in South America and Africa. • Matching early mammal fossils are found in South America and Africa. • Fossils in South America and Africa are found in rocks of identical age and type. • Matching rock types and mountain belts occur in North America and the British Isles. • Evidence of glaciers is present in regions with warm, dry climates. This indicates that continents that are close to the equator today were once closer to the South Pole in the distant past.

Figure 19.7: A summary of

Wegener’s evidence for continental drift.

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Evidence for sea-floor spreading A new Harry Hess wondered if it was possible that new ocean floor was created at hypothesis is the site of mid-ocean ridges. Hess knew about continental drift and born thought that Wegener was partly right. The continents had separated from a

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supercontinent, but not by plowing through the sea floor. Instead, Hess realized that if new ocean floor formed at these undersea mountains, then continents on either side would get separated apart during the process (Figure 19.8). Hess proposed that continents moved along as part of the growing sea floor. Hess called his hypothesis sea-floor spreading. A good idea Sea-floor spreading was an intriguing hypothesis. But for many years needs more scientists had viewed the continents as permanently fixed in place. Sea-floor evidence spreading would need strong evidence to support it before it would ever be

more than just a hypothesis. And so, a time of tremendously rapid scientific research and progress followed Hess’s sea-floor spreading hypothesis. Many scientists added to each other’s work and found the evidence needed to explain sea-floor spreading. Magnetic patterns and the age of rocks

Age (millions of years) 6

5

4

3

2

1

0

1

2

3

4

5

Mid-ocean ridge Young

Old

Young

Old

Matching magnetic patterns on either side of the ridge Oldest

Old

Old

Young

Crust Mantle Magma

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Oldest

6

The discovery of magnetic reversal patterns in the rocks on both sides of the mid-ocean ridges was a key piece of evidence. These striped patterns are formed as iron-bearing minerals in newly formed basalt align to Earth’s magnetic field as the rock cools. Scientists noticed that the magnetic patterns were symmetrical on either side of a ridge. They also noticed that the oldest rocks were farthest from the ridge. These observations showed that sea-floor spreading was occurring—the new ocean floor that forms at mid-ocean ridges moves away from the ridges as time passes.

mid-ocean ridge - a long chain of undersea mountains. sea-floor spreading - a hypothesis that new sea floor is created at mid-ocean ridges and that, in the process, the continents are separated from each other.

Harry Hess’s idea As new sea floor is made at mid-ocean ridges, the continents are separated. Mid-ocean ridge Continent

Continent New sea floor

(The water in the ocean is not shown)

Figure 19.8: Harry Hess wondered if it was possible that new ocean floor was created at the mid-ocean ridges. After more scientific evidence was collected, Hess’s idea was supported. New ocean floor is formed at mid-ocean ridges.

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Moving pieces of the lithosphere Tectonic plates After the breakthrough discovery of magnetic patterns, there was a lot of

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interest in the idea of sea-floor spreading. Scientists realized that large pieces of Earth’s surface moved about like rafts on a river. Today, we know these “rafts” are pieces of lithosphere called tectonic plates that move over the asthenosphere. Recall that the lithosphere, and therefore each plate, includes Earth’s crust and a portion of the upper mantle. A tectonic plate can be composed of both oceanic and continental crust. As you have learned, oceanic crust is relatively thin and mostly made of dense basalt. Continental crust is thicker, less dense, and made of mostly andesite and granite. The graphic below shows the relative thickness of the lithosphere depending on whether it is associated with oceanic or continental crust.

Earth’s lithosphere that move over the asthenosphere.

plate tectonics - a theory explaining how tectonic plates move on Earth’s surface.

Faster than a Moving Plate

Tectonic plates plates With continental crust Andesite and Granite (100-250 km thick)

tectonic plates - large pieces of

With oceanic crust Basalt (3-100 km thick)

Major plates Earth’s lithosphere is broken up into many small plates and seven major

plates. These are the Pacific, North American, South American, African, Eurasian, Indo-Australian, and Antarctic plates. Each of these plates moves as a unit and relative to the other plates. The speed at which a plate moves is very slow and ranges from 1 to 10 centimeters per year. Plate tectonics The theory of how these tectonic plates move on Earth’s surface is called plate tectonics. The word tectonics is derived from the Greek word for

Are you faster than the speed of a moving plate on Earth’s surface? The speed of a moving plate ranges from 1 to 10 centimeters each year. On average, that’s about as fast as your fingernails grow! So, even if you are walking slowly, you are moving quickly compared to a plate moving on Earth’s surface. Plates move so slowly that scientists measure their movement in millions of years. If a tectonic plate moved 5 centimeters per year for 1,000 years, how far would it have traveled during this time?

“builder.” The evidence that Alfred Wegener collected to support an ancient supercontinent is valid today as scientists continue to refine the theory of plate tectonics. The movement of tectonic plates—especially at plate boundaries, the subject of the next section— influences the formation of mountains, trenches, and rocks, and the occurrence of volcanic eruptions and earthquakes. On the next page you will learn how the plates move. 19.2 PLATE TECTONICS

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What drives tectonic plates? Convection cells As you read in Section 19.1, convection cells are present in Earth’s lower

mantle. These convection cells help drive the tectonic plates on the surface. Recall that as Earth’s core heats the rock material of the lower mantle, it expands, becomes less dense, and rises.

subduction - a process that involves a tectonic plate sinking into the mantle.

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The tectonic plate rides like a passenger on the asthenosphere underneath. Mantle material cools and sinks back toward the core. Mid-ocean ridge

What happens at The lower-mantle rock material then rises toward Earth’s surface. Tectonic mid-ocean plates move apart over the rising part of a convection cell. Basaltic material ridges? from the mantle, called magma, is extruded as lava between the plates along

Subduction zone

Mantle material expands and rises as a convection current. Mantle material is heated by the core.

a mid-ocean ridge. This material adds to the plates so that they grow in size. Over time, as newly formed plate material moves away from the mid-ocean ridge, it ages, cools, and becomes denser. Subduction By the process of subduction, the cooler, denser edge of a tectonic plate

eventually sinks below another tectonic plate and enters the mantle (Figure 19.9). The sinking edge pulls the rest of the plate along in the same way that pulling the edge of a tablecloth drags the rest of the cloth off a table. As the subducting plate enters the mantle, it cools the adjacent mantle material, making it denser. As a result, the plate sinks deeper, completing the mantle convection cell. Subduction also happens when a denser oceanic plate encounters a continental plate. The oceanic plate subducts under the less dense continental plate.

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Core

Hot, expanded, less dense, more buoyant Cool, contracted, denser, less buoyant

Figure 19.9: A convection cell in the lower mantle.

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How do scientists measure the motion of plates? A chain of One way that scientists measure the motion of plates is by studying a chain of islands islands such as the Hawaiian Islands on the Pacific Plate. These islands are

formed by a mantle plume hot spot. The biggest and youngest island, Hawaii, has been on top of this hot spot for the last 700,000 years.

mantle plume - heated lower mantle rock that rises toward the lithosphere and forms a hot spot on the overlying tectonic plate.

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Mantle plumes A mantle plume is heated, lower mantle rock that rises toward Earth’s

surface. Sometimes a single plume causes a volcanic eruption in the plate above it. If the eruption is strong and lasts long enough, the volcanic eruption might form a large, volcanic island on the plate. After the island forms, the movement of the plate carries it away from the hot spot. Without the heat from the mantle plume underneath, the volcano that formed the island becomes dormant or extinct. In the meantime, a new, active volcano begins to form on the part of the plate that is now over the hot spot. Measuring By studying the orientation, age, and length of a volcanic island chain, motion scientists can determine the direction and speed that a plate is moving. The

Hawaiian Island chain shows that the Pacific Plate is moving to the northwest at about 9 centimeters per year.

Tracking a Moving Plate The Pacific Plate is moving at 9 centimeters per year. 1. Draw a line on a piece of paper that is 9 centimeters long. What common objects are about this long? 2. How long will it take for this plate to travel 4.5 meters? 3. How far will the plate have traveled, in meters, after three years?

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Section 19.2 Review 1. What is plate tectonics? Is it an old or a new field of science? 2. Alfred Wegener (Figure 19.10) is featured in this section. Who was he? 3. The development of the theory of plate tectonics is a good example of the scientific process.

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a. How did Wegener follow the scientific method? b. Were scientists applying the scientific method when they rejected continental drift? Why or why not? c. Would most scientists in 1900 have thought that Earth’s surface was like a giant jigsaw puzzle? Why or why not? 4. List two pieces of evidence that illustrate that South America and Africa were once connected. How long ago were they connected to each other? 5. How were mid-ocean ridges discovered? 6. What was Harry Hess’s hypothesis regarding the ocean floor and how it was made? 7. Explain why magnetic patterns are important evidence for plate tectonics. 8. Tectonic plates move slowly over the _____, which is described as a zone of soft, weak rock between the upper mantle and lower mantle. a. b. c. d.

crust outer core inner core asthenosphere

9. How is the process of convection related to plate tectonics? 10. Do tectonic plates move quickly or slowly? Explain your answer. 11. Describe the process of subduction in your own words. What causes subduction to happen? 12. Describe the process of how an island chain is formed by a mantle plume. You might want to use a diagram in your answer.

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Figure 19.10: Alfred Wegener.

Measuring Plate Motion There are actually many ways to measure the motion of plates. One method was described in this section. Find out about another technique and write about it.

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19.3 Plate Boundaries In this section, you will learn how the movement of tectonic plates affects Earth’s surface. In particular, many events, such as earthquakes and volcanic activity, occur on Earth’s surface at plate boundaries. Why do you think that is? Read on to find out.

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Moving plates Three types of Imagine a single plate moving in one direction on Earth’s surface boundaries (Figure 19.11). One edge of the plate—the trailing edge—moves away from other plates. This edge is called a divergent boundary. The opposite

divergent boundary - a tectonic plate boundary where two plates move apart.

convergent boundary - a tectonic plate boundary where two plates come together. transform fault boundary - a tectonic plate boundary where two plates slide by each other.

edge—called the leading edge—bumps into any plates in the way. This edge is called a convergent boundary. The sides of our imaginary plate slide by other plates. An edge of a tectonic plate that slides by another plate is called a transform fault boundary. How plates Earth’s surface is covered with tectonic plates. Unlike our single imaginary move relative to plate, the boundaries of real plates touch each other. Plates move apart at each other divergent boundaries, collide at convergent boundaries, and slide by each

other at transform fault boundaries.

Plate boundaries Divergent

Convergent

Transform

Plates move apart

Plates come together

Plates slide past each other

One plate goes under another

Figure 19.11: This single plate on

Earth’s surface illustrates the difference between divergent, convergent, and transform fault boundaries.

Mountains form

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Divergent boundaries New sea-floor at Mid-ocean ridges in the oceans are divergent boundaries, where two plates mid-ocean are moving apart. This type of boundary is found over the rising part of a ridges mantle convection cell. Convection causes the two plates to move away from

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each other. As they move, molten rock fills the space created by their motion. The molten rock cools and becomes new ocean floor. Rift valleys Divergent boundaries can also be found on continents as rift valleys. When a East African Rift Valley Red Sea

rift valley forms on land, it might eventually split the landmass wide enough so that the sea flows into the valley. When this happens, the rift valley becomes a mid-ocean ridge. The East African Rift Valley is an example of rifting in progress that began about 20 million years ago, when Arabia split from Africa. This rift is marked by a series of long lakes that start near the southern end of the Red Sea and extend southward toward Mozambique.

Using Clues to Make Discoveries On the ocean floor, special lava formations called pillow lava are clues to the location of ancient mid-ocean ridges. The pillow lava forms when basaltic lava flows out under water. The water cools the surface of the lava, forming a crust. This crust stops the flow of lava for a moment. Then the crust cracks and a new jet of lava flows out. This process causes the lava to form what looks like a pile of pillows. Ancient mid-ocean ridges existed near pillow lava formations.

Mozambique

Write a paragraph describing a recent experience where you used a clue to discover something about a place or an object.

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Convergent boundaries Deep-ocean A deep-ocean trench is a valley on the ocean floor. These trenches are trenches formed when two oceanic plates or when oceanic and continental plates

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collide and one plate subducts under the other. The deepest trench on Earth, the Mariana Trench, has a maximum depth of 11 kilometers and is located in the western North Pacific Ocean.

deep-ocean trench - a valley in the ocean created when one tectonic plate subducts under another.

Why does one Density drives how plates interact, and a denser plate will subduct under a plate subduct less dense one. Since older oceanic plates are cooler, and therefore denser, under another? they tend to subduct under younger oceanic plates. Magma formed at the

older, subducting plate rises toward the younger plate and eventually forms an island arc, a row of volcanic islands.

Oceanic and What happens if an oceanic plate and a continental plate collide? Continental continental plate plates are largely made of andesite and granite. Andesite and granite are much subduction less dense than the basalt of oceanic plates. Additionally, a continental plate is

too buoyant and too thick to subduct under an oceanic plate. So, the oceanic plate subducts under the continental plate. For example, the oceanic Nazca Plate off the west coast of South America is subducting under the continental South American Plate (Figure 19.12).

Figure 19.12: The collision of the Nazca and South American plates has deformed and pushed up the land to form the high peaks of the Andes Mountains.

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Mountains and convergent boundaries What happens when two continents collide?

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What happens if an oceanic plate with a continental plate attached is subducted under another continental plate? Eventually all of the oceanic crust is subducted and the continental plates collide! The continent on the oceanic plate cannot be pushed down into the trench because its granite rocks are too buoyant to be subducted.

Colliding Vast mountain ranges are formed when continents collide. Millions of years continents form ago, India was a separate continent and not attached to southern Asia. The mountains Indo-Australian oceanic plate carried the landmass of India toward China as

it subducted under the Eurasian continental plate. The Himalaya Mountains are the result of this collision (Figure 19.13). The impact of the collision still causes earthquakes in China today. The formation of mountains is a slow process. The Himalaya Mountains are still growing, millions of years after the collision!

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Figure 19.13: The Himalaya

Mountains are the result of the slow but powerful collision between India on the Indo-Australian Plate and China on the Eurasian Plate.

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Transform fault boundaries Finding Once scientists began to understand tectonic plate boundaries, finding boundaries divergent and convergent boundaries was easy. Mid-ocean ridges and

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continental rift valleys are divergent boundaries. Deep-ocean trenches and mountain ranges occur at the locations of convergent boundaries. Finding transform fault boundaries is more difficult. Transform faults leave few clues to indicate their presence. Zig-zags are Sometimes the action of a transform fault will form a small valley along its clues line of movement. Often there will be ponds along the line. A good clue for

locating transform faults is offsetting. If a feature, such as a creek or a highway, crosses a transform fault, the movement of the fault will break, or offset, the feature. When seen from above, the feature will appear to make a zigzag pattern (Figure 19.14). Earthquakes are Another good way to detect transform fault boundaries is by the earthquakes another clue they cause. The San Andreas Fault is a well-known fault that causes

earthquakes in California (Figure 19.15). The San Andreas Fault is the transform fault boundary between two tectonic plates—the Pacific Plate and the North American Plate. Using plate tectonics to understand other events

Figure 19.14: The creek is offset to

the right as viewed from bottom to top in the photo.

Before plate tectonics was understood, scientists knew where earthquakes commonly occurred, but they didn’t know why they happened. This is an example of how understanding plate tectonics led to other new discoveries. Today we know that earthquakes occur at all three types of plate boundaries, whereas volcanic activity only occurs at convergent and divergent boundaries. You will learn more about earthquakes and volcanoes in the next chapter.

Figure 19.15: This line of students

stretches across part of the San Andreas Fault in California.

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Earth’s tectonic plates

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CHAPTER 19

Section 19.3 Review Earth’s Tectonic Plates

1. What kind of plate boundary is a mid-ocean ridge? 2. What is pillow lava and where is it formed? 3. Give an example of a divergent plate boundary on land.

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4. What happens when oceanic plates collide? What surface feature of Earth occurs when oceanic plates collide? 5. What feature of a plate determines whether one plate will subduct under another plate? 6. Which is more buoyant—a continental plate or oceanic plate? Which would subduct if the two were to collide? 7. What happens when two continental plates collide? Give an example of continents colliding today.

The map at the bottom of this page shows the largest tectonic plates that cover Earth (smaller plates have been combined with the larger ones to simplify the map). The map also shows the direction that some plates move. You can use this information to identify the type of plate boundary at a certain location. Identify the types of plate boundaries labeled A, B, and C. Then, see if you can answer the questions on the map.

8. What are two clues to finding transform faults? Simplified map of Earth's tectonic plates What is the name of the transform fault at this location?

Is this plate mostly an oceanic plate or a continental plate?

A

Choose a plate and find out one fact about it.

Eurasian Plate American Plate B Pacific Plate

Cocos Plate

Look at the large, detailed map of Earth’s larger and smaller tectonic plates on the previous page.

Pacific Plate

African Plate Nazca Plate C

Indo-Australian Plate Antarctic Plate

Identify the kind of plate boundary you see at locations A, B, and C.

19.3 PLATE BOUNDARIES

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19.4 Metamorphic Rocks

Making a metamorphic rock Where do you The boundaries between tectonic plates are locations with many interesting find heat and features such as mountains, volcanic eruptions, and earthquakes. pressure? Metamorphic rocks are also formed at these locations. In particular, rocks at

convergent plate boundaries are subjected to varying degrees of heat and pressure. If rocks at these boundaries melt, they will cool and crystallize as igneous rocks. However, rocks that are heated and squeezed, but remain intact, will change to become metamorphic rocks.

Metamorphic rocks are formed by heat and pressure at convergent plate boundaries. Regional Metamorphism is described by the size of the affected area. Large-scale metamorphism metamorphic events, called regional metamorphism, occur when tectonic

metamorphic rock - a rock formed when another rock is changed by heat and pressure.

Low

Temperature High

Low

Pressure

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Unlike an igneous or a sedimentary rock, a metamorphic rock is formed when another rock is changed by heat and pressure. In fact, the word metamorphic means “changed form.” Where on Earth’s surface might there be conditions for making a metamorphic rock? As you might imagine, high heat and pressure are created when tectonic plates come together. Near plate boundaries you find the right conditions for making metamorphic rocks.

Low-grade

Contact

metamorphism metamorphism

High-grade metamorphism High

Figure 19.16: Metamorphic rocks form under varying conditions of temperature and pressure.

plates subduct or collide. Metamorphic pressures and temperatures affect rocks for hundreds of kilometers along plate boundaries. Figure 19.16 provides the terms for smaller scale metamorphic events under varying conditions of heat and pressure. Contact Magma rising toward Earth’s surface heats surrounding rocks. Because this metamorphism heating takes place near the point of contact, contact metamorphism is the

result of high temperature but low pressure. Heat from a magma intrusion only penetrates the cool surrounding rock a few tens of meters, so contact metamorphism typically affects small areas. An example of contact metamorphism occurs when hot magma contacts limestone, a sedimentary rock and the limestone changes into marble (Figure 19.17).

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Figure 19.17: Limestone is

metamorphosed into marble when it comes in contact with hot magma.

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Metamorphic Metamorphic grade is a continuous scale that describes the intensity of grade metamorphism as temperature and pressure increase (Figure 19.16, previous

Pressure and Rocks When metamorphic rocks are formed, minerals in a rock change to form new minerals. For example, minerals in clay are altered to form mica. Increased pressure causes the new minerals to form in flat layers perpendicular to the direction of pressure. This is called foliation.

Changing rocks The differences between sedimentary and igneous rocks are clearly defined

based on how and where they are formed. However, describing the difference between metamorphic rocks and sedimentary or igneous rocks is harder. The table below describes what happens to sediment that undergoes changes in pressure and temperature. Pressure compacts silt and clay into mudstone, a sedimentary rock. Increased pressure changes mudstone into slate and more pressure forms phyllite. Both slate and phyllite are metamorphic rocks. Similarly, increased temperature causes some minerals in gneiss, a metamorphic rock, to melt. But when the rest of the rock melts, it becomes magma that forms igneous rocks. It is important to note that it is difficult to tell the difference between rock types at these transition stages.

Slate and phyllite

Earth process Sediments carried to low basins; grains in loose contact Compaction due to weight of sediments presses grains together; excess water removed Lithification (rock formation); pressure causes grain points to fuse; pore spaces may fill with other minerals

Metamorphic rock

Sedimentary rock

Class Material/Rock Loose silt and clay Compact silt and clay Mudstone

Schist

Clay minerals recrystallize to micas due to pressure; rock develops a tendency to split into sheets Minerals are recrystallized and micas increase in size

Gneiss Migmatite

New minerals form in alternating light and dark bands. Transition to igneous rock; some minerals in rock begin to melt

Igneous rock

Increasing Pressure and Temperature

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page). During metamorphism, solid minerals change into new solid minerals, without melting, through a process called recrystallization. Low-grade metamorphism occurs under conditions of low temperature and low pressure. Typically, clay minerals are recrystallized to form tiny mica flakes which grow perpendicularly to the direction of pressure. These flake-like minerals give the rock the tendency to split along one plane. Slate and phyllite are lowgrade metamorphic rocks that form from mudstone. During high-grade metamorphism, minerals recrystallize into new minerals. Gneiss is a highgrade metamorphic rock that has light and dark bands of recrystallized minerals that lie across the direction of pressure (see sidebar).

CHAPTER 19

Any

Rock melts forming magma; magma cools and cystallizes to form igneous rocks

Phyllite and gneiss (pronounced as “nice”) are two metamorphic rocks that are formed in this way. They have mica flakes that are layered (foliated) across the direction of pressure. Gneiss has light and dark bands of recrystallized minerals that lie across the direction of pressure.

19.4 METAMORPHIC ROCKS

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Metamorphic rocks tell great stories Rock detectives Geologists work like detectives. They use rocks as clues to understand the

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history of Earth. The only real difference is that detectives solve crimes that took place over days or weeks, but geologists study events that took place over hundreds of millions of years ago. Here are two examples of amazing events that are discovered using rock clues. Finding old High-grade metamorphism can occur at low temperature. Where do the subduction conditions of high pressure and low temperature exist? An ocean floor plate zones encounters great pressure when it subducts into Earth’s mantle. But it is cool

because it was covered by ocean water. High-grade metamorphism changes the sediments on the ocean floor to the metamorphic rock called blueschist. It also changes the basalt of the ocean floor to the metamorphic rock eclogite (Figure 19.18). When geologists find these metamorphic rocks they know that they have found the remains of an ancient subduction zone! Finding places where ancient mountains once existed

Mountains are formed when converging plates cause one continent to collide with another. These continental collisions produce both tremendous heat and pressure. High-grade metamorphic rocks, like gneiss, form at the core of the growing mountains. Plate movements change direction, and after some time, these collisions stop. Then the mountains stop growing, and weathering and erosion begin to wear them down. Some of the remains of once great mountain ranges are now just rolling hills. The igneous rock, gneiss, formed at the core of growing mountain ranges, is a clue that these giants once existed. Figure 19.18: Blueschist and

eclogite are formed by high-pressure metamorphism.

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Section 19.4 Review 1. What does the term metamorphic mean? 2. What two conditions can cause metamorphic rocks to form? 3. What is regional metamorphism?

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4. Describe the conditions for contact metamorphism and give an example of a rock formed by contact metamorphism. 5. Look at the rock images in Figure 19.19. Which image is most likely to be a metamorphic rock? Explain your answer. 6. Metamorphic rocks are commonly formed at what kind of plate boundary? Why? 7. Name one event that takes place at a convergent plate boundary that can cause a rock to be metamorphosed into another rock? 8. Compare and contrast phyllite and gneiss. 9. Schist is a metamorphic rock that contains mica flakes. What characteristic of these flakes allow geologists to be able to determine the direction of pressure that formed them? 10. Why is it sometimes hard to tell the difference between certain sedimentary rocks and metamorphic rocks? 11. Blueschist, eclogite, and gneiss are rocks that formed during certain types of events in Earth’s geologic past. Identify the type of event that each of these rocks signifies. 12. Copy the table below on your own paper and fill in the blank spaces. Examples of metamorphic rocks Example Slate Phyllite

Type of metamorphism

Figure 19.19: Question 5.

Marble Eclogite Gneiss

19.4 METAMORPHIC ROCKS

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Chapter 19 Assessment Vocabulary

Section 19.2

Select the correct term to complete the sentences.

10. _____, meaning “all land,” is the name for the great landmass that existed millions of years ago.

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Pangaea

core

seismologist

crust

sea-floor spreading

P-waves

lithosphere

seismic waves

S-waves

mantle

asthenosphere

mid-ocean ridges

12. The study of Earth’s tectonic plates is called _____.

tectonic plates

continental drift

plate tectonics

13. When a plate is drawn into the mantle, _____ is taking place.

subduction

mantle plume

deep-ocean trench

14. _____ move over the asthenosphere.

metamorphic rocks

11. The idea that the continents move around on Earth’s surface is called _____.

Section 19.1

15. New ocean floor is created at the locations of these undersea features called _____.

1.

_____ are seismic waves that do not pass through liquids.

16. Harry Hess proposed the idea of _____.

2.

A scientist that detects and interprets seismic waves at different locations on Earth is called a(n) _____.

17. A hot spot is caused by a(n) _____.

3.

Vibrations that travel through Earth are called _____.

4.

_____ are seismic waves that move in a forward-and-backward motion.

18. _____ form at convergent boundaries where conditions of high heat and high pressure exist.

5.

Tectonic plates slowly move over a soft, weak zone called the _____.

19. A(n) _____ is a geologic feature that occurs when one oceanic plate subducts under another.

6.

The largest part of Earth’s interior that is made of rock, but flows, is the _____.

Concepts

7.

The _____ is the inner iron-containing layer of Earth.

Section 19.1

8.

Made of the crust and upper mantle, the _____ makes up the plates that move about Earth’s surface.

1.

It is impossible to travel to the center of Earth. How then do scientists study what Earth looks like inside?

9.

The outermost surface of Earth is called the _____.

2.

What are the differences between a P-wave, an S-wave, and a surface wave?

3.

With all the layers that make up Earth, which layer is the densest and which is the least dense? Why?

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Section 19.3 and Section 19.4

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CHAPTER 19

4.

How does the density of continental crust compare to oceanic crust?

Section 19.4

5.

The inner core is really hot but solid. Why isn’t the inner core a liquid like the outer core?

16. Metamorphic rocks are commonly formed at convergent plate boundaries. Why?

6.

What do you think would happen if convection in Earth’s mantle ceased to occur?

17. What is the difference between regional and contact metamorphism?

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7.

The average thickness of the continental crust is 35 to 40 km, but sometimes the crust is as thick as 70 km. Describe and diagram a situation in which the crust might be 70 km thick.

18. How do patterns of mountain ranges, ocean bathymetry, earthquakes, and most volcanoes relate to the characteristics of Earth’s tectonic plates?

Section 19.2

Problems

8.

How do fossils support the idea of continental drift? Give one example.

Section 19.1

9.

The Mid-Atlantic Ridge is a mid-ocean ridge in the Atlantic Ocean. Is the Atlantic Ocean getting wider or narrower? Explain your answer.

1.

10. Where would you find the oldest rocks on the sea floor? Where would you find the youngest rocks? Explain your answer. 11. A mantle plume beneath the oceanic crust and the islands it forms are useful for measuring the speed and direction of a tectonic plate. How is this done?

a. b. 2.

13. What kind of geologic feature forms when two continental plates collide? What kind of plate boundary is this? 14. What type of boundary does the East African Rift Valley represent? Research and list a few countries and volcanoes that are within the East African Rift Valley.

100% more than 50%

c. less than 1% d. about 25%

For each of these statements, identify the described location: a.

Section 19.3

12. List the three types of plate boundaries. What famous feature in California represents one of these boundaries?

Scientists have only been able to drill down into the lower part of Earth’s crust. What percentage of Earth’s radius have scientists drilled into?

b. c.

6,000 kilometers below Earth’s surface where the temperature is more than 7,000°C. Convection cells occur in this, the largest layer of Earth’s interior. 10 kilometers below the Earth’s surface.

Section 19.2

3.

Make a sketch of the magnetic pattern that would appear on the other side of the ridge shown in the graphic below.

15. What type of plate boundary can be defined from a linear pattern of earthquakes?

CHAPTER 19 ASSESSMENT

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4.

5.

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If the speed of a plate is 8 centimeters per year, how far would it move in 200 years? Complete the following calculations. Use the formula distance = speed × time.

Applying Your Knowledge Section 19.1

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The oldest volcanic rocks on Kauai are 5.5 million years old whereas the oldest rocks on the “Big Island” of Hawaii are 0.7 million years old. Kauai is northwest of the “Big Island.” Both islands were formed by a mantle plume.

1.

a.

Section 19.2

b.

What is the length of time between the formation of the two islands? Given that Kauai and the “Big Island” are 240 kilometers apart, how fast has the Pacific Plate been moving? (speed = distance ÷ time)

2.

Pangaea broke up by forming two large pieces. Research and list the names of these pieces. Include one interesting fact that you discovered in your research.

3.

Plate tectonics has been developed by a number of scientists, including Bruce C. Heezen, Marie Tharp, Tanya Atwater, John Tuzo Wilson, Xavier Le Pichon, and Frederick Vine. Pick one and find out how they contributed to plate tectonics. Use your school library or the Internet to help you in your research. Write up your findings using a magazine-type essay format.

Section 19.3

6.

It takes 10 million years for the Pacific Plate to slide 600 kilometers past the North American Plate. How fast is the Pacific Plate moving in kilometers per million years? What kind of boundary exists between the Pacific Plate and the North American Plate?

7.

There are two islands on opposite sides of a mid-ocean ridge. During the last 8 million years, the distance between the islands has increased by 200 kilometers. What is the speed at which the two plates are separating in km/million years? What kind of boundary exists between these plates?

Since it is impossible to drill very deeply into Earth, scientists have used indirect evidence learned about the nature of the outer core. Describe an experience you have had in which you learned something new in an indirect way.

Section 19.3

4.

The mid-ocean ridge in the Atlantic Ocean goes through the country of Iceland. What effects does it having on this country? How does Iceland take advantage of these effects?

Section 19.4

Section 19.4

8.

5.

What type of metamorphism occurs under conditions of (a) high temperature and high pressure? (b) low temperature and low pressure? (c) high temperature and low pressure?

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This image of a metamorphic rock shows wavy layers. How do you think the layers formed? How do you think the layers became wavy? Answer these questions using the principles of relative dating and what you learned in this chapter.

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CHAPTER

20

CHAPTER 20

Earthquakes and Volcanoes

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What does an earthquake have in common with a volcano? In Chapter 19, you learned about plate tectonics and plate boundaries. Earthquakes and volcanoes are most common along plate boundaries. It would seem that, with our understanding of plates and plate boundaries, we should be able to predict earthquakes and volcanic eruptions accurately. But usually we can only estimate whether they are more or less likely to occur. There are simply too many variables involved for precise predictions. However, scientists who specialize in earthquakes and volcanoes are refining their prediction capabilities. Sophisticated global positioning system (GPS) receivers can detect remarkably small changes in position. These instruments can be used to detect magma rising in a volcano and stress building along a fault that precedes an earthquake. Additionally, improved instruments and methods are refining scientists’ ability to interpret seismic waves. United States Geological Survey volcanologist Bernard Chouet uses his knowledge of musical harmonics to interpret seismic wave recordings. Using Chouet’s research, volcanologists in Mexico predicted the eruption of Popocatépetl in 2000 and initiated an evacuation of the region 48 hours before the volcano erupted. As a result, no one was hurt!

4 Can one earthquake cause another? 4 Why are some volcanic eruptions explosive and some gentle?

4 Does the appearance of an igneous rock provide clues about magma and eruptions? Popocatépetl

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CHAPTER 20

EARTHQUAKES AND VOLCANOES

20.1 Earthquakes

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In Chapter 19, you read about the San Andreas Fault, which lies along the California coast (Figure 20.1). This fault passes right through San Francisco and part of Los Angeles. As you might know, earthquakes occur in California and future earthquakes are expected. This is because California is on the boundary between the North American Plate on the east and the Pacific Plate on the west. This section explains the relationship between earthquakes and tectonic plates.

Earthquakes and plate boundaries Where do When earthquake locations are plotted for many years, a map like the one you find below can be created. From the map we can see that earthquakes commonly earthquakes? occur at the boundaries of tectonic plates. Earthquakes occur less commonly

at faults that are inside plate boundaries. Earthquake Figure 20.2 illustrates that Japan, a country that experiences earthquakes, is zones near converging plate boundaries. Subduction of one plate under another is

Figure 20.1: The San Andreas Fault lies along the California coast.

causing seismic activity. Notice that the locations of earthquakes do not exactly follow the boundaries. At all plate boundaries including transform fault boundaries where the fault often branches, seismic activity occurs in zones called earthquake zones.

Figure 20.2: Earthquakes along converging plate boundaries do not occur in neat lines but in zones of seismic activity.

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When an earthquake occurs What is an You now know that earthquakes are likely to occur at plate boundaries, but earthquake? you might not know why this is the case. By definition, an earthquake is the

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sudden movement of Earth’s crust due to the release of built-up potential energy (stored energy) along a fault. A fault is a region on Earth’s surface that is broken and where movement takes place. Plates stick Tectonic plates slide past one another. As together, then this happens, the plates might stick together break due to friction. Often the brittle crust will

stick near the surface as the plastic upper mantle continues to flow underneath. Plastic here means “able to change shape without breaking,” like modeling clay. With the crust stuck above and the upper mantle moving below, the rocks at plate boundaries stretch or compress. As a result, potential energy builds in the plate. When potential energy exceeds the strength of the rock and friction—CRACK!—the rock breaks and slips as potential energy converts to kinetic energy. This motion is called stick-slip motion.

earthquake - the movement of Earth’s crust resulting from the release of built-up potential energy along a fault. fault - a region on Earth’s surface that is broken and where movement may take place. focus - the point below Earth’s surface where a rock breaks or slips and causes an earthquake.

epicenter - a point on Earth’s surface right above the focus of an earthquake.

Stick-slip Three conditions are necessary for stick-slip motion to occur. These are: (1) motion two objects are in contact and at least one of the objects can move, (2) a force

(or forces) causes the movement, and (3) friction is strong enough to temporarily prevent movement from starting so that potential energy builds. Stress relief for The sudden release of potential energy when plates “slip” causes earthquakes. plates In this sense, an earthquake is a stress reliever for tectonic plates. However,

the relief is only temporary. Potential energy starts building up again as soon as the quake ends. Earthquake The focus of an earthquake is the point below the surface where the rock terms breaks. After the break occurs, plates move along the fault. The energy of this

movement is spread by seismic waves. These waves are strongest at or near the epicenter of an earthquake, the point on Earth’s surface above the focus (Figure 20.3).

Figure 20.3: The focus, epicenter,

and seismic waves of an earthquake at an active fault.

20.1 EARTHQUAKES

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Tectonic plates have many sections Sections of plate Although a tectonic plate moves as a single unit, its boundary acts as though boundaries it were made of many sections. A line of grocery carts is a good analogy of

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tectonic plate movement (Figure 20.4). A line of grocery carts moves as a single unit, but there are small movements between each cart. When a person pushes the back end of a line, the carts at the front end remain still for a moment. It takes some time for the first cart to push the second, the second to push the next, and so on, until eventually, the front cart starts to move. The San A tectonic plate boundary might be thousands of kilometers long. Therefore, Andreas Fault it takes a long time for movement on one end of the boundary to affect a

section farther away. Like each cart in a line of carts, each section of a plate boundary can move before or after other sections. The San Andreas Fault is a well-known example of a transform plate boundary. Although most sections remain stuck together, other sections might move at any time. An earthquake happens each time a fault section moves, but only in the section that moved (Figure 20.5).

Figure 20.4: A moving line of

grocery carts is like a moving tectonic plate.

Frequency and Imagine two sections along the same fault. The first section has earthquakes strength a few times a year. The earthquakes are mild because relatively little energy

is released during each quake. These frequent earthquakes release potential energy before it can build up to a high level. Now, let’s say that earthquakes take place only once every 20 years in the second section. The long time period between earthquakes allows a great deal of potential energy to build up. Earthquakes in this section are likely to be devastating. One earthquake It is common for an earthquake in one section of a fault to cause an might trigger earthquake in a neighboring section. Imagine two neighboring plate sections. others One section is ahead of the other along the fault in the direction of plate

movement. Both sections have built up a lot of potential energy. Then, an earthquake occurs in the front section, reducing its potential energy. Now there is an energy difference between the first and second sections. This difference may trigger a new earthquake in the second section. It is common for one earthquake to have a ripple effect among sections along a fault.

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Figure 20.5: This graphic shows that activity along the San Andreas Fault occurs in sections.

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CHAPTER 20

Seismic waves Recording An earthquake involves the conversion of seismic waves potential energy into kinetic energy as

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movement along a fault. The fault movement generates seismic waves that radiate from the fault. The point on the fault that moves first is the earthquake focus. A seismograph records the arrival time and strength of the various seismic waves. Seismographs are located around the world at seismic stations on land and in the oceans. The picture above shows how older seismic stations recorded seismograms (records of seismic waves) on paper on a large drum. Today, most seismic data are recorded by computers.

seismograph - an instrument that records seismic waves. body waves - seismic waves that travel through the interior of Earth.

surface waves - seismic waves that can travel only along Earth's surface.

Body waves Seismic waves that travel through Earth are called body waves. The two

main types of body waves are P-waves and S-waves, also called primary and secondary waves. P-waves are faster and arrive first at a seismic station (Figure 20.6). As P-waves move through rock, it is pushed and pulled in the same direction as the waves move. Like sound waves, P-waves are longitudinal waves and can travel through any medium including solid and fluid rock. S-waves only move through solids, so they cannot travel through Earth’s liquid outer core. S-waves move side to side and cause rock to shear or break at right angles to the direction that the wave is moving. As seismic waves travel through Earth, their speed changes as the strength of the material that they are traveling through changes. Seismic waves travel faster in cool materials because these materials are stronger. The waves travel slower in hot materials because heat weakens a material. In addition, seismic waves bend or reflect as they pass through the different materials and layers of Earth. Surface waves Seismic waves that can only move along the surface of Earth are called surface waves. Surface waves are slower than body waves. Often larger

than body waves, surface waves can cause more damage to structures such as buildings. One kind of surface wave moves up and down as it moves back and forth causing a circular motion. Another type of surface wave moves from side to side. The side-to-side motion rather than the vertical motion of surface waves most often causes buildings to collapse.

Figure 20.6: After an earthquake

occurs, the fastest waves, the P waves, are recorded first. The slower S-waves are recorded next, and are followed by the surface waves.

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Locating the epicenter of an earthquake A seismic waves The difference in the arrival times of P- and S-waves at a seismic station can “race” be used to locate an earthquake’s epicenter. This analogy explains how it’s

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done. In a car race, all cars start together. In time, the fastest car gets ahead of the slowest car. The longer the race, the farther ahead the faster car gets. Like fast and slow cars, P- and S-waves have different speeds. The difference in the arrival time between P- and S-waves can be used to determine the distance to the epicenter from the seismic station. The larger the difference in arrival time, the farther the epicenter is from the seismic station.

Figure 20.7: An epicenter is located using data from at least three seismic stations labeled A, B, and C in this diagram.

How Far Away Is the Epicenter?

a circle around its location on a map. The radius of the circle is based on the calculated distance to the epicenter. The edge of each station’s circle represents all of the possible locations of the earthquake from that station. When all three circles are drawn on the same map, they will cross at a single point—the epicenter.

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S-P time difference vs. distance to the epicenter 5

Time (s)

Three seismic At least three seismic stations are needed to locate the epicenter of an stations are earthquake (Figure 20.7). First, each station determines the distance to the needed epicenter based on the P- and S-wave arrival times. Then each station draws

A time-distance graph is used to determine the distance to an epicenter. If the arrival time between P- and S-waves is 2.5 seconds, what is the approximate distance to the epicenter?

4 3 2 1 0 10

20

30

40

Distance (km)

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CHAPTER 20

Measuring earthquakes The Richter The Richter scale ranks earthquakes according to the magnitude of their scale seismic waves recorded on a seismograph. Seismic wave amplitude increases

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ten times for each Richter magnitude change. For example, a magnitude 6.3 earthquake has a wave amplitude that is ten times greater than a magnitude 5.3 earthquake. The largest recorded earthquake occurred in Chile in 1960 (Figure 20.8). It was off the Richter scale. Seismologists estimated this quake to have been a magnitude 9.5.

Richter scale - a scale that ranks earthquakes according to the magnitude of the seismic waves. Moment Magnitude scale - a scale that rates the total energy released by earthquakes.

The Richter scale Level

Magnitude

Effects* (*These descriptions are not part of the scale.)

Micro

Less than 2.0

Barely felt but recorded by seismographs

Very minor

2.0–2.9

Recorded but not felt by most people

Minor

3.0–3.9

Little damage but felt by people

Light

4.0–4.9

No serious damage; objects shake

Moderate

5.0–5.9

Major damage to poorly designed buildings

Strong

6.0–6.9

Serious damage over a 100-km area or less

Major

7.0–7.9

Serious damage over a larger area

Great

8.0–8.9

Serious damage over several hundred kilometers

Rare great

9.0 or greater

Serious damage over several thousand kilometers

The Moment The Moment Magnitude scale rates the total energy released by an Magnitude scale earthquake. The numbers on this scale combine energy ratings and

descriptions of rock movements. This scale can be used at locations that are close to and far away from an epicenter. The Richter and Moment Magnitude scales are similar up to magnitude 5. However, seismologists tend to use the more descriptive Moment Magnitude scale for larger earthquakes.

Figure 20.8: The 1960 Chile

earthquake, which caused devastating damage, was estimated to be a 9.5 magnitude on the Richter scale!

Energy and the Richter Scale Each higher value on the Richter scale represents a ten times increase in wave amplitude. However, in terms of energy, each higher number represents the release of about 31 times more energy!

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Measuring The Modified Mercalli scale has 12 descriptive categories. Each category is earthquake a rating of how an earthquake is experienced by people and the damage damage caused to structures. Because earthquake damage can be different from place

to place, a single earthquake will have different Mercalli numbers in different locations depending on the distance from the epicenter (Figure 20.9).

Modified Mercalli scale - a scale that rates how an earthquake is experienced by people and the damage caused to buildings.

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The Modified Mercalli scale Category

Effects

I. Instrumental

Not felt

II. Just perceptible

Felt by only a few people, especially on upper floors of tall buildings

Ill. Slight

Felt by people lying down, seated on a hard surface, or in the upper stories of tall buildings

IV. Perceptible

Felt indoors by many, by few outside; dishes and windows rattle

V. Rather strong

Generally felt by everyone; sleeping people might be awakened

VI. Strong

Trees sway, chandeliers swing, bells ring, some damage from falling objects

VII. Very strong

General alarm; walls and plaster crack

VIII. Destructive

Felt in moving vehicles; chimneys collapse; poorly constructed buildings seriously damaged

IX. Ruinous

Some houses collapse; pipes break

X. Disastrous

Obvious ground cracks; railroad tracks bent; some landslides on steep hillsides

XI. Very disastrous

Few buildings survive; bridges damaged or destroyed; all services interrupted (electrical, water, sewage, railroad); severe landslides

Xll. Catastrophic

Total destruction; objects thrown into the air; river courses and topography altered

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Richter scale (approximate)

Sample Modified Mercalli map for an earthquake in Washington

1–2 3 48º N

Puget Sound

3.5 Seattle

4

IX

47º N

4.5 5 5.5 6 6.5 7 7.5 8

Toledo

km 0

40

80

124º W

Intensity I II-III IV V VI VII VIII IX X+

123º W

122º W

121º W

Shaking

Damage

Not felt Weak Light Moderate Strong Very strong Severe Violent Extreme

None None None Very light Light Moderate Moderate/Heavy Heavy Very heavy

Figure 20.9: From the map, you can

see that the earthquake was a category IX on the Modified Mercalli scale in a very small area. Most of the surrounding areas experienced less shaking and damage.

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Section 20.1 Review Earthquakes in the Middle of Plates

1. The largest earthquake ever recorded occurred in Chile, which is on the west coast of South America. Why does Chile experience violent earthquakes? Explain your answer.

Throughout Earth’s history, tectonic plates have been torn apart, added to, and joined with other plates. As a result of this reshaping, there are old plate boundaries that are now faults inside of the plates we see today. The New Madrid Fault, for example, is a fault zone within the North American Plate. This zone is an “old” plate boundary that can break when the North American crust flexes as a result of plate tectonic activity. This can result in a major earthquake, such as the New Madrid events in 1811 and 1812.

2. What is the difference between the focus and the epicenter of an earthquake?

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3. What three conditions are needed for stick-slip motion? Describe how all three conditions are met at the boundary between two tectonic plates. 4. How is a tectonic plate like a line of moving grocery carts? 5. Can one earthquake cause another earthquake? Explain your answer. 6. In terms of the release of potential energy, which situation might cause more damage to a city—many small earthquakes or one big earthquake? Explain your answer. 7. What is the difference between body waves and surface waves? 8. List what can happen to a seismic wave as it moves from one material to another.

Find out more about this fault zone. What are the chances of a large earthquake happening here again?

9. How is the location of an earthquake epicenter determined? 10. At least how many seismic stations are needed to find the epicenter of an earthquake? Why?

The New Madrid seismic zone

11. How much greater is seismic wave amplitude in an earthquake that measures 3.0 on the Richter scale compared with an earthquake that measures 2.0?

NH WA

VT MT

WI

SD

MI

UT

IL

NM

K OK

MO O

0

CT NJ DE MD

RI

NC

T TN

SC

AK MS AL

TX

OH WV VA

KY

GA

LA

200 400 miles

FL

Area affected by an earthquake in 1895

Little damage, but shaking felt Minor to major damage

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IN

CO S KS

AZ

PA

IA

NE

NV CA

MA

NY

WY

12. What is the Moment Magnitude scale based upon? How is this different from the Richter scale?

14. Why is it possible for a single earthquake to have different Modified Mercalli scale ratings in different locations?

ME

MN

OR ID

13. A friend tells you that he witnessed books and other objects falling off a bookcase during an earthquake. What might have been the intensity of this earthquake on the Modified Mercalli scale? Give the Richter scale magnitude that approximates this intensity value.

ND

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20.2 Volcanoes Have you ever heard of the Ring of Fire? About half of the active volcanoes on Earth are present along the shores of the Pacific Ocean in this region. Mount St. Helens in Washington State (Figure 20.10) and Mount Fuji in Japan are part of the Ring of Fire. In this section, you will learn about the different kinds of volcanoes and how magma affects how they erupt and are shaped.

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Where you find volcanoes The Ring of Fire The Ring of Fire rims the Pacific Ocean along subduction zones where the

Pacific Plate is being subducted under other surrounding plates (see diagram below). The island of Japan and neighboring islands—also part of the Ring of Fire—are near subduction zones where three plates come together (Figure 20.11).

Figure 20.10: Mount St. Helens in Washington State erupted violently in 1980. A much quieter, three-year eruption that produced a “lava dome” ended in 2008.

Where else do In addition to being located at convergent plate boundaries such as you find subduction zones, volcanoes are also present along divergent boundaries and volcanoes? within plates. For example, the volcanic Hawaiian Islands have formed in

the middle of the Pacific Plate.

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Figure 20.11: Japan is part of the Ring of Fire.

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What is a volcano? Parts of a A volcano is an erupting vent through which melted rock, gases, ash, and volcano other materials from Earth’s mantle are released or erupted. During an eruption, melted rock called magma leaves the magma chamber and

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moves upward through the conduit and out of the vent at the top of the volcano. Once it leaves the vent, magma is called lava. The composition of the magma and lava and the character of the associated eruption affect the shape of a volcano. The cone-shaped, mountainous volcano below has layers of lava and ash. This is just one example of what a volcano can look like.

volcano - an erupting vent through which molten rock and other materials reach Earth’s surface, or a mountain built from the products of an eruption.

magma - underground melted rock. magma chamber - a location where magma collects inside Earth.

lava - magma that has erupted onto Earth’s surface and cooled.

Volcanoes have The life cycle of a volcano occurs in three phases: active, dormant, and a lifetime extinct. An active volcano, like Mount St. Helens, has erupted recently and is

expected to erupt again in the near future. A dormant volcano is not active now, but may become active again in the future. Many of the volcanoes along the northern Pacific coast of North America are dormant. An extinct volcano is at the end of its life and is no longer able to erupt. The now-solid magma that filled the conduit is exposed due to erosion of the surrounding volcano by wind and water. This solid core is called a volcanic neck. Examples of volcanic necks include Ship Rock in New Mexico and Devil’s Tower National Monument in Wyoming. Devil’s Tower was featured in the 1977 Steven Spielberg movie Close Encounters of the Third Kind (Figure 20.12).

Figure 20.12: The volcanic necks of

Ship Rock and Devil’s Tower have been exposed by erosion.

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What makes magma? Solid mantle The rock of Earth’s mantle is hot but solid. This rock melts and becomes rock melts magma under the right conditions. What are the conditions for rock to melt? Lowering Rocks melt when the temperature becomes greater than their melting point. pressure Neither the cool lithosphere nor the hot upper mantle is hot enough to melt

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rock. The only way to make magma is to lower the melting point of the rock. Lowering the pressure on rock is one way to lower its melting point. The hot rock of the mantle is solid because of the great pressure of the material above it. However, this solid material can melt if the pressure on the hot rock decreases. In fact, pressure on the underlying mantle is lowered near divergent plate boundaries where the plates pull apart. The melted rock, now magma, is less dense than the surrounding solid rock, so it rises and might eventually erupt onto Earth’s surface as lava. Adding water Another way to lower the melting temperature of rock is to mix water with

the rock. Water comes into the mantle at subduction zones as liquid and as part of the mineral composition of certain rocks. Once mixed with the solid mantle rock, the water is present as individual molecules that react chemically with the minerals in the mantle rock, causing it to melt.

Magma is made by lowering the melting point of mantle rock. Pressure and The two graphics in Figure 20.13 show how pressure and water affect the water affect melting of hot rock. melting temperature • Graph A: The rock in the bottom right corner of graph A is solid because

it isn’t hot enough to melt under high pressure. The rock above the solid rock is melting at the same high pressure because the temperature is higher. The rock in the bottom left corner is melting at a lower temperature because of lower pressure. • Graph B: In graph B, the rock in the bottom right corner is solid because it isn’t hot enough to melt when dry. The dry rock above is melting because the temperature is higher. The rock in the bottom left corner is melting at a lower temperature because it contains water.

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Figure 20.13: Two graphs of the conditions for making magma.

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Volcanoes vary in shape and type of eruption The shapes of The shapes of volcanoes depend on the composition of the magma that volcanoes formed them. Volcanoes can look like wide, flat mounds (shield volcanoes),

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like tall cones (composite volcanoes), or like a heap of rock bits (cinder cones). The graphic to the right illustrates the shapes of shield and composite volcanoes. Silica in magma affects how thick or runny it is

The amount of silica in magma changes its consistency, or viscosity. For example, magma that forms basalt, a low-silica rock, is dark in color and runny, or low in viscosity (think of ketchup). Magma that forms granite contains a higher proportion of silica. Granitic magma is light colored, less dense than basaltic magma, sticky like soft taffy, and thick (viscous).

Dissolved gas affects how gentle or explosive the eruption will be

Together with silica content, the amount of gas dissolved in magma determines the character of a volcanic eruption. Magma is under great pressure when it’s deep below the surface. This high pressure keeps gases such as sulfur dioxide in solution. Think about the carbon dioxide gas that gives soda its fizz. An unopened bottle of soda contains a large volume of dissolved carbon dioxide. Like soda, the gas in deep magma also is dissolved. However, the pressure drops as magma moves up toward the surface. The effect is like taking the cap off that soda bottle. The gas comes out of solution and forms bubbles within the magma. Some magma contains a large amount of gas, while other magma is like flat soda and contains much less gas. How this released gas moves through and around the magma greatly affects how lava erupts at the volcano’s vent. The table below and the graphic at the right show how silica and gas content in magma determine the type of volcanic eruption that will take place for shield and composite volcanoes. Low gas

High gas

Shield volcanoes

Low silica

• •

Runny magma, like ketchup Quiet eruption, lava flows easily

• •

Runny magma, bubbly Fire fountain, lava flows easily

Composite volcanoes

High silica

• •

Thick, sticky magma, like taffy Quiet eruption

• •

Thick, sticky magma Explosive eruption

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Volcanoes at divergent boundaries Mid-ocean ridge As tectonic plates move apart at a divergent boundary, mantle material below volcanoes is drawn toward Earth’s surface (Figure 20.14). The hot and flexible rock of

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the mantle is solid because of the great pressure of the material above it. However, as the rock rises, the pressure decreases. The lower pressure lowers the melting temperature of the rock so it melts and becomes magma that erupts underwater at the mid-ocean ridge. In effect, mid-ocean ridges are long chains of volcanoes! Low-silica The magma at mid-ocean ridges is chemically similar to mantle rock. It is magma dark colored, silica poor, and will form basalt. On land, basaltic lava flows

like spilled syrup (Figure 20.15). At underwater mid-ocean ridges, hot, oozing lava immediately hits cold seawater. The seawater causes the lava to form a solid skin. Flowing lava fills the skin like air fills a balloon. If the skin (now a brittle crust) cracks, more lava oozes out and the cycle repeats. The result is a volcanic formation called pillow lava (Figure 20.15). When geologists find pillow lava on land, they know that there was once a midocean ridge under an ancient ocean at that location. Iceland and Since mid-ocean ridges are mostly under the ocean, it is hard to study the Ethiopia volcanic activity that occurs at divergent boundaries. However, Iceland and

Figure 20.14: As the plates move

apart at a mid-ocean ridge, the mantle material is drawn upward. The pressure decreases as this material rises, causing the mantle material to melt.

Ethiopia are places that are affected by divergent boundaries above sea level. Iceland is separating along the Mid-Atlantic Ridge. Similarly, Ethiopia is the site of the East African Rift zone. Due to the separation of plates at these locations, each is intensely volcanic and, at some point in the future, the valleys created by the separation will probably fill with ocean water.

Figure 20.15: Basaltic lava and pillow lava.

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Volcanic island chains and mantle plumes Volcanic island Like mid-ocean ridge volcanoes, volcanic island chains are produced from chains basaltic magma. The magma that feeds mid-ocean ridge volcanoes comes

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from the upper part of the mantle at divergent plate boundaries. In contrast, volcanic island chain volcanoes are fed by a mantle plume, from the lower mantle, perhaps from near Earth’s outer core. Since these mantle plumes pass through the whole mantle, they are long-duration structures and essentially fixed in place. As you learned in Chapter 19, the top of the mantle plume is called a hot spot. Volcanic islands form on the plate above the hot spot. Although tectonic plates move very slowly, eventually their motion causes a plate to move off the hot spot. At that point, the island volcano is cut off from its magma source and becomes extinct while a new volcanic island begins to form over the hot spot. This process repeats and creates a string of volcanic islands—a volcanic island chain such as the Hawaiian Islands.

Geysers, Hot Springs, and Energy Geysers and hot springs are the result of water in the ground coming in contact with magma-heated rock below Earth’s surface. This geothermal energy (heat energy from the hot rock) heats the water and creates steam. Whether a geyser or a hot spring forms depends on the temperature of the rock, the amount of water present, and the shape of the water passage to the surface. Find out more about geothermal energy. Where is it used? Write a brief paragraph describing your findings.

Mantle plumes Volcanoes caused by mantle plume hot spots can be found anywhere a plate is

over the mantle plume. Volcanic island chains are formed when the mantle plume hot spot is under the ocean floor. Note that the Hawaiian Islands are in the middle of the Pacific Plate, nowhere near a plate boundary. Mantle plume hot spots are under continents, too. The geysers, hot springs, and other geothermal features of Yellowstone National Park are caused by a mantle plume hot spot. 20.2 VOLCANOES

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Shield and composite volcanoes What is a shield A shield volcano gets its name volcano? from its resemblance to a warrior’s

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shield lying on the ground. Their wide, flattened-pancake shape suggests that their magma is too runny to build a tall cone shape. As you might suspect, shield volcanoes are fed by basaltic magma. The Hawaiian Islands have many shield volcanoes.

shield volcano - a flat and wide volcano that has low-silica magma and lava with low or high levels of dissolved gas.

composite volcano - a tall, coneshaped volcano formed by layers of lava and ash.

Fire fountains A special condition occurs when runny, low-silica magma contains high from shield levels of dissolved gas. Large volumes of gas are released as the magma rises volcanoes in the conduit. This gas flings globules and ropes of glowing lava into the air

without much danger to onlookers standing at a distance. The effect is identical to shaking a soda bottle to produce a shower of soda. This brilliant spectacle is called a fire fountain and is common on the island of Hawaii (Figure 20.16). What is a A composite volcano is a tall cone composite formed by layers of lava and ash. volcano? Popocatépetl in Mexico, Mount St.

Helens in Washington State, and Mount Fuji in Japan are examples of composite volcanoes. The layers that make up a composite volcano accumulate over a long period of time. Unlike shield volcanoes and volcanoes formed at mid-ocean ridges or by a mantle plume, the lava of a composite volcano doesn’t flow quickly. Instead, the lava builds up in a tall heap because it is thick, sticky, and silica rich.

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Figure 20.16: A fire fountain.

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The source of silica-rich magma Composite volcanoes form in subduction zones

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Composite volcanoes form at subduction zones where water and sediment are carried downward as one plate slides beneath the edge of another plate. The subducted water combines chemically with hot mantle rock causing the subducting plate and sediments to melt. The resulting magma rises because it is less dense than the surrounding rock, and eventually melts through the overlying plate, forming a composite volcano (Figure 20.17).

Silica and Composite volcanoes are formed from silica-rich magma. Where does this magma magma come from? To begin to answer this question, let’s look at the

difference between shield and composite volcanoes. An important difference between these volcanoes is the distance between the magma source and the volcano on Earth’s surface. In Figure 20.17, notice that the newly formed magma must pass upward through a thick continental plate. In contrast, Figure 20.14 shows that magma has a short distance to travel to reach Earth’s surface to form volcanoes at mid-ocean ridges. The same is true for shield volcanoes. Clearly, something must change on this longer upward pathway. What’s The magma of both the mid-ocean ridge and a composite volcano starts out as different? silica-poor mantle material. This basaltic magma is released unchanged at mid-ocean ridges, but at subduction zones it must migrate upward before reaching the surface. During this migration, minerals begin to crystallize, first high-melting-point minerals, then lower-melting-point minerals. As these minerals crystallize, the silica increases in concentration. By the time this now silica-rich magma reaches the surface, it will form silica-rich rocks such as andesite and rhyolite. The table below summarizes this information. Shield volcanoes

Composite volcanoes

Volcano shape

•

Flattened, gradual slopes

•

Tall, steep slopes

Silica concentration

•

Silica poor

•

Silica rich

•

Mantle

•

Mantle (and melted subducted ocean crust and sediment)

Magma source Distance from magma source to volcano on Earth’s surface

•

Short

•

Long

Figure 20.17: Forming magma at a subduction zone.

Continents vs. Ocean Floors Granite and andesite form the mass of the continents. A key difference between these rocks and basalt, the rock of the ocean floor, is density. Both the ocean floor and the continents float on the mantle, but continents float higher because they have a lower density. As a result, we have dry land on which to live. The ocean floors are under the oceans because they are too dense to float higher on the mantle and rise above sea level. What would Earth be like if the ocean floors were less dense?

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Dissolved gas and cinder cones Dissolved gas in When silica-rich magma is low in dissolved gas, the lava comes out like sticky magma toothpaste and forms volcanic glass called obsidian. But if the silica-rich

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magma contains high levels of dissolved gas, pressure usually builds inside the volcano. In fact, the magma might be under so much gas pressure that a composite volcano cone bulges (see graphic below). In this situation, either the eruption will subside and the magma will return down the conduit, or the cone will explode. An explosive eruption results in a column of gas and bits of lava being expelled high into the atmosphere. The lava bits filled with gas bubbles break apart as the dissolved gas expands. The gas-filled fragments cool to produce pumice and ash (Figure 20.18). Pumice is a rock with lots of holes. Pumice has a low density because of its holes (which were made by gas bubbles) and will float in water. Ash is tiny particles of volcanic rock. Because ash is so fine, it drifts with the wind and might settle over a very wide area.

cinder cone - a volcano composed of a pile of solid lava pieces that form during a high-gas, low-lava eruption.

Figure 20.18: Pumice and ash form when a composite volcano explosively erupts.

Cinder cones The shapes of shield and composite volcanoes are largely determined by the composition of their lava flows. However, the form of a cinder cone, a

third type of volcano, is not the result of flowing lava (Figure 20.19). Rather, imagine a volcano that ejects a lot of gas with only small bits of lava. The lava bits (cinders) cool enough so that they are solid by the time they fall to the ground. Since they are not connected to one another, the falling bits form a loose, unstable pile. Sometimes the amount of magma produced increases enough to rise inside the cinder cone. The loose structure of the cinder cone conduit isn’t strong enough to contain the magma, so the cone wall gives way and the molten rock flows out from the side. There are more cinder cones associated with shield volcanoes than composite volcanoes, but cinder cones can be found on both.

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Figure 20.19: A cinder cone.

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Section 20.2 Review

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1. 2. 3. 4.

5.

6. 7. 8.

9. 10.

11. 12.

What causes the region called the Ring of Fire? What is the difference between a dormant volcano and an active volcano? What is the difference between magma and lava? A solid rock begins to melt: a. under what conditions of temperature and pressure? b. under what conditions of temperature and water content? The word viscosity was used in this chapter and introduced in Chapter 10. If you could increase the silica content of lava, would the lava become more viscous or less viscous? Explain your answer. What two ingredients in magma affect the type of eruption and shape of a volcano? Describe what a high-gas, high-silica eruption is like. Then, describe a low-gas, lowsilica eruption. What is the eruption of a cinder cone like? Answer continental plates or oceanic plates in response to the following questions. Justify your answer in each case. a. Where is runny lava found? b. Where is thick and sticky lava found? Describe the differences between a composite volcano and a shield volcano and give an example of each. Each of the following is a clue that indicates a type of volcanic activity. Identify the volcanic activity that would cause the formation of each. a. pillow lava b. pumice and ash c. fire fountain Ethiopia is a travel destination for individuals who want to see volcanoes. What explains Ethiopia’s volcanic features? Multiple choice: When volcanic island chains are formed, what moves? a. the mantle plume c. the plate above the mantle plume b. both the plate and the plume d. nothing moves

Katia and Maurice Krafft Documenting volcanic eruptions was the passion of Katia and Maurice Krafft of France. Having met at the University of Strasbourg, they married in 1970 and spent the next 21 years filming and photographing volcanic eruptions. Because they were extremely daring in their work, they were able to show the public breathtaking footage of volcanic eruptions. Their work helped convince public officials of the seriousness of eruptions so that they could act quickly to evacuate areas near pending eruptions. While filming Mount Unzen in Japan in 1991, the Kraffts and 40 journalists were killed during a pyroclastic flow. Search for amazing photos of and by the Kraffts on the Internet using the search phrase: “Katia and Maurice Krafft.”

Travel to Iceland Research, write, and design a travel brochure that describes to tourists what they would see when they visit volcanic Iceland. What kinds of volcanoes would they find on Iceland? Justify your answer.

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20.3 Igneous Rocks The formation of igneous rocks begins when rock melts below Earth’s surface. In this section, you will review how rock melts. Then, you will learn that the length of time for magma or lava to cool affects the size of the crystals in the rock. By the end of this section, you will be able to tell a lot about the history of an igneous rock.

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Melted rock Plastic mantle A good way to describe hot, solid mantle rock is that it is like stiff putty that rock takes millions of years to move. Material like this is described as being

plastic, or able to change shape without breaking. Pressure and You learned in section 20.2 that although mantle rock is very hot, it only water melts under certain conditions of pressure and water content. For example,

mantle rock melts when it is carried toward the surface at mid-ocean ridges. As the mantle rock rises, the pressure drops and the rock melts, becoming a liquid. Mantle rock also melts near a subducting plate where water is carried into the mantle. Both decreased pressure and the addition of water lower the melting temperature of mantle rock so that it melts (Figure 20.20). Why is the As you learned in Chapter 18, Earth is 4.6 billion years old. As materials mantle so hot? came together to form Earth, the collisions from these extraterrestrial

impacts generated heat. The interior of Earth is extremely hot because Earth is still cooling from when it formed so long ago. Also, as the denser components of Earth—iron and nickel—sank to Earth’s core, there was a conversion of potential energy to heat. In addition, some of the heat inside of Earth is caused by the decay of radioactive elements. From melted to Each of the rocks below is an igneous rock. They are all formed from melted solid rock rock; however, they differ in appearance. Why? You will learn the answer to

this question in the next few pages. Figure 20.20: Changes in pressure

and the addition of water cause the hot rock in the mantle to melt.

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How are igneous rocks formed? Where did Originally Earth was a ball of material that increased in size as the early igneous rocks planet gathered an ever-larger mass of particles from the gas and dust that come from? formed our solar system. Today Earth’s crust, mantle, and core are distinctly

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different from one another even though each layer was formed from the Earth’s original material.What happened to cause similar particles to become the different materials that we find today? Magma is a These different materials and the wide variety of igneous rocks result from complex changes that take place after magma forms. In the case of a simple substance substance such as water, the temperature at which it melts is equal to the temperature at

which it freezes, or crystallizes; in water’s case, 0°C. Magma, however, is a complex blend of many elements and compounds, each with a different melting point. The melting points vary over a large temperature range. What happens Imagine a magma chamber below Earth's surface. The graphic at right shows as magma a magma chamber at high temperature, but cooling. In the top panel, highgradually cools? melting-point minerals begin to form crystals. In the middle panel, the magma

continues to cool slowly, more of the original minerals crystallize, and new minerals with slightly lower melting points begin to crystallize also. In the bottom panel, the temperature has fallen significantly, the first and second mineral crystals are plentiful, and a third new mineral is beginning to crystallize. At this point, the magma is slushy because there are more solid crystals present than liquid melt. Convection currents within the still-hot magma slowly swirl the crystal slush. It is important to realize that the chemistry of the remaining melt changes as each mineral is removed by crystallization. Toward the end of this process, the remaining melt will produce granite rock. But other rocks might be produced if the crystallization process is interrupted earlier, by the magma erupting, for example.

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Crystals in igneous rocks Crystallization As melted rock cools, minerals in magma or lava form crystals that can be

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large, small, or microscopic depending on the rate at which cooling takes place. Crystallization is the process by which crystals form and increase in size. Crystallization begins when atoms in a liquid begin to collect on the surface of a solid particle called the seed crystal. When there is a long time for atoms to attach to the seed crystal and for the liquid to crystallize, large crystals form. If there is less time, only small crystals form.

crystallization - the process by which crystals form and grow in size.

How crystals increase in size

Short time

Smaller crystals

Long time Seed crystal

Figure 20.21: Often called volcanic glass, obsidian is an igneous rock that lacks crystals.

The Big Obsidian Flow Larger crystals

Large and small Igneous rocks formed from underground magma have larger crystals and a crystals coarse texture because magma tends to cool slowly. This is because the

surrounding ground acts as an insulator, keeping magma warm for a long time. Lava, flowing out of a volcano, tends to cool quickly when it is exposed to the air, cold water, or glaciers. Cooling lava forms igneous rocks with smaller crystals.

The Newberry Volcano in central Oregon last erupted 1,300 years ago and produced a huge amount of obsidian called the Big Obsidian Flow. Read more about the Newberry Volcano and write a short report on one of its interesting features.

Obsidian lacks As you saw on the first page of this section, obsidian is an igneous rock that crystals has no visible crystals. Obsidian, also called volcanic glass, is formed when

extruded lava cools so quickly that crystals do not have time to form. The large amount of silica in the lava that produces obsidian forms silica chains that effectively prevent mineral crystals from forming. As a glassy substance, obsidian has sharp edges (as thin as 3 nanometers wide) and has been used to make surgical scalpels (Figure 20.21).

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Interpreting igneous rocks Igneous rocks Having read about volcanoes and magma and how igneous rocks are formed, tell stories you might be surprised to learn that you can now figure out the story that an

igneous rock has to tell. Two characteristics that can be used to interpret the history of an igneous rock are its color and crystal size.

Interpreting Igneous Rocks Read the following text, then answer the questions below. •

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Color One of the most obvious

characteristics of an igneous rock is how light or dark it is. The general color of igneous rocks is a measure of the kinds of minerals present. Dark minerals are high in iron and magnesium and have higher melting points than light-colored silicate minerals. Look at the image at the right. The swirl of dark minerals probably formed early in the cooling of a magma chamber, whereas the light-colored feldspar crystals formed from the remaining magma. Crystal size As you learned on the previous

page, an igneous rock forms when minerals in magma or lava crystallize. Depending on the rate of cooling, the crystals might be invisible, small, or large. Large crystals form when magma cools slowly over a long time. Small to invisible crystals form when magma or lava cools quickly. Pegmatite, featured at the right, is an example of a rock that cooled slowly and formed large, visible crystals.

•

•

When you grind up a piece of pegmatite, the powder is light in color. Pegmatite forms from mature magma (high silica). High-meltingpoint minerals are removed from the melt by crystallization as indicated by pegmatite’s light color. The large crystals indicate slow cooling.

1. In which location listed below would pegmatite be likely to form? (a) At a mid-ocean ridge (where pillow lava commonly forms). (b) From the lava of a shield volcano. (c) Within a sub-surface magma chamber. 2. Describe the color and crystal size of a rock formed from young magma (low silica) that crystallizes slowly. 3. Andesite (a significant component of continents) is midway between granite and basalt in composition. What do you think andesite looks like in terms of color and crystal size?

20.3 IGNEOUS ROCKS

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Comparing igneous rocks

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Extrusive and On the previous page, you had to determine where pegmatite forms. The intrusive rocks correct answer was underground in a magma chamber. Because of where it cooled, pegmatite is an intrusive rock, an igneous rock that forms within Earth’s crust. Another example of an intrusive rock is granite. An extrusive rock is an igneous rock that cools and crystallizes above Earth’s surface.

Basalt is an extrusive rock. As you might suspect, intrusive rocks are more likely to have large crystals than extrusive rocks (Figure 20.22).

intrusive rock - an igneous rock that cools inside Earth’s crust; an example is granite.

extrusive rock - an igneous rock that cools outside of Earth’s crust; an example is basalt.

Low-silica Basalt and gabbro are formed from magma or lava of similar composition. rocks: basalt They are silica poor but rich in magnesium and iron. Basalt is formed from and gabbro low-silica, runny lava. Remember that oceanic crust is made of basalt. When

you compare the two silica-poor rocks, you see shiny, angular crystals in the gabbro, but no crystals are visible in the basalt. This tells you that the basalt cooled much faster than the gabbro. High-silica Both granite and obsidian are igneous rocks formed from silica-rich magma. rocks: granite Granite is made from magma that cooled slowly within Earth. It cooled so and obsidian slowly that it has large visible crystals. Granite forms much of the

continental crust. In contrast, obsidian, formed from lava, is so smooth that it is called volcanic glass. Obsidian contains almost no crystals. Crystals don’t have enough time to form in obsidian because the lava cools so quickly. Figure 20.22: Extrusive and intrusive rocks.

Granite for Your Kitchen Granite is commonly used for kitchen counters. Find out why.

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Section 20.3 Review 1. The rock of the mantle is described as being plastic. Why? 2. List two factors that cause mantle rock to melt. 3. The interior of Earth is extremely hot. Explain why.

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4. Is magma a simple or a complex substance? Provide a piece of evidence that supports your answer. 5. Multiple choice: The melting point of iron is 1,535°C. What happens when iron reaches this temperature? a. Solid iron melts. b. Liquid iron freezes. c. Liquid iron evaporates. d. All of the above. e. Only (a) and (b) are correct. f. Only (a) and (c) are correct. 6. What is crystallization? Explain why the rate of cooling affects the size of the crystals that form. 7. Why is obsidian called volcanic glass? 8. An igneous rock has very large crystals. Describe a possible history of this rock: Where was it formed? How was it formed?

Magma vs. Lava You might be wondering why there are two different names for molten rock. Do they have different names just because they are in different locations? Not exactly. You know that magma is present below Earth’s surface, and lava refers to magma that has reached Earth’s surface. Although lava is derived from magma, it does differ in its composition because it has less dissolved gas, including water vapor. So, in fact, magma and lava are different and not just because they are in different locations. One of the methods that scientists use to study volcanoes is lava sampling, which can be dangerous. Find out about this method and what kind of information is learned from it.

9. An igneous rock sample has light-colored minerals and a few dark-colored minerals. Which of these minerals formed first? Why? 10. What is the difference between an intrusive and an extrusive igneous rock? 11. Compare and contrast gabbro and granite. 12. Design and fill in a table that compares and contrasts basalt and granite. To design your table, first decide on the properties you will use to compare the rocks. For example, one property might be “density.” 13. Iceland is located on the Mid-Atlantic Ridge. Would you expect to find igneous rocks in Iceland? What kinds of igneous rocks might you find? Explain your answer. 20.3 IGNEOUS ROCKS

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Chapter 20 Assessment Vocabulary

Section 20.2

Select the correct term to complete the sentences.

11. A(n) _____ is formed by an eruption that includes a high amount of gas and comparatively little lava.

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body waves

crystallization

Richter scale

fault

earthquake

Moment Magnitude scale

lava

intrusive rock

Modified Mercalli scale

13. _____ is magma that has reached Earth’s surface.

magma

surface waves

focus

14. _____ is melted rock within the mantle and Earth’s crust.

volcano

composite volcano

shield volcano

epicenter

seismograph

magma chamber

cinder cone

extrusive rock

Section 20.1

The place on Earth’s surface above the location that rock breaks during an earthquake is the _____.

2.

Stick-slip motion between tectonic plates causes a(n) _____.

3.

The point below the epicenter is called the _____.

4.

A(n) _____ is a place where rocks break and there is movement.

5.

These seismic waves travel at Earth’s surface: _____.

6.

_____ are seismic waves that travel through the planet.

7.

The instrument used to record seismic waves is a(n) _____.

8.

Each number change on the _____ means a 10-fold increase in seismic wave amplitude.

9.

Eyewitness accounts of earthquake damage are incorporated into this earthquake measurement scale: _____

10. The _____ rates the total energy of an earthquake.

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15. Because low-silica lava is runny, it can’t build up a tall, cone-shaped _____. Low-silica, runny lava will result in a(n) _____, which is a flat and wide volcano. 16. A(n) _____ is a place where magma collects underground.

1.

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12. The products of an eruption can build a mountainous _____.

Section 20.3

17. A(n) _____ results from magma that cools underground. 18. A(n) _____ results from magma that cools at Earth’s surface. 19. A process that occurs when magma or lava cools to form an igneous rock: _____.

Concepts Section 20.1

1.

What geographic region has the most earthquakes? Explain your answer.

2.

Why is the motion between two plates that are sliding past each other described as stick-slip motion?

3.

Why is plastic a good term to describe the upper mantle?

4.

Describe stick-slip motion and give an example.

5.

When an earthquake takes place at a transform plate boundary, does it occur at every place along the boundary or in one location? Explain your answer.

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6.

How is potential energy involved in how one earthquake triggers another earthquake?

18. Do volcanoes ever form away from plate boundaries within plates? Explain your answer.

7.

Compare and contrast surface waves to P- and S-waves.

19. Volcanoes found near subduction zones have which of the following?

8.

Why is a seismograph useful for measuring the magnitude of an earthquake on the Richter scale?

9.

Is it possible that an earthquake could happen and you would not know it? Explain your answer.

10. Compare and contrast the Moment Magnitude scale and the Richter scale.

a. b. c. d.

20. Which of the following describe volcanoes on islands above a hot spot? a. b. c. d.

11. After an earthquake, one person says that the intensity of the quake was VI on the Modified Mercalli scale. Another person says that the intensity was III. Why might these individuals have had different experiences? Section 20.2

12. What is the difference between a conduit and a vent? 13. Describe the three phases in the life cycle of a volcano. 14. What factors affect the melting of solid rock in the mantle? 15. What is the main factor that affects the consistency of magma. at subduction zones at a transform plate boundary at a divergent plate boundary where two continental plates come together

17. Mount St. Helens formed at which kind of plate boundary? a. b. c. d.

convergent transform fault divergent mid-ocean ridge

made up of layers of granitic lava are shield volcanoes are made from thick, high-silica magma all of the above

21. Why do composite, shield, and cinder cone volcanoes look so different from one another? Section 20.3

22. Explain the role of crystallization in the formation of igneous rocks. Is it possible for an igneous rock to lack crystals? Why or why not? 23. Magma is the source material for all igneous rocks.

16. Where do composite volcanoes tend to be found? a. b. c. d.

magma with high silica content an explosive eruption large amounts of gas released during the eruption all of the above

a. b.

How is it that magma forms so many different kinds of igneous rocks? Describe how the magma that forms andesite, rhyolite, and granite becomes silica rich.

Problems Section 20.1

1.

You need three seismic stations to determine the location of the epicenter of an earthquake. Why wouldn’t just two stations provide enough information? Hint: You might need to make a diagram to help you answer this question. CHAPTER 20 ASSESSMENT

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2.

In 1960, an earthquake occurred in Chile that had a Richter scale magnitude of 9.5. How would the energy of this quake compare to one that had a 7.5 magnitude?

3.

You can use the time-distance graph below to determine the distance to an epicenter. a.

c. d.

The island of Hawaii sits on top of a hot spot. The hot spot has also formed the Mauna Loa and Kilauea volcanoes on the island. Currently, the hot spot is building the undersea volcano Loihi to the southeast of the island. When Loihi gets bigger and reaches the ocean surface, it will increase the size of Hawaii. a.

The arrival time difference between P- and S-waves is 1 second. What is the approximate distance to the epicenter? The arrival time difference between P- and S-waves is 4 seconds, what is the approximate distance to the epicenter? If the distance to an epicenter is 10 kilometers, how long after the P-waves did S-waves arrive at a seismic station? How would you describe the relationship between arrival time difference and distance to the epicenter?

b.

c.

S-P time difference vs. distance to the epicenter 5 4 Time (s)

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b.

5.

3

d.

2 1

e.

0 10

20 30 Distance (km)

40

4.

How do the sizes of volcanoes compare to the sizes of other types of mountains? First, research the size range for shield, composite, and cinder cone volcanoes. Then, find the height of the world’s highest mountain. Is it taller or shorter than the world’s highest volcano? Provide data that supports your answer.

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Section 20.3

6.

Section 20.2

What kind of lava forms these volcanoes? Justify your answer. Which volcano is older? Mauna Loa or Kilauea? Justify your answer. Loihi is 3,000 meters above the floor of the Pacific Ocean. How does its height compare to the height of Mount St. Helens? Prior to the 1970s, scientists thought Loihi was an oceanic feature called a seamount. Research and describe the events that led up to Loihi being described as an active volcano. How are scientists currently studying Loihi?

Igneous rocks vary by color and the size of their crystals. Identify the conditions of formation that would lead to the following igneous rocks. a. b. c. d.

a light-colored rock with large crystals a dark-colored rock with sharp edges and no crystals a dark-colored rock with large crystals a light-colored rock with small crystals

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Applying Your Knowledge

2.

Section 20.1

1.

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This United States Geological Survey (USGS) map illustrates how a 1999 earthquake in Hector Mine, California, was felt by surrounding communities. The magnitude of the quake at the epicenter was 7.1. The map is based on the Modified Mercalli scale. a. b.

Why does the distribution of color on this map make sense? List two communities that experienced an intensity of IV and two that experienced an intensity of V. Use the scale at the bottom of the map to estimate the area in square kilometers that experienced an intensity of IX.

c.

3.

In the text, you learned that at some point in the future, the valleys created from both Iceland and Ethiopia being pushed apart will fill with ocean water. This is the same way that the supercontinent Pangaea began to break up 200 million years ago. Can we better understand how Pangaea broke up by studying Iceland and Ethiopia? Why or why not? Justify your answer.

4.

At the beginning of the chapter, you learned a little about the ways in which earthquakes and volcanic eruptions can be predicted. It turns out that this is very challenging to do. Step 1: Pick either earthquakes or volcanoes. Explain your choice. Step 2: Research what scientists are doing to improve their ability to predict an earthquake or a volcanic eruption. Step 3: Write a paragraph about your findings.

LAS VEGAS SHOSHONE TRONA LISABELLA BAKER MOJAVE

35º N

BARSTOW

GORMAN

NEEDLES

PALMDALEACTORVILLE

34º N

Epicenter

TWENTYNINE PALMS

LOS ANGELES

PARKER

PALM SPRINGS IRVINE

BLYTHE

TEMECULA SALTON CITY JULIAN BRAWLEY

OCEANSIDE

33º N SAN DIEGO

Section 20.3

YUMA MEXICALI

km 0

32º N

119º W

Intensity Shaking Damage

50

5.

100

118º W

I II-III IV

117º W

V

Not felt

Weak

Light

None

None

None Very light

116º W

VI

115º W

VII

Moderate Strong Very strong Light

If you feel an earthquake, you can report what you experienced on the USGS website page entitled “Did You Feel It?” (www.usgs.gov). Making sure that the public understands hazards such as earthquakes is part of the mission of the USGS. Imagine that you have just been hired as an employee of the USGS. Your first task is to explain the ratings for earthquakes. Make a one-page informational sheet that describes the differences among the Richter scale, the Moment Magnitude scale, and the Modified Mercalli scale.

Section 20.2

Sample Modified Mercalli map for an earthquake

36º N

114º W

VIII

IX

X+

Severe

Violent

Extreme

Yosemite National Park is known for features called granite domes. Find out how these features are formed and write about them. What kind of plate boundary is associated with their formation?

Moderate Moderate/Heavy Heavy Very Heavy

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Unit 7 Earth’s Water CHAPTER 21 Water and

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Solutions

CHAPTER 22  Water Systems CHAPTER 23 How Water Shapes

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the Land

‹ Try this at home The ground can be used to filter water; does it do a good job? Try this to find out. Make some “polluted” water by adding dirt or sand, sticks, leaves, small pieces of cloth or paper, food coloring, and/or soap. Next get a 20 oz. soda bottle and cover the neck with a piece of cloth held in place with a rubber band. Cut the bottom of the bottle off with a pair of scissors. Hold the bottle upside down and fill it with some dirt, to represent the ground. Rest the bottle in a large cup. Mix the “polluted” water well and slowly pour a cup of it into the upside down bottle. Allow all the water to drip through until you have collected about a cup’s worth. Look at the water coming out of your dirt “filter”. How does it compare to the “polluted” water that you started with? What are the drawbacks of filtering our wastewater through the ground around our homes the way some septic systems do?

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CHAPTER 21

Water and Solutions FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

Let’s say you’re thirsty. You go to a convenience store and see a wide range of beverages. Which one do you choose? You might pick a plain bottle of water. Or, if you want something more interesting, you might buy carbonated water. Other types of drinks include sports drinks, sodas, fruit juice, and even tea and coffee drinks. What do these beverages have in common? For starters, they all contain an important substance—water. You and all living things need water to live. In fact, your body is made mostly of water. Another thing that all beverages have in common is that they are all solutions. In this chapter, you will learn what a solution is. Carbonated water, for example, is a fizzy solution of carbon dioxide gas dissolved in water. And you might be surprised to learn that the air you breathe is a solution of gases including nitrogen, oxygen, argon, and carbon dioxide. The last section of this chapter describes acids and bases. You will learn that water has a neutral pH. What does that mean? Here are some clues: It’s not acidic like orange juice, and it’s not basic like liquid soap. Since you definitely wouldn’t want to drink liquid soap, how do you know if a substance is acidic or basic? In this chapter, you will find out.

4 Why is water a universal solvent? 4 Is an unopened bottle of soda a saturated solution?

4 What’s the difference between an acid and a base?

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21.1 Water We live on a watery planet. All life on Earth depends on this combination of hydrogen and oxygen atoms. Fortunately, Earth has a lot of water—75 percent of our planet’s surface is covered with it! Interestingly, our bodies are mostly water, too—about 60 to 75 percent (Figure 21.1). With these facts in mind, let’s find out about the properties of water that make it so valuable.

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The shape of a water molecule How a water The chemical formula for water is H2O. Why is that? molecule is From the formula, we know that for each water molecule formed there are two hydrogen atoms that are each attached to an

1+

2–

Lone pairs

OH

oxygen atom by a chemical bond. Recall from Bonding pairs Chapter 13 that oxygen has an oxidation number of 2–. Oxygen has six valence electrons and needs eight to complete its outer shell. Hydrogen has an oxidation number of 1+ because it has one electron in its outer shell that it will share. Hydrogen needs two electrons to complete its smaller outer shell. This state is represented by a Lewis dot diagram for a water molecule (shown above at the right). When two hydrogen atoms share their electrons with one oxygen atom, a neutral molecule is formed (shown at left).

H

1+

neutral molecule (2–) + (1+) + (1+) = 0

The shape of a A water molecule forms a pyramid shape called a tetrahedron. An oxygen water molecule atom is in the middle of the tetrahedron, and the electron pairs form the legs.

Figure 21.1: The Earth’s surface and our bodies are mostly water.

Tetrahedron

Why does a water molecule form this shape? A water molecule has four pairs of electrons around the oxygen atom. Only two of these pairs are involved in forming the chemical bonds. These two pairs are called bonding pairs. The other two pairs of electrons are not involved in forming chemical bonds and are known as lone pairs.

H

Electron pairs Because negative charges repel, the four electron pairs around the oxygen repel each other atom are located where they can be the farthest apart from one another,

forming the tetrahedron shape (Figure 21.2). If you draw the molecule without the lone pairs, the oxygen and hydrogen atoms form a “V” (shown upside down in the diagram).

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H

V shape

Figure 21.2: The shape of a water molecule.

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CHAPTER 21

Water is a polar molecule What is a polar Water is a polar molecule, meaning it has a negative end (pole) and a molecule? positive end (pole). In a molecule of water, the oxygen atom attracts electrons

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so that they are shared unequally between the oxygen and hydrogen. The electrons are actually pulled toward the oxygen atom and away from the two hydrogen atoms. Therefore, the oxygen end of the molecule (the one with the lone pairs of electrons) has a partially negative charge, and the hydrogen end of the molecule has a partially positive charge (Figure 21.3).

polar molecule - a molecule that has a negative and a positive end, or pole. nonpolar molecule - a molecule that does not have distinctly charged poles.

Ammonia is Ammonia (NH3) is another example of a polar molecule. This molecule has another polar one lone pair of electrons and three bonding pairs of electrons. This gives the molecule ammonia molecule a pyramid shape. Figure 21.3 shows the shape of the

molecule with the three hydrogens forming the base of the pyramid (the positive pole). The top of the pyramid is the negative pole. Nonpolar Methane (CH4) is an example of a nonpolar molecule. Nonpolar molecules molecules do not have distinct positive and negative poles. As you can see in

Figure 21.3, a methane molecule does not contain any lone pairs of electrons. The electrons are shared equally between the carbon atom and each of the four surrounding hydrogen atoms. Comparing polar It takes energy to melt and boil compounds. The fact that the melting and and nonpolar boiling points of a polar molecule (water) are much higher than those of a molecules nonpolar molecule (methane) provides evidence that there are attractions

between polar molecules. This is because it takes more energy to pull apart molecules that are polar compared to nonpolar molecules. The table below compares the melting and boiling points of water and methane. Notice that the melting and boiling points of water are much higher than those of methane. Table 21.1: Comparing water and methane Compound

Melting point

Boiling point

Water

0°C

100°C

Methane

–183°C

–162°C

Figure 21.3: Examples of polar and nonpolar molecules.

21.1 WATER

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Water molecules are connected by hydrogen bonds A water How can a water molecule be like a magnet? Think about what happens if molecule is like you place a group of magnets together. A magnet has two sides, or poles. a magnet This means that two side-by-side magnets are attracted to each other’s

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Hydrogen bonds

A network of molecules

Ice has a honeycomb structure

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opposite pole. A group of magnets will form an arrangement so that they alternate poles because similar poles repel each other. The same is true if you put a group of water molecules together. The positive pole of one water molecule is attracted to the negative pole of another. In a group of water molecules, the positive and negative poles align among the molecules in the group. These polar attractions create organization among water molecules. A water molecule has two strong covalent bonds between the oxygen atom and the hydrogen atoms. The force that holds neighboring water molecules together is called a hydrogen bond. A hydrogen bond is an intermolecular force between a hydrogen atom on one molecule to a negatively-charged atom on another molecule. Hydrogen bonds are relatively weak. They constantly break and reform as water molecules collide. In Figure 21.4, you can see that the oxygen atom in a water molecule has two partially negative lone electron pairs. Each pair of electrons is available to form a hydrogen bond with the partially positive hydrogen atom of a neighboring water molecule. Many neighboring water molecules connected by hydrogen bonds form a network of water molecules. As temperature increases, the organized structure of the hydrogen bonds among water molecules decreases. As temperature decreases, the organized structure becomes greater. Frozen water, or ice, has a very organized structure that resembles a honeycomb because each water molecule forms hydrogen bonds with four other water molecules (Figure 21.4). This creates a six-sided arrangement of molecules that is evident if you examine snowflakes under a microscope (Figure 21.5). As water freezes, molecules of water separate slightly from one another as a result of hydrogen bonding. This causes the volume of water to increase slightly and the density to decrease. This explains why water expands when it is frozen and why ice floats. The density of ice is about 0.9 g/cm3, whereas the density of water is about 1 g/cm3.

hydrogen bond - an intermolecular force between the hydrogen atom on one molecule and a negatively charged atom of another molecule.

Figure 21.4: A hydrogen bond between two water molecules.

Figure 21.5: The honeycomb

structure of solid water (ice). Can you identify how each molecule forms four hydrogen bonds with other molecules?

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CHAPTER 21

Properties of water related to hydrogen bonding Water has a high You learned in Chapter 9 that water has a high specific heat compared to other specific heat substances. Specific heat tells us how much heat is needed to raise the

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temperature of one kilogram of a substance by one degree Celsius. A high specific heat means a lot of energy is needed for each degree of increase in temperature. For example, water’s specific heat value is 4,184 J/kg°C, whereas the specific heat for steel is only 470 J/kg°C. Water resists Water has a high specific heat value because of hydrogen bonds. Between temperature single molecules, hydrogen bonds are weak. However, at the group level, the changes polar attractions of the molecules (the hydrogen bonds) make more heat

necessary to make water molecules move faster. The temperature finally rises once the water molecules begin to move faster. The high specific heat of water means that a large amount of energy is needed to heat a volume of water, and this same amount will have to be taken away to cool it back to the starting temperature. This also explains why water cools more slowly than other substances. Water has a high Most of the water on Earth exists in liquid and solid states, rather than as a boiling point gas. This is because the hydrogen bonds hold the water molecules together

strongly enough so that individual molecules cannot easily escape as a gas at ordinary temperatures. The hydrogen bonds in water explain why water has such a high boiling point (100°C). In order for water to boil and turn into a gas (water vapor), enough energy must be added to separate the hydrogen bonds that hold the molecules of water together. Once these molecules are separated, they are able to enter the gaseous state (Figure 21.6).

Figure 21.6: In order for water to

boil, enough energy must be added to separate the hydrogen bonds that hold the water molecules together.

Hydrogen You might know that plants obtain water from their roots. How does water get bonding and from a plant’s roots to its leaves? The stem of a plant has microscopically plants thin, straw-like structures that allow the water to rise up from the roots to the

leaves. The water makes the entire journey from the roots to the leaves due to hydrogen bonding between water molecules (Figure 21.7). As water molecules evaporate from the leaves, other water molecules are pulled into place. It is as if water molecules hold hands. If one molecule moves, the ones behind follow because they are connected by hydrogen bonds.

Figure 21.7: Hydrogen bonds help

water travel from roots to stem to leaves.

21.1 WATER

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Water is a universal solvent Water dissolves Water is often called the “universal solvent.” While water doesn’t dissolve many things everything, it does dissolve many different types of substances such as salt

and sugar. Water is a good solvent because it is a polar molecule. This gives it the ability to dissolve ionic compounds and other polar substances.

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How water An example of an ionic compound is table salt (sodium chloride). Sodium dissolves salt chloride (NaCl) is an ionic compound that is made of sodium ions (Na+) and

chloride ions (Cl–). Suppose a sodium chloride (table salt) crystal is mixed with water. Because opposites attract, the negative ends of the water molecules are attracted to the Na+ ions and the positive ends are attracted to the Cl– ions of the crystal. This causes the atoms of the crystal to separate. The polar water molecules surround the sodium and chlorine ions, forming a solution. The process by which ionic compounds dissolve (become separated into positive and negative ions) is called dissociation (Figure 21.8).

How water Like water molecules, sugar molecules can form hydrogen bonds. In the case dissolves sugar of sugar, these bonds hold the molecules together as solid crystals. When

sugar is mixed with water, the individual molecules of sugar become separated from one another and are attracted to the opposite poles of the water molecules. Because sugar is a covalent compound, the sugar molecules do not dissociate into ions but remain as neutral molecules in the solution.

Like dissolves like. For example, polar solvents such as water dissolve polar substances. What doesn’t water dissolve?

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In general, “like dissolves like.” This means water, a polar solvent, dissolves polar substances. Nonpolar solvents (like mineral oil) dissolve nonpolar substances. Figure 21.9 lists some examples of polar and nonpolar substances.

Figure 21.8: Water dissolves sodium chloride to form a solution of ions.

Polar substances

Nonpolar substances

Water

Vegetable oil

Vinegar

Mineral spirits

Acohol

Turpentine

Sugar

Wax

Figure 21.9: Examples of polar and nonpolar substances.

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Section 21.1 Review

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1. Why does an oxygen atom only form two covalent bonds with hydrogen atoms?

The Importance of Water

2. Draw the Lewis dot diagram for water. Label lone pairs, bonding pairs, positive pole, and negative pole.

To understand why water is an important resource, complete one or more of the following.

3. Why is a water molecule able to form four hydrogen bonds? Use a diagram to explain your answer.

(1) Spend a day documenting how much water you use.

4. Identify which of the molecules below are polar molecules and which are nonpolar molecules. Justify your answer.

(2) Find out how your city or state government promotes water conservation or protection of local water areas. (3) Find out about how the federal government protects our water resources.

5. What is the difference between a bond in a polar molecule and a bond in a nonpolar molecule?

(4) Identify an organization that is involved in water conservation. Visit its website and find out what the organization does.

6. A single covalent bond is stronger than a single hydrogen bond, so why does a group of polar molecules tend to have a higher boiling point than a group of nonpolar molecules? 7. Compare and contrast a pair of magnets and a pair of water molecules. 8. Why is the density of ice less than the density of liquid water? 9. Water’s specific heat value is 4,184 J/kg°C and the value for steel is 470 J/kg°C. Based on this information, compare water and steel with regard to the time it would take to heat up or cool down these substances. 10. List three properties of water that are related to hydrogen bonding. 11. How is the process of evaporation of water from a plant leaf involved in moving water up the stem of a plant? Use the term hydrogen bond in your answer. 12. What does the phrase like dissolves like mean? 21.1 WATER

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21.2 Solutions If you walk down the beverage aisle of your local grocery store, you might see mineral water, spring water, flavored water, and seltzer (carbonated water) for sale. While the labels on the bottles might call what’s inside “water,” each bottle contains more than just pure water. These varieties of water are actually solutions that also contain dissolved substances.

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Solutions

solution - a mixture of two or more substances that is homogeneous at the molecular level.

alloy - a solution of two or more solids.

Homogeneous at A solution is a mixture of two or more substances that is homogeneous at the molecular level the molecular level. The word homogeneous means the particles in the water

are evenly distributed. For example, in mineral water there are no clumps of hundreds of mineral ions. Figure 21.10 illustrates some examples of other solutions. The particles in a true solution exist as individual atoms, ions, or molecules. Each has a diameter of between 0.01 and 1.0 nanometer (nm). A nanometer is one-billionth of a meter or one millionth of a millimeter. Muddy water is not homogeneous and it is not a solution. Muddy water is heterogeneous because it contains larger particles of soil or plant debris. Of course, muddy water also contains individual atoms, ions, and molecules too.

Heterogeneous mixtures

Solutions exist We often think of solutions as liquid. However, solutions exist in every in every phase phase: solid, liquid, and gas. A solution of two or more solids is called an of matter alloy. Steel is an alloy, or solution, of iron and carbon. Fourteen-karat gold is

Figure 21.10: Examples of solutions.

an alloy of gold and another metal such as copper or silver. Fourteen-karat means that 14 parts out of 24 parts of the alloy are gold. Carbonated water is a solution of a gas in a liquid. The sweet smell of perfume is a solution of perfume molecules in air. This is an example of a solution of gases.

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Mixtures that are not solutions Colloids A colloid is a mixture that contains clusters of atoms or molecules ranging in

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size from 1 to 1,000 nanometers. Colloids can look like solutions because the clusters, or particles, are evenly distributed in the fluid. The movement of the suspended particles in the fluid keeps them evenly distributed. Colloids can be either liquid or gaseous. Examples of colloids are mayonnaise, whipped cream, milk, jelly, detergent, ink, and fog. Suspensions You might notice that when you step into a pond or lake to go swimming, the

water suddenly becomes cloudy. Your feet cause the mud and other particles on the bottom of the pond or lake to mix with the water. However, if you stand still, the water eventually becomes clear again because the individual particles sink. In a suspension, such as muddy water, the particles are greater than 1,000 nanometers in diameter and can range widely in size. Most suspensions will settle when they are left sitting still for a period of time. Because a suspension is a heterogeneous mixture, the different-sized particles in a suspension can be separated by filtering.

colloid - a mixture that contains evenly distributed particles that are 1 to 1,000 nanometers in size. suspension - a mixture that contains particles that are greater than 1,000 nanometers. Tyndall effect - the scattering of light by the particles in a colloid.

The Tyndall It isn’t easy to separate colloids by filtering. However, there is a way to effect visually distinguish colloids from true solutions. The Tyndall effect is the

scattering of light by the 1- to 1,000-nanometer particles in a colloid. The Tyndall effect is occurring if you shine a flashlight through a jar of translucent fluid and see the light beam. The Tyndall effect helps distinguish a colloid from a true solution because the particles in a solution are too small to scatter light (Figure 21.11). An example of the Tyndall effect is when a car’s headlights are seen cutting through fog. The table below compares the properties of solutions, colloids, and suspensions. Table 21.2: Properties of solutions, colloids, and suspensions

Solutions Colloids Suspensions

Approximate size of solute particles

Do solute particles settle?

Will filtering separate particles?

Do particles scatter light?

0.01 to 1.0 nm

no

no

no

1.0 to 1,000 nm

no

only with special equipment

yes, if translucent

> 1,000 nm

yes

yes

yes, if translucent

Figure 21.11: The Tyndall effect

helps you tell the difference between a translucent colloid and a solution.

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Solvents and solutes What are A solution is a mixture of at least two substances: a solvent and a solute. The solvents and solvent is the substance that makes up the biggest percentage of the solutes? mixture. For example, the solvent in grape soda is water. Each of the remaining parts of a solution is called a solute. Sugar, coloring dyes,

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flavoring chemicals, and carbon dioxide gas are solutes in grape soda. Solutes dissolve When the solute particles are evenly distributed throughout the solvent, we in a solvent say that the solute has dissolved. Solutes dissolve in a solvent to form a

solution. For example, the illustration below shows the preparation of a sugar and water solution. The solute (sugar) is in the graduated cylinder on the left. Water (the solvent) is added and the mixture is carefully stirred. Once all the solid sugar has dissolved, the solution becomes clear.

solvent - the component of a solution that is present in the greatest amount.

solute - any component of a solution other than the solvent. dissolve - to separate and disperse a solid into individual particles in the presence of a solvent.

Dissolving and Dissolving of a solid (such as sugar) occurs when molecules of solvent temperature interact with and separate molecules of solute (Figure 21.12). Most

substances dissolve faster at higher temperatures. You might have noticed that sugar dissolves much faster in hot water than in cold water. This is because thermal energy is used to break the intermolecular forces between the solute molecules. The importance Dissolving only occurs where the solvent contacts the solute. A solute will of surface area dissolve faster if it has a large amount of exposed surface area. For this

Figure 21.12: For dissolving to take

place, molecules of solvent interact with, and carry away, molecules of solute.

reason, most things that are meant to be dissolved, such as salt and sugar, are finely ground and sold as powders. The small particles of a powder have a high amount of surface area exposed to the solvent so they dissolve faster.

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Solubility What is Solubility describes the amount of solute (if any) that can be dissolved in a solubility? volume of solvent. Solubility is often listed in grams per 100 milliliters of

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solvent. Solubility is always given at a specific temperature since temperature strongly affects solubility. For example, Table 21.3 shows that around 200 grams of sugar can be dissolved in 100 milliliters of water at 20°C. Insoluble Notice that there are no solubility values for chalk in Table 21.3. This substances do substance is insoluble in water because it does not dissolve in water. You not dissolve can mix chalk dust and water and stir them vigorously, but you will still just

have a mixture of chalk dust and water. The water will not separate the chalk dust into individual molecules because chalk does not dissolve in water.

solubility - the amount of solute that can be dissolved in a specific volume of solvent under certain conditions.

insoluble - when a solute is unable to dissolve in a particular solvent.

saturated - describes a solution that has as much solute as the solvent can dissolve under the current conditions.

Saturation Suppose you add 300 grams of sugar to 100 milliliters of water at 20°C? What

happens? According to Table 21.3, a little over 200 grams will dissolve in the water. The rest will remain solid. That means you will be left with about 100 grams of solid sugar at the bottom of your solution. Any solute added in excess of the solubility will not dissolve. A solution is saturated if it contains as much solute as the solvent can dissolve under current conditions. Dissolving 201.9 grams of sugar in 100 milliliters of water at 20°C creates a saturated solution because no more sugar will dissolve under these conditions. Table 21.3: Solubility values for common substances Substance

Solubility (grams per 100 mL H2O at 20°C)

Sugar (C12H22O11)

201.9

Sodium nitrate (NaNO3)

87.6

Calcium chloride (CaCl2)

74.5

Table salt (NaCl)

35.9

Potassium nitrate (KNO3)

31.6

Baking soda (NaHCO3)

approximately 10

Chalk (CaCO3)

insoluble

Dew Point Sometimes there is more water vapor dissolved in the air in your home than you might want. To prevent mildew, for example, a dehumidifier is used to remove water vapor dissolved in air. This device works by reducing the temperature of the air. The dew point is the temperature at which air is saturated with water vapor. If it becomes colder than the dew point, the air becomes supersaturated with water. Supersaturation is unstable and temporary because there is more water dissolved in the air than it can hold. The excess water condenses out of the air as liquid water, which is then collected by the dehumidifier. This process is similar to the natural process that causes dew to form on grass and rain clouds to form in air.

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Solving Problems: Solubility How much table salt can dissolve in 200 milliliters of water at 20°C?

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1. Looking for:

Grams of solute (table salt)

2. Given:

Volume (200 mL) and temperature (20°C) of solvent

3. Relationships:

35.9 grams of table salt dissolves in 100 milliliters of water at 20°C (Table 21.3).

4. Solution:

If 35.9 grams dissolve in 100 milliliters, then twice as much, or 71.8 grams, will dissolve in 200 milliliters. Your turn...

a. How much table salt can dissolve in 50 milliliters of water at 20°C? b. How much sugar can dissolve in 300 milliliters of water at 20°C? c. How much water would you need to dissolve about 30 grams of baking soda? d. You want to make one liter of a sodium nitrate solution at 20°C. How much sodium nitrate will you need to make this solution? e. In some laboratories, scientists only need to make a few milliliters or less of a solution at a time. At 20°C, how much of each solute would you need to make: a 1-milliliter saturated solution of sugar? a 2-milliliter saturated solution of table salt? a 3-milliliter saturated solution of calcium chloride?

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Solution Concentrations In chemistry, it is important to know the exact concentration of a solution—that is, the exact amount of solute dissolved in a given amount of solvent. The mass-percent is an accurate way to describe concentration. The concentration of a solvent in masspercent is the mass of the solute divided by the total mass of the solution. concentration =

(

mass of solute total mass of solution

)

× 100

Parts per million (ppm), parts per billion (ppb), and parts per trillion (ppt) are commonly used to describe very small concentrations of pollutants in the environment. These terms are measures of the ratio (by mass) of one material in a much larger amount of another. For example, a pinch (gram) of salt in 10 tons of potato chips is about 1 gram of salt per billion grams of chips, or a concentration of 1 ppb.

a. b. c. d. e.

18 grams 606 grams 300 milliliters 876 grams 2 grams of sugar; 0.72 gram of salt; 2.2 grams of CaCl2

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Solubility curves Solubility values The solubility values for solutes are easily determined if you have a solubility on a graph curve like the one below. The y-axis on the graph represents how many grams

O K

N

3

Solubility curve for salts

250

Solubility (g salt/100 mL water)

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

of solute will dissolve in 100 milliliters of water. The x-axis represents temperature in degrees Celsius. You will notice that the solutes (NaCl, KNO3, NaNO3) dissolve differently as temperature increases. In order for something to dissolve in water, the water molecules need to break the intermolecular forces between the solute molecules. Water dissolves various substances differently because the chemical bond strengths between atoms found in different solutes are not the same.

200

NO 3

Na

150

100

Figure 21.13: Using a solubility

0

graph helps you solve problems like the one above.

NaCl

50

0

20

40

60

80

100

Temperature (ºC)

Interpreting the The solutes on the graph above are sodium chloride (NaCl), potassium nitrate graph (KNO3), and sodium nitrate (NaNO3). Notice that the solubility of NaCl does

not change much as temperature increases. The effect of temperature on the solubility of KNO3 and NaNO3 is more noticeable. More KNO3 and NaNO3 will dissolve in 100 milliliters of water at higher temperatures than NaCl.

Using the graph How many grams of potassium nitrate (KNO3) will dissolve in 200 mL of

water at 60°C? In this example, you are asked for the mass in grams of solute and given temperature and volume. You can answer this question using a solubility curve. Figure 21.13 provides steps for solving this problem.

Using a Solubility Curve Answer the following using the solubility curve. (1) How much NaCl dissolves in 200 mL at 80°C? (2) Is a 100-mL solution saturated at 40°C if it has 40 grams of NaNO3?

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Equilibrium and supersaturation solution by dissolving; and (2) molecules of solute come out of solution by precipitating.

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Unsaturated When a solution is unsaturated, its concentration is lower than the solutions maximum solubility. In an unsaturated solution, a solute dissolves faster than

it comes out of solution. In time, the concentration increases and the rate of dissolving slows. However, the processes of dissolving and precipitating are still going on.

unsaturated - describes a solution with a concentration less than the maximum solubility.

equilibrium - the state of a solution in which the dissolving rate equals the rate at which the solute comes out of solution. supersaturated - describes a solution with a concentration greater than the maximum solubility.

Equilibrium The more molecules that are in solution (higher concentration), the faster concentration molecules come out of solution. As the concentration approaches saturation,

500

g Sugar / 100 g water

the dissolving process slows and at the same time, the undissolving process accelerates. Eventually the rate of dissolving and precipitating become equal. At that point, concentration cannot change any further and we say that the solution is in equilibrium. At equilibrium, a solution is saturated because the concentration is as high as it can go at that temperature. Supersaturation According to the solubility table in Figure 21.14, at 80°C, 100 grams of

water reaches equilibrium with 365 grams of dissolved sugar. At lower temperatures, less sugar can dissolve. What happens if we cool a saturated solution? As the temperature goes down, sugar’s solubility also goes down and the solution becomes supersaturated. A supersaturated solution means there is more dissolved solute than the maximum solubility. Growing crystals

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A supersaturated solution is unstable. Undissolving is now faster than dissolving. The excess solute comes out of solution and returns to its undissolved state. This is how the large sugar crystals of rock candy are made. Sugar is added to boiling water until the solution is saturated. As the solution cools, it becomes supersaturated. Solid sugar crystals form as the sugar comes out of the supersaturated solution.

450 400

r sa sat tu ura ra ted ted

Dissolving and When a solute such as sugar is mixed with a solvent such as water, two precipitating processes are actually going on continuously: (1) molecules of solute go into

350 300

pe su n u

250 200 150 0

20

40 60 80 100

Temperature (ºC)

Temp (ºC)

g Sugar 100 g H2O

Temp (ºC)

g Sugar 100 g H2O

0

181.9

50

259.6

10

190.6

60

288.8

20

201.9

70

323.7

30

216.7

80

365.1

40

235.6

90

414.9

Figure 21.14: A solubility graph and table for sugar in water.

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Solutions of gases and liquids

CHAPTER 21

Gas dissolves in Some solutions have a gas as the solute (see Table 21.4 below). For example, water in carbonated soda, the fizz comes from dissolved carbon dioxide gas (CO2). Table 21.4: Solubility of gases in water at 21°C and 1 atm

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

Gas solute

Solubility (g/kg)

Oxygen (O2)

0.04

Nitrogen (N2)

0.02

Carbon dioxide (CO2)

1.74

Solubility

Solubility of CO2 in water

Temperature (ºC)

Figure 21.15: The solubility of gases in water decreases as temperature increases.

Solubility of gas The solubility of gases in liquids increases with pressure. Soda contains a lot increases with of carbon dioxide because this gas is dissolved in the liquid at high pressure. pressure You release the pressure when you open a can or bottle of soda. Due to the

decrease in pressure, the solution immediately becomes supersaturated. This means the rate of undissolving is faster than the rate of dissolving and the CO2 quickly bubbles out of the water and causes your drink to fizz. Solubility of gas When temperature increases, the solubility of gases in liquid decreases decreases with because the molecules of gas begin moving faster and escape the liquid. This temperature relationship for carbon dioxide in water is shown in Figure 21.15. Dissolved

oxygen in water is important for fish and aquatic life (Figure 21.16). During warmer weather, these organisms stay near the bottom of ponds or rivers where there is cooler, more oxygenated water. Oxygen enters pond or river water by being mixed in from the air, and it is produced as a by-product of photosynthesis in underwater plants and phytoplankton.

Figure 21.16: Aquatic life is

sustained by dissolved oxygen in water.

Solubility of Some liquids, such as alcohol, are soluble in water. Alcohol and water are liquids polar substances. Other liquids, such as oil, are not soluble in water. Oil-and-

vinegar salad dressing separates because oil is not soluble in water-based vinegar (Figure 21.17). Liquids that are insoluble in water might be soluble in other solvents. For example, vegetable oil is soluble in mineral spirits, a petroleum-based solvent used to thin paint. Both of these substances are nonpolar.

Figure 21.17: Oil, a nonpolar

substance, does not dissolve in vinegar, a polar substance. Look for this phenomenon in some salad dressings.

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Solubility rules Ions versus In addition to nonpolar substances, such as oil, some ionic compounds water molecules dissolve poorly in water. Why do you think this might be? Since water has

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charged poles, it is capable of attracting the positive or negative ions in an ionic compound. However, sometimes the attraction of the ions for one another is stronger than their attraction to water. As a result, the ionic compound is described as insoluble in water. For example, iron sulfide (FeS2) is an ionic compound that is insoluble in water.

solubility rules - a set of rules used to predict whether an ionic compound will be soluble or insoluble in water.

What are A set of solubility rules helps predict when an ionic compound is soluble solubility rules? or insoluble in water (Table 21.5). If you understand the different types of

chemical reactions and know the solubility rules, you can predict the products of a chemical reaction. The Group 1 (alkali metals) and Group 2 (alkali earth metals) elements are on the left side (first two columns) of the periodic table (Figure 21.18). Table 21.5: Solubility rules Any ionic compound with...

... is...

Exceptions

Examples

Nitrate (NO3–)

soluble

none

KNO3 is soluble

Chloride (Cl–)

soluble

AgCl, Hg2Cl2, and PbCl2

CaCl2 is soluble

Sulfate (SO42–)

soluble

BaSO4, PbSO4, and SrSO4

CuSO4 is soluble

Carbonate (CO32–)

insoluble

NH4+ and Group 1 elements

Na2 CO3 is soluble

insoluble

Group 1 elements, Ba(OH)2, and Sr(OH)2; Ca(OH)2 is slightly soluble

Ba(OH)2 is soluble

Group 1 and Group 2 elements and NH4+

CaS is soluble

Hydroxide (OH–)

Sulfides (S2–)

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insoluble

Figure 21.18: Group 1 and 2 elements on the periodic table.

Solubility Rules Use the solubility rules in Table 21.5 to determine whether these compounds are soluble or insoluble. a. H2S

d. CuS

b. Ca(NO3)2

e. KCl

c. PbCl2

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Solution

Solute(s)

Section 21.2 Review

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

1. Tell which one of the following is NOT a solution and explain why. a. ocean water b. water mixed with chalk powder c. steel d. carbonated orange soda e. 24-karat gold f. water with food coloring 2. For each of the following solutions, name the solvent and the solute. a. ocean water (salt water) b. carbonated water c. lemonade made from powdered drink mix

Air

Solvent Nitrogen (gas) Water (liquid) Water (liquid) Alcohol (liquid)

Carbonated water Saline solution Rubbing alcohol Sterling Silver (solid) silver

Other gases CO2 (gas) Salt (solid) Water (liquid) Copper (solid)

Figure 21.19: Question 8.

3. Why is water often called the “universal solvent”? 4. When can you say that a solute has completely dissolved? 5. Does sugar dissolve faster in cold or hot water? Explain your answer. 6. Is the solubility of oxygen higher in cold or hot water? Explain. 7. Jackie likes to put a lot of sugar in her hot tea. When she finishes drinking her tea, she notices that there are sugar crystals at the bottom of the teacup. Explain her observation in terms of saturation. 8. The table in Figure 21.19 lists the solvents and solutes for a variety of solutions. List three statements you can make about solutions based on the information in this table. 9. Is the solution in Figure 21.20 in equilibrium? Why or why not? 10. Describe the solution in a can of soda before the can is opened and just after it is opened.

Figure 21.20: Question 9.

11. Use solubility rules to determine whether these compounds will dissolve in water: (a) FeSO4, (b) K2CO3, and (c) NH4OH. 12. Limestone, which is made of calcium carbonate (CaCO3), wears away over time as it is exposed to the atmosphere and weather. Find out why. 21.2 SOLUTIONS

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21.3 Acids, Bases, and pH

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Acids and bases are among the most familiar of all chemical compounds. Some of the acids you might have encountered include acetic acid (found in vinegar), citric acid (found in orange juice), and malic acid (found in apples). You might also be familiar with some bases, including ammonia in cleaning solutions and magnesium hydroxide found in some antacids. The pH scale is used to describe whether a substance is an acid or a base. This section is about the properties of acids and bases, and the pH scale.

acid - a substance that produces

hydronium ions (H3O+) when dissolved in water.

What are acids? Properties of An acid is a compound that dissolves in water to make a particular kind of acids solution. Some properties of acids are listed below and some common acids

are shown in Figure 21.21. Notes: You should NEVER taste a laboratory chemical. Be sure to wear goggles to protect your eyes when you use chemicals. • • • •

Acids create the sour taste in foods such as lemons. Acids react with metals to produce hydrogen gas (H2). Acids change the color of blue litmus paper to red. Acids can be very corrosive, destroying metals and burning skin through chemical action. • Acids can react with carbonate minerals to produce CO2 gas. Acids make Chemically, an acid is any substance that produces hydronium ions (H3O+) hydronium ions when dissolved in water. When hydrochloric acid (HCl) dissolves in water, it ionizes, splitting up into hydrogen (H+) and chlorine (Cl–) ions. Hydrogen ions (H+) are attracted to the negative oxygen end of a water molecule, combining to form hydronium ions. What an acid does in water

Figure 21.21: Some weak acids you might have around your home.

–

+ HCl Hydrochloric acid

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H2O Water

Cl

–

+ +

H3O+

Hydronium ion (+)

Chloride ion (–)

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Bases base - a substance that produces hydroxide ions (OH–) when dissolved in water; a base is also known as a proton (H+) acceptor.

Properties of A base is a compound that dissolves in water to make a different kind of bases solution, opposite in some ways to an acid. Some properties of bases are listed

below and some common bases are shown in Figure 21.22.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

• • • •

Bases create a bitter taste. Bases have a slippery feel, like soap. Bases change the color of red litmus paper to blue. Bases can be very corrosive, destroying metals and burning skin through chemical action. Bases produce A base is any substance that dissolves in water and produces hydroxide ions hydroxide ions (OH–). A good example of a base is sodium hydroxide (NaOH), found in many commercial drain cleaners. This compound dissociates in water to form sodium (Na+) and hydroxide (OH–) ions. What a base does in water Water

+

+ +

–

NaOH

Na

OH–

Sodium hydroxide (base)

Sodium ion (+)

Hydroxide ion (–)

Ammonia is a Ammonia (NH3), found in some cleaning solutions, is a base because it base increases the pH of water. It also is a base because it accepts a proton (H+).

This is another definition for a base—a proton acceptor. Notice that a hydroxide ion, from water, is formed in this reaction (below). Figure 21.22: Common bases

What ammonia (base) does in water

+

+ NH3 Ammonia

H2O Water

+

NH4

+

–

include ammonia, baking soda, soap, and drain cleaner.

OH– Hydroxide ion (–)

Ammonium ion (+)

21.3 ACIDS, BASES, AND PH

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Strength of acids and bases The strength of The strength of an acid depends on the concentration of the hydronium ions acids (H3O+) the acid produces when dissolved in water. Hydrochloric acid (HCl)

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

is a strong acid because HCl completely dissolves into H+ and Cl– ions in water. This means that every molecule of HCl that dissolves produces one hydronium ion.

Acetic acid is a Acetic acid (HC2H3O2), in vinegar, is a weak acid. When dissolved in water, weak acid only a small percentage of acetic acid molecules ionize (break apart) and

become H+ and C2H3O2– ions. This means that only a small number of hydronium ions are produced compared to the number of acetic acid molecules dissolved (Figure 21.23).

The strength of The strength of a base depends on the relative amount of hydroxide ions bases (OH–) produced when the base is mixed with water. Sodium hydroxide

(NaOH) is considered a strong base because it dissociates completely in water to form Na+ and OH– ions. Every molecule of NaOH that dissolves creates one OH– ion (Figure 21.24). Ammonia (NH3), on the other hand, is a weak base because only a few molecules react with water to form NH4+ and OH– ions.

Figure 21.23: Acetic acid dissolves

in water, but only a few molecules ionize (break apart) to create hydronium ions.

Water can be a One of the most important properties of water is its ability to act as both an weak acid or a acid and a base. In the presence of an acid, water acts as a base. In the weak base presence of a base, water acts as an acid. In pure water, the H2O molecule

ionizes to produce both hydronium and hydroxide ions. This reaction is called the dissociation of water.

What does the The double arrow in the illustration means that the dissociation of water double arrow reaction can occur in both directions. This means that water molecules can mean? ionize and ions can form water molecules. However, water ionizes so

slightly that most water molecules exist whole, not as ions.

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Figure 21.24: Sodium hydroxide

(NaOH) is a strong base because every NaOH molecule contributes one hydroxide (OH–) ion.

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The pH scale and pH What is pH? The pH scale is a range of values from 0 to 14 that describe a solution, with

0 being very acidic, 7 being neutral, and 14 being basic or very low acidity. The term pH is an abbreviation for “the power of hydrogen” and is a measure of the concentration of hydronium ions (H3O+) in a solution.

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The numbers on A pH of 7 is neutral, neither acidic nor basic. Distilled water has a pH of 7. the scale Acidic solutions have a pH less than 7. A concentrated solution of

pH scale - the pH scale goes from 0 to 14 with 1 being very acidic and 14 being very basic.

pH - a measure of the concentration of hydronium ions in a solution.

hydrochloric acid, a strong acid, has a pH of 1. Seltzer water is a weak acid at a pH of 4. Many foods we eat and many ingredients we use for cooking are acidic. Basic or alkaline solutions have a pH greater than 7. A concentrated solution of a strong base has the highest pH. For example, a strong sodium hydroxide solution can have a pH close to 14. Weak bases, such as baking soda, and weak acids have pH values that are close to 7. Many household cleaning products are basic (Figure 21.25).

The pH scale Strong acid

Neutral

Strong base

1

7

14

Acids

Bases

pH indicators Certain chemicals turn different colors when pH changes. These chemicals

are called pH indicators and they are used to determine pH. The juice of boiled red cabbage is a pH indicator that is easy to prepare. Red cabbage juice is deep purple and turns various shades ranging from purple to yellow at different values of pH. Litmus paper is another pH indicator that changes color. Red and blue litmus paper strips are pH indicators that test for acids or bases.

Figure 21.25: The pH scale showing common substances.

21.3 ACIDS, BASES, AND PH

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pH in the environment The best pH for The pH of soil directly affects nutrient availability for plants. Most plants, plants such as vegetables, grasses, and most shrubs, prefer a slightly acidic soil with

a pH between 6.5 and 7.0. Azaleas, blueberries, and conifers grow best in more acidic soils with a pH of 4.5 to 5.5 (Figure 21.26).

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Effects of pH too In highly acid soils (pH below 4.5), too much aluminum, manganese, and high or low other elements might leach out of soil minerals and reach concentrations that

are toxic to plants. Also, at these low pH values, calcium, phosphorus, and magnesium are less available to plant roots. At more basic pH values (above 6.5), iron and manganese become less available. pH and fish

The pH of water directly affects aquatic life. Most freshwater lakes, streams, and ponds have a natural pH in the range of 6 to 8. Most freshwater fish can tolerate a pH between 5 and 9, although some negative effects appear below a pH of 6. Trout (such as the California Golden shown above) are among the most pH-tolerant fish and can live in water with a pH from 4 to 9.5.

pH and amphibians

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Frogs and other amphibians are even more sensitive to pH than fish. This California tree frog and other frogs prefer a pH close to neutral and don’t survive below a pH of 5. Frog eggs develop and hatch in water with no protection from environmental factors. Research shows that pH values below 6 have a negative effect on frog hatching rates.

Figure 21.26: Blueberries grow best in soils with a pH between 4.5 and 5.5.

Acid Rain Many environmental scientists are concerned about acid rain. Do research to answer the following questions. 1. What kinds of acids are in acid rain? 2. What is the typical pH of acid rain? 3. What is the cause of acid rain? 4. What are some environmental impacts of acid rain? 5. What can be done to reduce acid rain?

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Acids and bases in your body Acids and bases Many reactions, such as the ones that occur in your body, work best at play a role in specific pH values. For example, acids and bases are very important in the digestion reactions involved in digesting food. The stomach secretes hydrochloric acid

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(HCl), a strong acid (pH 1.4). The level of acidity in your stomach is necessary to break down the protein molecules in food so they can be absorbed. A mucous lining in the stomach protects it from the acid it produces (Figure 21.27). Ulcers and Deep-fried foods, stress, or poor diet can cause the stomach to produce too heartburn much acid, or allow stomach acid to escape from the stomach. An ulcer might

occur when the mucous lining of the stomach is damaged. Stomach acid can then attack the more sensitive tissues of the stomach itself. Infections by the bacteria Helicobacter pylori can also damage the mucous lining of the stomach, leading to ulcers. The uncomfortable condition called heartburn is caused by excessive stomach acid backing up into the esophagus. The esophagus is the tube that carries food from your mouth to your stomach. The esophagus lacks the mucous lining of the stomach and is sensitive to acid.

Figure 21.27: The stomach secretes a strong acid (HCl) to aid with food digestion. A mucous lining protects the stomach tissue from the acid.

pH and your Under normal conditions, the pH of your blood is within the range of 7.3–7.5, blood close to neutral but slightly basic. Blood is a watery solution that contains

many solutes, including the dissolved gases carbon dioxide (CO2) and oxygen (O2). Dissolved CO2 in blood produces a weak acid. The higher the concentration of dissolved CO2, the more acidic your blood becomes. Blood pH is controlled through breathing

Your body regulates the dissolved CO2 level by breathing. For example, if you hold your breath, more carbon dioxide enters your blood and the pH falls as your blood becomes more acidic. If you hyperventilate (breathe more quickly than usual), less carbon dioxide enters your blood and the opposite happens—blood pH starts to rise, becoming more basic. Your breathing rate regulates blood pH through these chemical reactions (Figure 21.28).

Figure 21.28: Under normal

conditions, your blood pH ranges between 7.3 and 7.5. Holding your breath causes blood pH to drop. High blood pH can be caused by hyperventilating.

21.3 ACIDS, BASES, AND PH

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Neutralization reactions Mixing acid and When acid and base solutions are mixed in the right proportions, their base solutions characteristic properties disappear. The positive ions from the base combine

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with the negative ions from the acid and a new ionic compound forms. Water is also a product of this type of reaction, called neutralization. The graphic below shows what happens when the base, sodium bicarbonate (baking soda), is mixed with hydrochloric acid.

neutralization - the reaction of an acid and a base to produce a salt and water.

Test Your Soil

Neutralization of HCl by NaHCO3

Na

+

–

C

O

H

+

H

Most garden centers carry soil test kits. These kits have pH test papers inside and are designed to help gardeners

+

–

Cl

NaHCO3

HCl

Sodium bicarbonate

Hydrochloric acid

Na

+

Cl–

+

H

C

+

NaCl

H2O

CO2

Salt

Water

Carbon dioxide

Neutralization in Neutralization goes on in your body every day. As food and digestive fluids your body leave the stomach where the pH is very low, the pancreas and liver produce

bicarbonate (a base) to neutralize the stomach acid. Antacids, many of which are composed of sodium bicarbonate, have the same effect. The graphic above also illustrates what happens in your digestive system when you take an antacid. The antacid mixes with excess stomach acid to produce salt, water, and carbon dioxide. Adjusting soil Neutralization reactions are important in gardening and farming. For pH example, having soil that is too acidic (pH less than 5.5) is a common

measure soil pH. Get a soil test kit and test samples of soil from around your home or school. Repeat the test, taking new soil samples after a rainfall to see if the pH changes. Answer the following questions. 1. What kinds of plants thrive in the pH of the soil samples you tested? 2. What kinds of treatments are available at your local garden center for changing soil pH?

problem in the U.S. Grass does not grow well in acidic soil. For this reason, many people add lime to their yard. A common form of lime is ground-up calcium carbonate (CaCO3) made from natural crushed limestone. Lime is a weak base and undergoes a neutralization reaction with acids in the soil to raise the pH.

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Section 21.3 Review 1. What is a hydronium ion? 2. In this section, you learned about the properties of acids and bases. Make a table that organizes this information.

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3. Both strong acids and strong bases are corrosive. Come up with a hypothesis for why this is so. 4. Answer the following questions about water. a. Why is water considered to be a weak acid or a weak base? b. What is the pH of pure water? c. What does the double arrow mean in this reaction? 5. Nadine tests an unknown solution and discovers that it turns blue litmus paper red, and it has a pH of 3.0. Which of the following could be the unknown solution? Explain your choice. a. a solution of sodium hydroxide b. vinegar c. ammonia d. soap e. pure water 6. Is the solution in question 5 acidic or basic? 7. Is tomato juice acidic or basic? Justify your answer.

Current Solutions Svante August Arrhenius of Sweden was noted for his mathematical skills at an early age. In 1884, he submitted his dissertation, which included the idea that ions in solution conduct electrical current (rather than pure water or salt). Although his professors rejected this idea and barely passed him, other key scientists were supportive. In fact, Arrhenius’s work was so important that he was awarded the Nobel Prize in 1903! Chemicals that dissociate into ions in water are called electrolytes. Solutions with electrolytes can conduct current. All acids and bases and some salts are electrolytes. Find out more about how Arrhenius contributed to our understanding of acids, bases, and electrolytes.

8. Give two examples of a pH indicator. 9. Plants and animals live in environments that have conditions for which they are adapted. Is pH an important environmental factor for plants and animals? Why or why not? 10. Describe in your own words how the amount of carbon dioxide dissolved in your blood affects your blood pH. 11. What are the main reactants and products in a neutralization reaction? 12. Neutralization is an important part of digestion. Why? 21.3 ACIDS, BASES, AND PH

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Chapter 21 Assessment Vocabulary

12. When the dissolving rate equals the rate at which molecules come out of solution, the solution is in ____.

Select the correct term to complete the sentences.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

13. A(n) ____ solution has a concentration greater than the maximum solubility.

pH scale

acid

nonpolar molecule

solvent

pH

solute

equilibrium

dissolve

supersaturated

colloid

solubility

insoluble

base

Tyndall effect

hydrogen bond

15. Chalk is ____ in water.

alloy

suspension

saturated

polar molecule

solution

unsaturated

Section 21.3

Section 21.1

14. If you make a solution using the ____ value for a substance, you will make a(n) ____ solution.

16. A substance that produces hydronium ions (H3O+) in solution is called a(n) ____. 17. A substance that produces hydroxide ions (OH–) in solution is called a(n) ____.

1.

A oil molecule is an example of a(n) ____.

2.

An attractive force between a hydrogen on one molecule and an atom on another molecule is called a(n) ____.

18. The neutral value on the ____ is 7.

A water molecule is an example of a(n) ____.

19. The ____ of acids is less than 7.

3.

Section 21.2

4.

A solution with less than the amount of solute that can dissolve for a certain set of conditions is ____.

Concepts Section 21.1

5.

Muddy water is an example of a(n) ____.

1.

6.

You can see the ____ if you shine a light through a(n) ____ but not if you shine a light through a solution.

Describe two main differences between a water molecule (H2O) and a methane molecule (CH4).

2.

List two properties of water that are related to hydrogen bonding.

7.

A(n) ____ dissolves particles in a solution.

3.

8.

A substance dissolved in a solution is called the ____.

How is hydrogen bonding important in how water moves through a plant from its roots to its leaves?

9.

A mixture of two or more substances that is uniform at the molecular level is called a(n) ____.

4.

If you pour oil and vinegar into a jar, the two liquids stay separated. Explain why.

10. A solution of two or more metals is known as a(n) ____. 11. A solvent is used to ____ a solute to make a solution.

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Section 21.2

5.

Which of these substances (below) is a colloid and which is a suspension?

CHAPTER 21

16. How can ammonia (NH3) be a base if it doesn’t contain any hydroxide ions? 17. Describe what should happen and why when you mix vinegar and baking soda.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

18. If you hold your breath for a while, how is your blood pH affected? Why?

Problems Section 21.1

6.

Water is a solvent in which of the following solutions: air, liquid sterling silver, or saline (salt) solution?

1.

How much energy in joules would you need to raise the temperature of one kilogram of water by 2°C?

7.

What would happen to the solubility of potassium chloride in water as the water temperature increased from 25°C to 75°C? Why?

2.

Why is the HCl molecule shown below a polar molecule?

8.

What are two ways to increase the dissolving rate of sugar in water?

9.

What happens to a supersaturated solution when more solute is added? Use the word equilibrium in your answer.

Section 21.2

10. How might the fish in a lake be affected if large amounts of hot water from a power plant were released into the lake?

3.

Determine how much of the following materials will dissolve in 300 mL of water at 20°C: table salt, potassium nitrate, and chalk.

11. Why is a can of room-temperature soda more likely to fizz and spill over than a can that has been refrigerated?

4.

You add 20 grams of baking soda (NaHCO3) to 100 mL of water at 20°C.

12. In your own words, describe the solubility rule for hydroxide (OH–). Section 21.3

13. What determines the strength of an acid? What determines the strength of a base? 14. Does the pH of a solution increase or decrease when hydroxide ions (OH–) are added to the solution?

a. b. c.

Approximately how much of the baking soda will dissolve in the water? What happens to the rest of the baking soda? How could you increase the amount of baking soda that will dissolve in 100 mL of water?

15. If you add water to a strong acid, how will the pH of the diluted acid compare to the pH of the original acid?

CHAPTER 21 ASSESSMENT

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WATER AND SOLUTIONS

Use the following graph to answer the questions below.

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Solubility (g per 100 g of water)

Solubility vs. temperature for a variety of salts

Applying Your Knowledge Section 21.1

1.

90 80 70 60 50 40 30 20 10 0

Na2SO4 NaCl Ba(NO3)2 Ce2(SO4)3 • 9H2O Na2HAsO4 0

20

40

60

80

Section 21.2

2.

c. 6.

What is the solubility of Na2SO4 at 80°C? Would a solution of Ba(NO3)2 be saturated with 20 grams dissolved in 100 grams of water at 80°C? How does solubility vary with temperature for Na2HAsO4? For Ce2(SO4)3 • 9H2O?

Where on the graph shown in Figure 21.15 would you find saturated solution conditions?

Section 21.3

7.

8.

b.

3.

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Larry opens a new bottle of soda. He quickly stretches a balloon over the opening of the bottle. As he gently shakes the bottle, the balloon expands! Explain what is happening to cause the balloon to expand. Use at least three vocabulary words from this section.

4.

Most of the acid-base chemistry that occurs inside of your body happens through reactions involving weak acids and bases. For example, the coiling of a DNA molecule into a double helix is due to hydrogen bonding between weak bases. Find out more about the acid and base chemistry in your body. Possible topics include DNA, blood chemistry, digestion, and how your kidneys work.

5.

Luke and Shawn want to plant a vegetable garden in their yard. A soil testing kit measures the soil pH at 5.0, but the lettuce they want to plant in their garden does best at a pH of 6.5. Should they add an acid or a base to the soil to make it the optimum pH for growing lettuce?

Which solution is a base? Which solution is an acid? What would happen if you combined both solutions?

Predict the products of a chemical reaction between hydrochloric acid (HCl) and sodium hydroxide (NaOH). You might want to draw a diagram that illustrates what happens.

In addition to NaCl, what other solutes are dissolved in ocean water? Aside from it tasting bad, why is it not a good idea to drink ocean water? Answer this question in relation to your own body, which is mostly a watery solution.

Section 21.3

Solution A has a pH of 3 and solution B has a pH of 10. a. b. c.

Answer the following questions about ocean water. a.

100

Temperature (ºC)

a. b.

Explain why ice forms on the top of ponds and lakes, not on the bottom. How does this property of water help support life in lakes and ponds?

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CHAPTER 22

Water Systems FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

In addition to its ability to sustain life, Earth is unique because its temperature allows for water to exist in all three phases of matter (liquid, solid, and gas). The amount of water on Earth is mind-boggling and is about the same now as it was during the age of the dinosaurs, 65 to 220 million years ago. With about threequarters of its surface underwater, Earth is a blue, watery planet. Surprisingly, only a small amount of this water is available for household, agricultural, and industrial use. Where’s all the rest? It’s in the oceans or frozen in glaciers. You might also wonder why we haven’t run out of water since Earth has been around for such a long time. For millions of years, rain has fallen on mountaintops and flowed to rivers and oceans. Where does this rain come from? Does rainwater end up in rivers and oceans and stay there? What do you think? In this chapter, these questions and more will be addressed. You will learn how water moves naturally around Earth so that it is available year after year. You will also learn about Earth’s oceans and how they contribute to making Earth such a nice place to live.

4 Where is most of Earth’s water found? 4 How is a drying mud puddle part of the water cycle?

4 How do the oceans provide climate control?

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22.1 Water on Earth’s Surface About 70 percent of Earth’s surface is covered with water, and the amount of water on Earth has a volume of about 1.386 billion cubic kilometers. This huge amount of water is found in many places: in the atmosphere as a gas and in clouds as water droplets; in oceans, rivers, lakes, and under the ground; and in glaciers as ice.

hydrosphere - an Earth system that includes all the water on the planet.

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The hydrosphere What is the All the water on Earth is part of a large system called the hydrosphere hydrosphere? (Figure 22.1). This water is constantly on the move within the water cycle, a

set of processes driven by solar energy that keeps water moving from place to place. You will learn about the water cycle in the next section. Water phases on On Earth, water is able to exist in all three phases of matter—as a solid (ice), Earth as a liquid, and as a gas (water vapor). Recall that matter is anything that has

mass and takes up space, and as you just read in the introduction to this section, water takes up a lot of space on Earth. Most of this water is liquid found in oceans and seas. The next most common phase of water is ice. If all the ice on Earth melted, the level of the oceans would rise about 70 meters! Water in the Gaseous water is located in the atmosphere, the layer of gases that surrounds atmosphere Earth. Moisture in the atmosphere replenishes our water supplies when it

becomes rain or snow and returns to Earth.

Figure 22.1: Earth’s hydrosphere

Gas (water vapor) Solid (icecaps, glaciers)

includes all the water on the planet. The clouds in the picture are also part of the hydrosphere. Can you find the hurricane? It’s part of the hydrosphere, too.

Liquid (oceans, lakes, rivers, groundwater)

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The distribution of water on Earth Earth’s water

Salt water and a About 97% of Earth’s water is salt water found in oceans. Approximately 2% little fresh water of Earth’s water is frozen at the North and South Poles and on mountaintops,

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

leaving approximately 1% for humans, plants, and animals to consume. If all the water on Earth could fit into a one-liter bottle, the amount of fresh water available for human consumption would be about 10 milliliters (Figure 22.2).

All Earth’s water

1 LITER

Fresh water available for human consumption

Approximately 1% of Earth’s water is available for human consumption. An important Water is an important resource. Living things rely on water for growth and resource nourishment. Water is also used in agriculture to grow food and in industry

for many processes. Fortunately, the water cycle allows our limited supply of fresh water to be recycled and reused. The table below illustrates how water is distributed on Earth.

~ 10 mL Figure 22.2: If all the water on

Earth could fit into a one-liter container, the amount of fresh water available for human consumption would be equal to about 10 milliliters.

Distribution of water on Earth All water Fresh water Saline (oceans) 97%

Fresh water 3%

Other 0.9% Ice sheets and glaciers 68.7% Groundwater 30.1%

Surface water 0.3%

How Big Is a Cubic Kilometer?

Surface water

Rivers 2%

Swamps 11%

Lakes 87%

One cubic kilometer is 1,000 m × 1,000 m × 1,000 m or 1,000,000,000 m3 (one billion cubic meters)! If the volume of a swimming pool is 1,000 m3, how many swimming pools fit inside one cubic kilometer? To find out how many swimming pools equal all the world’s rivers, you would have to multiply the number you just got by 2,120! The volume of Earth’s rivers is 2,120 cubic kilometers.

Water available for human consumption

22.1 WATER ON EARTH’S SURFACE

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Places where water is found Where water After a rainstorm, water collects in low areas on the ground. These areas collects might be as small as mud puddles or as large as oceans, lakes, and rivers.

Earth’s water can also be found underground and in cold regions where water is frozen in glaciers and in the ground as permafrost.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

Surface water Surface water on Earth refers to water that collects on the ground. This water includes oceans, lakes, rivers, streams, and reservoirs. A reservoir is

a protected artificial or natural lake that is used to store water. Frozen water Frozen water is found at the poles and on mountaintops as glaciers and ice sheets. A glacier is a huge mass of ice that forms on land when snow and ice

accumulate faster than they melt (Figure 22.3). Sixty-seven percent of Earth’s fresh water is in the form of ice sheets and glaciers. Groundwater Groundwater is fresh water that infiltrates (absorbs into) the soil and

collects underground. This water represents 30.1% of all fresh water and is our most abundant, available water supply. Interestingly, although rainwater moves directly into streams and rivers through overland flow, most of the water in streams and rivers comes from groundwater supplies.

surface water - the water found on Earth’s surface in places like oceans, lakes, rivers, and reservoirs. reservoir - a protected artificial or natural lake that is used to store water. glacier - a huge mass of ice that forms on land when snow and ice accumulate faster than they melt. groundwater - water that collects underground.

water table - the upper level of water underground; below the water table, all spaces are filled with groundwater.

The water table Groundwater supplies are replenished as some of the water on Earth’s surface moves down through the soil to the water table. The water table is

the upper level of underground water. Below this level, the spaces between particles of soil and rock are saturated (filled) with groundwater. The depth to the water table changes depending on the season and can be gauged by checking the water level of a well.

Figure 22.3: A glacier.

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Water as a resource Water for life The temperature range on Earth’s surface is just right for water to exist in

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three phases: liquid, solid, and gas (Figure 22.4). Most water on Earth is in the liquid phase. Liquid water is extremely important for living things. For example, a human body is 60 to 75 percent water (Figure 22.5). You need water to keep your blood, brain, and lungs working properly. Water dissolves One of the reasons why water is so useful is that it can dissolve many things. many things When you eat food, water in your body dissolves nutrients so they can be

carried through your bloodstream. Oxygen is another important substance that is dissolved in your blood. Oxygen dissolved in river and lake water is available for fish and other organisms to breathe. Water also dissolves some of the minerals that make up rocks. Over long periods of time, water dissolves and wears down rocks and mountains through processes called weathering and erosion.

Sun

CHAPTER 22

Surface temperature range (ºC)

-170 to 390

Too cold and too hot

450 to 480

Too hot

-88 to 56

Just right for liquid water!

-89 to 20

Too cold

Mercury

Venus

Earth

Mars Planet sizes and distances not to scale.

Figure 22.4: Mercury, Venus, and

Mars are too hot or too cold for water to exist in all three phases. But Earth is just right!

Water shapes Water is a powerful agent in shaping land. What experience do you have that the land verifies this statement? Think about the flow of ocean water over a sand castle

at the beach. This water will cause the castle to seemingly disappear as the water dismantles the pile of sand. On a rainy day, you have seen how rainwater forms rivulets that wash away soil. This action mimics the way huge rivers like the Colorado or Amazon shape the land. And the immense weight of glacial ice forces changes within the glacier that cause it to flow and scrape the land. In Chapter 23, you will learn more about how water and other agents shape the land through the processes of weathering and erosion.

Figure 22.5: The human body is 60% to 75% water.

22.1 WATER ON EARTH’S SURFACE

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Section 22.1 Review 1. Earth is often called the “water planet.” Why?

Water in the Universe

2. How much of Earth’s surface is covered by water? How much is covered by land?

Earth has an abundance of water compared to other known places in the universe.

3. The hydrosphere contains all the water on Earth. Name four locations where water is located.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

4. How is Earth’s atmosphere part of the hydrosphere? 5. In what phase of matter is most water found on Earth—gas, solid, or liquid? 6. The second most abundant form of water on Earth is ice. Where is most of this frozen water located?

Find out why. Once you’ve done your research, write a short paragraph that describes your findings. Where else does water exist?

7. What would happen if all of the frozen water on Earth melted? How would this event affect people living in coastal areas? 8. Compare and contrast surface water and groundwater. 9. What is the water table? 10. In which place—desert or rain forest—would the water table be further underground? Explain your answer. 11. In which season might the water table be further underground—during a dry summer or during a rainy spring? 12. Give an example of how water shapes Earth’s surface. 13. Write a short paragraph describing a personal observation of how water shapes Earth’s surface. 14. Write a short paragraph that explains why water is so important for human beings. 15. Like people, animals depend on water. Identify the water environment in which each animal in Figure 22.6 lives. You might need to do research to find the answers. 16. Because water is moved about Earth via the water cycle, it can be considered an unlimited resource. Do you agree with this statement? How might this resource be limited by human activity?

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Figure 22.6: Question 15.

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22.2 The Water Cycle As with any system, the water cycle requires a source of energy to keep it going. Can you guess the source of energy for the water cycle? It’s the most powerful energy source around—the Sun. Solar energy keeps water moving through the hydrosphere by providing heat energy and by driving weather systems.

water cycle - a set of processes energized by the Sun that keeps water moving from place to place on Earth, also called the hydrologic cycle.

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Recycling water Sharing water For millions of years, only a small percentage of fresh water has been with the available to meet the basic needs of life on Earth. Remember that our total dinosaurs water supply today is the same as when the dinosaurs were around. Therefore,

the water you drink was probably used by other organisms during the past millions of years. The water cycle, which is also known as the hydrologic cycle, is a set of processes that keeps our water continuously recycled and naturally filtered. The Sun drives The Sun is the ultimate source of energy driving the water cycle. The Sun’s the water cycle energy heats Earth’s water and causes it to change state from a liquid to a gas.

The Sun also affects our atmosphere and drives our weather systems. Wind and weather are key elements that aid in the movement of water from place to place. Finally, gravity is an additional natural force that keeps water moving (Figure 22.7). Of course, people also play a role in transporting water on Earth. Think for a minute—how are you part of the water cycle? More about Weather patterns, especially those that include wind and storms, provide weather and forces that cause water to be blown or moved from one place to another. For gravity example, wind-blown clouds move water vapor from one place to another.

Gravity plays a role in the water cycle because water has mass. As you have learned, gravitational force acts on mass. Gravity is responsible for how precipitation (rain or snow) moves from the sky to the ground. For example, when raindrops get big enough (i.e., have enough mass), gravity causes them to fall to the ground. Gravity also causes water to run over land and down rivers to the sea (Figure 22.7). Finally, gravity is the primary force that moves water from Earth’s surface into the ground to become groundwater.

Figure 22.7: The Sun, wind,

weather, and gravity drive the water cycle.

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Water cycle processes Four main As with the rock cycle, which you learned about in Chapter 18, the water processes cycle does not have a beginning or an ending. There are many pathways

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within the cycle, and water is moving along these pathways at all times. The main processes of the water cycle are evaporation, transpiration, condensation, and precipitation. Evaporation Evaporation occurs when liquid water has enough energy to leave the liquid phase and become a gas called water vapor. The source of this

energy is heat from the Sun. The Sun warms the surface of Earth, including mud puddles, lakes, rivers, and oceans. As a result, water obtains enough energy to evaporate and become water vapor in the atmosphere. It takes about 539 calories of energy to evaporate 1 gram of liquid water. Transpiration Transpiration is the process through which plants lose water through tiny

pores in their leaves. The pores open to gain carbon dioxide for photosynthesis. Once the pores are open, the plants release water vapor and oxygen. The water vapor contributes to the water cycle. All animals benefit from the released oxygen. It’s what we breathe.

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evaporation - the process by which a substance in its liquid phase gains energy and enters its gaseous phase.

water vapor - water in gaseous form.

transpiration - the process by which plants lose water through tiny pores in their leaves.

Reviewing the Water Molecule Water is often called “H-two-O” and written as H2O. These ways of describing water refer to the composition of a water molecule. A water molecule includes two hydrogen atoms bonded to one oxygen atom. In this text, we represent the water molecule like this:

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Condensation Condensation occurs when water in its gaseous phase loses energy. For and example, since it takes 539 calories for 1 gram of water to evaporate, precipitation 539 calories will be released when 1 gram of water vapor condenses. This is

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why air temperatures are warmer when condensation (followed by precipitation) occurs. Precipitation is any form of condensed water vapor in the atmosphere falling back to Earth. Precipitation includes rain, snow, sleet, and hail. Condensation leads to precipitation when cooled water molecules slow down so much that they group and form droplets of liquid. High in the atmosphere, where most of the cooling takes place, droplets fall to Earth as rain when they become heavy enough. These droplets might also become part of a cloud, fog, or dew on a surface. Following the The diagram below illustrates the water cycle. Trace the path of water from water cycle the ocean to groundwater and back to the ocean. What other paths do you see

in the water cycle?

The water cycle Condensation Water vapor transport by wind

SUN

Water droplets

CHAPTER 22

condensation - the process by which a substance in its gaseous phase loses energy and enters its liquid phase.

precipitation - condensed water vapor in the atmosphere that falls back to Earth in the form of rain, snow, sleet, or hail.

A Water Cycle Tale Imagine you are a snowflake in an icecap on the top of a mountain. Describe what happens to you as the seasons change, starting with winter. Describe your path through the water cycle. Also, describe any points along your journey where you might interact with plants and human beings!

Precipitation Evaporation

Evaporation

Transpiration

Infiltration

Land and trees River Lake

Percolation

Water table level Ocean

Groundwater flow

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How water moves in the water cycle Surface runoff Precipitation that reaches Earth’s surface often flows over the land. This water, called surface runoff, eventually reaches lakes, rivers, and oceans.

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Surface runoff dissolves minerals from rocks and erodes (moves) nutrientrich soil as it flows. Many of the minerals and nutrients in both fresh water and salt water come from surface runoff (Figure 22.8). Percolation Water that flows over the land can infiltrate the soil and then percolate to the water table to become groundwater. Percolation is the process of water

seeping into the ground through soil and rock. Percolation happens when a substance is porous (has many tiny holes or “pores”). Most soils are porous.

surface runoff - water that flows over land until it reaches lakes, rivers, and oceans.

percolation - the process of water seeping into the ground through soil and rock.

aquifer - an underground area of sediment and rocks in which groundwater collects.

Aquifers An aquifer is an underground area of sediment and rocks where

groundwater collects. When groundwater is removed from an aquifer for human consumption, it can take thousands of years to replenish the supply. For this reason, groundwater is considered to be a nonrenewable resource in some areas. Once in an aquifer, groundwater can continue to flow through sediment and might eventually enter rivers, lakes, or oceans. The importance Aquifers are important water sources. For example, the water obtained from of aquifers the Ogallala Aquifer in the midwestern United States has made agriculture

profitable in this dry region. The Ogallala is one of the largest aquifers in the world. Its underground area (450,000 km2) is in parts of South Dakota, Nebraska, Wyoming, Colorado, Kansas, Oklahoma, New Mexico, and Texas. The Ogallala Aquifer is in danger of becoming depleted because there is a high demand for its water. Additionally, the water is being used faster than it can be replenished by the water cycle. How long does Within the hydrosphere, water is held in three main places: in the water stay in atmosphere, on Earth’s surface, and underground. The length of time that one place? water stays in one location within the cycle before it is renewed is called

residence time. Scientists estimate the residence time for water in the atmosphere is nine days. For comparison, residence time is 3,200 years for ocean water, and 100 to 10,000 years for groundwater depending on its depth.

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Figure 22.8: Surface runoff reaches

surface water locations or percolates into an aquifer. Groundwater that is not collected from the aquifer by cities flows to oceans.

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Watersheds What is a A watershed (also known as a drainage basin) is an area of land that catches watershed? precipitation and surface runoff. The boundaries of a watershed are often

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steep mountain ridges. Acting like a funnel, a watershed collects water flowing downhill into a body of water such as a river. Eventually, some of the collected water reaches an ocean (Figure 22.9). The largest watershed in United States and the third largest in the world supplies the Mississippi River, collecting water from 13 U.S. states and two Canadian provinces.

watershed - an area of land that catches precipitation and surface runoff and collects it in a body of water such as a river. Ocean

Watersheds The water in a watershed is directly related to the groundwater. Water collects

in a place such as a river, but some of the surface runoff becomes groundwater. The water provided to communities in the United States originates in a watershed that can be local or from another region.

Atlantic

An important Watersheds provide more than drinking water for communities. A watershed natural resource is an important natural resource because it also provides habitats for plants

and animals, areas of natural beauty, and bodies of water for recreation. Therefore, as land is developed in a region, communities must take into consideration the protection of watersheds.

Pacific

Watershed Glaciers

Precipitation

Indian

Arctic

Southern

Some sources of water St. Lawrence River, the Great Lakes, eastern North America, South America east of the Andes, northern Europe, western SubSaharan Africa, Caribbean Sea basin, Mediterranean Sea basin China, southeastern Russia, Japan, Korea, South America west of the Andes, Pacific Islands, and western North America Eastern coast of Africa, India, Myanmar, Australia, Indonesia, southeast Asia Most of Russia, western and northern Canada, and Alaska Antarctica

Figure 22.9: Some sources of water Parts of the watershed

for the world’s oceans. See if you can find these places on a globe!

Water Watershed divide (ridge)

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The water cycle and volcanic activity Volcanoes You might be surprised to learn that volcanoes are part of Earth’s water

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cycle. As you learned in Chapter 20, subducting oceanic plates carry water into the upper mantle. This water causes the mantle rock to melt, forming magma. The magma slowly makes its way toward the surface, taking the water with it. When a volcano erupts, it also releases large amounts of water vapor. The water vapor eventually condenses and falls as rain or another form of precipitation. In this way, volcanic water rejoins the water cycle.

Hot springs A hot spring results when water percolates into the ground and encounters

magma-heated rock below Earth’s surface (Figure 22.10). The heated water bubbles up at the surface in a steady flow. If the water flow is small or the heat source is especially hot, the water could arrive at the surface mixed with steam. In this case, the hot spring will sputter and spew boiling water.

Figure 22.10: A diagram of a geyser and a hot spring.

Geysers Old Faithful in Yellowstone National Park is a geyser, a special and very rare

type of hot spring (Figure 22.11). The difference is in the shape of the underground plumbing. There are several forms of geyser plumbing, but they all cause a large volume of water to act like a temporary plug over deeper, much hotter water. The trapped hot water is hotter than its boiling point, but the pressure of the plug keeps it from boiling. Eventually the hot water pressure overwhelms the water plug and water begins to move up the geyser shaft. This causes the pressure inside the geyser shaft to drop and the superheated water boils explosively. The boiling water and steam rocket out of the geyser vent in a spectacular display! Water that evaporates from geysers or hot springs becomes part of the water cycle.

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Figure 22.11: Old Faithful in

Yellowstone National Park is a geyser.

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Section 22.2 Review 1. List the sources of energy and forces that drive the water cycle. 2. Give an example of how people participate in the water cycle.

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3. All the water on Earth is recycled. What does that mean about the water you drank today? Give an example of where your drinking water could have been in the recent past. 4. What has to happen for liquid water to become water vapor? 5. Plants need water, but they lose water by opening pores in their leaves. Why do they open their pores? 6. Which process of the water cycle is similar to water droplets forming on a bathroom mirror when you take a shower? Pick the correct answer and explain your choice. a. condensation c. evaporation

Where Does Your Drinking Water Come From? Research the answers to these questions for your town or area. What is the name of the watershed or aquifer that your town uses for its drinking water? Is there a local organization that monitors the water quality of your watershed? What else do you know about your source of drinking water?

b. precipitation d. transpiration

7. Which of these items is porous under normal conditions? a. a cotton shirt c. a raincoat

b. a piece of steel d. a plastic cup

8. In which of these situations is percolation occurring? a. A mud puddle dries. c. Water goes through coffee grounds to make coffee.

b. You pour a glass of orange juice. d. Snow melts outside on a warm, sunny day.

9. What is the difference between an aquifer and a watershed? 10. The time to replenish groundwater removed from an aquifer may be thousands of years. Why might it take so long? 11. How are volcanoes involved in the water cycle?

STUDY SKILLS Learning New Words You can learn and remember the definitions of new words by using them in a sentence. For each of the vocabulary words in this section, write a sentence that uses the word correctly. You might want to make a drawing that helps you remember the new word. For example, make a drawing of the water cycle and fill in the terms you know!

12. Describe the roles of magma-heated rock, hot springs, and geysers in the water cycle. 22.2 THE WATER CYCLE

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22.3 Oceans Most of Earth’s water is contained in five oceans. The oceans cover most of Earth’s surface and are important to life on the planet. Although humans and all living things depend on water for survival, ocean water is not drinkable because it is too salty. In this section, you will learn why the oceans are salty. You will also learn about ocean currents.

salinity - a term that describes the amount of dissolved salts in water.

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Salt water Salt in ocean Ocean water is about 35 parts per thousand (ppt) salt. By comparison, fresh water water bodies, such as rivers, are 5 ppt salt or less. The word salinity is used

to describe the amount of dissolved salts. Most of the dissolved salt in ocean water is sodium chloride. You use sodium chloride (NaCl), or table salt, on your food. Sodium chloride is found in nature as the mineral halite (Figure 22.12). In some places like the Dead Sea, special ponds called salt evaporation ponds are set up to harvest salt from the ocean (Figure 22.13).

Figure 22.12: Sodium chloride, or table salt, comes from the mineral halite.

Sources of salt Dissolved salts in the oceans come from minerals in the ocean floor, from

gases released by volcanoes, and from rivers that carry dissolved minerals to the oceans. These dissolved minerals come from chemical weathering of rocks on the continents. For example, feldspars, one of the most abundant minerals in Earth’s crust, weather and release calcium, potassium, and sodium, which are carried in solution by surface runoff to oceans.

Figure 22.13: Salt evaporation

ponds in the Dead Sea are used to harvest salt for human consumption.

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Earth’s oceans Five oceans Astronauts are amazed when they see our blue planet from space. Earth is

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mostly bright blue because of its vast oceans. Four of Earth’s oceans are easy to identify because of the shape of the surrounding continents. These four oceans are the Atlantic, Pacific, Indian, and Arctic oceans. The fifth ocean, the Southern Ocean (also called the Antarctic Ocean), is composed of the waters surrounding Antarctica.

The importance Oceans are an important resource for many reasons. As a source of water for of Earth’s the water cycle, oceans help maintain Earth’s heat balance. Because water has oceans a high specific heat, the oceans do not heat up or cool down quickly. As a

result, our climate does not become too hot or too cold. You will learn more about this ocean feature on the next page. Ocean currents and waves spread energy and heat from the hot equator to the colder poles. Additionally, these currents help propel ships as they navigate the globe. Inhabitants in our oceans also make oceans vital resources. For example, microscopic photosynthetic organisms called phytoplankton live in the oceans and produce much of the oxygen in Earth’s atmosphere (Figure 22.14).

Figure 22.14: Phytoplankton

produce much of the oxygen in the atmosphere through photosynthesis. A phytoplankton “bloom” is a highconcentration of organisms caused by an increase in reproduction.

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Oceans and Earth’s climate

High specific heat

Storing heat in Earth’s oceans are warmed by the Sun during daylight hours, and that heat the oceans energy is stored. The oceans are able to store heat energy for two reasons.

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First, water has a high specific heat, so it takes a long time for it to cool down once it is warm. Second, solar radiation penetrates the water surface and allows the Sun’s heat energy to be stored many meters deep (Figure 22.15). Because of this heat storage, the water on Earth prevents the planet from getting too hot or too cold.

Warms slowly Mixing

Where do you The climates on coastlines are milder than they are inland (refer to graphic find milder below). This is because ocean-warmed wind and air masses move over the climates? oceans toward the land. In Europe, the prevailing westerlies (winds that blow

from the west) blow over the ocean toward the coastline (Figure 22.16). As a result, Europe tends to have mild winters. The northeastern United States has more severe winters because the prevailing westerlies blow away from its coast. But even so, the nearness of water makes the winters milder there than in places like the Great Plains of the United States. This area can be extremely cold because it is far from the ocean.

Average low temperatures in January

Heat Many meters

Figure 22.15: Two reasons why the oceans store heat energy.

Prevailing westerlies

London 1 ºC

Seattle 2 ºC

60º America

Great

Boston -6 ºC

Plains

San Francisco 6 ºC

Lincoln -11 ºC

Map not to scale

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L

North America

Washington D.C. -4 ºC

Europe

30º

H

Myrtle Beach 1 ºC Miami 17 ºC

Cools slowly

Lisbon 8 ºC

Figure 22.16: The prevailing

westerly winds between 30° and 60° N latitude.

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Surface currents and gyres Wind drives The Sun’s uneven heating of Earth and the Coriolis effect cause permanent surface ocean global wind patterns. You learned about these patterns in Chapter 11. As they currents blow across the ocean, these winds push water in the direction they are moving. This creates surface ocean currents that can travel for long

gyres - large rotating ocean current systems.

Surface currents Surface ocean currents move enormous quantities of water. One well-known transport heat current is the Gulf Stream. It transports about 80 million cubic meters of energy water per second as it passes Cape Hatteras, North Carolina (Figure 22.17).

Because the Sun heats surface water more strongly near the equator, these currents also transport heat energy toward the poles. You read on the previous page that Europe has mild winters due to the prevailing westerlies. Another reason for these milder winters is the heat energy transported by the Gulf Stream toward the northwest coast of Europe. Gyres The Coriolis effect and the shape of the coastlines cause surface ocean currents to form large rotating systems called gyres. Gyres north of the

equator, such as the North Atlantic gyre, turn in a clockwise direction. The North Atlantic gyre is composed of several surface ocean currents. The calm area within this gyre is called the Sargasso Sea. Gyres south of the equator turn in a counterclockwise direction. North Atlantic gyre North Atlantic Drift

S lf

tream

Canary C u r re n t

Gu

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distances. Small “pushes” to the surface ocean currents also come from the tides as they move in and out along coastlines.

surface ocean currents - winddriven currents that move at the ocean surface, often for long distances.

Saragasso Sea No

r

th

Equ

a t o r i a l C u r re

Figure 22.17: The Gulf Stream is a

surface ocean current and part of the North Atlantic gyre. The yellow color in the graphic indicates that the Gulf Stream is warmer than surrounding waters.

nt

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Deep ocean currents What is a deep Deep ocean currents move below the surface of the ocean. They are ocean current? slower than surface ocean currents. Unlike surface ocean currents, which are

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driven by the wind, deep ocean currents are driven by density differences. The temperature and salinity of these currents affect their density; for this reason, they are also called thermohaline currents. Thermo means temperature, and haline means salt. A warm and/or low salinity current is less dense and will float on a colder and/or higher salinity current. To test your understanding, do the Solve It! exercise in the sidebar. Evaporation The Sun’s heat can make a current warmer. How does a current become near the saltier? This happens when global wind patterns and heat speed up the equator evaporation of water near the equator. When ocean water evaporates, the

water leaves and the salt stays behind. As a result, surface ocean currents near the equator become saltier. Temperature A surface ocean current cools as it moves from the equator toward the poles. and density Because this water is saltier than surrounding water and because it is now

cooler, it sinks to the ocean floor as a huge underwater waterfall. What was once a warm surface ocean current now flows along the ocean floor as a cold deep ocean current. After hundreds to thousands of years, the slow-moving deep ocean current water returns to the surface in an upward movement, or an upwelling. Upwellings return the original surface water and nutrients from the ocean floor back to the ocean surface.

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deep ocean currents - densityand temperature-driven currents that move slowly within the ocean, also called thermohaline currents.

Will a Current Float or Sink? On average, salt water has a salinity of 35 parts per thousand, or 35 ppt*. Determine if the following fluids would sink or float in average salt water that is 25°C. a. Salt water that is 35 ppt and 50°C. b. Salt water that is 35 ppt and 4°C. c. Salt water that is 40 ppt and 25°C. d. Fresh water that is 10 ppt and 25°C. * The abbreviation “ppt” can also refer to “parts per trillion.”

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Features of the ocean floor The challenge of It is possible that scientists know more about space than about the oceans on studying the Earth. This is because scientists can use telescopes to see far away space ocean floor objects. But many of the important features of the oceans, especially the

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ocean floor, are hidden under deep water. The pressure deep in the ocean is immense and makes travel down to the ocean floor extremely challenging. The average depth of the ocean is 3.8 kilometers, or 2.4 miles!

continental margin - the region around continents that includes the continental shelf, continental slope, and continental rise.

The continental The ocean floor can be divided into the continental margin and the deep ocean margin floor. The continental margin is the region around continents that includes

the continental shelf, continental slope, and continental rise. The continental slope begins where the sea floor slopes toward the deep ocean floor. The continental rise is made of sediment that has washed down from the continental shelf and slope. Continental shelves surround many continents. They are shallow extensions of the continent, covered by ocean water that is approximately 100 meters deep (Figure 22.18).

Figure 22.18: The light blue color Features of the Two features of the continental shelf are barrier islands and banks. A barrier continental shelf island is a low, sandy island that lies parallel to the shoreline. It blocks waves

around the continents shows the continental shelf.

that come to shore and provides sheltered water (called a lagoon) between the island and the shore. The islands that comprise North Carolina’s Outer Banks are barrier islands (although they are called “banks”). A bank is a higher, flat region on the continental shelf. Its surface is relatively close to the ocean surface. An example of a large bank is Georges Bank, which is in the Atlantic Ocean and off the coasts of Massachusetts and Nova Scotia. These features are shown on the diagram on the next page. 22.3 OCEANS

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The deep ocean floor The abyssal The true ocean floor is called the abyssal plain. It is flat and smooth because plain a thick layer of sediment covers its features. It lies between 3,000 to 6,000

meters deep.

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Mountains, A seamount is a steep-sided mountain that rises from the ocean floor. trenches, and Seamounts may begin life as volcanoes over hot spots, but most of the islands seamounts become inactive as their oceanic plate moves them off the hot

spot. Some are tall enough to reach the surface and form an island. A guyot is a seamount that has eroded so that it has a flat top and is underwater. As you have learned, mid-ocean ridges mark places where two tectonic plates are separating and new ocean crust is being made. Mid-ocean ridges are a system of volcanic mountain ranges along the world’s ocean floors. Deepocean trenches are the deepest parts of the ocean. The world’s deepest trench, the Mariana Trench near Guam in the North Pacific Ocean, is more than 10 kilometers deep in some places. A volcanic island arc is a string of volcanic islands that lies in a curving line along a trench. These islands are formed by magma rising from a subducting plate.

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Discovering the Ocean Floor Each feature of the deep ocean floor was an interesting discovery. For example, guyots (pronounced “geeohs”) were discovered by Harry Hess, an important scientist in the development of plate tectonics. Pick one feature of the deep ocean floor and go on a “knowledge hunt” to find out more about it.

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Section 22.3 Review 1. What does the term salinity mean?

What Is Your City Like?

3. List two reasons why Earth’s oceans help make the planet suitable for life to exist.

In this section, you learned the average temperatures in January for certain cities.

4. In which of these places would winter be the most extreme: central Asia or western Canada? Explain your answer. If necessary, look at a globe.

Describe what winter is like in your city. Do you live near an ocean or another large body of water?

5. What keeps surface ocean currents moving? What drives deep ocean currents?

What is the average low temperature in January for your city?

2. Where does the salt in the oceans come from?

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6. At a coastline, fresh water flows into salt water. Which of these events might be occurring at a coastline? Explain your answer. a. The fresh water floats on top of the salt water. b. The fresh water sinks in the salt water.

How does this average temperature compare to those listed in the text?

7. It is possible that scientists know more about space than they do about Earth’s ocean floor. Why? 8. What three parts of the ocean floor are included in the continental margin? 9. What is the difference between a barrier island and a bank? 10. The abyssal plain is 3,000 to 6,000 meters deep. Convert this range to miles. Conversion factors: 1,000 meters = 1 kilometer = 0.62 mile. Show your work. 11. Many features of the deep ocean floor are volcanic. Why do you think this is so? 12. Research questions: a. Look at a globe and see if you can find an example of a volcanic island arc. Here is one example: the Lesser Antilles in the Caribbean Sea is a volcanic island arc (Figure 22.19). b. If you could explore a mid-ocean ridge, what would you find?

Figure 22.19: Question 12a.

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Chapter 22 Assessment Vocabulary

13. _____ occurs when water changes from being a liquid to a gas.

Select the correct term to complete the sentences.

14. _____ is the process by which plants release water.

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continental margin hydrosphere surface water reservoir condensation aquifer surface ocean current

glacier water cycle evaporation precipitation watershed water vapor gyre

groundwater water table salinity transpiration surface runoff percolation deep ocean current

Section 22.1

15. A(n) _____ is an underground area filled with groundwater. 16. _____ occurs when liquid water moves through a porous substance. Section 22.3

17. The continental shelf, slope, and rise make up the _____. 18. A circular ocean current system is called a(n) _____. 19. A density-driven current that moves slowly within the ocean is called a(n) _____. 20. The Gulf Stream is an example of a(n) _____.

1.

All the water on Earth is included in the _____.

2.

_____ is water that collects underground.

3.

A(n) _____ forms when more ice accumulates than melts.

Concepts

4.

A(n) _____ is a protected lake that is used to store water.

Section 22.1

5.

An ocean, lake, or river is an example of _____.

1.

How is Earth’s atmosphere a part of the hydrosphere?

6.

The upper surface of the underground, water-saturated zone is the _____.

2.

The amount of water on Earth has remained about the same for millions of years. How is this possible?

3.

True or false: The water table level stays the same year-round? Explain your answer.

4.

Why is Earth a good place to find ice, liquid water, and water vapor?

Section 22.2

7.

Evaporation is one of the processes in the _____.

8.

A(n) _____ is an area of land that catches and collects water.

9.

_____ is water that flows over land.

21. _____ describes the saltiness of water.

Section 22.2

10. Rain and snow are forms of _____.

5.

List a way that you participate in the water cycle.

11. Water in gaseous form is called _____.

6.

Is precipitation in the water cycle dependent on evaporation and condensation? Explain your answer.

12. _____ occurs when water changes from a gas to a liquid.

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7.

When plants open the pores in their leaves: a. b. c. d.

water enters the plant. sugar enters the plant. water and oxygen leave and carbon dioxide enters. sunlight enters the plant.

CHAPTER 22

20. In your own words, describe the difference between a coast and the continental margin of a continent. 21. Describe what the abyssal plain looks like. Why does it look this way? 22. What function do barrier islands naturally perform?

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8.

You are asked to do an analysis of the substances found in groundwater. What substances might be present? Why?

23. What is the difference between a seamount and a guyot?

9.

What land area is the watershed for the Southern Ocean?

Problems

10. Use a map of the United States to find the St. Lawrence River. It is located by the Great Lakes. a. b.

In what direction does it flow? Into what body of water does it flow?

Section 22.1

1.

Match these water resources with their percentage of Earth’s total water resources: Icecaps and glaciers Groundwater Ocean (salt water)

11. Describe the processes of the water cycle that are involved in a volcanic eruption.

a. less than 1% b. less than 2% c. 97%

12. Describe a geyser and give an example of one. Section 22.3

2.

13. What makes the oceans salty?

If all the water on Earth could fit in a one-liter container, the amount of frozen water would be equal to approximately 2% of this volume. Give this volume in milliliters.

14. Why are the oceans able to store heat energy?

Section 22.2

15. The interior of a continent is more likely to be extremely cold in the winter than a coastal area. Why?

3.

In a short paragraph, explain how the Sun, wind, and gravity are involved in the water cycle.

16. How do surface ocean currents affect the movement of heat at Earth’s surface?

4.

Explain how water could go from being precipitation, to surface runoff, to groundwater, to being part of an ocean.

17. List the factors that affect how:

5.

Imagine you are a raindrop.

a. b.

surface currents move. deep ocean currents move.

18. What two factors cause gyres? 19. Why are deep ocean currents also called thermohaline currents?

a. b.

Explain what could happen to you after you fall to the ground in a desert environment. Now, explain what could happen to you after you fall to the ground in an environment that is below 0°C. Note: Icy ground is not porous.

CHAPTER 22 ASSESSMENT

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Evapotranspiration is evaporation from surface water plus transpiration from plants. The graph below shows evapotranspiration over one year. Come up with a hypothesis to explain the data shown in the graph.

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Evapotranspiration (mm)

6.

WATER SYSTEMS

Annual evapotranspiration 120 90 60 30 Jan

Feb March April May June July Month

Aug Sept

Oct

Nov

Dec

Section 22.3

7.

8.

You pour a sample of 20°C water with a salinity of 37 parts per thousand (ppt) on top of a sample of water at the same temperature but with a salinity of 35 ppt. Does the poured sample sink or float on the 35 ppt sample? Predict which mass of water will sink and which will float in a mass of water that is 10°C with a density of 1.0260 g/cm3. a. b.

9.

c.

13. Imagine you could walk from the East Coast of the U.S. all the way to the Mid-Atlantic Ridge in the Atlantic Ocean. Describe what you would see on your journey. You might need to review Chapter 19 to answer this question.

Applying Your Knowledge Section 22.1

1.

15°C, density = 1.0255 g/cm 10°C, density = 1.0270 g/cm3

What would happen to the salinity of the sample over time? Would the amount of salt change in the sample over time? Why or why not? What would happen to the salinity of the sample if it started to rain into the beaker?

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What are the names of Earth’s five oceans? How much of Earth’s surface is covered by oceans? How much of Earth’s water is in the oceans?

12. Upwellings bring nutrient-rich water to the ocean surface. Why might areas where upwellings occur be important to humans?

3

A sample of ocean water in a beaker is allowed to sit outside in the Sun so that the water can evaporate. a. b.

a. b. c.

11. The Antarctic Circumpolar Current is a deep ocean current that encircles Antarctica. It aids in the circulation of deep and middlerange waters between the Atlantic, Indian, and Pacific oceans. The average speed is about 10 cm/s. How many kilometers would this represent for a day’s time? Show your work.

150

0

10. Answer these questions about Earth’s oceans.

Pick a fresh water lake that you know about and research it. Make a colorful brochure that highlights the benefits of this lake to people. Include photographs if available.

Section 22.2

2.

Select one of your favorite products and find out how water is involved in making it. How much water is involved? Make a poster to display your findings.

Section 22.3

3.

Find the meanings of the terms thermocline and estuary. Write a short paragraph about each one. Include a diagram to help explain each term.

4.

Find out about Marie Tharp. Who was she and what important contribution did she make to our understanding of the ocean floor?

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23

CHAPTER 23

How Water Shapes the Land FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

If you were to go to the south end of the South Island of New Zealand and walk out on Koekohe Beach, you would see the Moerkai Boulders. Scientists think it took about five million years for the boulders to form and even longer for them to look the way they do now. How did these groupings of large, spherical boulders get on the beach? Where did they come from? The local legend states that the boulders are the remains of baskets and food washed ashore when an ancient sailing canoe overturned. What might be the scientific explanation for the presence of these boulders? The focus of this chapter is how water—such as flowing water or the ice of glaciers— and other agents such as wind and even the force of gravity shape the land. In this chapter, you will also learn how pieces of rock become new sedimentary rocks.

4 What is the difference between weathering and erosion?

4 How do flowing water and the ice of glaciers shape the land?

4 How are sedimentary rocks formed?

Popocatépetl

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23.1 Weathering and Erosion

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You know from experience that rocks are hard objects. Sitting on a stone bench is not as comfortable as sitting on a sofa. And it takes a lot of work to break a rock into pieces. Over time though, rock does break down. This chapter describes how that happens and how rock is moved from place to place. Weathering is a term that describes how rock is broken down to form sediment. Erosion describes the transportation of sediment by water, wind, ice, and gravity. In time, even the hardest rock will weather to form small pieces and particles of sediment.

weathering - the process of breaking down rocks and minerals.

erosion - the process of moving rock and sediment by wind, water, ice, and gravity.

Comparing weathering and erosion Weathering You have seen the effects of weathering if you have noticed cracks in a

sidewalk or a large rock. You are seeing weathering in action if you have seen lichens or moss growing on a rock. Weathering is the process of breaking down rocks and minerals in place, with no movement. Weathering is caused by the formation of ice or salt crystals, changes in pressure, chemical reactions, and the actions of plants or animals. Erosion Weathering eventually breaks rock into bits and pieces called sediment

(Figure 23.1). When you sit on a sandy beach, you are sitting on sediment that might once have been a rocky mountaintop. How does sediment get from a mountain peak to a beach? The answer is erosion. Erosion is the process of moving pieces of rock and sediment by wind, water, ice, and gravity.

Weathering breaks down rock in place. Erosion moves rock and sediment. Energy and the In Chapter 18, you learned about the rock cycle. Earth’s internal energy rock cycle drives the rock cycle. Heat energy inside Earth results in the movement of

Figure 23.1: Weathering causes rock to break down into sediment.

tectonic plates on Earth’s surface so that mountains form and rocks are recycled. Earth’s internal energy and the Sun are the two main sources of energy that cause weathering and erosion, two processes in the rock cycle. The Sun drives the water cycle and weather patterns. Water and weather affect the landscape all the time.

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Forms of weathering Two forms of The two major forms of weathering are mechanical weathering and chemical weathering weathering. Rocks can be weathered by either form or by both. From the

images in Figure 23.2, can you figure out the difference between chemical and mechanical weathering?

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Mechanical Mechanical weathering (also called physical weathering) happens when weathering forces break or chip rocks and minerals into smaller pieces without changing

their composition. The formation of ice or salt crystals provides forces for breaking rock. Changes in pressure and the activities of living organisms also provide forces that are sufficient for breaking down rocks.

mechanical weathering - the process of breaking down rocks and minerals into smaller pieces by physical force without changing composition; also called physical weathering. chemical weathering - the process of breaking down rocks and minerals by chemical reactions.

Chemical Chemical weathering is the process of breaking down rocks and minerals weathering by chemical reactions between water and the rock or mineral particles. Other

agents of chemical weathering include oxygen and acids (from plants or acid rain). Minerals and rocks are chemically changed by this type of weathering. Some types of rocks are weathered more easily than others. For example, marble chemically weathers faster than granite. Chemical weathering has worn away the surfaces of many old marble statues (Figure 23.2). Soil is the result of weathering

The process of weathering affects sediment as well as rocks and minerals. In time, sediment combines with organic matter, making a rich mixture called soil (see the photo at the left). Soil also includes air, water, and living organisms such as bacteria, fungi, and insects. The quality of soil depends on the “parent material,” or type of rocks that are broken down to form it. Some parent rocks might produce rock grains with an abundance of minerals necessary for plant growth. Other parent rocks might lack a key mineral and produce soil that supports less or no plant growth. Where might soil be located relative to the parent material? Because of erosion by wind, water, and the force of gravity pulling sediment downhill, soil is often located at a distance from the parent material.

Figure 23.2: Mechanical and chemical weathering.

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Processes of mechanical weathering Frost wedging Frost wedging happens when water enters a crack in a rock and then

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freezes. Once the water freezes, it expands and the crack gets wider. If the process continues through many freeze-thaw cycles, the rock will eventually split into separate pieces. Frost wedging tends to happen in areas with available water and temperatures that fluctuate around the freezing point. Rocks that have many pores or cracks are susceptible to frost wedging. The photo in Figure 23.3 shows an example of frost wedging near the crest of Mount Hoffman in Yosemite National Park, California. You can see in the photo that many hand-sized rocks have been broken away by frost wedging.

frost wedging - mechanical weathering that results from freezing water.

Salt crystal In dry, hot environments and along coastlines, the growth of salt crystals weathering can cause mechanical weathering. Dry, hot environments are places where

salty solutions on rocks will evaporate quickly. Coastal environments are continuously subjected to salt water that leaves behind salt crystals once it evaporates. Salt crystals cause weathering because their formation and expansion within pores or cracks in rocks causes the rocks to weather. Salt crystals expand when they are heated. As you can see in the images below, weathering by salt crystals leaves interesting patterns. The image on the left shows salt weathering of stone bricks. The image on the right is an example of a tafoni formation. Tafoni formations are believed to be caused by salt weathering and other processes.

Figure 23.3: An example of frost wedging.

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Changes in Changes in temperature and pressure also cause mechanical weathering. For temperature and example, in desert environments, the air temperature changes from hot during pressure the day to cold at night. As you learned in Chapters 9 and 10, matter expands

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when its temperature increases. When rock expands as it is heated, the outer layers crack and split away. This process is called exfoliation. Exfoliation also happens when erosion removes outer layers of rock, causing inner layers to experience a decrease in pressure. Half Dome in Yosemite National Park is an example of how rock appears after pressure changes. Unloading and exfoliation domes

Half Dome is a mountain composed of intrusive igneous rock, meaning it was formed underground. After erosion exposed the mountain and removed its outer layers (like peeling an onion), the inner layers experienced decreased pressure and expanded. Expansion caused cracking of the newly exposed rock. In time, pieces of the rock broke off. This process is called unloading. The combination of erosion, unloading, and exfoliation has made Half Dome an example of an exfoliation dome. Geologists think that another “half” of Half Dome never existed. The flat face of Half Dome is the result of erosion of the original rock by Ice Age glaciers.

Figure 23.4: Over time, the roots of trees will split the rocks on this cliff by root wedging.

Biological Mechanical and chemical weathering by plants or animals is called biological weathering weathering. An example of mechanical weathering by plants happens when

roots grow into cracks in a rock. In this process, called root wedging, roots exert force on the rock as they grow and might cause the rock to split (Figure 23.4). Animals contribute to weathering when they dig into soil or burrow underground (Figure 23.5). The resulting holes and burrows become passageways for water to move deeper underground and speed up the weathering of underground rocks. Human activities—such as blasting rock to build roads—also cause mechanical weathering.

Figure 23.5: Burrowing animals create pockets for water to move underground and weather rocks.

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Agents of chemical weathering Water Water is often called a universal solvent because it dissolves many

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substances, including minerals in rock. Chemical changes can happen when minerals are exposed to water. Minerals might dissolve or a new mineral might be made. For example, the mineral feldspar reacts with water to form clay minerals, which are softer, meaning they have a lower number on the Mohs hardness scale. These clay minerals are more susceptible to erosion. Acid rain As precipitation, water also dissolves carbon dioxide gas from the

atmosphere. You read in Chapter 21 that dissolved carbon dioxide in water makes it a weak acid. For this reason, rainwater is naturally slightly acidic. Water that has a pH less than 5.6 is considered to be acid rain. Acid rain forms when pollutants or volcanic gases in the atmosphere acidify rainwater. Acid rain can weather rocks, including statues. If the statues are made of marble, they will weather more quickly than those made of granite (see the statue in Figure 23.2). Marble is made of calcite (calcium carbonate), which dissolves in acidic water. By comparison, granite statues do not weather as fast when exposed to acid rain because they contain minerals, like quartz, that are more resistant to chemical weathering.

Figure 23.6: Moss growing on rocks causes chemical weathering.

Oxygen in the Oxygen found in the atmosphere or dissolved in water also participates in atmosphere weathering. Oxygen combines with metals in minerals and changes them.

This process is called oxidation. For example, oxygen combines with iron in the minerals biotite and hornblende to make iron oxide, or rust. Rust commonly appears on iron-containing objects such as nails or bicycles that have been exposed to water. Biological Lichens and plants such as moss can cause chemical weathering. Chemicals weathering released by the plants eventually cause the rock on which they are growing

to break down (Figure 23.6). The two forms of Both chemical and mechanical weathering can affect a rock at the same time. weathering act Look at Figure 23.7. Here you see large cracks that might have been created together by frost wedging. Cracks and loose sediment in the cracks have provided a

place for plants to take root. Now, the rock will further break down as the growing plants cause both chemical and mechanical weathering.

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Figure 23.7: Both mechanical and

chemical weathering often occur at the same time.

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Factors that affect the rate of weathering Water and The presence of water and an area’s climate determine the type of weathering climate that takes place and how fast it happens. For example, frost wedging is

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common in cold and dry climates with frequent, often daily, freeze-thaw cycles. Chemical weathering is slowest in dry, cold climates. Rocks and minerals tend to chemically weather much faster in areas that have humid, warm climates. In general, chemical weathering is more likely to happen in humid or wet conditions. Plants and Weathering is also faster when biological weathering is possible. Plants animals growing on or near rocks can speed up weathering. Animals digging or

Nutrition from Rocks Macronutrients and trace minerals are important components of a healthy diet. Research the definition of macronutrients and trace minerals. Then, pick a macronutrient and a trace mineral to research. Answer the following questions. 1. What food sources supply this macronutrient?

burrowing increases how much exposure a rock has to weathering. Minerals The type of minerals found in a rock also affects how fast the rock weathers.

As you learned on the previous page, calcite in marble weathers faster than the minerals in granite. This is because calcite dissolves in acidic solutions (for example, acid rain). However, granite has other minerals, such as feldspar, that are susceptible to weathering. Feldspar chemically weathers to form clay.

2. How is this macronutrient important for the healthy functioning of your body? 3. Why are the “minerals” you eat called “minerals”?

Surface area Weathering commonly involves contact with water. Therefore, the greater the

surface area of a rock or mineral compared to its volume, the faster it will weather. For example, a thin, jagged rock will weather more quickly than a thick, rounded rock of the same volume (Figure 23.8). The thin, jagged rock has a greater surface area to volume ratio. You can increase the surface area to volume ratio of any solid by breaking it down into pieces. The importance You might consider that weathering is a negative process because it breaks of weathering down rocks and structures that have been constructed by humans. However,

weathering is important to life on Earth. Why? Weathering releases minerals in rocks so that they can become part of the soil. These minerals are then available as nutrients for plants to absorb. Animals and people are able to absorb these nutrients by consuming plants. Important chemical elements such as calcium (for building strong bones and teeth) and iron (for your blood) are originally from rocks.

Figure 23.8: A thin, jagged rock has a greater surface area to volume ratio than a thick, rounded rock.

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Erosion What is What happens after rock is weathered? The weathered fragments move! erosion? Through erosion, rock, rock pieces, sediment, and soil are transported by

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water, wind, ice, and other agents. Other agents include the force of gravity, which causes rock and sediment to move downhill, and erosion caused by animals (such as the overgrazing of livestock, which disturbs more soil and thus exposes it to increased erosion). Water and wind Water is a powerful force involved in erosion. You will learn more about erosion water erosion in Section 2 of this chapter. Wind is also a powerful force that

moves particles of sediment from one place to another. Small particles might be carried aloft by the wind. Larger particles and rocks are too heavy to be moved by the wind. Larger particles are rolled along on the ground, and the big rocks don’t move. The result might be a rocky desert pavement left behind after the removal of soil over time (Figure 23.9). Eroded sediment is eventually deposited when the wind dies down. Beach dunes are one example of large amounts of wind-deposited sand. Loess is another windblown deposit of fine sediment. Loess is an important resource because the deposit is rich with nutrients and makes good soil for growing plants.

Figure 23.9: Results of wind erosion.

The mystery of At the beginning of this chapter, you read about the Moeraki Boulders the Moeraki in New Zealand. The mystery behind these boulders is related to both Boulders weathering and erosion. Before the boulders formed, some type of material,

probably the remains of something that was once alive, were included in layers of fine sediment. As these sediment layers were changed into mudstone, a type of sedimentary rock, mineral crystals replaced this onceliving material. The mass of crystals is called a concretion. Millions of years later, the mudstone began to weather away, forming silt and leaving the more durable concretions—the Moeraki Boulders—behind. The boulders have moved only a little since they were exposed but the material surrounding them eroded. In other words, the main movement was the inland movement of the mudstone cliff face near the beach as it was washed away (Figure 23.10).

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Figure 23.10: A Moeraki boulder.

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Moving sediment by gravity Mass wasting Mass wasting is a form of erosion that involves the downhill movement of

large amounts of rock and sediment due to the force of gravity. Examples of mass wasting include landslides, rockfalls, mudflows, and slumps.

mass wasting - the downhill movement of large amounts of rock and sediment due to the force of gravity.

Landslides A landslide happens when a large mass of soil or rock

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slides down a steep slope. Wet conditions or a volcanic eruption can trigger a landslide. For example, the largest landslide ever recorded took place in 1980 when Mount St. Helens erupted. Rockfalls In the mountains, it is common to see boulders

alongside the rock outcrops that line the road. A rock outcrop is the part of a rock formation that is above ground and visible. A rockfall happens when a boulder is split off of a rock outcrop due to weathering or another event. Rockfalls speed up the weathering process by quickly breaking up large pieces of a rock formation. Mudflow A mudflow occurs when a large amount of rock and

sediment mixed with water flows down a mountain. Water adds weight to and lubricates the rock and sediment, reducing friction. Mudflows can be dramatic and fast events. They flow down a mountain very quickly, engulfing everything in their paths. The eruption of Mount St. Helens involved mudflows. Mudflows on and around a volcano are called lahars. Mud on a volcano is made from volcanic ash. Slumping Slumping occurs when loose soil becomes wet and

slides, or “slumps” (Figure 23.11). When soil is dry, friction between the grains of soil keeps it firm enough that you can build a house on it. However, if the soil is wet, the spaces between the grains are full of water. The water makes the grains slippery and friction is a lot lower. Slumping can happen after a period of very heavy rainfall.

Figure 23.11: Houses are at risk

of being damaged or destroyed by slumping when they are built on steep, loose soil or below hills that are made of loose soil.

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Section 23.1 Review 1. Compare and contrast weathering and erosion.

The Rate of Erosion

2. What energy sources drive weathering and erosion?

The following factors increase the rate of erosion for rocks and soil.

3. Explain the difference between mechanical and chemical weathering.

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4. For the following examples, state whether mechanical or chemical weathering is occurring. a. b. c. d. e.

A bicycle left in the rain becomes rusty. Water in a crack in a rock freezes causing the rock to split. A rock is covered with moss and lichens. An inscription on a 200-year-old marble slab is no longer legible. Salt crystals grow in the cracks of coastal rocks.

5. How is frost wedging similar to root wedging? 6. How are animals involved in the processes of weathering and erosion? 7. List the two events that lead to exfoliation. 8. Explain the role of water in chemical weathering. 9. What happens when carbon dioxide and air pollutants mix with rainwater? Is the resultant rainwater an agent of weathering or erosion? 10. Over time, how might the grass growing up through a crack in a sidewalk affect the sidewalk? Use the terms mechanical weathering and chemical weathering in your answer. 11. List three factors that affect how fast a rock weathers.

Climatic factors: Precipitation, temperature, and stormy weather. Type of rock and its location: Porous rock will erode faster; rock that is on a hill will erode faster. Amount of weathering that a rock has experienced: Weathered rock erodes faster than unweathered rock. The lack of vegetation: The root systems of trees, grass, and other plants protect soil from being eroded. The presence of plants or animals: Plant growth and animal movement can cause weathering that leaves rock and soil more vulnerable to erosion. Human activity: Any activity that removes trees and other plants from the land or that disturbs soil or rock makes an area susceptible to erosion.

12. Explain how the process of weathering benefits living organisms. 13. Which area might experience more soil erosion: a grassy field or an area that has been cleared of vegetation to construct a building? Why? 14. Explain the role of gravity in erosion.

Soil erosion is a very serious and little understood problem. Find out more about this global issue and write a short paragraph about it.

15. Describe two examples of mass wasting. Is mass wasting a form of weathering or erosion? Explain your answer.

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23.2 Shaping the Land

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Rivers and glaciers have played major roles in shaping Earth’s landscape. Both running water and glaciers alter the land by moving sediment to new locations. You might not be familiar with glaciers, but glaciers move and as they do, they take sediment along with them. An example of how glaciers shape the land is seen in Figure 23.12. You are probably more familiar with how running water such as rivers and streams move sediment.

Moving sediment by water Factors What factors might affect the amount of sediment that can be carried by

running water? The factors include the volume of water, the slope of the land, and how rocky or smooth the land is. Volume and More sediment will be moved if the volume of flowing water is high or the slope slope is steep. Water volume increases after heavy rains or when snow melts.

Figure 23.12: The Convict Lake

basin in the Sierra Nevada Mountains was carved by glaciers.

The steeper the slope, the faster the water and sediment will move over the land (Figure 23.13). Higher water velocity means that larger particles can be moved and more particles can be moved at one time. Rocky The presence of rocks in a landscape slows the process of moving sediment. landscapes This is because rocks trap sediment. Suspended sediment is likely to travel

farther in water running over a smooth bottom. Barriers or rocks can be used by people to stop the transport of sediment and reduce the effects of erosion.

Figure 23.13: A stream table can be used to model the effects of the slope on how fast water flows and how much sediment is transported.

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Depositing and sorting sediment by water Deposition As it is moved by water, sediment can be deposited in a variety of places.

The process of depositing sediment after it has been moved by water, wind, ice, or gravity is called deposition.

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Fast versus The steeper the slope of land, the greater the water velocity and energy of slow water flowing water. Both the speed of water and its energy are directly related to

the amount of sediment and the size of the particles that can be carried. Fast, high-energy water moves more sediment and bigger rock particles. Slowmoving water moves less sediment and more fine-grained particles. How sediment is During conditions when water is flowing, the size of sediment particles that sorted by water are deposited depends on the speed at which the water is flowing. As running

water slows down, rock particles settle out in order of size from largest to smallest. When a flowing river enters a lake or a pond, the water velocity decreases. Then, the sediment is deposited in order of size in a pattern called graded bedding. First, the largest particles settle to the bottom. Next, the medium-sized particles settle. Finally, the smallest, clay-sized particles settle. It’s common to find graded bedding in repeating layers, one on top of the other. For example, a stream that flows into a lake might run fast only during thunderstorms. The stream lays down a graded bed of sediment after each storm.

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deposition - the process of depositing sediment after it has been moved by water, wind, ice, or gravity.

graded bedding - layers of sediment with the largest particles at the bottom and smallest particles on top; the particles are deposited as flowing water slows down.

River Velocity You can measure the velocity of a river’s surface water using a floating object. For example, a floating twig is timed with a stopwatch as it travels 5 meters. If it takes the twig 10 seconds to travel this distance, what is the water velocity in meters per second?

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Rivers What is a river? A river is a large, flowing body of water. A stream is a small river. The path that a river or stream follows is called a channel. A delta is the landform

associated with the mouth of a river as it flows into an ocean, lake, or another river. The following paragraphs further describe how rivers shape land.

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River valleys A river valley is created where rivers erode the land. Rivers tend to cut

V-shaped valleys like the one shown in Figure 23.14. A V-shaped valley indicates that the river is fairly young or near its source (called the headwaters). In general, valleys are low-lying land features that are surrounded by higher land features such as hills and mountains. River valleys are changing environments because the amount of water that flows through them changes. The amount of water decreases or increases (even to the point of flooding) based on rain or snow melt.

river - a large body of water that flows into an ocean, lake, or another river.

stream - a small river. channel - the path that a river or stream follows.

floodplain - flat land alongside a river that tends to flood. A floodplain is usually located at a distance from the headwaters of the river.

Floodplains Along the length of the river and toward the mouth (the place where the river meets the ocean), the river widens and forms a floodplain. A floodplain is

flat land alongside a river that tends to flood. A floodplain also forms over time as the river erodes the land on each of its sides. A floodplain is very good land for growing plants because seasonal flooding of the river deposits nutrients in the soil. However, because flooding occurs regularly, these areas are not ideal for buildings or homes. A river valley V-shaped valley

Headwaters (source of river)

Oxbow lake Floodplain

Figure 23.14: A V-shaped valley cut by a river.

Floodplain

Delta (mouth of river)

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River meanders What are The diagram of the river valley on the previous page illustrates S-shaped meanders? curves. These river features are called meanders (Figure 23.15). They are

meanders - S-shaped curves in a river.

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formed because water flows at varying speeds in a river. After a meander forms, the speed of water flow varies depending on its position in the channel. The fastest flow is on the outside of each curve, while the slowest flow is on the inside. Fast-moving water erodes sediment. Slow-moving water deposits sediment. The fast-moving water erodes the outside riverbank and at the same time, the slower water deposits sediment on the inside bank. The sediment that settles near the inside bank forms a point bar. The point bar adds to the inside of the meander curve and extends it. A channel bar is formed by sediment that is eroded from the riverbank. The extra sediment is too much for the stream to transport, so it is deposited in the channel. Why can’t the stream carry this extra sediment? Because the velocity of the water flow is too low. Moving Once a river has meanders, the combination of erosion on the outside bank meanders and depositing on the point bar (inside bank) causes the river to shift its

course side to side. Sometimes this process causes a meander to become cut off from the river, and it forms a curved lake called an oxbow lake (see the river valley diagram on the preceding page).

Figure 23.15: A diagram of a meandering river.

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CHAPTER 23

Glaciers move sediment What is a In Chapter 22, you learned that a glacier is frozen water found at the poles glacier? and on mountaintops as huge masses of ice or ice sheets. A glacier can be

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many kilometers thick and thousands of kilometers across. A glacier forms on land when snow and ice accumulate faster than they melt. The stages of accumulation can take place over hundreds or thousands of years as snow piles up in the winter and does not entirely melt during the warmer summer months. Glaciers move As layers and layers of snow accumulate, pressure builds and changes the

snow to thick ice. The thick ice becomes so heavy that it becomes plastic and flows (Figure 23.16). Plastic means “able to change shape without breaking.” Recall that the term plastic was also used to describe hot rock in the mantle in Chapter 20. The force of gravity drives the movement of glaciers. Glacial valleys As the ice of a glacier flows down a valley, it grinds the valley floor with are U-shaped pieces of rock caught up in the ice (Figure 23.17). This grinding, or abrasion,

smooths the rock it encounters and changes the shape of the valley so that it is U-shaped. The highest parts of the ridges surrounding the valley are usually rough because abrasion by the glacier didn’t occur that high up. A change from rough to smooth rock is common in glacial valleys and indicates the highest point that the glacier abraded the mountain. Present day

Figure 23.16: Erosion by a glacier.

During last ice age Rough rock

The height reached by the glacier

Glacial valley

Smooth rock

U-shaped glacial valley

Figure 23.17: A glacier passed over

this rock, moving from left to right. The scratches were made by rocks caught in the moving ice.

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The effects of ice and glaciers on land and our climate Glaciers deposit About 30% of Earth’s surface was covered by glaciers 10,000 years ago. As sediment Earth’s climate warmed, glaciers melted—except for those near the poles

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and at higher elevations. The movement, or “retreat,” of glaciers toward the poles as the climate warmed and the glaciers melted deposited huge piles of rocks, scratched surfaces of rocks, and eroded valleys and mountaintops. Long Island, in New York, was created by a glacier bulldozing and depositing rocks and sediment as the glacier retreated. Rocky soil in New England is evidence of glaciers moving and depositing rocks and sediment. Retreating glaciers often leave behind large blocks of ice, surrounded by rock and sediment. After the blocks melt, steep-sided depressions are left called kettle holes. If these kettle holes extend below the water table, a kettle lake forms. Most of the deep lakes of southern New England are kettle lakes. Ice and global In Chapter 15, you learned about global climate change and its effects on warming Earth. Indicators that global climate change is happening include a decrease

Figure 23.18: The Athebaska

Glacier in Alberta, Canada, in retreat.

in the amount of sea ice and permafrost on Earth and the significant retreat of glaciers. One possible side effect of the loss of sea ice is the opening of the Northwest Passage north of Canada. Concerned about this possibility, Canada has recently made policies that state its ownership of the passage should it thaw and become a major channel for shipping goods. Permafrost is permanently frozen soil (Figure 23.19). Although the amount of permafrost on Earth is decreasing, another concern worries scientists—the potential release of billions of tons of greenhouse gases such as methane from the frozen ground, which will further increase global warming. Glaciers and Interestingly, glaciers are talked about by scientists as having “health.” The global warming size of a glacier is determined by the rate at which it accumulates snow

and ice near its head, and by the rate of ice loss farther down the glacier. A healthy glacier has a growing, or steady, ice mass balance. Glaciers retreat when the rate of ice loss exceeds the rate of ice gain (Figure 23.18). According to scientists, worldwide glacial retreat has been taking place since 1850 and at a faster rate since 1995 due to global warming. As you read in Chapter 15, a consequence of glacial retreat is increased global sea level as glaciers melt.

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Figure 23.19: Permafrost along the coast of Alaska. This image shows the erosion of permafrost by the ocean.

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CHAPTER 23

Section 23.2 Review 1. What factors affect how much sediment is transported by moving water? 2. What factor causes a river to flow faster? 3. What effect might a steep slope have on the erosion of a hillside? Why?

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4. What is deposition? 5. A rainstorm causes a stream to flow faster and deposit more sediment into the lake that already has one graded bed. A week later, another rainstorm occurs. What would the sediment of this lake look like now? 6. Why are floodplains good areas for growing plants? Why are floodplains not good areas for building housing developments? 7. In a meandering river: a. Where does the water flow fastest? What happens at this location? b. Where does the water flow slowest? What happens at this location?

Figure 23.20: Question 8.

8. Look at Figure 23.20. Name the feature that the arrow is pointing to in this photograph. 9. Scientists can use a wading rod, a spinning propeller device, and a velocity sensor to measure the velocity of flowing water at any point in the river. Refer to Figure 23.21 and answer the questions below. a. Where is the river flowing the fastest? b. Where is the river flowing the slowest? c. Come up with a hypothesis for why the river is flowing the slowest at this location. 10. What is the difference in shape between a river valley and a valley shaped by a moving glacier? 11. A glacier is a mass of solid ice, yet it flows. Explain why. 12. What type of evidence would indicate that a landscape has experienced erosion by running water? a glacier? 13. Sea ice, permafrost, and glaciers have all been affected by global climate change. Explain why the effects are problematic for people. Do your own research to expand your ability to answer this question.

Figure 23.21: Question 9.

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23.3 Sedimentary Rocks

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So far in this chapter, you have learned about weathering and erosion. You have also learned that one of the results of weathering is the formation of sediment and soil. What happens next? To answer this question, think back to Chapter 18, when you learned about the rock cycle. The processes of weathering and erosion are very important in the rock cycle because these processes lead to the formation of sedimentary rocks.

Sedimentary rocks

compaction - the process by which sediment is pressed together as more and more layers, or beds, of sediment are deposited on top of one another. cementation - the process by which sediment particles are “glued” together to make a sedimentary rock.

The rock cycle The processes of weathering and erosion are important in the rock cycle. and a downhill Weathering is the main recycling mechanism for rocks on Earth’s surface. journey Sunlight, wind, water, ice, and changing temperature and pressure cause all

rocks to form cracks, break into smaller pieces and might eventually become sediment. By the process of erosion, rock pieces move downhill due to the force of gravity and eventually reach a lake or sea. Larger pieces of rock break into smaller, smoother particles as they move along on their downhill journey. Layers of In time, the downhill movement results in the buildup of thick layers (or sediment beds) of sediment in low places. Beds of sediment are compacted and

cemented to form sedimentary rocks. Because igneous, metamorphic, and sedimentary rocks all weather and become sediment, the most common rock found on Earth’s surface is sedimentary. Sedimentary rocks cover 75 percent of the land area in many places. Figure 23.22 illustrates the path that sediment takes to become a sedimentary rock. Compaction and As rock particles settle on top of previously deposited beds of sediment, cementation water and air are squeezed out from between particles. Compaction is the

pressing together of layers of sediment. Even though compacted sediment beds are hard and might be difficult to dig into, the particles are still separate grains and not yet sedimentary rock. Cementation is the process by which grains become “glued” together to form a sedimentary rock. Groundwater containing dissolved minerals seeps into the pore spaces between grains. Then, the dissolved minerals crystallize in these pore spaces.

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Figure 23.22: Compaction and cementation.

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Types of sedimentary rock The size of One way to classify sedimentary rocks is by particle size (Figure 23.23). Clay particles and silt particles form mudstone. Grains of clay are microscopic and cause

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mudstone to feel smooth. Silt is barely visible and feels gritty. Sand particles that you can see and feel form sandstone. Conglomerate, a lumpy rock, is made of rounded particles and rock pieces of varying size. Crystals in water Some sedimentary rocks also form by precipitation of dissolved minerals

from solution. Here, precipitation means that the dissolved minerals crystallize as solid particles as the water evaporates. This group of sedimentary rocks includes rock salt and rock gypsum.

CHAPTER 23

Rock type

Particle size (mm)

Sediment

Mudstone

< 0.06

Clay or silt

Sandstone

0.06–2

Sand

Conglomerate

>2

Gravel

Figure 23.23: Types of sedimentary rocks.

Sediment from The settling process that forms sedimentary rocks in water is ideal for animals and forming rocks from once-living things. The hard parts of dead marine plants plants and animals sink to the ocean floor and form layers of shells, lime, and mud.

Over millions of years, these layers eventually become sedimentary rock. Most limestone, a sedimentary rock, is formed this way. Peat and bituminous coal are sedimentary rocks made from ancient plant remains. Fossils in Most fossils are found in sedimentary rocks. This is because many animals sedimentary live near low areas (that hold water) where sediment accumulates, and the rocks process of forming a sedimentary rock is good for preserving fossils. Fossil

formation might begin when an organism’s body is quickly covered in sediment from an event like a mudflow. Body parts that do not decay quickly, such as shells, bones, and teeth, are buried under sediment layers. After a long time, these harder body parts might be preserved or replaced by other minerals. Fossils are the remains, or traces (like footprints), of prehistoric organisms. Eventually, the sediment and fossils are compacted and cemented into sedimentary rock (Figure 23.24). The Moeraki Boulders formed in sedimentary rock

The Moeraki Boulders are concretions. Although geologists are not entirely sure what triggers the formation of a concretion, most think it is some form of organic material. Once begun, the process is the same. Mineral material, often calcite, replaces the original material. Since mudstone that once encased the boulders was softer than the mineral of the concretion, it eventually weathered away.

Figure 23.24: The process that

forms sedimentary rocks also preserves fossils.

23.3 SEDIMENTARY ROCKS

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Interpreting layers of sediment Direction of All rocks hold clues to the past. By studying rocks, you can learn something younging about the conditions under which they formed. What clues about the past do

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sedimentary rocks hold? One of these clues is the “up” direction. You learned that large particles settle before small particles, forming graded bedding. Figure 23.25 shows two graded beds. A layer of the finest particles is on the top of each bed. This layer of fine particles helps you know which direction is up. If you know the up direction, you know the direction of younging—this is the direction of younger layers of sediment. Graded bedding is preserved when sediment becomes sedimentary rock.

direction of younging - the order in which sediment is deposited—from larger to finer particles.

cross bedding - a pattern of inclined beds of sediment that often form as dunes or ripples of sediment are moved by wind and water.

Cross bedding Compared to graded bedding, cross bedding is a more complicated

sedimentary structure that tells stories about ancient conditions. Crossbedding appears as a pattern of inclined graded beds. The pattern forms as dunes or ripples of sediment are moved in a flowing current of water or wind. The images below show cross-bedding patterns for an ancient stream channel. The angles of beds in cross bedding also provide clues for the direction of motion for ancient water or wind currents.

Figure 23.25: Direction of younging. This graphic shows two graded beds.

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CHAPTER 23

Section 23.3 Review 1. Explain how the processes of weathering and erosion are involved in forming a sedimentary rock.

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2. In this section, you read that sedimentary rocks are the most common type of rock on Earth’s surface. Why? 3. What is the difference between compaction and cementation? 4. Describe one way that sedimentary rocks are classified.

Cool Things in Sedimentary Rocks Concretions: You have learned that the mysterious Moeraki Boulders formed in mudstone, a sedimentary rock. Similar concretions, such as the one below, form in other types of sedimentary rock. This one formed in sandstone.

5. Why are fossils found in sedimentary rocks? 6. Mudstone, peat, and rock gypsum are all sedimentary rocks. Describe how each is formed. 7. Rock salt is a rock composed of the mineral halite (see Section 22.3). Where do rock salt and halite form? What are the uses for rock salt? 8. After reading about sedimentary rocks and how they are formed, Jane checked her email inbox. While doing that, she thought to herself: An email inbox is similar to a sedimentary rock. a. Explain what Jane means by her statement. b. Write a short paragraph that explains how an email inbox is both alike and different from a sedimentary rock. 9. How you can tell which layer in a sedimentary rock is the youngest? 10. Explain the terms graded bedding and cross bedding. 11. Review the rock cycle. a. List the three groups of rocks and give an example of each. b. Give a brief description of the processes involved in the formation of each group of rock. c. Since the rock cycle is called a “cycle,” one would think that the process of this cycle follows a certain sequence or order. Is that true? Explain your answer.

Geodes: Geodes also form in sedimentary rocks. Here’s a challenge: Find out what makes a geode different from a concretion. You might need to talk to a geologist to get your question answered. Fossils: Sedimentary rocks are also a good place to look for fossils. Talk to a paleontologist (a scientist who studies fossils) to find out how scientists decide where to look for fossils. Do you think they search for areas that have sedimentary rocks?

23.3 SEDIMENTARY ROCKS

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Chapter 23 Assessment Vocabulary

Concepts

Select the correct term to complete the sentences.

Section 23.1

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direction of younging frost wedging compaction cementation cross bedding

mechanical weathering meander chemical weathering deposition

channel erosion mass wasting graded bedding

1.

Can both mechanical and chemical weathering affect a rock at the same time? If so, describe an example.

2.

Would you see evidence of frost wedging in locations near Earth’s equator? Why or why not?

3.

Explain how the formation of salt crystals causes mechanical weathering.

4.

Tree roots, burrowing organisms, and mosses all cause rocks to weather. What is the name for this type of weathering?

5.

A sand castle built on a beach completely disappears over time. Is this an example of weathering or erosion? Explain.

6.

Gravity is an important force involved in mass wasting. How is water involved? Give one example from the reading.

Section 23.1

1.

Breaking a rock into two pieces is an example of _____.

2.

_____ is mechanical weathering caused by ice.

3.

Moving water is one of the most important agents of _____.

4.

An old, worn-down marble statue is an example of _____.

5.

A rockfall and a landslide are examples of _____.

Section 23.2

6.

How sediment is “dropped” on a floodplain: _____ (a process)

7.

Sediment particles, when deposited by water, settle in order from largest to smallest, forming a pattern called _____.

8.

The path that a river or stream follows is called a(n) _____.

9.

An oxbow lake was once a(n) _____ in a river.

Section 23.3

11. _____ is a pattern of tilted or inclined beds that often form as wind or water deposit sediment. 12. Two processes involved in the formation of sedimentary rocks after deposition are _____ and _____.

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7.

Weathering “ages” mountains. How do you think an old mountaintop might appear compared to a relatively young mountaintop?

8.

The size of rock particles that can be moved by running water is determined by what factor?

9.

Describe a “healthy” glacier.

Section 23.3

10. The _____ is the order in which sediment is deposited—from larger to finer particles.

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Section 23.2

10. If you were shown samples of mudstone and conglomerate rocks, how might you be able to tell them apart? 11. A sedimentary rock has two graded beds. How do you know which of the graded bed patterns formed last? Explain your answer.

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Problems Section 23.1

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1.

Draw a cross-sectional view of each type of a river valley and a glacial valley. Label each.

2.

In which situation will weathering happen faster? Pick the correct situation for each and explain your choice. a. b. c.

3.

a tropical rain forest or a dry desert an environment with a yearly freeze-thaw cycle or one with daily freeze-thaw cycles a rock with a high surface area to volume ratio or a rock with a low surface area to volume ratio

Stonehenge in England is about 5,000 years old and attracts many visitors each year. People are allowed to look at this landmark only from a distance. They cannot touch the stones. Why do you think this is so?

Section 23.2

4.

Use the scale at the bottom of the map to answer the questions. First measure the scale bar with a ruler. Then, use the ruler to measure the distances on the map. a.

b.

How many kilometers of the Tuolumne River are located in Yosemite National Park? How far would sediment have to travel to go from Modesto to San Francisco?

Section 23.3

5.

The different types of sedimentary rocks have special names. Rocks made of fragments of other rock particles are clastic. Rocks made of parts of living organisms such as shells are called biological sedimentary rocks. Sedimentary rocks made when minerals crystallize after deposition are called chemical sedimentary rocks. Identify each of the following sedimentary rocks as being clastic, biological, or chemical. (a) mudstone (b) sandstone (c) rock gypsum and (d) limestone

Applying Your Knowledge Section 23.1

1.

A number of famous caves and caverns have been formed by chemical weathering of underground limestone. Research Mammoth Cave in Kentucky. How was this cave formed?

2.

Karst topography describes a landscape that results from the chemical weathering of underground limestone. Research karst topography. Where does it occur in the U.S. and why?

Section 23.2

3.

Find out what clues indicate the previous location of a meandering river.

4.

As white reflective surfaces, sea ice and glacial ice reflect the Sun’s light and heat. How then might the reduction of sea ice and glacial coverage due to global warming affect Earth’s climate? Write your ideas in a short paragraph.

Section 23.3

5.

Review the rock cycle in Chapter 18. List the rock cycle processes that are involved in forming each group of rocks. (a) igneous (b) metamorphic (c) sedimentary.

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Unit 8 Waves Waves and Sound

Chapter 25

Light and Optics

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Chapter 24

‹ Try this at home What affects the pitch of a sound? Find a rectangular container, like a baking pan, plastic food storage container, or a shoebox. You will also need a few large rubber bands of different sizes and a pencil or long handled wooden spoon. Place the rubber bands around the container lengthwise. Pluck each rubber band and listen to the sound it makes. Insert the pencil or spoon so it runs widthwise under the rubber bands. Now pluck the rubber bands; do they make higher or lower pitched sounds? Why? Finally, try moving the stick up and down the length of the box. Does the position of the stick make a difference in the sound you get? Why do you think so?

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CHAPTER

24

CHAPTER 24

Waves and Sound

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Humans were making musical instruments to produce sounds around 20,000 years before the wheel and axle were invented! Over centuries, instruments gradually improved from simple flutes and drums to modern standards like the violin. A violin’s sound is rich and complex because the vibrations of its wooden parts create a unique blend of frequencies. Among instrument builders, Antonio Stradivari (1644–1737) is perhaps the most famous. Stradivari built violins in the small town of Cremona, Italy, during the period between 1667 and 1730. He worked tirelessly experimenting with different woods and varnishes, searching for the perfect sound. Over time, he developed a secret formula for varnish, as well as special ways to carve and treat the all-important vibrating parts of the violin. In the 300 years since Stradivari lived and worked, the mystery of his genius has lived on in his creations. Today, a Stradivarius violin is the most highly prized of all musical instruments. Its unique sound has never been duplicated.

4 How can you describe the speed of a wave? 4 How are water waves and sound waves similar and different?

4 What makes each human voice unique?

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24.1 Harmonic Motion

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We all use linear motion to travel from one place to another, either on foot or by bicycle or car. Linear motion goes from one place to another without repeating (Figure 24.1A). This chapter is about another type of motion. Harmonic motion is motion that repeats in cycles (Figure 24.1B). For example, water waves are a form of harmonic motion. The four seasons are caused by Earth’s harmonic motion. Other types of harmonic motion cause your heartbeat and create sounds.

linear motion - motion that goes from one place to another without repeating.

harmonic motion - motion that repeats in cycles.

cycle - a unit of motion that repeats. pendulum - a device that swings

Motion in cycles What is a cycle? To describe harmonic motion, we need to learn how to describe a repeating action or motion. A cycle is one unit of harmonic motion. This motion can

back and forth due to the force of gravity.

be back and forth or a full revolution, or rotation. One full swing of a child on a swing is one cycle. As the child continues to swing, the back-and-forth motion, or cycle, repeats over and over again. Looking at A pendulum is a device that swings back and forth. We can use a pendulum one cycle to better understand a cycle. Each box in the diagram below is a snapshot of

the motion at a different time in one cycle. The cycle of a pendulum Begin

End Begin next cycle

Figure 24.1: (A) A sprinter is a good

1

2

3

4

5

example of linear motion. (B) A person on a swing is a good example of harmonic motion.

The cycle of a The cycle starts with (1) the swing from left to center. Next, the cycle pendulum continues from (2) center to right, and (3) back from right to center. The

cycle ends when the pendulum moves (4) from center to left because this brings the pendulum back to the beginning of the next cycle. Once a cycle is completed, the next cycle(s) begins without any interruption in the motion.

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CHAPTER 24

Frequency and period Oscillators An oscillator is a physical system that has repeating cycles (harmonic

motion). A child on a swing is an oscillator, as is a vibrating guitar string. A wagon rolling down a hill is not an oscillator.

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A period is the Because the speed of an oscillator constantly changes during its cycle, we time to complete don’t use the term speed to describe how quickly a cycle repeats itself. one cycle Instead, we use the terms period and frequency. The time it takes for one complete cycle to happen is called a period. A clock pendulum with a period

of one second will complete one full back-and-forth swing each second. Frequency is the number of cycles per second

oscillator - a physical system that has repeating cycles. period - the time it takes for one complete cycle to happen.

frequency - how often something repeats, expressed in hertz.

hertz - the unit of frequency. One hertz is one cycle per second.

The frequency is the number of complete cycles per second. The unit of one cycle per second is called a hertz (Hz). Something that completes 10 cycles each second has a frequency of 10 Hz. A guitar string playing the note A vibrates back and forth at a frequency of 220 Hz (Figure 24.2). Your heartbeat has a frequency from one-half to two cycles per second (0.5 Hz–2 Hz).

Frequency is the Frequency and period are inversely related. The period is the number of inverse of seconds per cycle. The frequency is the number of cycles per second. For period example, if the period of a pendulum is 2 seconds, its frequency is 0.5 cycles

per second (0.5 Hz).

When to use While both period and frequency tell us the same information, we usually use period or period when cycles are slower than a few per second. A simple pendulum has frequency a period from 0.9 to 2 seconds. We use frequency when cycles repeat faster.

For example, the vibrations that make sound in musical instruments have frequencies from 20 to 20,000 Hz.

Figure 24.2: All musical

instruments use harmonic motion to create sound.

24.1 HARMONIC MOTION

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Solving Problems: Frequency and Period The period of an oscillator is 2 minutes. What is the frequency of this oscillator in hertz?

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1. Looking for:

You are asked for the frequency in hertz.

2. Given:

You are given the period in minutes.

3. Relationships:

Convert minutes to seconds using the conversion factor 60 s/1 min. Use the formula f = 1/T .

4. Solution:

2 minutes × 60 seconds/1 minute = 120 seconds The period (T) is 120 seconds.

Figure 24.3: The parts of a pendulum clock.

f = 1/120 s = 0.008 Hz Your turn...

a. A pendulum completes one cycle every 5 seconds. What are the period and frequency of this pendulum? b. The period of an oscillator is 1 minute. What is the frequency of this oscillator in hertz? c. How often would you push someone on a swing to create a frequency of 0.4 hertz? d. Figure 24.3 shows the parts of a pendulum clock. The minute hand moves 1/60 of a turn after 30 cycles. What is the period and frequency of this pendulum? e. A ferris wheel spins 5 times in 10 minutes. Calculate the period and frequency of the ferris wheel.

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a. The period is 5 seconds and the frequency is 0.2 Hz. b. The frequency is 0.02 Hz. c. You would need to push once every 2.5 seconds. d. There are 30 cycles/second, so the frequency is 30 Hz. The period is 0.03 second. e. The frequency is 0.008 Hz. The period is 120 seconds, or 2 minutes.

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CHAPTER 24

Amplitude Amplitude The “size” of a cycle is called amplitude. Figure 24.4 shows a pendulum describes the with a small amplitude and one with a large amplitude. With a moving object “size” of a cycle like a pendulum, the amplitude is often a distance or angle. With other types

amplitude - the amount that a cycle moves away from equilibrium.

How do you The amplitude is measured as the measure maximum distance the oscillator amplitude? moves away from its equilibrium

position. For the pendulum in Figure 24.5, the amplitude is 20 degrees because the pendulum moves 20 degrees away from the equilibrium position in either direction. The amplitude can also be found by measuring the distance between the farthest points the motion reaches. The amplitude is half this distance. The amplitude of a water wave is often found this way.

Figure 24.4: Small amplitude versus large amplitude.

Damping and Look at the illustration below. Friction slows a pendulum down, just as it friction slows all motion. That means the amplitude gets reduced until the pendulum

is hanging straight down, motionless. We use the word damping to describe the gradual loss of amplitude. If you wanted to make a clock with a pendulum, you would have to find a way to keep adding energy to counteract the damping of friction so the clock’s pendulum would work continuously. Damping is the gradual loss of amplitude Start

After 1 minute

After 2 minutes

After 3 minutes

Amplitude

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of oscillators, the amplitude might be voltage or pressure. The amplitude of an oscillator is measured in units appropriate to the type of harmonic motion being described.

Figure 24.5: A pendulum with an Time

amplitude of 20 degrees swings 20 degrees away from the center in both directions.

24.1 HARMONIC MOTION

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Graphs of harmonic motion Graphing It is easy to recognize cycles on a graph of harmonic motion. Figure 24.6 harmonic illustrates the difference between a graph of linear motion and a graph of motion harmonic motion. The most common type of harmonic-motion graph places

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time on the x-axis (horizontal) and position on the y-axis (vertical). The graph below shows how the position of a pendulum changes over time. The repeating “wave” on the graph represents the repeating cycles of motion of the pendulum.

Typical linear-motion graph Position

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Time

Typical harmonic-motion graph

Position

One cycle

Time

Figure 24.6: A harmonic-motion graph shows repeating cycles.

Finding the In the graph above, the pattern repeats every 1.5 seconds. This repeating period pattern represents the period of the pendulum, which is 1.5 seconds. If you

were to cut out any piece of the graph and slide it left or right 1.5 seconds, it would line up exactly. Using positive Harmonic-motion graphs often use positive and negative values to represent and negative motion on either side of a center (equilibrium) position. Zero usually positions represents the equilibrium point. Notice that zero is placed halfway up the y-

Measuring Amplitude Use a protractor to find the amplitude (in degrees) of the pendulum in the graphic below.

axis so there is room for both positive and negative values. This graph is in centimeters, but the motion of the pendulum could also have been graphed using the angle measured relative to the center (straight down) position. Showing The amplitude of harmonic motion can also be seen on a graph. The graph amplitude on a above shows that the pendulum swings back and forth from +20 centimeters graph to –20 centimeters. The equilibrium position is represented as the zero line.

Therefore, the amplitude of the pendulum is 20 centimeters.

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Natural frequency and resonance Natural An oscillator will have the same period and frequency each time you start it frequency moving. This phenomenon is called natural frequency, the frequency at

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which a system naturally oscillates. Musical instruments use natural frequency. For example, guitar strings are tuned by adjusting their natural frequency to match musical notes (Figure 24.7). Changing The natural frequency of an oscillator changes according to its length. In the natural case of a vibrating guitar string, you can shorten the string to increase the frequency force pulling the string back toward equilibrium. Greater force means greater

natural frequency - the frequency at which a system oscillates when disturbed. periodic force - a repetitive force. resonance - an exceptionally large amplitude that develops when a periodic force is applied at the natural frequency.

acceleration, so the natural frequency is higher and the period is shorter. Lengthening an oscillator results in a lower frequency and a longer period. How mass For oscillators with side-to-side movement, increasing the mass means the affects oscillator moves slower and the period gets longer. This is because of oscillators Newton’s second law of motion—as mass increases, the acceleration

decreases proportionally. However, for a pendulum, changing the mass does NOT affect its period (also because of Newton’s second law). This is because the force of gravity keeps the pendulum moving through a center, or equilibrium, position. As in free fall, if you add mass to a pendulum, the added inertia is exactly equal to the added force from gravity. The acceleration is the same; therefore, the period stays the same. Periodic force and resonance

A force that is repeated over and over is called a periodic force. A periodic force supplies energy to an oscillator and has a cycle with an amplitude, frequency, and period. Resonance happens when a periodic force has the same frequency as the natural frequency. For example, small pushes (a periodic force) to someone on a swing add together if they are applied at the right time (once each cycle). In time, the amplitude of the motion grows and can become very large compared to the strength of the force!

Figure 24.7: This guitarist is tuning his guitar by adjusting the natural frequency of the strings to match particular musical notes.

24.1 HARMONIC MOTION

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Section 24.1 Review 1. Which is the better example of a cycle: a turn of a wheel or a slide down a ski slope? 2. Describe one example of an oscillating system you would find at an amusement park. 3. What is the relationship between period and frequency?

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4. Every 10 seconds a pendulum completes 2 cycles. What are the period and frequency of this pendulum? 5. What is the difference between a graph of linear motion and a graph of harmonic motion? 6. A graph of motion of a pendulum shows that it swings from +5 centimeters to –5 centimeters for each cycle. What is the amplitude of the pendulum? 7. What is the period of the oscillation shown in the diagram below?

Figure 24.8: Question 8.

8. Figure 24.8 shows a sliding mass on a spring. Assume there is no friction. Could this system oscillate? Explain why or why not. 9. Which pendulum in Figure 24.9 will have the longer period? Justify your answer. 10. Why does mass NOT affect the period of a pendulum? 11. Resonance happens when: a. b. c. d.

a periodic force is applied at the natural frequency. an oscillator has more than one natural frequency. a force is periodic and not constant. the amplitude of an oscillator grows large over time.

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Figure 24.9: Question 9.

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24.2 Properties of Waves In this section, you will apply your understanding of harmonic motion to waves. A wave is a traveling oscillation that has frequency, wavelength, and amplitude. Types of waves include water waves, sound, and light. To understand how these waves are alike and different, let’s examine the properties of waves.

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What is a wave?

wave - a traveling oscillation that has properties of frequency, wavelength, and amplitude.

wavelength - the distance from any point on a wave to the same point on the next cycle of the wave.

Defining a wave If you poke a floating ball, it oscillates up and down. Then the surface of the

water oscillates in response, and the oscillation spreads outward from where it started. As you read above, this traveling oscillation is a wave. Waves are a traveling form of energy because they can cause changes in the objects they encounter. As they travel, waves can carry information, such as sound, pictures, or even numbers. For this reason, technology depends on waves. All the information that reaches your eyes and ears comes in waves.

Waves are Like all oscillators, waves have cycles, frequency, and amplitude. The oscillators frequency of a wave is a measure of how often it goes up and down at any one

Figure 24.10: The parts of a wave.

place. The frequency of one point on the wave is the frequency of the whole wave. A wave carries its frequency to every place it reaches. Wave frequency is measured in hertz (Hz). A wave with a frequency of one hertz (1 Hz) causes everything it touches to oscillate at one cycle per second. Wavelength A wave has a moving series of high points called crests and low points called

troughs. The amplitude of a wave is the average distance, or one-half the distance, between the crest and the trough (Figure 24.10). Wavelength is the distance from any point on a wave to the same point on the next cycle of the wave (Figure 24.11). For example, the distance between one crest and the next crest is one wavelength. We use the Greek letter lambda for wavelength. A lambda (λ) looks like an upside-down y.

Figure 24.11: The wavelength can be measured from crest to crest.

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The speed of waves

Start

Waves spread Wave motion is due to the spreading of the wave from where it begins. For a

water wave, the water itself stays in the same average place. Therefore, to gauge the speed of a wave, you measure how fast the wave spreads—not how fast the water surface moves up and down.

1/4 cycle

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Measuring wave The graphic below shows what happens in water when you begin a wave in speed one location. You can measure the speed of this spreading wave by timing

how long it takes the wave to affect a place some distance away. The speed of a typical water wave is about 1 m/s. Light waves are extremely fast—300,000 km/s (or 186,000 mi/s). Sound waves travel at about 1,200 km/hr (or 660 mph).

1/2 cycle

3/4 cycle

Speed is In one complete cycle, a wave moves one wavelength (Figure 24.12). The frequency times speed is the distance traveled (one wavelength) divided by the time it takes wavelength (one period). We can also calculate the speed of a wave by multiplying

wavelength and frequency. This is mathematically the same because multiplying by the frequency is the same as dividing by the period. These formulas work for all types of waves, including water waves, sound waves, light waves, and even earthquake waves.

Complete cycle

Figure 24.12: A wave moves one wavelength in each cycle.

Remember these relationships: period = T frequency = 1/T Speed = wavelength ÷ period Speed = frequency × wavelength

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Solving Problems: Wave Speed

Making Waves

The wavelength of a wave on a string is 1 meter and its speed is 5 m/s. Calculate the frequency and the period of the wave.

Make a harmonic-motion graph of a wave. Place time on the x-axis and position on the y-axis. The period is 2 seconds and the amplitude is 5 centimeters. On your graph, label a crest, trough, and the wavelength.

1. Looking for:

You are asked to find the frequency (f ) and period (T) of a wave.

2. Given:

You know the wavelength of the wave is 1 meter and its speed is 5 m/s.

3. Relationships:

The formulas you know include: speed = frequency × wavelength f = 1/T and T = 1/f

4. Solution:

Solve for frequency. frequency = speed ÷ wavelength frequency = 5 m/s ÷ 1 m = 5 Hz Then solve for period. a. The speed is 0.25 m/s.

period = 1/f = 1/5 Hz = 0.20 s

b. The speed is 2,500 m/s. The period is 0.04 second.

The frequency of the wave is 5 Hz, and the period is 0.20 second. Your turn...

a. The wavelength of a wave is 0.5 meter and its period is 2 seconds. What is the speed of this wave? b. The wavelength of a wave is 100 meters and its frequency is 25 hertz. What is the speed of this wave? What is its period?

c. 2 minutes = 120 seconds. 120 s ÷ 15 s/cycle (or wavelengths) = 8 cycles (or wavelengths). 8 wavelengths pass the point.

c. If the period of a wave is 15 seconds, how many wavelengths pass a certain point in 2 minutes?

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The four wave interactions Boundaries Four interactions are possible when a wave encounters a surface—reflection,

refraction, diffraction, or absorption. Reflection, refraction, and diffraction usually occur at the boundary between two materials. Absorption also occurs at a boundary, but it happens to a greater extent within the body of a material.

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Reflection Reflection is the process of a wave bouncing off a surface. A reflected wave

is like the original wave, but moving in a new direction. The wavelength and frequency are usually unchanged. An echo is an example of a sound wave reflecting from a distant object or wall. People who design concert halls pay careful attention to the reflection of sound from the walls and ceiling. Refraction Refraction occurs when a wave bends as it crosses a boundary. The process

of light refraction through eyeglasses helps people see better. The lenses in a pair of glasses bend, or refract, incoming light waves so that an image is correctly focused within the eye.

reflection - the process of a wave bouncing off surfaces. refraction - the process of a wave bending as it crosses a boundary between two materials.

diffraction - the process of a wave bending around a corner or passing through an opening. absorption - the process of diminishing the amplitude and energy of a wave as it passes through a material.

Diffraction The process of a wave bending around a

corner or passing through an opening is called diffraction. Diffraction usually changes the direction and shape of the wave front (the leading edge of a moving wave). You can see this happening in the graphic at the right. Diffraction explains why you can hear sound through a partially closed door. Diffraction causes the sound wave to spread out from any small opening. Absorption Absorption of a wave means that its amplitude gets smaller and smaller as

it passes through a material. As this happens, the wave’s energy is transferred to the absorbing material. Theaters often use heavy curtains to absorb sound waves so the audience cannot hear backstage noise. The tinted glass or plastic in the lenses of your sunglasses absorbs some of the energy in light waves. Cutting down the energy of light makes your vision more comfortable on a bright, sunny day so you don’t have to squint.

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Figure 24.13: The four wave interactions.

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Transverse and longitudinal waves

CHAPTER 24

p

Wave pulses A wave pulse is a short “burst” of a traveling wave. A pulse can be produced

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with a single up-down movement. The illustrations below show wave pulses in springs. You can see the difference between the two basic types of waves—transverse and longitudinal—by observing the motion of a wave pulse.

transverse wave - a wave is transverse if its oscillations are not in the direction it moves. longitudinal wave - a wave is longitudinal if its oscillations are in the direction it moves.

Transverse The oscillations of a transverse wave are not in the direction the wave waves moves. For example, the wave pulse in the illustration below moves from left

to right. The oscillation (caused by the boy’s hand) is up and down. Water waves are an example of a transverse wave (Figure 24.14 top). Making a transverse wave pulse

Wave pulse

Longitudinal The oscillations of a longitudinal wave are in the same direction that the waves wave moves (Figure 24.14 bottom). A sharp push-pull on the end of the

spring makes a traveling wave pulse as portions of the spring compress then relax. The direction of the compressions is in the same direction that the wave moves. Sound waves are longitudinal waves. Making a longitudinal wave pulse

Figure 24.14: Transverse and longitudinal waves.

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Constructive and destructive interference Wave pulses If you have a long elastic string attached to a wall, you can make a wave

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pulse. First, you place the free end of the string over the back of a chair. The string should be straight so that each part of it is in a neutral position. To make the pulse, you pull down a short length of the string behind the chair and let go. The pulse then races away from the chair all the way to the wall. You can see the wave pulse move on the string. Each section of string experiences the pulse and returns to the neutral position after the wave pulse has moved past it.

Constructive Suppose you make two wave pulses on a stretched string. One comes from interference the left and the other comes from the right. When the waves meet, they combine to make a single large pulse. Constructive interference happens

when waves combine to make a larger amplitude (Figure 24.15).

constructive interference when waves add up to make a larger amplitude.

destructive interference - when waves add up to make a smaller, or zero, amplitude.

Figure 24.15: This is an example of constructive interference.

Destructive Wave pulses do not always combine to make a larger pulse when they meet. interference When one pulse is on top of the string and the other is on the bottom, these

pulses cancel each other out as they meet in the middle. (Figure 24.16). One pulse pulls the string up and the other pulls it down. The result is that the string flattens and both pulses vanish for a moment. In destructive interference, waves add up to make a wave with smaller, or zero, amplitude. After interfering, both wave pulses separate again and travel on their own. This is surprising if you think about it. For a moment, the middle of the string is flat, but a moment later, two wave pulses come out of the flat part and race away from each other. Waves still store energy, even during destructive interference. Noise-canceling headphones are based on technology that uses destructive interference.

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Figure 24.16: This is an example of destructive interference.

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Section 24.2 Review Noise-Canceling Headphones

1. The distance from the crest of a wave to the next crest is 10 centimeters. The distance from a crest of this wave to a trough is 4 centimeters. a. What is the amplitude of this wave? b. What is the wavelength of this wave?

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The graphic below illustrates how noise-canceling headphones work. Study the graphic and write a description that explains why noisecanceling technology is a good way to reduce noise. Verify your description by doing some research about these special headphones.

2. What is the wavelength of the wave shown in this harmonic- motion graph? 3. What is the speed of a wave that has a wavelength of 0.4 meter and a frequency of 10 hertz? 4. A wave has a wavelength of 1 m and a speed of 20 m/s. What is the period of this wave? 5. For each of the examples below, identify whether reflection, refraction, diffraction, or absorption is happening. a. The black surface of a parking lot gets hot in the summer when exposed to sunlight. b. A straw in a glass of water looks funny (Figure 24.17). c. When you look in a mirror, you can see yourself. d. Sound seems muffled when it is occurring on the other side of a wall. e. Light waves bend when they move from water to air. f. The wave front of a wave changes as it passes through an opening. 6. When a wave is being absorbed, what happens to the amplitude of the wave? Use the term energy in your explanation. 7. Compare and contrast transverse waves and longitudinal waves. 8. Two waves combine to make a wave that is larger than either wave by itself. Is this constructive or destructive interference?

Figure 24.17: Question 5b.

9. When constructive interference happens between two sound waves, the sound will get louder. What does this tell you about the relationship between amplitude and volume of sound?

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24.3 Sound How do we know that sound is a wave? First, it has both frequency and wavelength. We also know sound is a wave because it does all the things other waves do. Sound can be reflected, refracted, and absorbed. Sound also shows diffraction and interference. Resonance occurs with sound waves and is especially important for understanding how musical instruments work.

sound - a traveling oscillation of atoms or pressure.

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Sound is a traveling oscillation of atoms What is sound? Depending on the material, sound is a traveling oscillation of atoms or

pressure. Since these oscillations are in the same direction as the sound travels, sound is a longitudinal wave. Sound in solids In solids and liquids, sound involves oscillations of neighboring atoms. If and liquids you push one atom, it pushes its neighbor, and so on. The pushes among

atoms cause them to oscillate back and forth like tiny beads on springs. The oscillation spreads through the connections between atoms to make a sound wave. Sound in air and In air and gases, atoms are spread out and interact by colliding with one gases another. Sound travels in air and gases as a traveling oscillation of pressure.

A layer of high pressure pushes on the next group of atoms and causes those atoms to squeeze together. Then, the pattern repeats.

Looking at a Figure 24.18 illustrates what a sound wave might look like if you could see sound wave the atoms (the effect of sound on air molecules is exaggerated). Sound from

a stereo reaches your ears when the surface of a speaker moves back and forth at the same frequencies as the sound waves being produced. If you touch the surface of a speaker, you can “feel” the sound as vibrations. These vibrations create a traveling sound wave of alternating high and low pressure.

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Figure 24.18: This is what a sound

wave might look like if you could see the atoms. The effect of sound on air molecules is exaggerated.

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Frequency and pitch Frequency and The frequency of sound indicates how fast air pressure oscillates back and pressure change forth. The purr of a cat, for example, might have a frequency of 50 hertz. This

Most sound has Almost all the sounds you hear contain many frequencies at the same time. In more than one fact, the sound of the human voice contains thousands of different frequency frequencies—all at once (see the image below). Because voices have different

mixtures of frequencies, you can identify one person’s voice from another. Figure 24.19 shows the frequency spectrum for three people saying hello. A frequency spectrum shows loudness on the y-axis and frequency on the x-axis. What differences do you see among the graphs?

0

Loudness

pitch, like the rumble of a big truck or a bass guitar. A high-frequency sound has a high pitch, like the scream of a whistle or siren. Animals might hear a wider range of frequencies, or higher or lower frequencies than humans.

Loudness

Frequency and Your ears are very sensitive to the frequency of sound. The pitch of a sound pitch is how you hear and interpret its frequency. A low-frequency sound has a low

0

Loudness

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means the air pressure alternates 50 times per second. The frequency of a fire truck siren might be 3,000 hertz. This corresponds to 3,000 vibrations per second in the pressure of the air.

pitch - the perception of high or low that you hear at different frequencies of sound.

0

Voice A

2.000 Frequency (Hz)

4.000

Voice B

2.000 Frequency (Hz)

4.000

Voice C

2.000 Frequency (Hz)

4.000

Figure 24.19: The frequencies in The frequency Anything that vibrates creates sound waves, as long as there is contact with range of sound other atoms. However, not all “sounds” can be heard. Humans can hear in the waves range from 20 to 20,000 Hz. Bats can hear high-frequency sounds from 2,000

three people’s voices as they say the word hello. Each person’s voice is made up of a mixture of frequencies.

to 110,000 Hz, and elephants hear lower-frequency sounds from 16 to 12,000 Hz.

24.3 SOUND

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Intensity and loudness of sound Decibels The unit for the intensity, or strength, of a sound is the decibel (dB). We can

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measure sound intensity with scientific instruments just like we can measure mass with a balance. The decibel scale (shown below) is convenient to use because most sounds fall between 0 and 100. The amplitude of a sound increases 10 times for every 20-decibel increase (Figure 24.20).

decibel - a unit of measure for the intensity or strength of a sound.

Comparing decibels and amplitude Decibels (dB)

Amplitude

0

1

20

10

40

100

60

1,000

80

10,000

100

100,000

120

1,000,000

Figure 24.20: The decibel scale measures amplitude (loudness).

Equal loudness curve

Loudness When you experience a loud sound, you experience the effects of its

Acoustics Acoustics is the science and technology of sound. Knowledge of acoustics is

used to design facilities like libraries, recording studios, and concert halls. A design might address how to reduce sound intensity and/or whether sound needs to be absorbed, amplified, or even prevented from entering a room.

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80 Maximum sensitivity of human hearing

60 40

10,000

0

1,000

20 100

Decibel level

intensity and frequency. An equal loudness curve compares how loud you hear sounds of different frequencies (Figure 24.21). As you can see, the human ear responds differently to high and low frequencies. This curve shows that for you to hear low-frequency sounds (below 100 Hz) the same as sounds from 100 to 1,000 Hz, the decibel value needs to be higher for the low-frequency sound. Notice that the numbers are not evenly spread out on the x-axis of this graph. This type of spacing is called a logarithmic scale. You read the graph in the same way that you would read an evenly spaced graph.

100

Frequency (Hz)

Figure 24.21: All points on an equal loudness curve have the same loudness.

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The speed of sound Sound is slower You might have noticed that the sound of thunder often comes many seconds than light after you see lightning. Lightning is what creates thunder, so they really

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happen at the same time. You hear a delay because sound travels much slower than light. The speed of sound is about 1,200 km/h (745 mph). Light travels at 300,000 km/s (186,000 mi/s).

supersonic - a term to describe speeds faster than the speed of sound.

Subsonic and Objects that move faster than sound are called supersonic. If you were on supersonic the ground watching a supersonic plane fly toward you, there would be

silence (Figure 24.22). The sound would be behind the plane, and reach your ears after the plane had passed over you. Some military jets fly at supersonic speeds. Passenger jets are subsonic because they travel at speeds from 600 to 800 km/h. Sound in liquids Sound travels through most liquids and solids faster than through air and solids (Figure 24.23). Sound travels about 5 times faster in water and about 18 times

faster in steel. Why? Recall that a pendulum keeps moving through its cycle because the force of gravity continually pulls it back to an equilibrium position. For a pendulum, gravity is the restoring force. Sound also depends on restoring forces. The forces holding steel atoms together are much stronger than the forces between the molecules in air. Stronger restoring forces increase the speed of sound. Sound speed depends on temperature and pressure

In air, the energy of a sound wave is carried by the motion of atoms. Therefore, anything that affects the motion of atoms affects the speed of sound. For example, molecules move more slowly in cold air, and the speed of sound decreases. At 0°C, the speed of sound is 330 m/s, but at 21°C, the speed of sound is 344 m/s. Also, when pressure increases, atoms become more crowded and the speed of sound increases because collisions between atoms increase. If the pressure decreases, the speed of sound decreases.

Sound speed Lighter atoms and molecules (those with lower molecular weights) move and molecular faster than heavier ones at the same temperature. The speed of sound is higher weight in helium gas because helium atoms are lighter (and faster) than either the

Figure 24.22: The boundary

between hearing and not hearing the plane is the “shock wave.” The person in the middle hears a sonic boom as the shock wave passes over him.

Material

Sound speed (m/s)

Air

330

Helium

965

Water

1,530

Wood (average)

2,000

Gold

3,240

Steel

5,940

Figure 24.23: The speed of sound in various materials (helium and air at 0°C and 1 atmospheric pressure).

oxygen (O2) or nitrogen (N2) molecules that make up air. 24.3 SOUND

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The wavelength of sound Range of The wavelengths of sound in air can be compared to the size of everyday wavelengths of objects (Table 24.1). As with other waves, the wavelength of a sound is sound inversely related to its frequency (Figure 24.24). A low-frequency, 20-hertz

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sound has a wavelength the size of a large classroom. At the upper range of hearing, a 20,000-hertz sound has a wavelength about the width of a finger. Table 24.1: Frequency and wavelength for some typical sounds Frequency (Hz)

Wavelength

Typical source

20 100 500 1,000 2,000 5,000 10,000 20,000

17 m 3.4 m 68 cm (27”) 34 cm (13”) 17 cm (6.7”) 6.8 cm (2.7”) 3.4 cm (1.3”) 1.7 cm (0.67”)

rumble of thunder bass guitar average male voice female soprano voice fire truck siren highest note on a piano whine of a jet turbine highest-pitched sound you can hear

standing wave - a wave that is confined in a space. fundamental - the lowest natural frequency of an oscillator.

harmonic - one of the many natural frequencies of an oscillator.

Standing waves A wave that is confined in a space is called a standing wave. It is possible to make

standing waves of almost any type, including sound, water, and even light. You can experiment with standing waves using a vibrating string. Vibrating strings create sound on a guitar or piano. Like all oscillators, a string has natural frequencies. The lowest natural frequency is called the fundamental. A vibrating string also has other natural frequencies called harmonics. The diagram at the right shows the first three harmonics. You can find the harmonic number by counting the number of “bumps,” or places of greatest amplitude. The first harmonic has one bump, the second has two, the third has three, and so on. The place of highest amplitude on a string is the antinode. The place where the string does not move is called a node.

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Figure 24.24: The frequency and

wavelength of sound are inversely related. When the frequency goes up, the wavelength goes down proportionally.

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How we hear sound The ear

The cochlea The cochlea provides us with our ability to interpret sound—in other words,

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our sense of hearing. However, the cochlea is in the inner ear (Figure 24.25). Sound has to reach the cochlea by first entering the ear canal, where it encounters the eardrum. Here, the sound waves cause the eardrum to vibrate. Then, three delicate bones of the middle ear transmit these vibrations to the side of the cochlea. In turn, fluid in the spiral channel of the cochlea vibrates and creates waves. Nerves along the channel have tiny hairs that shake when the fluid vibrates. Near the entrance, the channel is relatively large, so the nerves respond to longer-wavelength, lower-frequency sound. The nerves at the small end of the channel respond to shorter-wavelength, higher-frequency sound.

Ear canal Eardrum

Middle ear bones Three semicircular canals (balance)

The semicircular As you know, the function of our ears is hearing. But did you know that your canals ears also provide you with your sense of balance? Near the cochlea in the

Cochlea (hearing)

inner ear are three semicircular canals. Like the cochlea, each canal contains fluid. The movement of this fluid in the canals indicates how the body is moving (left–right, up–down, or forward–backward). Human hearing In general, the combination of the eardrum, bones, and the cochlea limit the

range of human hearing from 20 hertz to 20,000 hertz. However, hearing varies greatly among different people, and it changes with age. Some people can hear sounds above 15,000 Hz and other people can’t. On average, people gradually lose high-frequency hearing with age. Most adults cannot hear frequencies above 15,000 hertz, while children can often hear to 20,000 hertz. Hearing can be Hearing is affected by exposure to loud or high-frequency damaged by noise. Listening to loud sounds for a long time can cause the loud noise hairs on the nerves in the cochlea to weaken or break off,

causing permanent damage. Therefore, it is important to always protect your ears by keeping the volume of noise at a low or reasonable level. It is also important to wear ear protection if you have to stay in a loud place. In concerts, many musicians wear earplugs onstage to protect their hearing.

20,000 Hz 2,000 Hz Eardrum und Soaves w

50 Hz

Waves in cochlear fluid

Figure 24.25: The structure of the

inner ear. When the eardrum vibrates, three small bones transmit the vibrations to the cochlea. The vibrations make waves inside the cochlea, which shake hairs attached to nerves in the spiral. Each part of the spiral is sensitive to a different frequency.

24.3 SOUND

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1,000 Hz

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Beats and the Doppler effect Beats When two frequencies of sound are not exactly equal in value, the loudness of the total sound seems to oscillate, creating a beat The superposition principle

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states that sound waves occurring at the same time combine to make a complex wave. The sound (amplitude) of this wave is louder than either wave separately when the waves are in phase due to constructive interference. When the waves are out of phase, the sound is quieter due to destructive interference. We hear the alternation in amplitude as beats. Why we hear beats In phase

beat - the oscillation between two sounds that are close in frequency. Doppler effect - an increase or decrease in frequency caused by the motion of the source of an oscillation (such as sound).

Bats and Beats

Wave 1 Wave 2 Out of phase Wave 1 + Wave 2 Beat

Beat

The Doppler The Doppler effect is a shift in the frequency of an oscillation caused by effect is caused motion of the source of the oscillation. If a stationary object is producing by motion sound, listeners on all sides will hear the same frequency (see diagram

below). When the object is in motion, the frequency will not be the same for all listeners. People moving with the object hear the frequency as if the object were at rest. To the side (positions B and D) a slightly higher frequency is heard as it approaches, and then a slightly lower frequency as it passes. A higher frequency is heard at position A as the approaching sound waves are compressed. A lower frequency is heard at position C. The Doppler effect occurs at speeds below the speed of sound.

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Bats use echolocation to navigate and find insects for food. Like a “sonic flashlight,” the bat’s voice “shines” ultrasound waves into the night. The sound occurs as “chirps,” short bursts of sound that rise in frequency. When the sound reflects off an insect, the bat’s ears receive the echo. Since the frequency of the chirp is always changing, the echo comes back with a slightly different frequency. The difference between the echo and the chirp makes beats that the bat can hear. The beat frequency is proportional to how far the insect is from the bat. A bat can even determine where the insect is by comparing the echo it hears in its left ear with what it hears in its right ear.

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Section 24.3 Review 1. What is the relationship between pitch and frequency? 2. If you looked at the frequency spectrums of two friends saying the word dog, would they look the same or different? Explain your answer.

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3. What two variables affect how loudly you hear sound? 4. How do the amplitudes of a 120-decibel sound and a 100-decibel sound compare? 5. Would an object moving at 750 km/h be supersonic or subsonic? 6. Would an object moving at 100 mph be supersonic or subsonic? Use the conversion factor 1 mile = 1.6 kilometers.

Figure 24.26: Question 8.

7. Why does sound travel faster through water than through air?

Doppler Radar

8. The first five harmonics for a vibrating string are shown in Figure 24.26. a. For each harmonic, identify the number of wavelengths represented. b. For each harmonic, identify the number of nodes and antinodes that are present (include the ends of the string in your count). c. Which of the five harmonics has the highest natural frequency? d. Make a drawing that shows what the 6th harmonic would look like.

Doppler radar is a way to measure the speed of a moving object at a distance. A transmitter sends a pulse of microwaves. The waves reflect from a moving object, such as a car. The frequency of the reflected wave is increased if the car is moving toward the oncoming microwaves and decreased if the car is moving away. The difference in frequency between the reflected and transmitted wave is proportional to the speed.

9. If two sound waves have exactly the same frequency, will you hear beats? Why or why not? 10. How does the cochlea allow us to hear both low-frequency and high-frequency sound? 11. If you were talking to an elderly person who was having trouble hearing you, would it be better to talk in a deeper voice (low-frequency sound) or a higher voice (highfrequency sound)?

Do research to find out how Doppler radar is used in weather forecasting.

12. A paramedic in an ambulance does not experience the Doppler effect of the siren. Why? 13. You hear an ambulance in your neighborhood that is traveling a few blocks from where you are. The pitch of the siren seems to be getting lower and lower. Is the ambulance traveling toward you or away from you? How do you know? 14. What happens when two sound waves are out of phase? 24.3 SOUND

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24 Chapter 24 Assessment Vocabulary

Section 24.2

11. A(n) ____ is a traveling oscillation.

Select the correct term to complete the sentences.

12. The distance from one crest to the next is a wave’s ____.

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standing wave

cycle

decibels

wave

fundamental

diffraction

period

reflection

absorption

refraction

pendulum

harmonics

beats

Doppler effect

linear motion

frequency

constructive interference

harmonic motion

15. ____ is when waves bend when they enter another material, and ____ is when waves bend around an object or outward after exiting a hole.

oscillator

amplitude

hertz

16. The amplitude of two waves will cancel when ____ occurs.

resonance

wavelength

natural frequency

17. The amplitude of two waves gets larger when ____ occurs.

transverse wave

longitudinal wave

pitch

18. Sound waves are an example of this type of wave: ____.

periodic force

destructive interference

supersonic

19. Water waves are an example of this type of wave: ____.

sound

13. The process of a wave bouncing off a surface is called ____. 14. ____ is the process of the amplitude of a wave diminishing as it enters another material.

Section 24.3

Section 24.1

1.

The harmonic motion of a boy on a swing is like the motion of a(n) ____.

2.

An object with repeating cycles of motion is a(n) ____.

3.

The note A in the musical scale has a(n) ____ of 220 Hz.

4.

One unit of harmonic motion is called a(n) ____.

5.

The motion of a girl running is called ____, and the motion of a girl riding a ferris wheel is called ____.

6.

The formula for ____ is the inverse of the formula for frequency.

7.

One ____ equals one cycle per second.

8.

When the periodic force matches the natural frequency of an object, the object experiences ____.

9.

To have a high ____ on a swing, your friend needs to push you with a(n) ____.

20. Two sounds that are out of phase will cause you to hear ____. 21. Compared to a whistle, a vacuum cleaner produces sound with a low ____. 22. The threshold of human hearing is zero ____. 23. An oscillator in motion can produce the ____. 24. You can make a(n) ____ using a length of string. 25. The natural frequency of an object is called the ____, and additional natural frequencies are called ____. 26. A(n) ____ object moves faster than the speed of sound. 27. As ____ travels in a solid or liquid, neighboring atoms oscillate.

10. When you hit a drum, it will vibrate at its ____.

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Concepts

8.

Section 24.1

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1.

State whether the following are linear or harmonic motions. a. skiing downhill b. riding on a merry-go-round c. hiking uphill d. jumping on a trampoline

2.

Describe how you find the amplitude of a pendulum and of a water wave.

3.

For the wave in the diagram, which measurement shows the amplitude? Which measurement shows the wavelength?

4.

What will happen to the period of a pendulum if you: a. increase its mass? b. increase its length? c. Challenge: increase the amplitude?

Section 24.2

CHAPTER 24

Read the descriptions below and indicate which of the four types of wave interactions (absorption, reflection, refraction, or diffraction) has occurred for each. a. The distortion of your partially submerged arm makes it look “broken” when viewed from the air. b. You hear the music even though you are seated behind an obstruction at a concert. c. You see yourself when you look at a polished car hood. d. Heavy curtains are used to help keep a room quiet.

Section 24.3

9.

Give an example of a sound with a high pitch and an example of a sound with a low pitch.

10. Do all frequencies of sounds at 40 decibels seem equally loud to your ears? Explain. 11. Why do sound waves travel faster in steel than in water? 12. Explain why the range of human hearing is limited to a particular range of frequencies. 13. A car honking its horn moves toward you. Does the horn’s pitch sound higher or lower than it would if the car were parked? Explain.

5.

Explain how you would make a transverse wave and a longitudinal wave with a long spring toy.

Problems

6.

Below are diagrams representing interactions between waves and boundaries. Identify each interaction by name.

1.

A bicycle wheel spins 25 times in 5 seconds. Calculate the period and frequency of the wheel.

2.

The piston in a gasoline engine goes up and down 3,000 times per minute. For this engine, calculate the frequency and period of the piston.

3.

Determine the period and frequency of the second hand on a clock. Here’s a hint: how long does it take for the second hand to go around?

7.

Can two waves interfere with each other so that the new wave formed by their combination has NO amplitude? Explain your answer.

Section 24.1

CHAPTER 24 ASSESSMENT

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24 4.

Make a harmonic-motion graph for a pendulum. Place time in seconds on the x-axis and position on the y-axis. The period of the pendulum is 0.5 second and the amplitude is 2 centimeters. a. What is the frequency of this pendulum? b. If you shortened the string of this pendulum, would the period get shorter or longer?

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Section 24.2

5.

A wave has a frequency of 10 hertz and a wavelength of 2 meters. What is the speed of the wave?

6.

A sound wave has a speed of 400 m/s and a frequency of 200 Hz. What is its wavelength?

7.

If the frequency of a wave is 30 hertz, how many wavelengths pass a certain point in 30 seconds?

8.

Make a graph of two cycles of a transverse wave with an amplitude of 4 cm and a wavelength of 8 cm. If the frequency of this wave is 10 Hz, what is its speed? You hear the dishwasher with a loudness of 40 dB and a siren outside with a loudness of 60 dB. How much greater is the amplitude of the siren’s sound than the amplitude of the dishwasher’s sound?

10. A sound wave takes 0.2 seconds to travel 306 meters. What is the speed of sound in this material? Through which of the materials in Figure 24.23 is the wave traveling? 11. The diagram to the right shows a harmonic of a standing wave on a vibrating string. a. Which harmonic is shown? b. How many wavelengths are shown? c. What is the length of one wavelength?

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Applying Your Knowledge Section 24.1

1.

How are Newton’s laws of motion helpful in understanding harmonic motion? Use a pendulum as an example.

2.

The Tacoma Narrows Bridge in the state of Washington collapsed in 1940. Research this bridge to find out what caused “Galloping Gertie” to fall. Describe your findings in a paragraph.

Section 24.2

Section 24.3

9.

12. A wave with a period of 1 second comes from the left. At the same time, a wave with a period of 2 seconds comes from the right. The amplitude of each wave is 5 centimeters. Draw a harmonic-motion graph for each of these waves with time on the x-axis and position on the y-axis. Overlay two wavelengths of the 1-second wave on one wavelength of the 2-second wave. Use the superposition principle to determine whether these two waves interfere by constructive interference, destructive interference, or both.

3.

One of the four wave interactions is very important to how plants use light to grow. Guess which interaction this is, and write several sentences to justify your answer.

Section 24.3

4.

When you watch fireworks, sometimes you see the explosion and then hear the sound. Why do you think this is?

5.

People can usually hear sounds with frequencies from 20 to 20,000 hertz. Some animals can hear higher or lower frequencies than people can. Research to find out the hearing ranges of several different animals.

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CHAPTER

25

CHAPTER 25

Light and Optics

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Earth’s most important source of energy is the Sun. Research is currently under way to develop technologies that will be more efficient at capturing this renewable energy resource. In time, we might not need to depend on fossil fuels for heat and electricity. The Sun is also our most important source of light. Plants use sunlight to grow. How do humans use light? For starters, we need light to see. In complete darkness, sight is impossible. If you can see at all in a dark room, it’s because a small amount of light is present. The light might be coming from under a door or from the glow of a digital clock. In this chapter, you will learn about light’s properties. As you read, you will discover that light is unusual. For example, it doesn’t have mass or shape like matter. Light is produced as a result of a disturbance in a magnetic or electric field. Fortunately, the complex topic of light is colorful! Light is involved in how you see color, and how color is produced on paper or a TV screen. In this chapter you will also learn how light is used to enhance vision and to see objects that are miniscule or astronomically far away!

4 What makes a color of light unique but also similar to an X-ray?

4 How do printers and TV screens produce color?

4 How do lenses take advantage of the properties of light?

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25.1 Properties of Light Whether you are looking at the flame of a candle, a car, or this book, light brings information to your eyes. In fact, seeing means forming images in your mind from the light received by your eyes (Figure 25.1). What are the properties of this amazing thing called light?

light - a form of electromagnetic energy.

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Light is fast-moving energy How fast is When you shine a flashlight on a wall, the light leaves your flashlight, travels light? to the wall, bounces off, and comes back to your eyes. You don’t notice this

happening because it happens very fast. Suppose the wall is 170 meters away. The light travels to the wall and back in about one-millionth of a second (0.000001 s). Sound travels much slower than light. If you shout, you will hear an echo one full second later from the sound bouncing off the wall and back to your ears. Light travels almost one million times faster than sound!

Figure 25.1: This girl sees a page in

her book when reflected light carries information about the page to her brain.

The speed of The speed at which light travels through air is about 300 million meters per light, c = 3 × 108 second. Light is so fast, it can travel around the entire Earth 7.5 times in m/s one second. The speed of light is so important in physics that it is given its

own symbol, a lowercase c. When you see this symbol in a formula, remember that it means the speed of light (c = 300,000,000 m/s). What are the Light is a form of electromagnetic energy. The properties of light are that it: other properties of light? • travels extremely fast and over long distances;

• • • • •

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carries energy and information; has color; varies in intensity, which means it can be bright or dim; travels in straight lines; and bounces and bends when it comes in contact with objects.

Light Is Faster than Sound You can use the speed of sound to estimate how far away a lightning strike has occurred. When you see lightning, begin counting the seconds until you hear thunder. Divide the number of seconds you count by five. The result is an estimate of the distance in miles between where you are and where the lightning struck.

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CHAPTER 25

Most light comes from atoms Light is Light is mostly produced by atoms when they release energy. For example, produced by when you stretch a rubber band, you give the rubber band elastic energy. This atoms energy, once released, could become the kinetic energy of a launched paper

airplane. An atom’s released energy produces light.

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Incandescent Atoms release light when they have extra energy. Adding heat is one way to light bulbs give atoms extra energy. Making light with heat is called incandescence.

Incandescent bulbs use electric current to heat a thin wire, or filament. Atoms in the filament convert electrical energy to heat and then to light. However, incandescent bulbs are not very efficient. Only a fraction of the energy of electricity is converted into light, and the rest becomes heat. But, some incandescent bulbs are designed and used to make heat (Figure 25.2). Compact A more efficient type of electric light comes from compact fluorescent lamps, fluorescent light or CFLs (Figure 25.3). A CFL uses about 75 percent less energy, produces bulbs 75 percent less heat, and lasts 10 times longer than a standard incandescent

incandescence - a process that makes light with heat.

fluorescence - a process that makes light when the energy is supplied by electromagnetic radiation, often ultraviolet light.

photon - the smallest possible amount of light, in the form of a wave bundle.

Incandescent bulb Hot, glowing filament emits light

bulb. For this reason, the U.S. Department of Energy recommends replacing incandescent bulbs with CFLs in schools, businesses, and homes. Making light To make light, CFLs use high-voltage electricity to energize atoms of gas in with the lamp. These atoms release the electrical energy directly as high-energy fluorescence ultraviolet light (not heat), the same kind of light that causes sunburn. The

ultraviolet light is absorbed by other atoms in a white coating on the inside surface of the bulb. This coating re-emits the energy (fluoresces) as white light that we can see in a process called fluorescence. Even with this twostep process, fluorescent lamps are still more efficient at producing light than incandescent bulbs. Photons

Light energy comes in tiny wave bundles called photons. Each photon has its own energy. The energy of photons is seen as color. The lowest-energy photons we can see are dull red and the highestenergy photons are violet.

Figure 25.2: An incandescent bulb

makes light by heating a metal filament.

Compact fluorescent lamp Atoms in white coating

Visible light

Ultraviolet light

Energized atoms

Figure 25.3: How fluorescent light is produced.

25.1 PROPERTIES OF LIGHT

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Color and energy What is color? Color is how we perceive the energy of light. All of the colors in the

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rainbow are light of different energies. As you learned on the previous page, red light has the lowest energy we can see, and violet light has the highest energy. As we move through the rainbow from red to yellow to blue to violet, the energy of the light increases. You can use this information to identify that the blue light from a gas flame has higher energy than the yellow-red light from a match (Figure 25.4).

color - the sensation created by the different energies of light falling on your eye.

white light - visible light containing an equal mix of all colors.

White light When all the colors of the rainbow are combined, we see light without any color. We call the combination of all colors white light. The light that is all

Energy, frequency, wavelength, and color

around us most of the time is white light. Sunlight and the electric light in your home and school are examples of white light. Energy and frequency are directly related properties of light. As with other waves, wavelength and frequency of light are inversely related (see the table below). Where wavelength is very small, frequency is extremely high. In fact, the wavelength of light is so small, it is measured in nanometers. One nanometer (nm) is one-billionth of a meter (1.0 × 10–9 m). And the frequency of light waves is so high that scientists use units of terahertz (THz) to measure light waves. One THz is a trillion Hz (1,000,000,000,000 Hz). Now, look at the table to see how color corresponds to the energy, frequency, and wavelength of light. Note: Frequency and wavelength are often given as ranges rather than the single values shown here. Table 25.1: Wavelengths and frequencies of light

Figure 25.4: High-energy flames

such as the ones from a gas stove produce blue light. Fire flames are lower energy and produce yellow-red light.

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CHAPTER 25

What kind of wave is light? Light comes A water wave is an oscillation of the surface of water. A sound wave is an from electricity oscillation of air. What is oscillating in a light wave? The answer is electricity and magnetism and magnetism. Imagine you have two magnets. One hangs from a string and

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the other is in your hand. If you move the magnet in your hand back and forth, you can make the magnet on the string sway back and forth, too (Figure 25.5). How does the oscillation of one magnet get to the other one? In Chapter 17 you learned that magnets create an invisible magnetic field around themselves. When you move a magnet in your hand back and forth, you make a change in the magnetic field. The changing magnetic field causes the other magnet to move. In a similar way, the force between two electric charges is carried by an electric field.

electromagnetic wave - a wave of electricity and magnetism that travels at the speed of light. Light is an electromagnetic wave.

Electromagnetic Any change in an electric or magnetic field travels at the speed of light. If you waves could shake your magnet (or electric charge) back and forth 100 million times

per second, you would make an electromagnetic wave. In fact, it would be an FM radio wave at 100 million Hz (100 MHz). An electromagnetic wave is a traveling oscillation in the electric and magnetic fields. The hard way to make red light

If you could shake the magnet up and down 462 trillion times per second, you would make waves of red light. Red light is a traveling oscillation (wave) in the electric and magnetic fields with a frequency of about 462 THz. From the previous page, what else do you know about red light?

Oscillations of electricity or magnetism create light waves

Anything that creates an oscillation of electricity or magnetism also creates electromagnetic waves. If you repeatedly switch electricity on and off in a wire, the oscillating electricity makes an electromagnetic wave. This is how radio towers make radio waves. Electric currents oscillate up and down the metal towers and create electromagnetic waves of the correct frequency to carry radio signals.

Figure 25.5: Magnets influence each other through the magnetic field. Charges influence each other through the electric field.

25.1 PROPERTIES OF LIGHT

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The electromagnetic spectrum Waves in the The entire range of electromagnetic waves, including all possible electromagnetic frequencies, is called the electromagnetic spectrum. The electromagnetic spectrum spectrum includes radio waves, microwaves, infrared light, ultraviolet light,

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X-rays, and gamma rays. As you can see from the chart below, we use electromagnetic waves for many technologies.

electromagnetic spectrum - the entire range of electromagnetic waves, including all possible frequencies, such as radio waves, microwaves, X-rays, and gamma rays.

The electromagnetic spectrum Radio and television

Microwaves

Radar Radio

Cooking Cellphones

TV Wireless networking

Lower energy Lower frequency Longer wavelength

Infrared Visible Ultraviolet light light light

X-rays

Gamma rays

Sterilizers Black lights

Medicine Industry

Medicine Research

Research

Nuclear energy

Heat lamps TV remote controls

Higher energy Higher frequency Shorter wavelength

Who discovered that white light contains all colors? How was the discovery made? When was it made? This famous scientist is mentioned in this book but not in connection with light!

Properties of You can see that visible light is a small group of frequencies in the middle of electromagnetic the spectrum between infrared and ultraviolet light. The rest of the spectrum waves is invisible for the same reason you cannot see the magnetic field between

two magnets. The energies are either too low or too high for the human eye to detect. Visible light includes only the electromagnetic waves with the range of energy that can be detected by the human eye. Some insects and animals can see or detect other frequencies, including infrared (snakes) and ultraviolet light (bees and birds).

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CHAPTER 25

Section 25.1 Review

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1. Which of the following is NOT a property of light? a. Light is a form of matter less dense than air. b. Light travels in straight lines. c. Light can be different colors. d. Light has different intensities and can be bright or dim.

The speed of light is calculated as frequency multiplied by wavelength (the same as for other waves). Suppose you make light with a frequency of 600 THz.

2. If a room were completely dark, could you see your hand? Explain.

b) Describe what color the light would appear to your eye.

3. What is the source of most light? 4. What is white light? 5. The highest pitch sound you can hear has a wavelength of 1.7 centimeters. How does the wavelength of this sound compare to the size of the items shown in Figure 25.6?

a) What is the wavelength of this light?

You will have to use scientific notation to solve this problem with your calculator. If necessary, ask your teacher or a friend for help.

6. Waves of orange light have a length of only 0.0000006 meter. a. What is this wavelength in nanometers? b. How does the size of this wavelength compare to the wavelength of green light? 7. One hertz equals one cycle per second. Write the frequency of red light (462 THz) in units of cycles per second. 8. The range of wavelengths for one color of light is 570 to 590 nm. What is the color of this light? 9. Which electromagnetic wave has less energy than visible light and more energy than radio waves? a. microwaves b. ultraviolet light c. gamma rays d. X-rays 10. How are all electromagnetic waves similar? How are they different? 11. How does infrared light compare to a gamma ray in terms of energy, frequency, wavelength, and use in technology?

Figure 25.6: Question 5. 25.1 PROPERTIES OF LIGHT

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25.2 Color and Vision The energy of light explains how different colors are physically different. But it doesn’t explain how we see colors. How does the human eye see color? The answer to this question also helps explain why TVs can make virtually all colors by combining only three colors!

photoreceptors - light-sensitive cells on the surface of the retina.

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The human eye Photoreceptors Light enters your eye through the lens and then lands on the retina. On the surface of the retina are light-sensitive cells called photoreceptors

(Figure 25.7). When light hits a photoreceptor cell, the cell releases a chemical signal that travels along the optic nerve to the brain. In the brain, the signal is translated into a perception of color. Cone cells Our eyes have two types of photoreceptors, called cones and rods. Cones respond to color (or cone cells) respond to color (Figure 25.7). There are three types of cone

cells. One responds best to low-energy (red) light. Another responds best to medium-energy (green) light. The third type responds best to higher-energy (blue) light. Rod cells The second type of photoreceptors are rods (or rod cells). Rods respond to respond to light differences in light intensity, but not color (Figure 25.7). Rod cells “see” intensity black, white, and shades of gray. However, rod cells are much more sensitive

than cone cells. At night, colors seem washed out because there is not enough light for cone cells to work. When the light level is very dim, you see “black-and-white” images from your rod cells.

Cone cells detect color. Rod cells detect intensity. Black-and-white A human eye has about 130 million rod cells and 7 million cone cells. Each vision is sharper cell contributes a “dot” to the image assembled by your brain. Because there than color vision are more rod cells, things look sharpest when there is a difference between

light and dark. Black letters on a white background are easier to read than colored letters because each cone cell “colors” the signals from the surrounding rod cells. Because there are fewer cone cells, our color vision is less sharp than our black-and-white vision.

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Figure 25.7: The human eye has two

types of photoreceptors—cones and rods.

What Is Light Intensity? The intensity of light is measured in watts per square meter covered. Light intensity from a small source follows an inverse square law. This means light intensity diminishes as the square of the distance increases. For example, light intensity at 2 meters from the source will be 1/4 less than it was at 1 meter. What will light intensity be at 3 meters from the source?

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CHAPTER 25

How we see colors The additive Because there are three types of cone cells, our eyes work by adding three color process signals to “see” different colors. The color you “see” depends on how much

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energy is received by each of the three types. The brain thinks “green” when there is a strong signal from the green cone cells but no signal from the blue or red cone cells (Figure 25.8). How we perceive color

What color would you see if light creates signals from both the green cones and the red Yellow cones? If you guessed yellow, you are correct. We see yellow when the brain sees yellow Green Red light, or when it gets an equally strong signal White from both the red and the green cone cells at the same time. Whether the light is actually yellow, or a combination of red and green, the Magenta Cyan Blue cones respond the same way and we perceive yellow. If the red signal is stronger than the green signal, we see orange (Figure 25.9). If all three cones send an equal signal to the brain, we see white. The additive primary colors

Figure 25.8: If the brain gets a

signal from only the green cones, we see green.

Two ways to see The human eye can be “tricked” into seeing any color by adding different a color percentages of red, green, and blue. For example, an equal mix of red and

green light looks yellow. However, the light itself is still red and green! The mix of red and green creates the same response in your cone cells as does true yellow light. Do animals see There is much to be learned about color vision in the animal kingdom. To the colors? best of our knowledge, primates (such as chimpanzees and gorillas) are the

only animals with three-color vision similar to that of humans. Some birds, fish, and insects can see ultraviolet light, which humans cannot see. Dogs and cats are thought to have weak color vision due to having only two types of cone cells and a lower proportion of them compared to rod cells. Although both octopi and squid can change their body color better than any other animal, scientists believe that most species cannot see color.

Figure 25.9: If there is a strong red signal and a weak green signal, we see orange. 25.2 COLOR AND VISION

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Making an RGB color image The RGB color Color images in TVs and computers are based on the RGB color model. process RGB stands for red, green, and blue. If you look at a TV screen with a magnifying glass, you will see thousands of tiny red, green, and blue pixels

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(Figure 25.10). A television makes different colors by lighting red, green, and blue pixels to different percentages. For example, a light brown tone is about 50 percent red, 33 percent green, and 17 percent blue. A computer monitor works the same way.

RGB color model - a model for tricking the eye into seeing almost any color by mixing proportions of red, green, and blue light. pixel - a single dot that forms part of an image made of many dots.

Pixels make up TVs, digital cameras, and computers make images from thousands of pixels. images An ordinary TV picture is 640 pixels wide × 480 pixels high, for a total of

307,200 pixels. A high-definition picture looks sharper because it contains more pixels. In the 720p format, HDTV images are 1,280 pixels wide × 720 pixels high, for a total of 921,600 pixels. This is three times as sharp as a standard TV image.

How video Like the rods and cones in your retina, a video camera has tiny light sensors cameras create on a small chip called a CCD (charge-coupled device). There are three color images sensors for each pixel of the recorded image: red, green, and blue. In HDTV,

that means each recorded image contains 921,600 × 3 = 2,764,800 numbers. To create the illusion of motion, the camera records 30 images per second. In terms of data, the HDTV movie you watch represents 2,764,800 × 30, or about 83 million numbers every second.

Figure 25.10: A television makes

colors using tiny glowing dots of red, green, and blue.

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How objects appear to be different colors What gives Your eye creates a sense of color by responding to red, green, and blue light. objects their You don’t see objects in their own light; you see them in reflected light. color? A blue shirt looks blue because it reflects blue light into your eyes

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(Figure 25.11). However, the shirt did not make the blue light. The color blue is not in the cloth. The blue light you see is blue light mixed into white light that shines on the cloth. You see blue because the other colors in white light have been subtracted out (Figure 25.12). The subtractive Colored fabrics and paints get color from a color process subtractive color process. Chemicals

known as pigments in dyes and paints absorb some colors and reflect other colors. Pigments work by taking away colors from white light, which is a mixture of all the colors. The shades in between red, blue, and green happen when small amounts of other colors are reflected. For example, a magenta shirt reflects blue and green light.

The subtractive primary colors Red

Yellow

Magenta Black

Blue

Cyan

Figure 25.11: Why is a blue shirt Green

blue?

The subtractive To make all colors by subtraction, we need three primary pigments. We need primary colors one that absorbs blue (reflects red and green). This pigment is yellow. We

need another pigment that absorbs green (reflects red and blue). This is a pink-purple pigment called magenta. The third pigment is cyan, which absorbs red (reflects green and blue). Cyan is a greenish shade of light blue. Magenta, yellow, and cyan are the three subtractive primary colors (see the illustration above). Different proportions of the three subtractive primary colors change the amount of reflected red, green, and blue light. How the quality of white light affects what we see

A blue shirt won’t look blue in red light. It will look black! The subtractive color model assumes a painted or dyed surface is seen in white sunlight that contains a precise mix of colors. If the “white” has a different mix than sunlight, colors don’t look right. This is why home videos made under fluorescent lights often look greenish. The white from fluorescent lights has a slightly different mix of colors than the white from sunlight.

Figure 25.12: The pigments in a

blue cloth absorb all colors except blue. You see blue because blue light is reflected to your eyes.

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The CMYK color process A subtractive The subtractive color process is often called the CMYK color process for color process the four pigments it uses. CMYK stands for cyan, magenta, yellow, and

black. The letter K stands for black because the letter B is used for the color blue in RGB. Color printers and photographs use CMYK.

CMYK color process - the subtractive color process using cyan, magenta, yellow, and black to create colors in reflected light.

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CMYK are The three pigments—cyan, magenta, and yellow—combine in different pigments proportions to make any color of reflected light. Figure 25.13 shows how

CMYK pigments make green. Theoretically, mixing cyan, magenta, and yellow should make black, but in reality the result is only a muddy gray. This is why a fourth color, pure black, is included in the CMYK process.

Figure 25.13: Creating the color green using cyan and yellow paints.

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Why plants are green Light is Plants absorb energy from light and convert it to chemical energy in the form necessary for of sugar. This process is called photosynthesis. The vertical (y) axis of the photosynthesis graph in Figure 25.14 shows the percentage of different colors of light that are

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absorbed by a plant. The x-axis shows the colors of light. The graph line shows how much and which colors of visible light are absorbed by plants. Based on this graph, can you explain why plants look green? Why most plants are green

The important molecule that absorbs light in a plant is called chlorophyll. There are several forms of chlorophyll. They absorb mostly blue and red light, and reflect green light. This is why most plants look green. The graph in Figure 25.14 shows that plants absorb red and blue light to grow. A plant will die if placed under only green light!

Plants reflect Why don’t plants absorb all colors of light? The reason is the same reason you some light to wear light-colored clothes when it’s hot outside. Like you, plants must reflect keep cool some light to avoid absorbing too much energy and overheating. Plants use

visible light because the energy is just enough to change certain chemical bonds, but not enough to completely break them. Ultraviolet light has more energy but would break chemical bonds. Infrared light has too little energy to change chemical bonds. Why leaves The leaves of some plants, such as sugar maple trees, turn brilliant red or gold change color in the fall. Chlorophyll masks other plant pigments during the spring and

summer. In the fall, when photosynthesis slows down, chlorophyll breaks down and red, orange, and yellow pigments in the leaves are revealed.

Figure 25.14: Plants absorb energy from light. The plant pigment chlorophyll absorbs red and blue light, and reflects green light. This is why plants look green.

What About Red Plants? All plants that use sunlight to grow have chlorophyll, but some do not look green. Come up with a hypothesis to explain this observation.

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Section 25.2 Review

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1. If humans have only three types of color photoreceptors, how can we see so many different colors? 2. Why is it easier to read black text on a white background than to read green text, or text of any light color, on a white background? 3. Why might it be a good idea to put a light in your clothes closet? (Hint: What kind of vision do we have in dim light?) 4. How does the human eye detect the color magenta? 5. Do you think this text book was printed using the CMYK color process or the RGB color process? Explain your answer. 6. If you were going to design the lighting for a play, would you need to understand the CMYK color process, the RGB color process, or both? Explain your answer. 7. Suppose you have cyan, magenta, yellow, and black paint. Which colors would you mix to get blue? 8. How is a CCD like the retina in a human eye? 9. How is the color black produced in the CMYK color process? How does this differ from the RGB color process? 10. A red shirt appears red because: a. the shirt reflects red light. b. the shirt absorbs red light. c. the shirt emits green and blue light. d. the shirt reflects magenta and blue light. 11. Explain the role of chlorophyll in plants. How does this pigment molecule help plants survive? 12. What would happen if you tried to grow a green plant in pure green light? Would the plant live? Explain your answer. 13. Propose an explanation for how the top image in Figure 25.15 is related to the four images below it.

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Figure 25.15: Question 14. Pictures from Dots A color printer, such as an inkjet printer, makes color images by printing small dots. If there were only four dots per inch, your eye would see the individual dots instead of the picture the dots are supposed to make. How many dots must there be (per inch) to trick the eye into seeing a smooth image? How many dots per inch do printers in your home or school use?

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25.3 Optics Optics is the science and technology of light. Almost everyone has experience with optics. For example, trying on new glasses, checking your appearance in a mirror, looking through binoculars, or admiring the sparkle from a diamond ring all involve optics.

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Basic optical devices Lenses A lens bends light in a specific way. A converging lens bends light so that the

lens - an optical device for bending light rays.

mirror - a surface that reflects light rays.

prism - a glass shape with flat, polished surfaces that can both bend and reflect light.

light rays come together in a point. This is why a magnifying glass makes a hot spot of concentrated light (Figure 25.16). A diverging lens bends light so it spreads light apart instead of bringing it together. An object viewed through a diverging lens appears smaller than it would look without the lens. Mirrors A mirror reflects light and allows you to see yourself. Flat mirrors show a

true-size image. Curved mirrors distort images. The curved surface of a fun house mirror can make you appear thinner, wider, or even upside down! Prisms A prism, usually a solid piece of glass with flat polished surfaces, can both

bend and reflect light. Telescopes, cameras, and laser scanners use prisms of different shapes to bend and reflect light in precise ways. A prism also bends the colors of white light so that you can see that it is made up of a rainbow of colors. A cut diamond is a kind of prism with many flat, polished surfaces. The “sparkle” that makes diamonds so attractive comes from light being reflected many times as it bounces around the gem.

Figure 25.16: A magnifying glass is a converging lens. This is why a magnifying glass can be used to make a hot spot of concentrated light. You should NOT try this yourself—the science is interesting but can be unsafe.

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Ways that matter affects light Light’s The following list describes what can happen when light interacts with interactions matter such as glass, wood, or anything else. You can see these interactions

illustrated in Figure 25.17.

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• Transparency: light passes through almost unchanged • Translucency: light passes through but is scattered • Reflection: light bounces off • Absorption: light transfers its energy Transparency Materials that allow light to pass through are called transparent. Polished glass is transparent, as are some kinds of plastic. Air is also transparent. You can see an image through a transparent material if the material’s surface is smooth, like a glass window.

transparent - describes matter that allows light rays to pass through without scattering.

translucent - describes matter that allows light rays to pass through but also scatters them in all directions.

Translucency An object is translucent if it scatters light in many directions as it allows

the light to pass through. Tissue paper and frosted glass are translucent materials. Try holding a sheet of tissue paper up to a window. You can’t see an image through it. Reflection and Almost all surfaces reflect some light. A mirror is a very good reflector, but a absorption sheet of white paper is also a good reflector. The difference is in how they

reflect. When light is absorbed, its energy is transferred. This is why a black road surface gets hot on a sunny day. A perfect absorber looks black because it absorbs most of the light that falls on it. All interactions at once

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When light encounters matter, it can interact in multiples ways. For example, a green shirt both absorbs and reflects colors of light. Although it is mostly transparent, a glass window does absorb some light. Glass also reflects and scatters some light (translucency). A material interacts differently with light depending on how well the surface is polished. For instance, the rough surface of frosted glass makes it translucent.

Figure 25.17: The four interactions of light with matter.

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Light rays What are light When light moves through a material, it travels in straight lines. Diagrams rays? that show how light travels use straight lines and arrows to represent light rays. Think of a light ray as a thin beam of light, like a laser beam. The arrow

shows the direction in which the light is moving.

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Reflection and When light rays move from one material into another, the rays might bounce refraction or bend. Reflection happens when light bounces off a surface. Refraction

happens when light bends while crossing a surface or moving through a material. Reflection and refraction cause many interesting changes in the images we see.

light ray - an imaginary line that represents a beam of light.

reflection - the process of light rays bouncing off a surface. Light reflects from a mirror. refraction - the process of bending while crossing a surface. Light refracts when passing from air into water.

Reflection When you look in a mirror, objects that are in front of the mirror appear as if creates images they are behind the mirror. Light from the object strikes the mirror and in mirrors reflects to your eyes. The image reaching your eyes appears to your brain as if

the object really was behind the mirror. This illusion happens because your brain “sees” the image where it would be if the light reaching your eyes had traveled in a straight line. Refraction When light rays travel from air to water, they refract. This is why a straw in a changes how glass of water looks broken or bent at the water’s surface (Figure 25.18). objects look Look at some objects through a glass of water; move the glass closer and

Figure 25.18: Refraction bends light rays so the straw appears to be in a different place!

farther away from the objects. What strange illusions do you see?

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Reflection What is When you look into a mirror, your image appears to be the same distance reflection? from the other side of the mirror as you are on your side of the mirror. If you

step back, so does your image. Reflected light forms images in mirrors.

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The angle of incidence equals the angle of reflection

Imagine a ray of light striking a mirror. The incident ray is the light ray that strikes the surface of the mirror. The reflected ray is the light ray that bounces off the surface of the mirror (Figure 25.19, top).The lower part of Figure 25.19 shows the reflection of a light ray. The angle of incidence is the angle between the incident ray and an imaginary line drawn perpendicular to the surface of the mirror called the normal line. Perpendicular means “at a 90-degree angle”; it is also called a right angle. The angle of reflection is the angle between the reflected light ray and the normal line. The law of reflection states that the angle of incidence is equal to the angle of reflection.

specular reflection - “shiny” surface reflection, where each incident ray produces only one reflected ray.

diffuse reflection - “dull” surface reflection, where each incident ray produces many scattered rays.

Reflection

The law of reflection: angle of incidence equals angle of reflection Specular and You see your image when you look in a mirror because parallel light rays diffuse hitting the mirror at the same angle are all reflected at the same angle. This is reflection called specular reflection. You can’t see your image when you look at a

white piece of paper because even though it seems smooth, its surface has tiny bumps on it. When parallel light rays hit a bumpy surface, the bumps reflect the light rays at different angles. Light rays reflected at different angles cause diffuse reflection. Many surfaces, such as polished wood, are in between rough and smooth and create both types of reflection. Specular reflection

Diffuse reflection

Mirror The angle of incidence is always equal to the angle of reflection. Normal line (perpendicular to mirror) Angle of incidence

Angle of reflection

Specular and diffuse reflection Incident ray

30º 30º

Reflected ray 90º

Mirror

Figure 25.19: This diagram Mirror

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Concrete

Polished wood

illustrates the law of reflection.

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Refraction The index of Eyeglasses, telescopes, binoculars, and fiber optics are a few inventions that refraction use refraction to change the direction of light rays. Different materials have different abilities to bend light. Materials with a higher index of refraction

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bend light by a greater angle. The index of refraction for air is approximately 1.00. Water has an index of refraction of 1.33. A diamond has an index of refraction of 2.42. Diamonds sparkle because of their high index of refraction. Table 25.2 lists the index of refraction for some common materials. Table 25.2: The index of refraction for some common materials Material

Index of refraction

Air Water Ice Glass Diamond

1.00 1.33 1.31 1.45–1.65 2.42

The direction a When light goes from air into glass (A), it bends toward the normal line light ray bends because glass has a higher index of refraction than air. When the light goes

index of refraction - a number that measures how much a material is able to bend light.

A Trick of Refraction If two materials have the same index of refraction, light doesn’t bend at all. Here’s a neat trick you can do with a glass rod. You see the edges of a glass rod because of refraction. The edge appears dark because light is refracted away from your eyes. Vegetable oil and glass have almost the same index of refraction. If you put a glass rod into a glass cup containing vegetable oil, the rod disappears because light is NOT refracted around its edges!

from glass into air again (B), it bends away from the normal line. Coming out of the glass, the light ray is going into air with a lower index of refraction than glass.

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Lenses A lens and its An ordinary lens is a polished, transparent disc, usually made of glass. The optical axis surfaces are curved to refract light in a specific way. The exact shape of a

lens’s surface depends on how strongly and in what way the lens needs to bend light.

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How light travels Common lenses have surfaces shaped like part of a sphere. Any radius of a through a sphere is also a normal line to the surface. When light rays fall on a spherical converging lens surface from air, they bend toward the normal line (Figure 25.20). For a converging lens, which has convex surfaces, the first surface (air to glass)

converging lens - a lens that bends exiting light rays toward the focal point.

diverging lens - a lens that bends exiting light rays outward, away from the focal point.

bends light rays toward the normal line. At the second surface (glass to air), the rays bend away from the normal line. Because the second surface “tilts” the other way, it also bends rays toward the focal point. Focal point and Light rays that enter a converging lens parallel to its axis bend to meet at a focal length point called the focal point (see the illustration below). Light can go through

a lens in either direction, so there are always two focal points, one on either side of the lens. The distance from the center of the lens to the focal point is the focal length. The focal length is usually (but not always) the same for both focal points of a lens. Focal point

Converging lens

Focal point

Figure 25.20: Most lenses have spherically shaped surfaces.

Optical axis of lens

Focal length

Focal length

Diverging lenses Figure 25.21 shows how parallel light rays enter and then exit a diverging lens, which has concave surfaces. As with the converging lens, light bends

toward the normal line when it enters and away from the normal line when it exits the lens. However, because of the shape of the lens surfaces, the light ends up bending away from the optical axis and away from the focal point. For a diverging lens, you can show the focal point in a diagram by extending the path of the exiting light rays back through the lens. These extended lines are drawn as dotted lines in Figure 25.21.

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Figure 25.21: Diverging lens.

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Section 25.3 Review

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1. What process takes place when light rays enter a lens? a. reflection b. refraction c. absorption d. transparency 2. Can light be reflected and refracted at the same time? If so, give an example. 3. What optical devices do you use during an average day? 4. Name an object that is mostly transparent, one that is translucent, one that is mostly absorbent, and one that is mostly reflective. 5. Windows that look into bathrooms or other private spaces are often translucent instead of transparent. Why? 6. Why can you see your own reflected image in a mirror but not on a dry, painted wall?

Twinkling of Stars Another example of the refraction of light is the twinkling of a star in the night sky. To reach your eyes, starlight must travel from space through Earth’s atmosphere, which varies in temperature and density. Cold pockets of air are more dense than warm pockets. Starlight is refracted as it travels through the various air pockets. Since the atmosphere is constantly changing, the amount of refraction also changes. The image of a star appears to “twinkle,” or move, because the light coming to your eye follows a zigzag path due to refraction.

7. Describe how your brain interprets the light rays reflected off a mirror. 8. How are light rays shown in diagrams? 9. Make a diagram that shows a light ray striking a mirror. Label the angle of incidence, the angle of reflection, and the normal line. 10. The index of refraction describes: a. the color of a material. b. the focal length for a lens. c. how much a material bends light rays. d. whether a material is transparent or translucent. 11. A clear plastic rod seems to disappear when it is placed in water. Based on this observation and Table 25.1, predict the index of refraction for the plastic. 12. Fill in the blank. When light travels from water into air, the refracted light ray bends __________ (away from or toward) the normal line. 13. What is the difference between a converging lens and a diverging lens? 25.3 OPTICS

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Chapter 25 Assessment Vocabulary

Section 25.3

13. A surface with ____ produces a single reflected light ray for each incident ____.

Select the correct term to complete the sentences.

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fluorescence

translucent

CMYK color process

pixel

RGB color model

incandescence

prism

index of refraction

photon

light

white light

diffuse reflection

light ray

transparent

electromagnetic wave

mirror

converging lens

diverging lens

reflection

specular reflection

photoreceptors

refraction

electromagnetic spectrum

color

15. Three examples of optical devices are: ____, ____, and ____. 16. Glass is a(n) ____ material because light passes through it without scattering. 17. ____ materials allow light to pass through but scatter it in all directions. 18. The ____ of water is 1.33. 19. Surfaces that scatter light when it reflects have ____.

lens

20. A(n) ____ bends light rays inward toward the focal point.

Section 25.1

1.

Visible ____ is what the human eye uses to see.

2.

You can use light produced by ____ to heat food.

3.

Atoms produce light by ____.

4.

A(n) ____ travels at the speed of light.

5.

A light wave at 500 THz is the ____ orange.

6.

You see all the colors of ____ when you see a rainbow.

7.

Ultraviolet light and microwaves are part of the ____.

8.

A(n) ____ is the smallest possible amount of light.

Section 25.2

9.

14. ____ occurs when light enters a material and bends.

21. A(n) ____ bends light rays away from the focal point. 22. ____ happens when light rays interact with a mirror.

Concepts Section 25.1

1.

List four properties of light.

2.

Are the properties of visible light the same as the properties of electromagnetic waves? Why or why not?

3.

What role do atoms play in producing light?

4.

What is the relationship between the frequency and wavelength of light?

5.

Compare the speed, energy, wavelength, and frequency of red light and blue light.

6.

Describe an electromagnetic wave. How is one made? Is it possible for a human being to make an electromagnetic wave? Why or why not?

An HDTV screen has more ____(s) than a regular TV screen.

10. Magenta is a pigment used in the ____. 11. The ____ is used by video cameras to achieve a range of colors. 12. ____ are special cells on the surface of the retina that detect color and light intensity.

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7.

A flame from a Bunsen burner is reddish at the top and blue near the opening of the burner. Where is the flame hottest? Explain your answer.

Section 25.2

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

8.

Describe the types, number, and sensitivity of the photoreceptors in the human eye.

9.

Your brain perceives color by an additive process. How would you see the following combinations of light colors? a. red + blue b. blue + green c. red + green d. red + blue + green

10. For stage lighting for a play in a theater: a. a magenta spot of light is created along with a green spot of light. What happens when these two spots of light combine? b. light from a blue spotlight is combined with light from a green spotlight. What color light is produced? 11. In the CMYK color process, why is black pigment used instead of mixing cyan, magenta, and yellow pigments?

CHAPTER 25

Section 25.3

18. How is a prism different from a mirror? 19. How do transparent and translucent materials differ? 20. Name the ways in which light can interact with matter. Give an example of a situation where more than one interaction happens at the same time. 21. Describe the difference between refraction and reflection. 22. List the different types of light interactions that are taking place in this image of stained glass. 23. Diamond has a higher index of refraction than water. What does this mean? 24. Explain how a converging lens changes the direction of light. 25. What is the difference between the focal length of a lens and its focal point?

Problems Section 25.1

1.

Red light can have a wavelength of 0.0000007 meters. What is this wavelength in units of nanometers?

2.

14. What primary additive colors of light will be allowed to pass through a magenta filter?

Frequencies of 462 THz, 517 THz, and 638 THz represent the frequencies of three colors: blue, red, and yellow. Match each frequency to its color.

3.

15. Describe the difference between the light you would see from a flashlight and the light you see from a printed page.

Lightning strikes in the distance and six seconds later, thunder is heard. How far away was the lightning strike?

4.

16. Compare the way color is produced by a TV screen with how color is printed in an illustration in this book.

How long does it take for light to travel from the Sun to Earth (about 150 million kilometers)?

5.

A 20-watt compact fluorescent lamp (CFL) costs about $5.00, and a 75-watt incandescent bulb costs only $1.00. Both devices produce similar amounts of light. Why might it be worth it to buy the more expensive CFL?

12. Most objects do not make their own light, so how do we see the colors of these objects? 13. What colors of light are reflected by the pigment cyan?

17. Why do the leaves of most plants look green?

CHAPTER 25 ASSESSMENT

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6.

LIGHT AND OPTICS

Use this table to answer the following questions.

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a.

b.

c.

You can remember the order of the colors of light by remembering the name “Roy G. Biv.” Each letter stands for a color. How would you describe the order of these colors in terms of wavelength, frequency, and energy? A friend says to you that his favorite color on this table is the third highest in terms of frequency but not as high energy as the color blue. What color is your friend talking about? Why is the energy of a wave directly related to its frequency? Come up with a hypothesis.

Section 25.2

7.

What color will a blue shirt appear in pure red light?

8.

Which of the CMYK colors would you mix if you wanted to produce the following colors of ink? a. red b. green c. blue

9.

Compare the quality of the images produced by your eyes, a regular TV screen, and an HDTV screen in terms of pixels.

10. Identify the color process (RGB or CMYK) used in each step. a. Take a photograph with a digital camera. b. The image appears on a computer monitor. c. Print the image using a laser printer. d. See the image on paper with your eyes. 11. Answer the following questions using the absorption graph shown. a. Which colors of light are absorbed the most by plants? b. Which colors of light are reflected the most by plants? c. Based on the information from the absorption graph, explain why a plant will grow more quickly if it is grown in white light rather than green light.

Absorption of light by plant pigments 100

Absorption (%)

CHAPTER 25

80 60 40 20 0

Red

Green

Low

Blue High

Energy

Section 25.3

12. Glare from headlights can make it hard to see when driving at night, and glare is worse when the roads are wet. Explain why, in terms of the two types of reflection. 13. Why do ambulances often have the word AMBULANCE reversed on the front? 14. The angle of reflection for a light ray reflecting off a mirror is 40 degrees. What is the angle of incidence for the incident ray? Justify your answer. 15. A light ray bends away from the normal line when passing from glass to a liquid. Based on this information, how does the index of refraction for the liquid compare to the index of refraction for the glass? 16. A clear plastic ball seems to disappear when placed in a liquid. What does this tell you about the indices of refraction for the clear plastic and the liquid?

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Applying Your Knowledge

8.

When you learned about waves in Chapter 24, you learned about diffraction and interference. Light waves can also be diffracted and they experience interference. In the early 1800s, Thomas Young used these properties of light to provide evidence of the wave theory of light. Find out more about Young’s work and write a paragraph about it.

9.

Research how the human eye works. a. Based on your findings, describe the roles of the iris, pupil, retina, cornea, optic nerve, and lens. b. The following diagram illustrate how light from an object forms an image on your retina. This diagram implies that we see all objects upside down. Is that true? Of course not! Find out why.

Section 25.1

1.

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Electromagnetic waves are useful for sending data and information from one place to another. For example, cell phones use microwaves and televisions use radio waves. Explain why these waves are so effective. Pick one device that uses electromagnetic waves to send information and explain how it works.

2.

Thomas Edison is just one of many inventors who contributed to making electric light accessible to people. Research how one or more scientists contributed to the electric incandescent bulb. What is the general feeling about these types of light bulbs today?

3.

Describe the health connection between ultraviolet light and vitamin D.

4.

Make a chart that compares a photon and an atom.

CHAPTER 25

Section 25.2

5.

Pick a common animal and find out about this animal’s eyesight. Does it see colors? Is the animal nocturnal?

6.

Color blindness is a condition in which a person has difficulty distinguishing certain colors. a. Explain more about color blindness. b. How common is color blindness? c. How has society made modifications to assist people with color blindness?

Section 25.3

7.

Find out how white light is split into the colors of visible light by the following objects. Identify which light interaction is involved in splitting the light. a. Glass prism b. Water droplets in the atmosphere c. Spectrometer

10. Challenge: A ray diagram is a special diagram that helps you see how light passes through a lens and forms an image. Ray diagrams for converging and diverging lenses were shown in this chapter. From those diagrams, you can tell that each lens forms images and refracts light differently. Find out the answers to the following questions. a. What is the difference between a real image and a virtual image? b. Which of these types of lenses is used for magnifying objects? How does this lens magnify objects? c. Which of these lenses forms a smaller, virtual image? Why?

CHAPTER 25 ASSESSMENT

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Matter and Motion in the Universe Chapter 26

The Solar System

Chapter 27

Stars

Chapter 28

E xploring the Universe

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‹ Try this at home Did you ever wonder how people study objects in space with out being able to travel to them or touch them? To do this, astronomers use a technique called remote sensing. Try this activity to get an idea how remote sensing works. Fill three glasses to the same level with water. Get a small lamp and remove the shade. Collect three bulbs each with different wattage. Put the lowest wattage bulb in the lamp. Use a thermometer to measure the temperature of the water in the first glass. Point the light toward the glass and turn the light on for 5 minutes. Measure the temperature at the end of the five minutes. Repeat the procedure for each of the bulbs. Which bulb has the most power? Since you didn’t actually measure the power, how did you know? What did you measure?

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26

CHAPTER 26

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The eight major planets of our solar system combined contain 250 times the surface area of Earth. This vast territory includes environments baked by heat and radiation (Mercury) and frozen colder than ice (Neptune). Venus, the most Earth-like planet in size, has an atmosphere of carbon dioxide and sulfuric acid that would be instantly fatal to any form of life on Earth. Our own crystal blue world is unique in having the right balance of temperature and environment to sustain life—or is it? Might there be unusual forms of life, unknown to us, on the other planets? Scientists have recently discovered living organisms that feed off hot sulfur emissions from volcanoes on the ocean floor. These organisms might be able to survive on Venus. In this chapter, you will read about the planets, the Sun, and other objects in our solar system.

4 How did scientists develop the model for our solar system?

4 Why do we observe various astronomical cycles on Earth?

4 What makes a planet a planet?

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26.1 Motion and the Solar System

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Many objects in the sky appear to change position, and sometimes their shape, over time. For example, the Moon appears to change its shape each night along with the time and position that it rises and sets on the horizon (Figure 26.1). Ancient astronomers kept track of those changes and developed calendars based on their observations. Eventually, a conceptual model of our solar system and its motion began to develop. In this section, you will learn how that model developed and changed over time.

constellation - a group of stars that, when seen from Earth, form a pattern.

Observing patterns in the sky The position of the sunset and sunrise changes over time

Have you ever noticed that the position of the sunrise and sunset appears to shift along the horizon throughout the year? Ancient astronomers used a landmark, such as a building or tree, to mark the point where the Sun rose or set each day. By marking the extreme positions of the Sun at sunrise or sunset, they could determine the passage of one year. Figure 26.1: The Moon appears to change its shape and the time and position at which it rises and sets.

The rising and setting positions of the stars do not change over time

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In contrast to the Sun and the Moon, the rising and setting positions of the stars do not appear to change along the horizon over short periods of time. However, the time that stars rise or set each night gradually changes during a year. A result of this gradual change in rising and setting times is that different constellations are visible in the night sky at different times of the year. A constellation is a group of stars that, when seen from Earth, form a pattern. Perhaps the most familiar of the 88 recognized constellations is the Big Dipper, which is part of a larger constellation called Ursa Major—the Great Bear (Figure 26.2).

Figure 26.2: The Big Dipper is part of a larger constellation, Ursa Major.

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CHAPTER 26

The Earth-centered model Wandering stars Through their observations of the night sky, ancient astronomers noticed that

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five bright objects seemed to wander among the constellations. They called these five objects planets, from the Greek word meaning “wandering star,” and named them Mercury, Venus, Mars, Jupiter, and Saturn. It took hundreds of years, and many scientists, to figure out an explanation for the motion of the planets. Even though they did not have telescopes, ancient astronomers found ways to predict the motion of the planets and began to develop early models of our solar system. The apparent Early astronomers had difficulty explaining the apparent paths of the planets. paths of the If you observe the position of a planet among the constellations each night planets over many months, you will notice that it appears to travel in a certain path.

Figure 26.3: The apparent path of a planet over many months.

On a daily basis, a planet appears to travel from West to East against the background of constellations. Occasionally a planet appears to reverse direction, and travels from east to west. Then, the planet goes back to its west to east path. Figure 26.3 shows the apparent path of a planet over the course of many months. Ptolemy’s model of the solar system

In 140 AD, the Greek astronomer Ptolemy developed a model that explained the apparent path of the planets (Figure 26.4). He hypothesized that each planet moved on a circle, which, in turn, moved on a larger circle around Earth. Ptolemy reasoned that the smaller circles caused the apparent “backward” path of the planets (see the diagram at the left). In his model, the stars moved on a “celestial sphere” beyond the planets. Ptolemy’s model assumed that Earth was at the center of the solar system. However, his model allowed others to only approximately predict the motions of the planets.

Figure 26.4: Ptolemy’s model

explained the apparent path of the planets.

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The Sun-centered model The Sun is at the In 1543, the Earth-centered model of the solar system was challenged by a center of the Polish astronomer named Nicolas Copernicus. While the Ptolemaic model solar system could predict the positions of the planets, Copernicus found that its predictions

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became less and less accurate over the centuries. In Copernicus’ model, the Sun was at the center of the solar system and the planets, including Earth, orbited in circles around the Sun. Copernicus reasoned that the apparent backward paths of the planets were the result of Earth's motion, combined with the motion of the other planets (Figure 26.5). Planets reflect The invention of the telescope supported the Sun-centered model of the solar light from the system. Before telescopes, it appeared that the planets gave off their own Sun light. Today, we know that we see the planets because they reflect light from

the Sun. For example, Venus appears as a crescent like the Moon, becoming dark at times. This is because Venus does not give off its own light. When Earth is on the same side of the Sun as Venus, we see Venus’s shadowed side. Galileo and the The phases of Venus, discovered by telescope Galileo in the 1600s, were part of the

evidence that eventually overturned Ptolemy’s model. Using a telescope he built himself, Galileo made two discoveries that strongly supported Copernicus’ ideas. First, he argued that the phases of Venus could not be explained if Earth were at the center of the planets (right, top). Second, he saw that there were four moons orbiting Jupiter (right, bottom). This showed that not everything in the sky revolved around one central object such as Earth.

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Figure 26.5: The Copernicus model

of the solar system placed the Sun at the center. His model also showed how the apparent paths of the planets were the result of Earth’s motion, combined with the motion of the other planets.

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Gravitational force All objects In 1687, Isaac Newton’s addition to our understanding of gravity helped attract astronomers explain why objects in the solar system orbit each other. Gravitational force is the force of attraction between all objects. The

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Gravitational force is relatively weak

The law of universal gravitation

gravitational force that you are most familiar with is the one between you and Earth. We call this force your weight. But gravitational force is also acting between the Sun, Earth, and the other planets. All objects that have mass attract each other through gravitational forces. You don’t notice the attractive force between ordinary objects because gravity is a relatively weak force. For example, a gravitational force exists between you and this book, but you cannot feel it because both masses are small (Figure 26.6). It takes a huge mass, such as Earth’s, to create gravitational forces that are strong enough to feel and measure. The law of universal gravitation explains how the strength of the force depends on the mass of the objects and the distance between them. As you can see from the equation below, gravitational force increases as the masses of the objects increase. The distance between objects also affects gravitational force but in an inverse way. The closer objects are to each other, the stronger the gravitational force between them. The farther apart, the weaker the gravitational force.

gravitational force - the force of attraction between all objects. law of universal gravitation states that the strength of the gravitational force depends on the mass of the objects and the distance between them.

Comparing gravitational forces Person Mass = 50 kg Book Mass = 2 kg Gravitational force = 0.000000003 N

Gravitational force = 490 N

Earth Mass = 6 trillion kg

Gravity on Earth The strength of gravity on the surface of Earth is 9.8 N/kg. Like pounds, and the Moon newtons are a measure of force. There are 4.448 newtons per one pound.

Earth and a 1-kilogram object attract each other with 9.8 newtons of force. In comparison, the strength of gravity on the Moon is only 1.6 N/kg. Your weight on the Moon would be one-sixth what it is on Earth. The Moon’s mass is much less than Earth’s, so it creates less gravitational force.

Figure 26.6: The gravitational force

between you and Earth is stronger than the force between you and your book because of Earth’s large mass.

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Orbits Kepler and An orbit is a regular, repeating path that an object in space follows around orbits another object. In 1600, German mathematician Johannes Kepler determined

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that the orbits of the planets were not perfect circles but slightly elliptical in shape. This explained the small irregularities in the path of the planets across the sky. Kepler also explained that a planet orbits more slowly when it is farther from the Sun and faster when it is closer to it. Why the Moon Earth and the other planets in our does not fall to solar system orbit the Sun. The Earth Moon orbits Earth. Why doesn’t the

force of gravity pull Earth into the Sun (or the Moon into Earth)? To answer this question, imagine kicking a ball off the ground at an angle. If you kick it at a slow speed, it curves and falls back to the ground. The faster you kick the ball, the farther it goes before hitting the ground. If you could kick it fast enough, the curve of the ball’s path would match the curvature of Earth. The ball would go into orbit instead of falling back to Earth. An object launched at 8,000 m/s will orbit Earth.

orbit - a regular, repeating path that an object in space follows around another object.

Two of Kepler’s laws 1. The orbits of the planets are not perfect circles but are slightly elliptical. 2. A planet moves more slowly when it is farther from the Sun and faster when it is closer to it.

Inertia and Isaac Newton explained that an orbit results from the balance between gravitational inertia (the forward motion of an object in space), and gravitational force. force According to Newton’s first law, inertia causes objects to tend to keep

moving in a straight line. Force is needed to change an object’s speed or direction. Because of inertia, the planets are moving in a direction at a right angle to the pulling force of gravity. This means that without the pull of gravitational force, a planet would travel off into space in a straight line. The balance between the planet’s inertia and the gravitational force between the planet and the Sun results in the planet’s orbit (Figure 26.7).

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Figure 26.7: An orbit results from the balance between inertia and gravitational force.

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The current model of the solar system The discovery of At the time of Copernicus and Galileo, astronomers thought that there were two additional only six planets: Mercury, Venus, Earth, Mars, Jupiter, and Saturn. The distant planets planets Uranus and Neptune are far from the Sun and don’t reflect much light

solar system - the Sun and all objects that are bound by gravitational force to the Sun.

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back to Earth. These planets were not discovered until telescopes became powerful enough to see very faint objects. Solar system Today, we define the solar system as the Sun and all objects that are bound definition by gravitational force to the Sun. The gravitational force of the Sun keeps the

solar system together just as gravity keeps the Moon in orbit around Earth. The solar system includes eight major planets and their moons, and a large number of smaller objects (dwarf planets, asteroids, comets, and meteors). The inner solar system

The outer solar system

Earth

The orbits of the planets are not true circles, but ellipses. An ellipse is shaped like an oval. While the actual paths are nearly true circles, the Sun is not at the center, but is off slightly to one side. For example, Mercury’s orbit is shifted 21 percent to one side of the Sun.

Neptune Venus

Saturn

SUN

Mars

Jupiter Mercury Uranus Pluto (dwarf planet)

Inner and outer The solar system is roughly divided into the inner planets (Mercury, Venus, planets Earth, and Mars) and the outer planets (Jupiter, Saturn, Uranus, and Neptune).

The dwarf planet Pluto is the oldest known member of a smaller group of frozen worlds orbiting beyond Neptune. The diagram above shows the orbits of the planets (the planets are not shown to scale). Notice that Neptune is farther from the Sun than the dwarf planet Pluto over part of Neptune’s orbit.

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Comparing sizes and distances in the solar system Relative sizes The Sun, which will be discussed in Chapter 27, is by far the largest object in

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the solar system. The next largest objects are the planets Jupiter, Saturn, Uranus, and Neptune. As you can see from the scale diagram below, the planets Mercury, Venus, Earth, and Mars appear as small specks when compared with the size of the Sun.

astronomical unit - equal to 150 million km, or the average distance from Earth to the Sun.

Figure 26.8: One AU is equal to 150

million kilometers. If Earth is 1.0 AU from the Sun, then Mercury, with a distance of 58 million kilometers, is 0.39 AU from the Sun.

Distance Astronomers often use the average distance of Earth from the Sun as a measurement of distance in the solar system. One astronomical unit (AU)

is equal to 150 million kilometers, or the average distance from Earth to the Sun. Mercury averages 58 million kilometers from the Sun. To convert this distance to astronomical units, divide this distance by 150 million kilometers. Mercury is therefore, 0.39 AU from the Sun (Figure 26.8). Figure 26.9 lists the planets and their average distance from the Sun in astronomical units.

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Planet

Average distance from the Sun (AU)

Mercury

0.39

Venus

0.72

Earth

1.0

Mars

1.5

Jupiter

5.2

Saturn

9.5

Uranus

19.2

Neptune

30.0

Figure 26.9: Average distances of the planets from the Sun in AU.

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Section 26.1 Review 1. How did ancient astronomers distinguish the planets from other stars in the night sky?

Astronomical Distances

2. How did Ptolemy explain the apparent motion of the planets among the constellations?

Solve the following distance problems using the information in Figure 26.9.

3. How is Copernicus’ model different than Ptolemy’s model of the solar system?

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4. What important contribution did Newton make to our solar system model? 5. What important contribution did Kepler make to our solar system model? 6. What makes planets visible in the night sky? 7. Name the planets in order of how far they are from the Sun, starting with the planet nearest to the Sun. 8. The force that holds the solar system together is called ________. 9. What is an astronomical unit? 10. Gravitational force gets weaker as _____ increases and gets stronger as the _____ of the objects increases.

1. The average distance of Jupiter from the Sun is 5.2 AU. What is Jupiter’s average distance from the Sun in kilometers? (Hint: 1 AU = 150,000,000 km) 2. What is the average distance of Neptune from the Sun in kilometers? 3. The average distance of dwarf planet Pluto from the Sun is 5,913,520,000 km. How far is Pluto from the Sun in AU? 4. The minimum distance of Mars from Earth is 56,000,000 km. Express this distance in AU.

11. Gravity exists between all objects with mass. Why, then, don’t you notice the force of gravity between you and all of the objects around you? 12. What is inertia? 13. The orbit of a planet is a balance between the planet’s _______ and the gravitational force between the planet and the ________. 14. Is a satellite orbiting Earth free from Earth’s gravity? Why or why not?

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26.2 Motion and Astronomical Cycles

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Everything in the solar system is moving. Earth spins on its axis at about 1,600 kilometers per hour at the equator. To make a complete trip around the Sun in one year, Earth must orbit at an average speed of about 108,000 kilometers per hour! In this section, you will learn how motion affects the astronomical cycles we observe. Please note that illustrations are not drawn to scale.

Rotation and revolution The shape of Recall that the orbits of the orbits planets around the Sun are

slightly elliptical. What’s more significant is that the Sun is at a point called the focus that is offset from the center of the orbit. This causes the distance from the Sun to vary as a planet orbits. Figure 26.10 depicts Earth’s orbit and distances from the Sun. Rotation An axis is the imaginary line

that passes through the center of a planet from pole to pole. The spinning of a planet on its axis is called its rotation. Earth, like most of the other planets, spins from west to east. One complete rotation is called a day. One Earth day is exactly 23 hours, 56 minutes, and 4.09 seconds long. This means it takes Earth almost 24 hours to complete one rotation on its axis. A day on Jupiter, the fastest rotator of the planets, is only about 10 hours long. Revolution and All of the planets orbit, or revolve, around the Sun in the same direction years (counter-clockwise). A year is the time it takes a planet to complete one

revolution around the Sun. A year on Earth takes approximately 365.25 days. A year on Mars takes 686.98 Earth days. The farther a planet is from the Sun, the longer it takes it to complete one revolution. One year on Neptune, the outermost planet, is 164.81 Earth years long!

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axis - the imaginary line that passes through the center of a planet from pole to pole.

rotation - the spinning of a planet on its axis.

year - the amount of time it takes for a planet to complete one revolution around the Sun.

Earth’s seasons in the Northern Hemisphere Autumn

150 million km 147 million km

153 million km Sun

Winter

Summer 149 million km

Spring Illustration not to scale.

Figure 26.10: Orbits are almost

circular (ellipses). The Sun is at the focus that is offset from the center. The diagram above shows Earth’s distance from the Sun at the start of each season in the northern hemisphere.

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Motion and keeping track of time

CHAPTER 26

Calendars throughout History

Calendars A calendar is a means of keeping track of all the days in a year. Ancient

civilizations developed calendars based on their observations of the Sun, Moon, and stars. Many such civilizations independently invented almost identical calendars. (See the sidebar at the right).

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Years and days Recall that one year is the amount of time it takes Earth to complete one

revolution around the Sun. This is approximately 365.25 days. Each day is one rotation of Earth on its axis. Since Earth spins from west to east, the Sun appears to travel across the sky from east to west. Ancient observers thought that the Sun really did move across the sky. Can you see why? Leap years The ancient Egyptian calendar described in the sidebar added up to 365 days

and eventually evolved into the calendar we use today. However, because we know that one year is approximately 365.25 days long, our calendar adjusts for this. It has eleven months with 30 or 31 days each, and one month—February— with 28 days. In a leap year, February has 29 days. The extra day every four years makes up for the extra 0.25 day that occurs each year. The time of day A clock is a device that is used to mark the division of the day into equal parts

(Figure 26.11). The sundial is the oldest known “clock.” A sundial uses the shadow of a pointer that moves from one side of the base to the other as the Sun appears to travel from east to west during the day. Markers are placed around the base to determine the hour. Water clocks were stone containers with sloping sides that allowed water to drip at a constant rate through a small hole in the bottom. Markings on the inside surface of the container measured the passage of “hours.”

7,000 BCE. Babylonians kept a calendar with 29- and 30-day months. They needed to add an extra month every eight years. 4,000 BCE. The Egyptians adopted a calendar with 365 days in a year, divided into 12 months, each with 30 days, and an extra five days at the end. 2,000 BCE. Mayans of Central America calculated that there were 365.25 days in a year. 700 BCE. The Roman calendar consisted of 10 months in a year of 304 days. It ignored the remaining 61 days, which fell in the middle of winter. 46 BCE. Romans adopted the Julian calendar, named after Julius Caesar. It is close to the Gregorian calendar, adopted in the 1500s and still used today.

Modern clocks Today, we divide each rotation of Earth into 24 equal parts called hours. Each

hour is divided up into 60 parts called minutes and each minute into 60 parts called seconds. Like the water clock, modern clocks use a constant, repetitive action or process to keep track of equal increments of time. Where the water clock used the constant dripping of water, modern clocks use a pendulum, vibrating crystal, balance wheel, electromagnetic waves, or even atoms to mark time. Figure 26.11: Three types of clocks. 26.2 MOTION AND ASTRONOMICAL CYCLES

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The lunar cycle What is the lunar The revolution of the Moon around Earth makes the Moon appear as if it is cycle? gradually changing shape each night. The cycle of change in the appearance

of the Moon is called the lunar cycle. The lunar cycle occurs because of the relative positions of Earth, the Moon, and the Sun.

lunar cycle - the cycle of change in the appearance of the Moon due to the positions of Earth, the Moon, and the Sun.

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What causes the The orbit of the Moon is tilted about 5 degrees from Earth’s orbit lunar cycle? (Figure 26.12). This means the Moon is not in Earth’s shadow except during

a rare lunar eclipse. The Sun-facing side of the Moon is lit by sunlight almost all the time. The lunar cycle is caused by the angle the Moon makes with Earth and the Sun as the Moon orbits Earth, not by Earth’s shadow falling on the Moon. Moon phases What you see when you

look at the Moon depends on its location in relationship to the Sun and Earth. As the Moon revolves, we see a different fraction of sunlight being reflected from the Moon to Earth. Remember, the Moon doesn’t give off light; it reflects the light of the Sun. Although the lunar cycle is a continuous process, there are eight recognized phases. Waxing means the lit portion of the Moon is getting larger and waning means it is getting smaller. The length of the The lunar cycle—from new Moon to new Moon—takes 29.5 days to lunar cycle complete (above). This roughly corresponds to one month. However, if we

based our calendar on the lunar cycle, we would soon get ahead of an Earth year. Why? Because a year of lunar cycles adds up to only 354 days, not 365.25, leaving a balance of 11.25 days each year!

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Figure 26.12: The orbit of the Moon is tilted at a 5 degree angle compared with Earth’s orbit around the Sun (upper diagram). This means that the Moon can be either above or below the line from the center of the Sun to the center of Earth (lower diagram).

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Lunar eclipses The Moon’s orbit A lunar eclipse occurs when the Moon passes through Earth’s shadow. If is tilted you look at the lunar cycle diagram on the previous page, you may wonder

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why Earth’s shadow doesn’t cover the Moon when it is between the Moon and the Sun. Instead, you get a full Moon (Figure 26.13). The reason a lunar eclipse doesn’t occur very often is because of the 5 degree tilt of the Moon’s orbit.

lunar eclipse - an event that occurs when the Moon passes through Earth’s shadow.

Lunar eclipses Because of its tilted orbit, in most months, Earth’s shadow does not block the

sunlight from hitting the Moon. However, sometimes the Moon’s orbit is perfectly aligned with Earth’s orbit during a full Moon. Because of this alignment, Earth’s shadow temporarily blocks the sunlight from hitting the Moon, causing a lunar eclipse. As the Moon continues to move in its orbit, it gradually moves into a position where the sunlight hits it again. During a lunar eclipse, the Moon is still visible and appears reddish because some of the sunlight is being refracted into the shadow by Earth’s atmosphere.

Full Moon

Earth Ea Eart E Ear arrth th th

Sun's rays Illustration not to scale.

Figure 26.13: This alignment results in a Full Moon.

Total and partial lunar eclipses

A lunar eclipse can be total or partial and all observers on the dark side of Earth can see it at the same time. A partial eclipse (shown left) occurs when only part of the Moon falls in Earth’s shadow. Figure 26.14 shows an alignment for a partial eclipse. Figure 26.14: This alignment results in a partial lunar eclipse.

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Solar eclipses Solar eclipses A solar eclipse occurs when the Moon’s shadow falls on Earth. During a

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new Moon, the Moon lies between Earth and the Sun. At this time, only the unlit side of the Moon faces Earth. Most of the time, however, the Moon appears to be just above or below the Sun in the sky because of the 5 degree tilt of its orbit so at least a portion of its lit side is visible. During a solar eclipse, the new Moon is directly between Earth and the Sun and the Moon’s shadow hits part of Earth as shown below.

solar eclipse - an event that occurs when the Moon’s shadow falls on Earth.

Total solar The darkest part of the Moon’s shadow is cone-shaped and falls on only a eclipse small part of Earth’s surface. Viewers in this region experience a total eclipse

of the Sun because the light is completely blocked by the Moon. During a total eclipse, the Sun gradually disappears behind the Moon and then gradually reappears (Figure 26.15). This is because the Moon revolves around Earth, so it gradually moves into the path of the sunlight, and then gradually moves out again. The Sun is completely blocked by the Moon’s shadow for about two or three minutes. Partial solar In the diagram above, you can see that the Moon casts a larger, lighter eclipse shadow on Earth’s surface. Viewers in this region of the Moon’s shadow

experience a partial eclipse. During this time, only part of the Sun is blocked. Remember, you should NEVER look directly at the Sun—even during a total or partial eclipse!

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Figure 26.15: A total eclipse is

caused by the Moon blocking out the Sun.

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The seasons Seasons As Earth revolves around the Sun, we experience different seasons. The

seasons are caused by the 23.5 degree tilt of Earth’s axis with respect to the plane of its orbit around the Sun. As Earth rotates around the Sun, its axial tilt remains fixed.

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The axial tilt During summer in the northern hemisphere, the north end of the axial tilt is causes the facing toward the Sun. This results in more direct sunlight and higher seasons temperatures. Six months later, the north end of the axial tilt is facing away

from the Sun. The sunlight is more spread out and is less intense. This brings winter to the northern hemisphere (Figure 26.16). The opposite happens in the southern hemisphere. The fact that Earth’s axial tilt is fixed also explains why the position of the Sun in the sky appears to change over the course of a year (Figure 26.17). N

1st day of Autumn

Axial tilt

(Northern Hemisphere)

23.5º

Figure 26.16: During winter in the

northern hemisphere, Earth’s axial tilt is facing away from the Sun. This means the sunlight in the northern hemisphere is more spread out and less intense. Therefore, temperatures are lower in winter. 1st day of Winter 1st day of Spring and Autumn 1st day of Summer

S

Autumn

Summer N

N

1st day of Winter

1st day of Summer

Sun

W

(Northern Hemisphere)

(Northern Hemisphere)

S

S

Winter

N

Spring

S

N E

Figure 26.17: The diagram shows 1st day of Spring S (Northern Hemisphere)

the apparent path of the Sun across the sky in the northern hemisphere during the year.

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Tides Tides are As Earth rotates beneath the Moon, its mass feels a small, “Moonward” force caused by the of 0.00003 N from the Moon’s gravity. Earth is made of rock that resists this Moon’s gravity small force, but because water flows, the Moon causes water to slide toward

tide - a cycle of rising and falling ocean levels.

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the place directly under the Moon on Earth’s surface (Figure 26.18). In most places, ocean levels rise and fall twice each day as the Moon revolves around Earth and Earth rotates. The daily cycle of rising and falling ocean levels is called a tide. The Moon passes overhead once every 24 hours. So, you would expect the tide to rise only once every 24 hours. But the oceans on the side of Earth directly opposite the Moon also rise. What causes this “second” tide? The center of mass

The answer is that the Moon does not really orbit Earth as if Earth were fixed in place. Instead, Earth and the Moon orbit around a common center of mass. Imagine balancing Earth and the Moon on a giant see-saw. There is a point at which the see-saw balances even though Earth is much heavier than the Moon. That point is the center of mass of the Earth−Moon system.

Figure 26.18: The cause of the Moon-side tide.

Explaining the When you turn a corner sharply in a car, your body slides to the outside of “second” tide the curve, away from the center. This happens because your body wants to

move in a straight line in the direction it was going before the turn. This is the explanation for the tide on the side of Earth that does not face the Moon. As Earth revolves around the center of mass, the ocean on the opposite side from the Moon is “flung outward” a little by its own inertia (Figure 26.19).

Figure 26.19: The cause of the farside tide. Note: The tides shown in the diagram are much larger than actual tides.

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Section 26.2 Review 1. Study Figure 26.10. During which season in the northern hemisphere is Earth closest to the Sun?

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2. What determines the length of a day on a planet? What determines the length of a year on a planet? 3. Approximately how long does it take Earth to make one revolution around the Sun?

The Sun is 400 times larger in diameter than the Moon. It is also 400 times farther away from Earth than the Moon. Because of this coincidence, the Sun and Moon appear to be the same size in the sky.

4. Approximately how long, in hours, does it take Earth to make one rotation on its axis? 5. What is a leap year? Why does a leap year occur every four years? 6. The lunar cycle is closely related to which part of our calendar—a year, a month, or a day? 7. True or false: The phases of the Moon are caused by Earth’s shadow falling on the Moon? 8. Explain how you could use the shadow of a streetlight pole to track the time of day on a sunny day. 9. Explain the difference between solar and lunar eclipses. 10. Match the letters on the diagram with the correct terms. You may use a letter more than once.

The photo above shows a total eclipse of the Sun. Using the information above, explain why a solar eclipse occurs.

_____First day of summer _____First day of winter _____First day of spring _____First day of autumn

11. What are tides? What causes tides on the Moon-side of Earth to occur?

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26.3 Objects in the Solar System

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On August 24, 2006, the International Astronomical Union (IAU) passed a new definition of a planet. The new definition excludes Pluto as a planet. According to the new definition, Pluto is classified as a dwarf planet. Recently, astronomers have begun to find dozens of objects similar to Pluto—all small, icy, rocky, and with similar orbits. The change in Pluto’s status as a planet is a good example of the scientific method in progress. New discoveries sometimes cause scientists to revise scientific knowledge. In this section, you will read about planets, moons, and other objects in the solar system. The Sun will be discussed in Chapter 27.

planet - a celestial body that (1) is in orbit around the Sun; (2) is nearly round in shape; and (3) has cleared its orbit of other objects.

Planets and moons

moon - a natural satellite orbiting a planet or other body, such as a dwarf planet.

Defining a A planet in the solar system is a celestial body that (1) is in orbit around the planet Sun; (2) is nearly round in shape; and (3) has cleared its orbit of other

terrestrial planets - Mercury, Venus, Earth, and Mars. gas planets - Jupiter, Saturn, Uranus, and Neptune.

objects. What this last part means is that a planet is large enough that, as it revolves around the Sun, the other objects in its orbit have either become part of the planet by fusing with it or have collided with the planet and moved out of the planet’s orbit. Classifying the The planets are commonly classified into two groups. The terrestrial planets planets include Mercury, Venus, Earth, and Mars. The terrestrial (rocky)

planets are mostly made of rock and metal. They have relatively high densities, slow rotations, solid surfaces, and few moons. The gas planets include Jupiter, Saturn, Uranus, and Neptune. They are made mostly of hydrogen and helium. These planets have relatively low densities, rapid rotations, thick atmospheres, and many moons. Moons Earth has one moon which we call the Moon. Most of the other planets have moons too. A moon is a natural satellite that orbits a planet or other body,

such as a dwarf planet. The planet the moon orbits is called the primary. As of this writing, 240 objects in our solar system are classified as moons. Of those, 166 orbit the eight planets while the rest orbit dwarf planets and smaller solar system objects. Among the largest moons in the solar system are Earth’s moon; one of Jupiter’s moons, Io, Europa (shown in Figure 26.20), Ganymede, and Callisto; Saturn’s moon, Titan; and Neptune’s moon, Triton.

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Figure 26.20: Jupiter’s moon,

Europa, is one of the largest moons in the solar system.

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Earth and the Moon Earth statistics Earth’s atmosphere is mostly nitrogen (78 percent) and oxygen (21 percent).

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Earth is one of only two bodies in the solar system known to have liquid water (the other is Europa, a moon of Jupiter). As far as we know, Earth is the only planet in the solar system to support life. Although space probes have begun searching for life on other bodies, no evidence has yet been found. Moon statistics The Moon, which has no atmosphere, revolves around Earth at an average

distance of 384,400 kilometers. The Moon’s diameter is 3,476 kilometers, or about one quarter the size of Earth. The Moon’s mass is 7.3 × 1022 kilograms, which is about one one-hundredth of Earth’s mass. Because of the Moon’s relatively small mass, its gravity does not attract an atmosphere. Its density is 3.34 g/cm3, which is much lower than Earth’s. Figure 26.21 compares Earth and the Moon.

Property

Earth

Moon

Diameter

12,756 km

3,476 km

Gravity

9.8 N/kg

1.6 N/kg

Mass

24

6.0 × 10

kg 7.3 × 1022 kg

Density

5.52 g/cm3

3.34 g/cm3

Rotation period

1 day

27.3 days

Figure 26.21: Comparing Earth and

the Moon.

Gravitational The Moon’s gravitational force is about one sixth as strong as Earth’s. Earth force exerts a gravitational force of 9.8 newtons on a 1-kilogram object while the

Moon exerts a force of only 1.6 newtons on the same object. This means that a 1-kilogram object weighs 9.8 newtons (2.2 pounds) on Earth and the same object weighs only 1.6 newtons (0.36 pounds) on the Moon. Gravitational If you have ever observed the Moon, you may have noticed that the same side locking of it faces Earth at all times. This does not mean that the Moon does not

rotate. The Moon rotates much more slowly than Earth. Over millions of years, Earth’s gravity has locked the Moon’s rotation to its orbit around Earth. One lunar “day” takes 27.3 Earth days, exactly the same time it takes the Moon to complete one orbit around Earth (Figure 26.22). The length of the lunar cycle is different than the Moon’s rotation period

Why is there a difference between the lunar cycle (29.5 days) and the Moon’s rotation period (27.3 days)? As the Moon orbits Earth, the Earth–Moon system orbits the Sun. In the 27.3 days it takes the Moon to rotate and orbit Earth, the Earth–Moon system has revolved about 27 degrees (out of 360 degrees in a circle) of its total orbit around the Sun. It takes a few more days for the Moon to move along its orbit to compensate for the change in angle of the Sun’s rays. In the meantime, the Earth–Moon system has moved even farther in its orbit around the Sun.

Figure 26.22: The amount of time it

takes the Moon to complete a rotation is the same amount of time it takes it to revolve around Earth. Can you see why only one side of the Moon faces Earth at all times?

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How the Moon was formed Where did the Throughout history, there have been many different theories about the origin Moon come of the Moon. Before the Apollo landings that began in 1969, there were three from? main theories.

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Analyzing lunar rocks

1.

Some scientists hypothesized that the Moon split off Earth during a period of very fast rotation.

2.

Others thought that the Moon formed somewhere else and was “captured” by Earth’s gravity.

3.

Still others proposed that the Moon and Earth were formed together from a group of smaller chunks of matter when the solar system formed. When scientists analyzed lunar rocks, they found that they were composed of much less iron and nickel than Earth. Recall that Earth’s core is composed mostly of iron and nickel. The composition of lunar rocks closely resembled that of Earth’s mantle. They also found that the Moon’s density was the same as Earth’s mantle and crust combined.

giant impact theory - a scientific theory that explains how the Moon was formed.

The giant impact These discoveries gave rise to the giant impact theory that is widely theory accepted today. This theory proposes that about 4.5 billion years ago, an

object about the size of Mars collided with Earth, causing material from Earth’s mantle and crust to break off. This material, combined with material from the colliding object, was thrown into orbit around Earth and became the Moon. The Moon’s spherical shape was a result of gravity and the remaining particles impacted the Moon to form craters. Figure 26.23 shows how the Moon was formed based on this theory. Figure 26.23: The giant impact theory of the Moon’s formation.

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Mercury, Venus, and Mars Mercury Mercury, the closest planet to the Sun, is the smallest in both size and mass.

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Mercury appears to move quickly across the night sky because its period of revolution is the shortest of all of the planets. Mercury rotates on its axis very slowly—only one and a half times for every revolution around the Sun. This makes one day on Mercury about 59 Earth days, although its year is not much longer—about 88 Earth days! Only 40 percent larger than Earth’s moon, Mercury is a rocky, cratered world, more like the Moon than like Earth. Like the Moon, Mercury has almost no atmosphere (except for traces of sodium). Mercury has no moons. The side of Mercury that faces the Sun is very hot, about 400°C, while the other side is very cold, about –170°C. Venus Venus appears as the brightest planet and the third brightest object in our sky

(after the Sun and the Moon). It has a very thick atmosphere and an atmospheric pressure at its surface that is 90 times that at Earth’s surface. Because the atmosphere on Venus is 96 percent carbon dioxide, the greenhouse effect makes it the hottest planet in the solar system, with a surface temperature of more than 500°C. Venus rotates “backward,” that is, east to west. Its rotation is the slowest of all of the planets; Venus makes a little less than one rotation for each revolution around the Sun. This means that 1 day on Venus is 243 Earth days, while 1 year is shorter—225 Earth days! Like Mercury, Venus has no moons. Mars Mars appears as a reddish point of light in the night sky. It has a widely varied

surface that includes deserts, huge valleys and craters, and volcanic mountains that dwarf those on Earth. The atmosphere of Mars is very thin (about 0.7 percent as thick as that of Earth) and is composed mostly of carbon dioxide, while the rest is nitrogen and argon. The temperatures are below freezing most of the time. Like Earth, Mars has polar ice caps, but they are composed of a combination of water and frozen carbon dioxide. Because it has an axial tilt, Mars experiences seasons like Earth. A day on Mars (24.6 hours) is similar in length to Earth, while a year (687 days) is not. Mars has two small moons named Phobos and Deimos.

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The gas planets Jupiter Jupiter is the largest of the planets, and the fastest rotator, spinning on its axis

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about once every 10 hours. A year on Jupiter is about 12 Earth years. Jupiter is more liquid than gaseous or solid—more than half of its volume is an ocean of liquid hydrogen. Its atmosphere is about 88 percent hydrogen and 11 percent helium. It has a stormy atmosphere and one storm, known as the Great Red Spot, has been observed for more than 300 years. Jupiter has 63 moons and a series of rings that were first found by Voyager 1 in 1979. Saturn Saturn, at almost 10 times the size of Earth, is the second largest planet.

Saturn’s atmosphere is made mostly of hydrogen and helium. Saturn is a fast rotator, though slightly slower than Jupiter, with a day on Saturn lasting just longer than 10 Earth hours. A year on Saturn is about 29 Earth years. The most striking feature of Saturn is its system of rings, which are visible from Earth with a telescope. Saturn’s rings are made up of billions of particles of rock and ice ranging from microscopic to the size of a house. Although they are hundreds of thousands of kilometers wide, the rings are less than 100 meters thick. Saturn has 47 moons. Uranus The seventh planet from the Sun, Uranus can barely be seen without a good

telescope and was not discovered until 1781. It rotates “backward” and has an axis that is tilted 98 degrees to the plane of its orbit. A day on Uranus is only 18 Earth hours, but a year takes 84 Earth years. Uranus has at least 27 moons, all of them relatively small. Titania, the largest, has only 4 percent of the mass of Earth’s moon. Uranus also has a series of faint rings. Neptune Neptune, the eighth planet from the Sun, is the outermost of the gas planets.

It was discovered in 1846 and its discovery almost doubled the diameter of the known solar system because of its great distance from the Sun. A day on Neptune is only 16 hours long, but a year takes 165 Earth years! Neptune has a series of faint rings invisible from Earth but that have been seen in photographs taken by space probes. Neptune has 13 known moons, 6 of which were found in photographs taken by Voyager 2 in 1989. Of the 13 moons, only Triton is bigger than a few hundred kilometers in diameter.

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Comparing the properties of the planets

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Triton, Pluto, and the Kuiper Belt Triton and Pluto Triton is Neptune’s largest moon (Figure 26.24). Pluto is a dwarf planet, and

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most of the time it is the farthest object from the Sun. Triton and Pluto are similar objects in both composition and size. In fact, Pluto is slightly smaller than Triton and only a fraction larger than Earth’s moon. Some astronomers believe Pluto may actually be an “escaped” moon of Neptune. In this section, you will learn about dwarf planets like Pluto and other solar system objects like asteroids and comets. Pluto

The Kuiper Belt

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Discovered in 1930 by Clyde Tombaugh, Pluto was named for the Roman god of the underworld. The first dwarf planet discovered, Pluto rotates slowly—one turn every six Earth days—and backward. Its orbit is strongly elliptical and Pluto crosses the path of Neptune for about 20 years out of the 249 years it takes to revolve around the Sun. Their orbits are not in the same plane, so Neptune and Pluto will never collide. Because it is so far away, little is known about Pluto. The image above, from the Hubble Space Telescope, shows Pluto and its single “moon,” Charon. Outside the orbit of Neptune is a region called the Kuiper (rhymes with viper) Belt (Figure 26.25). The Kuiper Belt stretches from 50 to 1,000 AU out from the Sun and is believed to contain a few Pluto-size objects and many smaller ones. Kuiper Belt Objects (KBOs) are icy bodies found inside the Kuiper Belt and include the dwarf planets found there. As of this writing, it contains at least three dwarf planets: Pluto, Haumea, and Makemake. Quaoar (above left) is the second largest object in the Kuiper Belt at about half the size of Pluto. Unlike Pluto, Quaoar’s orbit around the Sun is nearly circular. Quaoar was recognized as a KBO in 2002 by Astronomer Mike Brown and his colleagues who also suggest it is made of ice and rock.

Figure 26.24: Triton is Neptune’s

largest moon. Some astronomers believe that Pluto may be an “escaped” moon of Neptune. Photo courtesy of NASA.

Figure 26.25: The Kuiper Belt lies beyond Neptune. It is named after astronomer Gerard Kuiper (1905 to 1973).

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Asteroids and comets Asteroids

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Between Mars and Jupiter, at a distance of 320 million to 495 million kilometers, there is a huge gap that cuts the solar system in two. This gap is called the asteroid belt because it is filled with thousands of small, rocky bodies called asteroids. An asteroid is an object that orbits the Sun but is too small to be considered a planet. So far, more than 10,000 asteroids have been discovered and more are found each year (Figure 26.26).

asteroid - an object that orbits the Sun but is too small to be considered a planet.

comet - an object in space made mostly of ice and dust.

The size of Most asteroids are small—less than a kilometer in diameter—but many have asteroids been found that are over 250 kilometers in diameter. The largest asteroid,

named Ceres, is 933 kilometers across. While the majority of asteroids are found in the asteroid belt, many have highly elliptical orbits that allow them to come close to Mercury, Venus, and even Earth. About 65 million years ago, a large asteroid hit Earth near Mexico, leaving a huge crater. Some scientists believe this event led to the extinction of the dinosaurs.

Figure 26.26: The asteroid shown in this picture, named Ida, is about 54 km wide. Photo courtesy of NASA.

Comets Scientists believe comets are made mostly of ice and dust. Comets revolve

around the Sun in highly elliptical orbits. In 1997, the comet Hale-Bopp could be clearly seen in the night sky without a telescope. However, we still know little about the composition and structure of comets. Several recent spacecraft have made close approaches to comets and each new piece of evidence they gather has lead to new insights about what comets are made of and how they formed. Evolution of a As a comet approaches the Sun, some of its ice turns into gas and dust and comet forms an outer layer called a coma. The inner core of the comet is called the

nucleus. As a comet nears the Sun, the solar wind (charged particles emitted by the Sun) causes the formation of a tail. Comet tails can be over 1 million km long! A comet’s tail always faces away from the Sun (Figure 26.27) because of the forces caused by the solar wind. Each time a comet passes the Sun, it loses some of its mass.

Figure 26.27: A comet’s tail faces

away from the Sun and can stretch for millions of kilometers in space.

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Meteors and meteorites

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Meteors Occasionally, chunks of rock or dust break off from a comet or asteroid and form a meteor. Imagine a tennis ball traveling at about 48,000 kilometers

meteor - a chunk of burning rock

per hour. That’s about the size and speed of most meteors. These chunks of dust or rock travel through space and some of them end up hitting Earth’s atmosphere. When this happens, meteors rub against air particles and create friction, heating them to more than 2,000°C. The intense heat vaporizes most meteors, creating a streak of light known as a “shooting star.” Occasionally, larger meteors cause a brighter flash called a fireball. These sometimes cause an explosion that can be heard up to 48 kilometers away. If you live or find yourself away from any city lights, look at the sky on a clear night and chances are that, if you look long enough, you will see a meteor. On average, a meteor can be seen in the night sky about every 10 minutes.

meteorite - a meteor that passes through Earth’s atmosphere and strikes the ground.

traveling through Earth’s atmosphere.

Meteor showers When a comet nears the Sun, a trail of dust and other debris burns off and

remains in orbit around the Sun. As Earth orbits the Sun, it passes through this debris, creating a meteor shower as the small bits of dust burn up in the atmosphere. During a meteor shower, you can see tens and even hundreds of meteors per hour. Because Earth passes the same dust clouds from comets each year, meteor showers can be predicted with accuracy. Meteorites

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If a meteor is large enough to survive the passage through Earth’s atmosphere and strike the ground, it becomes a meteorite. Meteorites are thought to be fragments from collisions involving asteroids. Most meteorites weigh only a few pounds or less and cause little damage when they hit. Most fall into the oceans that cover almost 75 percent of our planet’s surface. Meteor Crater in Winslow, AZ (above), is believed to have been caused by a giant, 50-meter-diameter meteorite about 50,000 years ago. The Holsinger meteorite (Figure 26.28) is the largest known piece of this 300,000-ton meteorite, most of which vaporized on impact.

Figure 26.28: The Holsinger

meteorite is a large piece of a much larger meteorite that blasted out Meteor Crater in Arizona about 50,000 years ago. This meteorite, while no taller than your thigh, weighs 1,400 lbs.

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Section 26.3 Review

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1. Use the table on page 679 to answer the following questions. a. Which planet has the largest diameter? The smallest? b. On which planet is gravity the strongest? The weakest? c. A day is the time it takes a planet to rotate once on its axis. Which planet has the longest day? The shortest day? d. A year is the time it takes a planet to revolve once around the Sun. Which planet has the longest year? The shortest year? e. Which planet is the most dense? The least dense? f. Which planet is approximately 10 AU from the Sun? g. Make a graph of orbital velocity vs. average distance from the Sun. Does your graph support Kepler’s ideas about the orbital velocity of planets that you read about on page 662? Explain your answer. 2. Why are we able to see a certain comet one year but not again until many years later? 3. What is the difference between a meteor and a meteorite?

Use the data from the table on page 679 to make a graph of surface temperature vs. distance from the Sun for the eight planets. Graph the distance on the x-axis and the temperature on the y-axis. Use these values for the surface temperature of the four inner planets: Mercury 167°C; Venus 465°C, Earth 15°C, Mars –65°C. What does your graph show about the relationship between temperature and distance from the Sun? Do the planets perfectly follow this relationship? What other factors might affect the surface temperature of the planets?

4. What is the asteroid belt and where is it located? 5. Which planet has an atmosphere that consists mostly of carbon dioxide? 6. Compared with Earth’s diameter, Saturn’s diameter is roughly: a) the same b) 5 times larger c) 10 times larger d) 50 times larger 7. What is the Kuiper Belt and where is it located? 8. Which former planet is now considered a dwarf planet? 9. What is a planet? 10. The giant impact theory proposes that about 4.5 billion years ago, an object about the size of Mars collided with Earth, causing material from Earth’s mantle and crust to break off. This material, combined with material from the colliding object, was thrown into orbit around Earth and became the Moon. Describe the scientific evidence that supports this theory.

Suppose you were given the opportunity to travel to another planet or a moon of another planet. Would you go? Why or why not? Would you go to Neptune, knowing the trip would last 20 years? What if you could bring along anything and anyone you wanted? Write an essay exploring your answers to these questions.

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Chapter 26 Assessment Vocabulary

Section 26.3

Select the correct term to complete the sentences.

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solar system

axis

gas planets

meteor

law of universal

lunar eclipse

planet

gravitation

constellation

solar eclipse

asteroid

comet

giant impact theory

lunar cycle

orbit

astronomical unit

tide

rotation

year

terrestrial planets

moon

gravitational force

meteorite

13. A(n) ____ is a massive object orbiting a star. 14. A(n) ____ is a chunk of burning rock traveling through Earth’s atmosphere. 15. A(n) ____ is a meteor that passes through Earth’s atmosphere and strikes the ground. 16. A(n) ____ is an object that orbits the Sun, but is too small to be considered a planet. 17. A(n) ____ is an object in space made mostly of ice and dust. 18. ____ include Mercury, Earth, Venus, and Mars. 19. ____ include Jupiter, Saturn, Uranus, and Neptune.

Section 26.1

1.

A(n) ____ is a group of stars that form a pattern in the night sky.

2.

The force of attraction between all objects is called ____.

3.

The ____ states that the strength of gravity depends on the mass of the objects and the distance between them.

4.

One ___ is equal to the average distance between Earth and the Sun.

5.

A planet’s ____ is the path that it follows around the Sun.

6.

The ____ includes all objects bound by gravity to the Sun.

20. A natural satellite orbiting a planet or other body such as a dwarf planet is called a(n) ____. 21. The Moon contains material from Earth’s crust and mantle. This evidence supports the ____.

Concepts Section 26.1

1.

How did ancient astronomers distinguish the planets from other objects in the night sky?

2.

Explain the major differences between Ptolemy’s and Copernicus’ models of the solar system.

3.

What important discoveries did Galileo make about the solar system? How was he able to make those discoveries?

4.

Why was Copernicus’ model eventually accepted over Ptolemy’s model?

5.

What contribution did Newton make to our model of the solar system?

Section 26.2

7.

Earth spins on its ____.

8.

A(n) ____ is a cycle of rising and falling ocean levels.

9.

When the Moon’s shadow falls on Earth, a(n) ____ occurs.

10. When the Moon passes through Earth’s shadow, a(n) ____ occurs. 11. The spinning of a planet on its axis is called ____. 12. The amount of time it takes for a planet to complete one revolution around the Sun is called a(n) ____.

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6.

What contribution did Kepler make to our model of the solar system?

21. Why does the same side of the Moon face Earth at all times?

7.

Which is the best unit for comparing the orbits of the planets to Earth? a. astronomical units (AU) b. light years c. kilometers

22. Explain the current theory of how the Moon was formed.

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8.

Name the factors that determine the strength of the gravitational force between two masses.

9.

Why is the Sun at the center of the solar system?

10. Describe the factors that keep a planet in orbit.

23. What is the difference between a meteor and a meteorite? 24. Compare asteroids to comets by filling in the blanks of the table below: Object

Size

Material

Orbit Shape

Location

Asteroid Comet

Section 26.2

25. Why does a comet form a visible tail as it approaches the Sun?

11. Name two examples of astronomical cycles. For each, describe an event that is directly related to it. Example: The Moon revolves around Earth resulting in the phases of the Moon.

26. Which planet has the most moons?

12. What is the difference between a sundial and a water clock?

27. Earth has a day that is 24 hours long. Which other planet has a day of about the same length as Earth’s?

13. What causes the lunar cycle to occur?

28. Mercury is closer to the Sun than Venus, but Venus has higher surface temperatures. Explain why.

14. A complete lunar cycle (29.5 days) roughly corresponds to one month. Why don’t we base our calendar on the lunar cycle?

29. Which planet is the closest to Earth?

15. Seasons are mainly caused by: a. the distance between Earth and the Sun. b. the tilt of Earth’s axis. c. the orbit of Earth. 16. Explain the difference between solar and lunar eclipses. 17. The Moon-side tide is caused by the attraction of the Moon’s gravity pulling on the oceans. What causes the tide on the opposite side of Earth from the Moon?

30. Which planet has a day that is longer than its year? 31. Which planets, beside Earth, have an atmosphere? 32. What is the Great Red Spot observed on Jupiter? 33. What is important about Jupiter’s moon, Io? 34. Name the three brightest observable objects from Earth. 35. Which planet has a climate most like Earth’s? What sort of opportunity does this represent?

Section 26.3

18. What is a planet? 19. Name the gas planets. 20. Why would an object weigh less on the Moon than on Earth? CHAPTER 26 ASSESSMENT

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Problems

Section 26.3

5.

Section 26.1

1.

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Newton’s law of universal gravitation explains the strength of the gravitational attraction between Earth and the Moon. a. If the mass of Earth suddenly doubled, what would happen to the gravitational force between Earth and the Moon? b. If the mass of Earth and the mass of the Moon were both doubled, what would happen to the gravitational attraction between them? c. If the distance from Earth to the Moon were doubled, what would happen to the gravitational attraction between them?

Applying Your Knowledge

Section 26.2

2.

Use the data in the table on page 679 to answer the following questions. a. Which planet would float in a giant bathtub of water? b. Which planet has the most moons? What data from the table explains why? c. Which planets have similar atmospheres? Why do you think their atmospheres are similar? d. Make a graph of mass vs. gravitational force. Does the graph show a strong, medium, or weak relationship? Explain the reason behind your answer.

How would the Moon appear from Earth if it were in the position shown in the diagram below?

Section 26.1

1.

Create a time line leading to our current model of the solar system. Include the year, scientist, discovery, and how the discovery contributed to the model. You may also include scientists and discoveries that were not discussed in this chapter.

Section 26.2

2.

Conduct research on the Internet to find out when the next total solar eclipse will occur. Will it be visible where you live? Useful information can be found at http://eclipse.gsfc.nasa.gov/eclipse.html

Section 26.3

3. 3.

During one revolution around the Sun, how many rotations of Earth occur?

4.

How long does it take Earth to revolve around the Sun in seconds? Show all of your math.

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You have just discovered a new solar system object (shown right)! Write a letter to another astronomer about your discovery. Classify it as one of the objects you learned about in this chapter and explain your choice. Give it a name.

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27

Hubble Space Telescope image courtesy of European Space Agency

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Stars

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Stargazing is an awe-inspiring way to enjoy the night sky, but humans can learn only so much about stars from our position on Earth. The Hubble Space Telescope (HST) is a school-bus-size telescope that orbits Earth every 97 minutes at an altitude of 568 kilometers and a speed of about 28,000 kilometers per hour. The Hubble Space Telescope transmits images and data from space to computers on Earth. In fact, HST sends enough data back to Earth each week to fill thousands of books. Scientists store the data on special disks. In January of 2006, HST captured images of the Orion Nebula, a huge area where stars are being formed. HST’s detailed images revealed over 3,000 stars that were never seen before. Information from the Hubble will help scientists understand more about how stars form. In this chapter, you will learn all about the star of our solar system, the Sun, and about the characteristics of other stars.

4 Why do stars shine? 4 What kinds of stars exist? 4 What is the life cycle of a star?

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27.1 The Sun Can you imagine life without the Sun? The Sun is the source of energy that sustains all life on Earth. What is the Sun? Why does it produce so much energy? Read on to find the answers to these questions, and many more.

star - a giant, hot ball of gas held together by gravity.

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The Sun is a star The Sun is a star A star is an enormous, hot ball of gas held together by gravity. Gravity

squeezes the density of a star so tightly in the core that the electrons are stripped away and the bare nuclei of atoms almost touch each other. At this high density, nuclear fusion occurs, releasing tremendous amounts of energy. The nuclear fusion that powers the Sun combines 4 hydrogen atoms to make helium, converting 2 protons to neutrons in the process (Figure 27.1). The minimum temperature required for fusion to occur is 7 million degrees Celsius. The Sun’s core reaches a temperature of 15 million degrees Celsius. The Sun’s dense The high density and temperature needed for fusion occurs in the center, or core core of a star (Figure 27.2). The density at the Sun’s core is about 158.0 g/

cm3. This is about 18 times the density of solid copper. In order to reach this high density, a star must have a mass much larger than a planet. For example, the Sun has a mass that’s around 330,000 times larger than the mass of Earth.

Figure 27.1: This diagram shows what happens during nuclear fusion inside the Sun.

A medium-size The Sun is medium-size star. Its diameter is about 1.4 million kilometers. star Approximately 1 million Earths could fit inside the Sun! By contrast, one of

the star “supergiants” called Betelgeuse sometimes reaches a diameter that is almost 600 times that of the Sun. If the Sun grew to the size of Betelgeuse, it would swallow up Mercury, Venus, Earth, and Mars! What is the Sun The Sun is about 75 percent hydrogen and 25 percent helium, with very made of? small traces of other elements. Unlike Earth, the Sun does not have a solid

surface—instead, it is made completely of gas. Because of its size, the Sun contains 99.8 percent of the mass of the solar system. Because of its mass, the Sun’s gravitational force is strong enough to hold the entire solar system—including the planets, dwarf planets, asteroids, and comets—in orbit.

Figure 27.2: A cross section of a star like the Sun.

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Anatomy of the Sun The Sun has The apparent surface of the Sun that we can see from a distance is called three regions the photosphere, which means “sphere of light.” Just above it is the chromosphere. This is a very hot layer of plasma, a high-energy state of matter. The corona is the outermost layer of the Sun’s atmosphere, extending

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millions of kilometers outward.

chromosphere - the inner atmosphere of the Sun which consists of a very hot layer of plasma.

corona - the outermost layer of the Sun’s atmosphere that extends millions of kilometers outward.

sunspot - an area of gas on the Sun that is cooler than the gases around it; sunspots appear as dark spots on the Sun’s photosphere.

Sunspots A safe method for viewing the Sun is to use a telescope to project the Sun’s

image onto a white surface (Remember, you should NEVER look directly at the Sun). When the Sun is observed in this way, small, dark areas can be seen on its surface. These areas, called sunspots, may look small, but they can be as large as Earth. A sunspot is an area of gas that is cooler than the gases around it. Because they don’t give off as much light as the hotter areas, sunspots appear as dark spots on the photosphere (Figure 27.3).

Figure 27.3: Sunspots appear as dark spots on the photosphere.

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Features of the Sun Prominences Sunspots are linked to other features of the Sun. Occasionally, large “loops” and solar flares of gas called prominences can be seen jumping up from groups of sunspots.

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These can be observed during eclipses and appear as loops that extend beyond the chromosphere. Sometimes prominences from different sunspot regions suddenly connect, releasing very large amounts of heat and light known as solar flares (Figure 27.4). The Sun gives off more than just heat and light. It also gives off something called solar wind. Solar wind is an electrically charged mixture of protons and electrons. Evidence of solar wind comes from the tails of comets, which always face away from the Sun. A comet’s tail, which is made of vaporized gases, acts like a “wind sock” and shows that there is a continuous flow of particles coming from the Sun.

Solar wind

aurora - a phenomenon that occurs when the solar wind energizes the protective layers of the atmosphere.

Figure 27.4: Solar flares release large amounts of heat and light.

Magnetic storms Solar flares can greatly increase the amount of solar wind given off by the

Sun. These solar wind particles can affect Earth’s upper atmosphere, causing magnetic storms. Magnetic storms can disrupt radio and television signals, interfere with telephone and cell phone signals, and even cause electrical power problems for homes and businesses. Auroras Solar winds sometimes cause a mysterious phenomenon known as an aurora to occur. Auroras (known in the northern hemisphere as the northern

lights or aurora borealis) occur when the protective layers of our atmosphere are energized by solar winds. This energy causes atoms and molecules in the upper atmosphere to give off light. The most common color produced is a yellow-green caused by oxygen atoms at an altitude of about 60 miles. The aurora appears as curtains of light above the horizon (Figure 27.5).

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Figure 27.5: Solar winds can cause auroras to occur.

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Solar energy Solar energy and electromagnetic waves

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Solar energy is a term that refers to radiant energy from the Sun. The radiant energy of the Sun reaches Earth in the form of electromagnetic waves. Recall that we classify these waves according to their energy as shown in Figure 27.6. The type of electromagnetic wave we can detect with our eyes is called visible light, a tiny portion of the electromagnetic spectrum. We can use solar energy to heat buildings and generate electricity.

Passive solar Buildings that use passive solar heating heating are designed to trap sunlight.

Houses can be built with large glass windows that face the direction of the Sun. Sunlight passes through the windows and heats the air in the room. The glass traps the warm air inside, causing a “greenhouse effect.”

Figure 27.6: The Sun emits waves in all frequencies of the electromagnetic spectrum. The only waves we can detect with our eyes we call visible light.

Circulated solar A building that uses circulated solar heating has large glass panels covering heating part of its roof. Underneath the glass panels, a liquid is circulated through

tubes. The liquid is heated by radiant energy from the Sun and flows into the building. The heated liquid can also be stored in an insulated tank for use at night. Solar cells Photovoltaic (or PV) cells, also called solar cells, are devices that convert

sunlight directly into electricity. You may already be using solar cells on calculators, watches, or some outdoor light fixtures. They are made out of at least two layers of a semiconductor material such as silicon. One layer has a positive charge, and the other has a negative charge. When light falls on the cell, some of it is absorbed by the semiconductor atoms, freeing electrons from the solar cells’ negative layer. These electrons then flow through an external circuit and back into the positive layer. The flow of electrons produces electric current (Figure 27.7).

Figure 27.7: Sunlight enters the PV cells, causing electrons to flow through a circuit to produce electric current.

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More about the Sun’s energy How much Each second, about 700 million tons of hydrogen inside the Sun are energy does the converted to about 695 million tons of helium through nuclear fusion. Notice Sun produce? that the total mass of helium produced is slightly smaller than the total mass

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of hydrogen used. The “missing” mass (about 5 million tons) is converted directly into energy. This mass creates an energy output of 3.9 × 1026 watts! In 1905, Albert Einstein proposed that matter can be converted into energy. His famous equation (E = mc2) shows how huge amounts of energy can be created from a smaller mass (Figure 27.8). This helps explain why such a huge amount of energy is produced by nuclear fusion.

solar constant - the amount of energy from the Sun that actually reaches the edge of Earth’s atmosphere.

The solar The amount of this energy from the Sun that reaches the outer edge of constant Earth’s atmosphere is known as the solar constant. While the solar

constant varies slightly, the accepted value is 1,386 watts per square meter (W/m2). To visualize this amount of energy, imagine the energy of thirteen 100-watt light bulbs spread over a square meter surface (Figure 27.9). Theories about The number of sunspots seems to vary over an average of 11 years and is sunspots known as the sunspot cycle. Many scientists speculate that there is a

Figure 27.8: Einstein’s famous equation for energy.

relationship between the sunspot cycle and variations in our global climate. Two decades of satellite research have shown that at times when there is a higher number of sunspots, the value of the solar constant increases slightly. While sunspots are cooler areas of the Sun, as their numbers increase, so does the number of solar flares that release large amounts of heat. The Sun powers Except for nuclear power, the original source for almost all of our energy our energy comes from the Sun. Sunlight causes water to evaporate, which later falls as needs rain into rivers and streams. This flowing water can be used to generate

electricity. Energy from the Sun also drives the wind (created by uneven heating of Earth), which also can be used to generate electricity. Even the energy we get from coal, natural gas, petroleum, and wood comes from the Sun. That is because these fuels are created from photosynthesis. In this process, plants store energy from the Sun in the form of carbon compounds. The foods you eat also contain energy from the Sun that was trapped by plants using photosynthesis.

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Figure 27.9: While the solar

constant varies slightly, its accepted value is 1,386 watts per square meter of Earth’s atmosphere.

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Section 27.1 Review 1. What is a star? How is a star different from a planet or a moon? 2. Why does the Sun give off heat and light?

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3. The Sun is made mostly from which of the following elements? a. helium b. lead c. hydrogen d. nitrogen 4. On the diagram below, label the following: photosphere, chromosphere, core, corona.

Solar Energy Research There are many ways to collect sunlight and use it to produce energy for our everyday needs. When we use energy from the Sun, it is called solar energy. Photovoltaic (or PV) cells, also called solar cells, are devices that convert sunlight directly into electricity. You may have seen solar cells on calculators, watches, or some outdoor light fixtures. Research solar cells and find the answers to the following questions. 1. How do solar cells work? 2. How efficient are solar cells at converting sunlight into energy? 3. What are the drawbacks to using solar energy? 4. How are scientists trying to make solar cells more efficient?

5. Explain the meanings of the following terms. a. sunspot b. magnetic storm c. solar flare d. solar wind e. aurora

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27.2 Stars

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During most of the day, we see only one star, the Sun, which is, on average, 150 million kilometers away. On a clear night, about 6,000 stars can be seen without a telescope. Ancient astronomers believed that the Sun and the stars were different from each other. Today we know that the Sun is just one star like all the others in the night sky. The others appear to be so dim because they are incredibly far away. The next closest star to Earth is Proxima Centauri: 4.2 light years (40 trillion kilometers) away.

Classifying stars How are stars Stars come in a range of sizes and temperatures. The Sun is an average star in classified? many ways. Some stars are larger and hotter. Other stars are smaller and

cooler. Astronomers classify stars according to size/mass, temperature, color, and brightness. Size and mass Stars come in a range of masses (Figure 27.10). The largest stars have a mass of stars of about 60 times the mass of the Sun. The smallest stars are about one-

twelfth the mass of the Sun. This is about the minimum mass required to create enough gravitational pressure to ignite fusion reactions in the core. The Sun is a medium-size star, as is Alpha Centauri, the nearest star to the Sun.

Figure 27.10: Comparing different sizes of stars.

Giant stars There are two types of giant stars. Blue giant stars are hotter and much more

massive than the Sun. Rigel, in the constellation of Orion, is a blue giant star. Red giants are of similar mass to the Sun and much cooler. The red giants are huge because they began as Sun-like stars but have expanded out past the equivalent of Earth’s orbit. As they expanded they cooled down. The photograph in Figure 27.11 shows V838 Monocerotis, a red giant star. Light from this star is illuminating the nebula around it. Dwarf stars Stars that are smaller than the Sun come in two main categories, dwarfs and

neutron stars. Dwarf stars are about the size of the smaller planets. Sirius B, the largest known dwarf star, is slightly smaller than Earth. Neutron stars such as B1257 in the constellation Virgo are even smaller. Their diameter is only 20 to 30 kilometers, about the size of a big city.

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Figure 27.11: V838 Monocerotis, a red giant star illuminating the nebula around it.

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Temperature and color Temperatures of If you look closely at the stars on a clear night, you might see a slight reddish stars or bluish tint to some stars. This is because stars’ surface temperatures are

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different. Red stars are cooler than white stars (Figure 27.12), and blue stars are the hottest. Table 27.1 lists some stars, their colors, and their surface temperatures. Table 27.1: Stars, their colors, and their surface temperatures Star

Color

Temperaturerange (°C)

Zeta Orionis

blue

25,000 to 50,000

Rigel

blue-white

11,000 to 25,000

Sirius

white

7,500 to 11,000

Polaris

yellow-white

6,000 to 7,500

Sun

yellow

5,000 to 6,000

Arcturus

orange

3,500 to 5,000

Betelgeuse

red

2,000 to 3,500

Figure 27.12: Sirius, the Dog Star,

in the constellation of Canis Majoris, is a good example of a white star.

The color of light is related to its energy. Red light has the lowest energy of the colors we can see. Blue and violet light have the most energy. Yellow, green, and orange are in between. White light is a mixture of all colors at equal brightness.

Color and When matter is heated, it first glows red at about 600°C. As the temperature temperature increases, the color changes to orange, yellow, and finally, white. The graph

in Figure 27.13 shows the colors of light given off at different temperatures. The curve for 2,000°C crosses red and yellow, but drops off before getting to blue. That means a surface at 2,000°C gives off mostly red and some yellow. At 10,000°C, a star gives off an even mix from red to blue so it appears white. At 20,000°C, the emitted light is white with a bluish color.

Figure 27.13: The range of light

given off by a star depends on its temperature. Stars at 2,000°C give off mostly red and some yellow light. At 10,000°C, a star gives off an even mix from red to blue, so the light appears white.

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Brightness and luminosity Light radiates in You can see a bare light bulb from anywhere in a room because the bulb all directions emits light in all directions. When the rays of light are represented by arrows,

the light coming from a bulb looks like Figure 27.14. A star also radiates light equally in all directions.

brightness - measures the amount of light reaching Earth. luminosity - the total amount of light given off by a star.

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Light intensity From experience, you know that as you move away from a source of light, the brightness decreases. Brightness, also called intensity, describes the

amount of light energy per second falling on a surface, such as the ground, your eye, or a telescope. The brightness of a star is described as the light reaching Earth. Light intensity follows an inverse square law

For a distant source of light like a star, the brightness decreases as the inverse square of the distance. For example, a star that is twice as far away will appear only 1/4 as bright because 1/4 is 1/22. A star that is three times as far away will appear 1/9 as bright (1/9 = 1/32). Figure 27.14: Light emitted from the Sun or from a light bulb.

Luminosity The brightness of a star also depends on how much light the star gives off. Luminosity is the total amount of light given off by a star in all directions.

Luminosity is a fundamental property of a star, whereas brightness depends on both luminosity and distance. To understand stars, we wish to know their luminosity. All we can measure is their brightness. To find the luminosity of a star we need to know both its brightness and its distance from Earth. We can then apply the inverse square law to calculate the luminosity from the brightness and distance.

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Brightness is measured in units of power. In the laboratory, the brightness of a light source is often expressed in watts. Because the brightness of objects in space is so great, astronomers developed solar luminosity units. One solar luminosity unit is equal to the brightness of the Sun at the outer edge of Earth’s atmosphere (about 3.9 × 1026 watts). This is comparable to the combined brightness of 400 trillion trillion 100-watt light bulbs!

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The temperature and luminosity of stars H-R diagrams In the early 1900s, Danish astronomer Ejnar Hertzsprung and American

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astronomer Henry Russell developed an important tool for studying stars. They made a graph that showed the temperature of the stars on the x-axis and the luminosity on the y-axis. The result is called the Hertzsprung-Russell, or H-R diagram. Each dot on the diagram below represents a star with a particular luminosity and temperature.

main sequence star - a stable star in the main sequence category in the H-R diagram.

white dwarf - a small star with a high temperature and low brightness.

red giant - a large star with low temperature and high brightness. supergiant - very large, bright star that may be blue or red, depending on its temperature.

Reading H-R diagrams are useful because they help astronomers categorize stars into H-R diagrams groups. Stars that fall in the band that stretches diagonally from cool, dim stars to hot, bright stars are called main sequence stars. Main sequence stars, like the Sun, are in a very stable part of their life cycle. White dwarfs

are in the lower left corner of the diagram. These stars are hot and dim and cannot be seen without a telescope. Red giants appear in the upper right side of the diagram. These stars are cool and bright and some can be seen without the aid of a telescope. Supergiants, both red and blue, are found in the extreme upper portion of the diagram. You can observe red and blue supergiants in the constellation Orion (Figure 27.15).

Figure 27.15: If you locate Orion in the night sky, you can see Betelgeuse, a red supergiant, and Rigel, a blue supergiant. It is easy to find this constellation because of the three stars that form its belt.

27.2 STARS

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Section 27.2 Review 1. List the four variables astronomers use to classify stars. 2. How does the size of the Sun compare with the size of other stars? 3. What is a light year?

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4. Regulus, the brightest star in the constellation Leo, is approximately 77 light years from Earth. Which year did Regulus give off the light you see when looking at the star today? 5. What can you tell about a star by looking at its color? 6. What happens to the brightness of a star as you observe it from farther away? 7. Explain the difference between a star’s brightness and its luminosity. 8. Suppose one star is three times farther away than another. If both stars have the same luminosity, how will their brightness compare?

A light year is the distance light travels in one year. Other units can be defined according to the distance light travels in a certain amount of time. For example, a light second is the distance light travels in one second. Calculate the number of meters each of the following units represents. 1. Light second 2. Light minute 3. Light nanosecond (a nanosecond is one-billionth of a second)

9. Describe the four types of stars categorized in a Hertzsprung-Russell (H-R) diagram. 10. True or false: A white dwarf star is about the same size as the Sun? 11. The star in Figure 27.16 is a: a. b. c. d.

red giant star. blue giant star. main sequence star. white dwarf star.

Figure 27.16: The H-R diagram for question 11.

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27.3 The Life Cycles of Stars Like living organisms, stars have life cycles. Of course, stars are not truly “alive,” but astronomers sometimes use the terms “born,” “live,” and “die” to represent parts of that cycle. The Sun, a medium-size star, was “born” about 5 billion years ago. Because most medium-size stars have a life span of around 10 billion years, it will live for another 5 billion years before it dies.

nebula - a huge cloud of dust and gas from which stars form.

protostar - the first stage in the life cycle of a star.

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Nebulae, birth, and life span of stars How are stars A star, regardless of its size, begins its life inside a huge cloud of gas (mostly born? hydrogen) and dust called a nebula (Latin for “mist”). Gravitational forces

cause denser regions of the nebula to collapse, forming a protostar. A protostar is the earliest stage in the life cycle of a star. The gases at the center of the protostar continue to collapse, causing pressure and temperature to rise. A protostar becomes a star when the temperature and pressure at its center become great enough to start nuclear fusion. This is the nuclear reaction in which hydrogen atoms are converted into helium atoms and energy is released. Figure 27.17 shows a portion of the Eagle Nebula, the birthplace of many stars.

A star is born when temperature and pressure at its center become great enough to start nuclear fusion. Main sequence Once nuclear fusion begins, a star is in the main sequence stage of its life stars cycle (Figure 27.18). This is the longest and most stable part of a star’s life.

The time a star stays on the main sequence depends on the star’s mass. The Sun will stay on the main sequence for about 10 billion years. You might think that high-mass stars live longer than low-mass stars because they contain more hydrogen fuel for nuclear fusion. However, the opposite is true. High-mass stars burn brighter, and hotter, using up their hydrogen faster than low-mass stars. Consequently, high-mass stars have much shorter life spans. For example, a star with 60 times the mass of the Sun only stays on the main sequence for a few million years, a lifetime a thousand times shorter than the Sun’s.

Figure 27.17: A NASA/HST photo

of a portion of the Eagle Nebula. The bright area is lit by young stars forming from clouds of molecular hydrogen (H2).

Figure 27.18: The main sequence on an H-R diagram is where most stars spend most of their lives.

27.3 THE LIFE CYCLES OF STARS

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The old age of Sun-like stars The formation of Eventually, the core of a star runs out of hydrogen. Gravity then causes the a red giant core to contract, raising the temperature. At higher temperatures, other

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nuclear fusion reactions occur that combine helium to make carbon and oxygen. The hotter core radiates more energy, pushing the outer layers of the star away. The star expands into a red giant as the outer layers cool. In its red giant phase, the Sun will expand to beyond the orbit of Mars, and the inner planets, including Earth, will be incinerated. Fortunately, this event is still 4 billion years in the future. White dwarf stars

Sun-like stars don’t have enough mass (gravity) to squeeze their cores any hotter than what is needed to fuse helium into carbon and oxygen. Once the helium is used up, the nuclear reactions essentially stop. With no more energy flowing outward, nothing prevents gravity from crushing the matter in the core together as close as possible. At this stage, the core glows brightly and is called a white dwarf. It is about the size of Earth, yet has the same mass as the Sun. Because of its high density, a spoonful of matter from a white dwarf would weigh about the same as an elephant on Earth.

Planetary During the white-dwarf stage, the outer layers of the star expand and drift nebulae away from the core. In more massive stars this creates a planetary nebula

(Figure 27.19). The planetary nebula contains mostly hydrogen and helium, but also some heavier elements that were formed in the core. Over time, the matter in a planetary nebula expands out into the rest of the universe and becomes available for forming new stars. Planetary nebulae are one of nature’s ways of recycling the matter in old stars and distributing new elements.

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planetary nebula - the expanding outer shell of a Sun-like star. This matter is blown away as the core shrinks to become a white dwarf.

Figure 27.19: A planetary nebula

forms when a star blows off its outer layers leaving its bare core exposed as white dwarf. This may occur with stars that have a mass between 1.5 and 5 times the mass of the Sun.

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Supernovae and synthesis of the elements The origin of the Scientists believe the early universe was mostly hydrogen, with a small elements amount of helium and a trace of lithium. Heavier elements, such as carbon

supernova - the explosion of a very large star.

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and oxygen, did not exist. So, where did they come from? All the heavier elements are created by nuclear fusion inside the cores of stars—including the elements in your body. Every carbon atom in your body, which is 53 percent of the solid matter of your body, was once inside a star. The creation of Stars with masses more than 12 times the mass of the Sun have a violent end. elements As the core runs out of helium, gravity compresses and heats the core hot

enough for other types of nuclear fusion to start. The new fusion reactions combine carbon and oxygen into neon, sodium, magnesium, sulfur, silicon, and even heavier elements up to iron. Nuclear fusion reactions are exothermic, releasing energy only up to iron (Fe, atomic number 26). After that, the reactions become endothermic, using energy rather than releasing it. When the core of the star contains mostly iron, nuclear fusion stops. Supernovas If a star’s iron core reaches 1.4 times the mass of the Sun, gravity becomes

strong enough to combine electrons and protons into neutrons. The core of the star collapses in moments to form a single “nucleus,” a tiny fraction of its former size. The rest of the star rushes in to fill the empty space left by the core, then bounces back off the nucleus with incredible force. The result is a spectacular explosion called a supernova. A supernova is brighter than 10 billion stars and can outshine an entire galaxy for a few seconds. More than 90 percent of the mass of the star is blown away (Figure 27.20). During this brief period, heavier elements such as gold and uranium are created, as atomic nuclei are smashed together. Neutron stars The light and heat produced by a supernova fades over time, and the remnants

Figure 27.20: The Crab nebula is

the remains of a supernova that occurred in 1054 AD and was recorded by Chinese astronomers.

become a nebula that can be used to make more stars. All that remains of the original star is a core made entirely of neutrons called a neutron star. This super-dense object is no more than a few kilometers in diameter!

27.3 THE LIFE CYCLES OF STARS

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Examining light from stars What is We know what elements are in distant stars from the light the stars produce. spectroscopy? Astronomers analyze the light given off by stars, and other “hot” objects in

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space in order to figure out their temperatures and what they are made of. Spectroscopy is a tool of astronomy in which the electromagnetic waves (including visible light) produced by a star or other object (called its spectrum) is analyzed.

spectroscopy - a method of studying an object by examining the visible light and other electromagnetic waves it creates.

Figure 27.21: When hydrogen gives

Chemical Astronomers use a tool called a spectrometer to split light into a spectrum of composition of colors. A spectrometer displays lines of each color along a scale that stars measures the wavelength of light in nanometers (nm). Light waves are

off light, four visible lines are seen at 656 nm (red), 486 nm (blue-green), 434 nm (blue-violet), and 410 nm (violet) on the scale of a spectrometer.

extremely small. A nanometer is one-billionth of a meter. Each element has its own unique pattern of lines—like a fingerprint. For example, when light from hydrogen is examined with a spectrometer, four lines are seen: red, bluegreen, blue-violet and violet (Figure 27.21). Astronomers use spectroscopy to determine what elements are present in stars. A star’s speed, temperature, rotation rate, and magnetic field can also be determined from its spectrum. The composition In 1861, Sir William Huggins, an amateur astronomer from England, used of the Sun spectroscopy to discover that the Sun and the stars are made mostly of

hydrogen. A few years later, Sir Joseph Norman Lockyer observed a line at the exact wavelength of 587.6 nanometers. Since no known element had a line at this wavelength, he concluded that this must be an undiscovered element and named it helium, after the Greek name for the Sun, Helios. Today, we know that hydrogen is the most common element in the universe, with helium second (Figure 27.22). Helium is abundant in the Sun but rare on Earth.

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Figure 27.22: Spectral lines for

helium and lithium. Each element has its own unique pattern of spectral lines (spectrum).

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Section 27.3 Review 1. How many years do scientists believe are left before the Sun runs out of hydrogen in its core and leaves the main sequence? 2. All stars begin inside a huge cloud of dust and gas called a _____.

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3. What force causes a nebula to form a protostar? 4. What happens to the temperature and pressure in a protostar as it collapses?

The last supernova to be observed in our galaxy occurred in 1604. It was named Kepler’s supernova after the German astronomer Johannes Kepler (1571–1630). The supernova was visible to the naked eye as the brightest object in the night sky. Use the Internet to research Kepler’s supernova to find the answers to the following questions.

5. How long does the main sequence stage of a Sun-like star normally last? 6. Why do stars with smaller masses burn longer than stars with larger masses? 7. What happens when a Sun-like star runs out of hydrogen fuel in its core? 8. How do scientists believe heavier elements such as carbon and oxygen were created? 9. What is a supernova? 10. Is it probable that the Sun will become a supernova? Why or why not? 11. What can scientists learn about a star by studying the light it gives off?

1. Was the supernova named after Kepler because he was the first person to see it? 2. How many light years from Earth was the supernova? 3. How did the occurrence of the supernova help support Galileo’s view of the universe?

12. How is the spectrum for an element similar to a person’s fingerprint? 13. Compared with the age of the Sun, a blue giant star is likely to be: a. younger. b. about the same age. c. older. 14. Fusion reactions that combine light elements release energy only until what element is created?

27.3 THE LIFE CYCLES OF STARS

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Chapter 27 Assessment Vocabulary Select the correct term to complete the sentences.

11. A very large, bright star that may be blue or red, depending on its temperature is called a(n)____. Section 27.3

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protostar

nebula

star

brightness

supergiant

solar energy

12. A(n) ____ is a huge cloud of dust and gas from which stars form.

sunspot

supernova

luminosity

13. The first stage in the life cycle of a star is called a(n) ____.

solar constant

auroras

main sequence star

14. A(n) ____ is the expanding outer shell of Sun-like star.

red giant

white dwarf

planetary nebula

15. The explosion of a very large star is called a(n) ____.

spectroscopy

16. ____ is a method of studying the light emitted by a star.

Section 27.1

1.

A(n) ____ is a giant, hot ball of gas held together by gravity.

Concepts

2.

A(n) ____ appears as a dark spot on the Sun’s photosphere.

Section 27.1

3.

When the solar wind energizes Earth’s upper atmosphere, ____ can often be seen.

1.

4.

Passive solar heating, circulated solar heating, and solar cells are all examples of uses of ____.

5.

The amount of energy from the Sun that actually reaches the edge of Earth’s atmosphere is called the ____.

The Sun’s energy is produced in the: a. chromosphere b. core c. corona d. photosphere

2.

Arrange the layers of the Sun listed below in order from innermost to the outermost layer. a. chromosphere b. core c. corona d. photosphere

3.

What are sunspots? Name two features of the Sun that are linked to sunspots.

4.

Name three ways we use solar energy.

5.

How does Einstein’s equation, E = mc2, explain why such a large amount of energy is produced by nuclear fusion?

Section 27.2

6.

____ is a measure of the amount of light reaching Earth from a star.

7.

____ measures the total amount of light given off by a star.

8.

A stable star in the middle portion of the H-R diagram is called a(n) ____.

9.

A small star with a high temperature and low brightness is called a(n) ____.

10. A large star with low temperature and high brightness is called a(n)____.

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Section 27.2

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6.

Describe the color changes that occur in matter as it is heated.

7.

Which has the highest surface temperature? a. a red star b. a white star c. a blue star

8.

Name the two most common elements in the universe. Are they also the most common elements on Earth?

9.

Describe our Sun in terms of color, brightness, size, and temperature compared to other stars in the galaxy.

Problems Section 27.1

1.

Would you expect the amount of energy from the Sun that reaches Earth’s surface to be greater, equal to, or less than the solar constant? Explain your answer.

Section 27.2

2.

Three identical blue giant stars are located 100 light years, 200 light years, and 300 light years away from Earth. How does their brightness compare from Earth?

3.

Arrange the stars in the table below in order, from highest temperature, to lowest temperature.

Section 27.3

10. The smallest stars have a mass of about 1/12 of our Sun. Why don’t stars with less mass exist? 11. Red giants are of similar mass to our Sun. Why is the size of red giants so much bigger than the Sun’s size? 12. A spectroscope is a useful tool for astronomers. a. How does it work? b. What information can an astronomer find using a spectroscope? 13. What does the lifespan of a star depend on? 14. List the stages in the life cycle of a typical, medium-size star like the Sun. 15. Describe what astronomers believe will happen to the Sun after it leaves the main sequence.

CHAPTER 27

Star

Color

A

White

B

Orange

C

Blue

D

Red

E

Blue-white

F

Yellow

Section 27.3

4.

Which star would you expect to have a longer lifespan, the Sun or Sirius, a star whose mass is about twice as great as the Sun? Explain your answer.

CHAPTER 27 ASSESSMENT

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STARS

Use the H-R diagram below to answer the following questions.

Applying Your Knowledge The table below lists data for six stars. Use the table, and what you learned in this chapter, to answer the questions below.

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a. b. c.

What is the main difference between a typical white dwarf star and a typical supergiant? Which category of star is Vega, with a surface temperature of 10,000°C and a luminosity of 1? Predict which category Vega will enter next in its evolution.

Star

Color

A

white

1.0

.02

carbon, helium

B

red

6.0

400

magnesium, sodium

C

yellow-white

1.5

1.5

hydrogen

D

blue

12.0

900

hydrogen, helium

E

blue

1.5

1.5

hydrogen, helium

F

red

1.5

250

carbon, helium

a.

b. c. d. e. f.

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Solar Solar Prominent mass diameter spectral lines (× mass of (× diameter (elements present) the Sun) of the Sun)

Which star is in the final stage of a Sun-like star’s life cycle? Explain your answer. What is the name astronomers give to this type of star? Which star is the most like the Sun? Justify your answer. Which star is a blue supergiant? Which star will have the shortest life span? Explain why. Which stars are most likely main sequence stars? Explain your answer. Which star resembles what the Sun will become in about 5 billion years? Explain your answer.

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28

CHAPTER 28

Exploring the Universe

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How big is “everything”? How long is forever? In science, the term everything means the universe, including all matter and energy. In science, forever means the amount of time the universe has existed or will exist. As a start to answering these complex questions, think about the night sky. It’s dark. But why is the night sky dark? Imagine the universe stretched off to infinity in all directions. This would mean that in any direction you looked, you would eventually see a star. If there are stars in every possible direction, why isn’t the night sky light, not dark? This has puzzled people for a long time. A possible answer to this question is that the universe is not infinite in all directions, but has a finite size. Time had a beginning between 10 billion and 20 billion years ago and it may or may not have an end. Of course, we are not sure all our answers are correct. In this chapter, you’ll read about galaxies and the universe. Once you’ve finished, revisit the question posed here. What do you think?

4 What is the universe and how is it organized?

4 Does the universe have a beginning and an end?

4 How do astronomers study the universe?

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28.1 Tools of Astronomers

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The universe is defined as everything that exists and includes our solar system, the stars in our galaxy, and all other galaxies. In other words, it’s HUGE! The Hubble Space Telescope is one of many tools astronomers use to study objects in the universe. This powerful instrument constantly sends computerized images from space to Earth. Astronomers view these images on computer screens and then store the data for later use. Since the objects they observe are so far away, astronomers have developed their own units to measure them. In this section you will learn about the tools astronomers use to study the universe.

universe - everything that exists including all matter and energy.

scientific notation - an abbreviation in which a number is expressed as a number between 1 and 10 multiplied by a power of ten.

Astronomical numbers Scientific When you look up at the night sky, do you ever think about how far away the notation stars are? The closest star—Proxima Centauri—is 42,000,000,000,000

kilometers away. Writing out such astronomical distances as 42 trillion requires a lot of zeros. Scientific notation is a mathematical abbreviation for writing very large (or very small) numbers. Using this method, numbers are written as a value between 1 and 10, multiplied by a power of 10. For example, 42 trillion km can be written as 4.2 × 1013 km. Below is a stepby-step example of how to write numbers in scientific notation. The steps are shown in Figure 28.1. Steps to writing The average distance from Earth to the Sun is 150,000,000 kilometers. Write a number using this value using scientific notation. scientific notation 1. Move the decimal until you get a value that is between 1 and 10. Count

the number of times you move the decimal.

2.

Write down the new number without all of the zeros.

3.

Write × 10 after the number.

4.

Write the number of times you moved the decimal as the power of 10 (the exponent). If you moved the decimal to the left, the exponent will be positive. If you moved the decimal to the right, the exponent will be negative.

Answer: Earth is approximately 1.5 × 108 km from the Sun.

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Figure 28.1: Writing a number using scientific notation.

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Astronomical distances Light years You learned about light years (ly) in Chapter 1. Even though the name may

sound like it, this unit does not measure time. One light year is equal to the distance that light travels through space in one year.

The Age of Light

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A light year is the distance light travels through space in one year (9.46 × 1012 kilometers). Parsecs Recall that a parsec (pc) is another unit of distance used by astronomers. A

parsec is about 3.26 light years. A star’s luminosity is defined as the brightness that star would have if it were 10 parsecs from Earth. Ten parsecs is about 32.6 light years. A parsec is a unit derived by using geometry and trigonometry to describe the position and distance of objects in space, relative to Earth.

Solving Problems: Converting Astronomical Distances How far is 10 parsecs in kilometers? Use scientific notation in your answer. 1. Looking for:

Distance in km

2. Given:

Distance in 10 pc

3. Relationships:

1 pc = 3.26 ly and 1 ly = 9.46 × 1012 km

When you look at Proxima Centauri in the night sky, how “old” is the light you are seeing? In other words, how long did it take that light to get to Earth? The answer is easy if you use your head. Think about the definition of a light year and you’ll figure out the answer! Hint: This star is 4.2 light years away.

4. Solution:

⎛ 3.26 ly ⎞ ⎛ 9.46 ×1012 km ⎞ 13 10 pc × ⎜ ⎟×⎜ ⎟ = 3.08 ×10 km 1ly ⎝ 1pc ⎠ ⎝ ⎠

a. 1.14 × 1015 km b. 78 pc

Your turn...

a. A star is 37 pc from Earth. How far is this in kilometers? b. A star is 255 ly from Earth. How far is this in parsec? 28.1 TOOLS OF ASTRONOMERS

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Determining distances to closer objects in the universe Measuring the Astronomers use a method called parallax to determine the distance of stars distance of that are closer than 1,000 light years to Earth. To illustrate parallax, hold one closer stars finger about six inches from your nose. Close your left eye and look at your

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finger with your right eye. Next, close your right eye and look at your finger with your left eye. Because your eyes are in different positions, your finger appears to move. The same is true of stars in the sky. As Earth revolves around the Sun, the nearby stars appear to change positions in the sky over the course of one year. It is actually Earth that is changing position as it revolves around the Sun, while the stars remain fixed in the fixed background (Figure 28.2). Parallax only Parallax only works for stars that are relatively close to Earth because as works for closer distance from Earth increases, the change in the angle of a star becomes less stars measurable. You can demonstrate this by looking at a finger held before your

nose as you did before. This time, try moving your finger farther and farther away from your nose while looking at it with each eye. You will notice that the farther away it is, the smaller the movement appears to become until you can detect no movement at all.

Figure 28.2: As Earth revolves

around the Sun, the nearby stars appear to change positions in the sky.

How to measure To use parallax, astronomers determine the position of a star in the sky in distance using relation to other stars that are too far away to show movement. Next, they parallax look at the star six months later—when Earth is on the opposite side of the

Sun, and measure its change in position in relation to the faraway stars. Using geometry, they can determine the distance of the star from Earth (Figure 28.3 and below).

Figure 28.3: Using parallax to measure the distance to a star.

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Light, distance, and time Light years and The Solve It sidebar on page 709 brings up an interesting point: The light time from an object that reaches Earth is as old as the number of light years the

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object is from Earth. For example, the light we see from Proxima Centauri left that star 4.2 years ago. When we look at light from faraway objects in space, we are actually looking back in time. When astronomers view a faraway object, such as the Andromeda galaxy (2.5 million ly from Earth), they are looking back in time 2.5 million years (Figure 28.4)! Time as a tool of The farther away an object is, the farther back in time we are looking. This astronomy fact has become an important tool that astronomers use to develop theories

about the universe. For example, by comparing stars that are relatively near with stars that are very far away, astronomers have developed theories about how stars are born, how they live, and how they die.

Solving Problems: Communication Delays in Space How long does it take for radio waves to travel from the Moon to Earth? See sidebar (right). 1. Looking for:

Time (seconds) for radio waves to travel to Earth from the Moon.

2. Given:

The distance from the Moon to Earth is 384,400 kilometers. The speed of light is 300,000 kilometers per second.

3. Relationships:

Since speed is distance divided by time, you can rearrange the variables to solve for this quantity.

4. Solution:

Time = distance ÷ speed 384,400 km ÷ 300,000 km/s = 1.28 s

Figure 28.4: When astronomers

study the Andromeda galaxy, they are looking back in time 2.5 million years.

In 1969, Neil Armstrong and Buzz Aldrin were the first to land a lunar module on the Moon, 384,400 km from Earth. You may have heard Armstrong’s famous phrase, spoken when he stepped out of the module onto the Moon’s surface: “That’s one small step for a man, one giant leap for mankind.” When he spoke, he was not heard immediately on Earth because of the Moon’s distance. How long (in seconds) did it take the radio waves to travel to Earth so that those words could be heard by millions of listeners? (See solution steps at the left.)

Your turn...

How long does it take light from the Sun to reach Earth? Assume the Sun is 150 million km from Earth.

Your Turn: 500 s

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Telescopes History of the In the 1600s, Galileo was the first to use a telescope for astronomical telescope observations. He made some important discoveries including craters on the

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Moon, tiny moons around Jupiter, and the rings of Saturn (which he thought looked like ears). Since then, astronomers have developed increasingly powerful telescopes that continue to add to our knowledge of the universe. What is a A telescope is a device that makes objects that are far away appear closer. telescope? Telescopes come in many different shapes and sizes, from a small tube

telescope - a device that makes objects that are far away appear closer.

Telescope Milestones

weighing less than a pound, to the Hubble Space Telescope, weighing several tons. Most of the telescopes used today are of two types: refracting telescopes that use lenses and reflecting telescopes that use mirrors. Both types accomplish the same thing, but in different ways. How does a Have you ever tried to read the writing on a penny from 100 feet away? The telescope work? reason you can’t read it with your naked eye is that the image of a penny

from 100 feet away does not take up much space on your retina (the screen of your eye). Telescopes work by collecting the light from a distant object with a lens or mirror and bringing that light into a concentrated point, called the focal point. The bright light from the focal point is then magnified by another lens so that it takes up more space on your retina. This makes the object appear much larger and closer.

3500 BCE Phoenicians discover glass while cooking on sand. 1350 CE Craftsmen in Venice begin making lenses for spectacles. 1608 CE Hans Lippershey applies for a patent for the refracting telescope. 1609 CE Galileo is the first to use a telescope to view craters on the Moon. 1704 CE Newton invents the reflecting telescope. 1897 CE World’s largest refracting telescope built and housed in Yerkes Observatory, Wisconsin. 1990 CE The Hubble Space Telescope is launched from the space shuttle Discovery.

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Refracting and reflecting telescopes Refracting Refracting telescopes use lenses to refract light and magnify objects. They telescopes are made from a long tube, a glass objective lens that you point toward the

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sky, and an eyepiece—another glass lens that magnifies the object. The tube holds the two lenses the correct distance from one another. The objective lens is convex, that is, wider in the middle than at the edges. This lens gathers light from an object and bends it to a focal point near the back of the tube. The eyepiece lens can be either convex or concave (thinner in the middle and wider at the edges) (Figure 28.5). The diagram below shows how light rays travel through a refracting telescope to your eye. The lens with the shorter focal length is nearer to the eye.

refracting telescope - a telescope that uses lenses to gather light and magnify objects. reflecting telescope - a telescope that uses mirrors to gather light and a lens to magnify the object.

Figure 28.5: Concave and convex lenses.

Reflecting Reflecting telescopes use mirrors instead of lenses to gather and focus telescopes light and a lens to magnify the object (Figure 28.6). A mirror is made by

coating the surface of a concave lens with a reflecting material. This mirror (called the primary mirror) is placed at the back of a tube. Light rays enter the tube and are reflected off the primary mirror to a focal point. Another small, flat mirror (the secondary mirror) is placed in the path of the focal point at an angle that reflects the light rays to an eyepiece, located at the side of the tube. The eyepiece is a lens that performs the magnification of the image, just like in a refracting telescope. Because the secondary mirror is so small compared with the primary mirror, it only blocks a small fraction of the light entering the telescope.

Figure 28.6: The light rays in a reflecting telescope.

28.1 TOOLS OF ASTRONOMERS

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Telescopes and electromagnetic waves Electromagnetic So far, the telescopes you have read about collect and focus visible light and waves are referred to as optical telescopes. Objects in the universe give off many

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other types of electromagnetic waves that we can’t detect with our eyes, including radio waves, infrared waves, and X-rays. These waves all travel at the speed of light in space and have energies (frequencies) that increase as their wavelengths become smaller. Astronomers use different types of telescopes to view the different types of waves emitted by objects in space. Figure 28.7 shows an images of the Crab Nebula (the remnants of an exploded star) captured by different telescopes including optical (visible light), radio, infrared and X-ray. Radio A radio telescope works like an extremely powerful receiver that picks up telescopes radio waves from space. Astronomers aim these telescopes toward an object,

such as a star, and tune them until they receive waves in the correct frequency. The information is analyzed by a computer that draws an image of the source of the radio waves. Astronomers use radio telescopes to produce images of stars and galaxies, analyze the chemical composition of objects, and map the surfaces of planets. Infrared Another type of telescope looks at infrared waves. Since this type of wave is telescopes mostly absorbed by Earth’s atmosphere, infrared telescopes are often placed

on satellites that orbit above Earth. In 1983, the Infrared Astronomical Satellite (IRAS) was launched to map the entire sky at infrared wavelengths. It discovered a new comet, found evidence of another solar system, and discovered a new type of galaxy. X-ray telescopes X-ray telescopes are designed to detect high-energy radiation (X-rays) from

space. Since these waves cannot penetrate our atmosphere, X-ray telescopes are always placed on satellites. One of the most powerful, NASA’s Chandra X-ray Observatory, was launched on the space shuttle Columbia in 1999. Its mission is to observe X-rays that are emitted by high-energy objects in the universe, such as stars that have exploded.

Figure 28.7: Images of the crab

nebula taken with different types of telescopes.

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Satellites and other spacecraft Satellites Recall that the Moon is a natural satellite that orbits Earth. On October 4,

Arthur Walker

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1957, the former Soviet Union launched Sputnik I, the first artificial satellite to orbit Earth. Since then, hundreds of satellites have been launched. These important tools of astronomy (and many other sciences) continuously send data back to computers on Earth for analysis. The Hubble The Hubble Space Space Telescope Telescope (or HST),

named after American astronomer Edwin Hubble (1889 to 1953) is a satellite that orbits Earth at a distance of about 600 km. This powerful telescope, placed out of reach of “light pollution,” sends images from deep space to computers back on Earth. A NASA image captured by the HST is shown above. Most of the objects in the image are not stars—which appear to have “spikes”—but galaxies; most of them billions of light years away! You’ll read more about galaxies in the next section. A larger and more powerful telescope—The James Webb Space Telescope (JWST) will replace the aging HST in 2018. James Edwin Webb (1906–1992) was the second administrator of NASA, serving from 1961 to 1968. The JWST will allow astronomers to see even deeper into space and farther back in time.

Arthur Walker was born in 1936. Arthur was an excellent student. He decided to take the entrance exam for the Bronx High School of Science. Arthur passed the exam, but when he entered the school a teacher told him that the prospects for an African-American scientist were bleak. Arthur’s mother visited the school and told them her son would pursue whatever course of study he wished. Walker went on to earn a Ph.D. in physics from the University of Illinois. He spent three years in the Air Force, designing a rocket probe and satellite experiment to measure radiation that affects satellite operation. Later, Walker worked to develop the first X-ray spectrometer used aboard a satellite. It helped determine the temperature and composition of the Sun’s corona. In 1974, Walker joined the faculty at Stanford University. There he used a new multilayer mirror technology to develop telescopes that were launched into space on rockets. The telescopes produced detailed pictures of the Sun and its corona, bringing about significant changes in our understanding of them.

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Spacecraft Space probes Space probes are unmanned spacecraft that carry scientific instruments on

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board. Space probes are not designed to return to Earth, but many have landed on other planets or flown past planets, taking pictures as they go (Figure 28.8). Still others have remained in orbit around a planet for long periods of time to study them in great detail. Launched in 1977, the NASA Voyager 1 and 2 probes have traveled farther from Earth than any other manmade object. Voyager 1 is now more than twice as far from Earth as Pluto. Both Voyagers are still sending information back to Earth via radio waves as they continue to speed toward the edge of our solar system. Piloted In April, 1961, Yuri Gagarin of the former Soviet Union was the first human spacecraft to travel in space, followed on May 5 by Alan Shepard of the United States.

This led to the NASA Manned Lunar Program known as Apollo, which lasted from 1963 to 1972, and in which humans successfully landed on the Moon. Since Apollo, we have not sent humans back to the Moon, or to any other bodies in space, mainly because of the cost of such missions. However, piloted spacecraft are still useful tools of astronomy.

Figure 28.8: This image of Jupiter’s Great Red Spot was captured by Voyager 1.

Space shuttles Space shuttles are piloted spacecraft that launch from rocket “boosters” and and stations can land back on Earth like an airplane. Developed by NASA, they are used

to conduct experiments in space, to launch and repair satellites, and to transport people to and from space stations, such as the International Space Station (or ISS). The ISS is a joint project of six nations that orbits 450 kilometers above Earth’s surface. On board, scientists conduct numerous experiments, many of which depend on the constant free fall (microgravity) conditions provided by the space station. Unmanned NASA’s Mars Exploration Rover (MER) Mission began in 2003 with the missions to sending of two unmanned rovers (Spirit and Opportunity) to explore the Mars surface features and geology of Mars. NASA’s Phoenix lander (Figure 28.9),

launched in August, 2007 contains a robotic arm that digs through the Martian soil and brings samples onboard for scientific analysis. The goal of the Phoenix mission is to study the history of water on Mars and search for the large organic molecules found in living things.

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Figure 28.9: The Phoenix lander.

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Section 28.1 Review 1. Convert the distances in Figure 28.10 to kilometers. Express your answers in scientific notation. 2. Convert the distances in Figure 28.10 to parsecs.

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3. What is a light year? Why do astronomers use light years to measure distances in space? 4. What is parallax? Why does parallax work only for stars that are relatively close to Earth? 5. Why does observing faraway objects help astronomers develop theories about the history of the universe? 6. Suppose the Sun suddenly stopped emitting light. How long would it take, in seconds, for the Sun’s light to disappear on Earth? (Hint: The Sun is an average of 150 million km from Earth).

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Object

Distance from Earth (light years)

Sirius (brightest star in the sky)

8.8

Betelgeuse (appears as a red star in the sky)

700

Crab Nebula (remnant of an exploded star)

4,000

Andromeda galaxy

2.3 million

Figure 28.10: Use the table above to answer questions 1 and 2.

7. Explain the difference between a reflecting telescope and a refracting telescope. 8. Is the statement below true or false? All telescopes use light waves to form images.

NASA Missions

9. What are the advantages to placing a telescope on a satellite orbiting Earth? What are the disadvantages? 10. Name an example from the text of each of the following spacecraft. a. unmanned mission b. piloted spacecraft c. space probe

NASA has had many missions to Mars and some planned for the future. Using the keywords “NASA missions to Mars” conduct internet research. Choose a past, current, or future mission and write a page about it in your journal. Answer the following questions. What is the name of the mission? What is the major goal of the mission? What did you find interesting about the mission?

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28.2 Galaxies In the twentieth century, we became aware that the Sun is one of billions of stars in the Milky Way galaxy, and that there are billions of other galaxies in the universe. In the past 50 years, astronomers have found evidence that the universe is expanding and that it originated 10 billion to 20 billion years ago. In this section, you will learn about galaxies and how they are studied.

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What is a galaxy?

galaxy - a group of stars, dust, gas, and other objects held together by gravitational forces.

Milky Way galaxy - the galaxy to which our solar system belongs.

The discovery of A galaxy is a huge group of stars, dust, gas, and other objects bound together by other galaxies gravitational forces. The Sun, along with an estimated 200 billion other stars, belongs to the Milky Way galaxy. The Milky Way has “arms” that appear to

spiral outward like the Whirlpool galaxy (Figure 28.11). From above, it would look like a giant pinwheel, with arms radiating out from the center (Figure 28.12). Although some stars are in globular clusters above and below the main disk, the majority are arranged in a disk that is more than 100,000 light years across and only 3,000 light years thick. Figure 28.11: The Whirlpool galaxy.

Our Sun is 26,000 light years from the center

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The disk of the Milky Way is a flattened, rotating system that contains young to middle-aged stars, along with gas and dust. The Sun sits about 26,000 light years from the center of the disk and revolves around the center of the galaxy about once every 250 million years. When you look up at the night sky, you are looking through that disk of the galaxy. On a crystal clear night, you can see a faint band of light stretching across the sky. This is the combined light of billions of stars in the galaxy, so numerous that their light merges.

Figure 28.12: An artist’s rendering of the Milky Way galaxy.

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Types of galaxies The discovery of At the turn of the twentieth century astronomers believed the Milky Way other galaxies galaxy was the entire universe. As more-powerful telescopes were developed,

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some “smudges” that were thought to be nebulae in the Milky Way were recognized to be whole galaxies far outside our own. The discovery was made in the 1920s by Edwin Hubble, an American astronomer. When he focused a huge telescope on an object thought to be a nebula in the constellation Andromeda, Hubble could see that the “nebula” actually consisted of faint, distant stars. Since Hubble’s time (1889–1953), astronomers have discovered a large number of galaxies. In fact, many galaxies are detected each year using the Hubble Space Telescope, or HST, named after Edwin Hubble. Galaxy shapes

Astronomers classify galaxies according to their apparent shapes (Figure 28.13). Spiral galaxies consist of a central, dense area surrounded by spiraling arms. Barred spiral galaxies have a bar-shaped appearance in the center. Elliptical galaxies look like the central portion of a spiral galaxy without the arms. Lenticular galaxies, sometimes called “armless spirals,” have a central bulge, but no apparent spiral arms because they are seen edge-on. Irregular galaxies exhibit peculiar shapes and do not appear to rotate like those galaxies of other shapes. NGC 6822 (above, left) is an example of an irregular galaxy.

Galaxies change Astronomers theorize that the shapes of galaxies change over time. Because it shape over time may take hundreds of millions of years, they have never actually seen the

changes taking place. However, by looking at many galaxies, astronomers hypothesize that they can see similar galaxies at different times in their histories. This observational data has allowed astronomers to develop computer-based models that calculate how a galaxy may change over hundreds of millions of years. One hypothesis is that the barred spiral form is just one phase of a regular spiral. Computer simulations show how the “bar” may form and disappear repeatedly as a spiral galaxy rotates.

Figure 28.13: Some representative galaxy apparent shapes.

28.2 GALAXIES

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The central black hole theory The center of the Since we are located in the outer part of the galaxy, dust between the stars galaxy blocks out much of the visible light coming from objects in the disk. Because

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of this, astronomers use infrared and radio telescopes to study our galaxy. They have learned that the core of the galaxy is crowded with older stars and hot dust (Figure 28.14). Recent studies have suggested that a black hole, with a mass of more than a million Suns, exists at the very center of the galaxy.

black hole - an object with such strong gravity that its escape velocity equals or exceeds the speed of light.

Evidence for the The evidence for a huge black hole comes from measurements of the orbital black hole velocities of stars and gas at the center of the galaxy. In one study, an theory infrared telescope was used to measure the orbital velocities of 20 stars over

a three-year period. It was determined that these stars were orbiting at velocities of up to 1,000 kilometers per second. This extremely high orbital velocity requires an object with a mass that is over 2 million times that of the Sun. Relativity One of the strangest predictions of Einstein’s theory of relativity is the predicts black existence of black holes. To understand a black hole, imagine throwing a ball holes fast enough to leave Earth completely. If the ball does not go fast enough,

Earth’s gravity eventually pulls it back. The minimum speed an unpowered projectile must have to escape the planet’s gravity is called the escape velocity. The stronger gravity becomes, the higher the escape velocity.

Figure 28.14: The core of the Milky Way is in the direction of the constellation Sagittarius.

The escape If gravity becomes strong enough, the escape velocity can reach the speed of velocity of a light. A black hole is an object with such strong gravity that its escape black hole velocity equals or exceeds the speed of light. When the escape velocity

equals the speed of light, nothing—including light—can get out. The name black hole comes from the fact that nothing that is pulled in by the object’s gravity can escape. Since no light can escape, the object is “black” (Figure 28.15). To make a black hole, a very large mass must be squeezed into a relatively tiny space. For example, to make Earth into a black hole, you would have to squeeze the mass of the entire planet down to the size of a marble.

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Figure 28.15: Light from a black

hole cannot escape because the escape velocity is higher than the speed of light.

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Distances between galaxies Galaxies are a million times farther away than stars

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The distances between stars are 10,000 times greater than the distances between planets. The distances between galaxies are a million times greater than the distances between stars. For example, the distance from Earth to Proxima Centauri, the nearest star, is 4.2 light years, but the distance from Earth to the Whirlpool galaxy is over 30 million light years.

The local group The Milky Way belongs to a group of about 30 galaxies called the Local of galaxies Group. This group includes the Large Magellanic Cloud (179,000 ly away)

and the Small Magellanic Cloud (210,000 ly away). These Magellanic Clouds are small, irregular galaxies of less than 100,000 stars. The Local Group also includes Andromeda, an elliptical galaxy 2.5 million light years away (Figure 28.16).

Figure 28.16: The Andromeda

galaxy is an elliptical galaxy in the Local Group.

Galactic Galaxies may move through space singly and in groups. Some galaxies collisions appear to collide with each other in slow dances of stars that may take

millions of years to complete (Figure 28.17). Determining the Figuring out the distance between galaxies is one of the more difficult tasks in distance to astronomy. A faint (low brightness) object in the night sky could be a dim nearby galaxies object that is relatively nearby or a bright object that is far, far away. The most

reliable method for estimating the distance to a galaxy is to find a star whose luminosity is known. The process for determining distance using luminosity is discussed on the next few pages.

Figure 28.17: Two galaxies that are near to colliding.

Distant galaxies This method works for the closest galaxies. However, the vast majority of

galaxies are too far away to see single stars even with the best telescopes. Beyond 150 million light years, astronomers compare size and type with closer galaxies to estimate the luminosity of the farther ones. This method is not as accurate and, consequently, the distances to far galaxies are known only to within a factor of two. 28.2 GALAXIES

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Determining the distances to galaxies The inverse Light is very important to astronomers in measuring the distances to galaxies square law and stars that are more than 1,000 light years away. Recall that the brightness

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of an object depends on how far away it is, and how much light it actually gives off (its luminosity). The mathematical relationship between these variables is known as the inverse square law of light and is used to determine the distance to faraway stars and galaxies.

inverse square law of light relates the mathematical relationship between brightness, luminosity, and distance.

Brightness vs. distance 25

Brightness

20 15 10 5

Brightness vs. distance

Solving for distance

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The inverse square law shows how the brightness of an object decreases as you move away from it. The amount of decrease in brightness can be quantified using the formula at the left. The symbol α indicates a proportional relationship. For example, if you are looking at a candle from 1 meter away, and then you move to 2 meters away, its brightness will decrease by a factor of four. If you move to 3 meters away, its brightness will decrease by a factor of nine. By what factor will its brightness decrease if you move to 10 meters away? If you did an experiment where you measured the brightness of a candle at various distances, starting at 1 meter, your graph would look similar to Figure 28.18. 1 Bα 2 D

The inverse square law is important to astronomers because L if they know the brightness and luminosity of an object, they D= 4π B can determine its distance by rearranging the variables to solve for D as shown in the equation at the left. Recall that brightness (B) can be easily measured using a photometer. The challenge facing astronomers is how to determine the luminosity (L) of faraway objects.

0 0

2

4 6 Distance

8

10

Figure 28.18: A graph of the

brightness of a candle vs. distance.

Brightness is measured in units of power. In the laboratory, you can measure the brightness of a light source in watts. A larger unit is solar luminosity units. One solar luminosity unit is equal to the brightness of the Sun, or about 3.9 × 1026 watts. This is comparable to the combined brightness of 400 trillion trillion 100watt light bulbs! Our galaxy emits as much light as 1.0 × 1010 Suns.

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Standard Astronomers have found a way to infer values for luminosity (L) using a candles source of light called a standard candle. A standard candle is an object,

such as a star, whose luminosity is known.

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standard candle - an object, such as a star, whose luminosity is known.

Measuring the You are already familiar with one type of standard candle called main distance to stars sequence stars. Recall that main sequence stars are found in a diagonal band in the Milky Way on the H-R diagram. It is estimated that 90 percent of all stars are main

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sequence. Through observation, astronomers can determine if a star is a main sequence star by comparing it to stars on the H-R diagram. By determining the unknown star’s temperature (using a spectrometer), they can infer its luminosity by choosing a similar main sequence star on the H-R diagram as shown in Figure 28.19. Next, they measure the unknown star’s brightness, and use the inverse square law to calculate its distance. Astronomers use this method to measure distances to stars in the Milky Way and nearby galaxies—out to distances of about 200,000 light years. Beyond that, astronomers cannot see main sequence stars and must rely on other types of standard candles. Measuring A second type of standard candle is called a Cepheid star. This type of star distances to was discovered by Henrietta Leavitt (1868–1921), an American astronomer, galaxies in the early 1900s. Cepheid stars “pulsate” in regular periods ranging from a

few days to a few weeks. Leavitt discovered that there is a relationship between the period of a Cepheid star and its luminosity. This meant that by measuring the period of a Cepheid star, astronomers could determine its luminosity and then, use the inverse square law to calculate its distance. Astronomers locate Cepheids in faraway galaxies and use them to map distances between galaxies in the universe. The Hubble Space Telescope actively searches for Cepheids in faraway galaxies. Going even Beyond 100 million light years, Cepheid stars are too faint to observe—even farther with the HST. For these distances, astronomers must rely on a third type of

standard candle—a certain type of supernova. By observing the rate at which light from the supernova fades after the initial explosion, astronomers can use a mathematical formula to determine its luminosity, and then use the inverse square law to infer the distance to the galaxy in which the supernova resides.

Figure 28.19: Inferring the

luminosity of an unknown star using the H-R diagram and main sequence stars as a standard candle.

The North Star The North Star is the brightest Cepheid star. Because it is only 390 light years from Earth, its distance can also be measured using parallax. This is one of the stars that helped astronomers refine the use of Cepheids to determine distances. The Cepheid star first discovered, Delta Cephei, is also relatively close to Earth at 300 light years.

28.2 GALAXIES

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Section 28.2 Review 1. Which is bigger, a supergiant star or a galaxy? 2. In which galaxy do we live? 3. The number of stars in our home galaxy is closest to:

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a. b. c. d.

200 200,000 200,000,000 200 billion

4. Name the two important discoveries credited to astronomer Edwin Hubble that are discussed in this section. 5. List four galaxy shapes. 6. The distances between galaxies are in the range of: a. b. c. d.

100 kilometers 100 light years 1 million light years 1 billion light years

7. How do astronomers estimate the distance between galaxies? 8. What do scientists believe is at the center of the Milky Way galaxy? 9. Why does a black hole appear black? 10. Which graph in Figure 28.20 best shows the relationship between how bright a glowing object appears and its distance from the observer? 11. What is a standard candle? How do astronomers use standard candles?

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Figure 28.20: Use the graphs to answer question 10.

When reading about black holes, you learned that Earth would have to be squeezed into the size of a marble one centimeter in diameter to make its gravity strong enough to be a black hole. Use what you learned about density in Chapter 10 to calculate how dense Earth would be if it were compressed to this size. Compare your calculated density to that of common materials such as lead and steel.

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28.3 Theories about the Universe

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While there are many theories about how the universe began, the one that has gained credibility among scientists is called the Big Bang theory. The Big Bang theory states that the universe began as a huge explosion that occurred somewhere between 10 and 20 billion years ago. In this section, you will read about how scientists gathered evidence to support the Big Bang theory and other theories about the universe.

Big Bang theory - states that the universe began as a huge explosion. Doppler shift - a change in the wavelength of a wave that occurs when an object is moving toward or away from an observer.

Doppler shift Doppler shift In the 1800s, Christian Doppler (1803–1853), an Austrian physicist, discovered

that when the source of a sound wave is moving, its frequency changes. You may have noticed the Doppler effect if you have heard a car drive by with its horn blaring. As the car approaches, you hear the horn playing high “notes,” and as the car passes, you hear the horn shift to lower notes as the car moves farther away. The change in sound you hear is caused by a Doppler shift. You do not have to be standing still for a Doppler shift to occur. A Doppler shift is related to the net change between the source of the waves and the observer. How does it As the car is moving toward you, the sound waves are compressed relative to work? where you are standing. This shortens the wavelength and causes the

frequency to increase (recall that wavelength and frequency are inversely related). As the car moves away, the sound waves are stretched out, causing longer wavelengths and lower frequencies (Figure 28.21). The sound of the horn changes as the car passes by because the sound waves are being compressed and then stretched. If you could measure the rate of change in the frequency, you could measure the speed of the car. Doppler shift and electromagnetic waves

Doppler shift also occurs with electromagnetic waves, such as visible light, X-rays, and microwaves. This phenomenon is an important tool used by astronomers to study the motion of objects in space. For example, if an object is moving toward Earth, the light waves it emits are compressed, shifting them toward the violet end (shorter wavelengths, higher frequencies) of the visible spectrum. If an object is moving away from Earth, the light waves it emits are stretched, shifting them toward the red end (longer wavelengths, lower frequencies) of the visible spectrum (Figure 28.22).

Figure 28.21: Doppler shift occurs when an object is moving toward or away from an observer.

Figure 28.22: Doppler shift is used to study the motion of objects in space.

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The expanding universe Sirius is moving In the 1890s, astronomers began to use spectroscopy to study the stars and away from Earth other objects in space. One of the first stars they studied, Sirius, had spectral

Redshift Redshift is a type of Doppler shift caused by relative motion that increases

with the distance from the source to the observer. The faster the source of light is moving away from the observer, the greater the redshift. The opposite (blueshift) happens when an object is moving toward the observer. A star moving toward Earth would show a spectrum for hydrogen that was shifted toward the blue end of the scale. Discovery of the In the late 1920s, Edwin Hubble began to measure the distance and redshift expanding of galaxies. Much to his surprise, he discovered that the farther away a universe galaxy was, the faster it was moving away from Earth. By the early 1930s, he

Figure 28.23: The spectral lines

have shifted toward the red end of the spectrum in the moving star.

had enough evidence to prove that galaxies were moving away from each other with a speed proportional to the distance between them (Figure 28.24). This concept came to be known as the expanding universe. The Big Bang The expanding universe was a great surprise to scientists. Before Hubble’s theory discovery, people believed the universe had existed in its same form for all

time. The fact that the universe was expanding implies the universe must have been smaller in the past than it is today. In fact, it implies that the universe must have had a beginning. Astronomers today believe the universe exploded outward from a single point smaller than an atom into the vast expanse of galaxies and space we see today. This idea is known as the Big Bang theory.

Redshift vs. distance of galaxies

Redshift

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lines in the same pattern as the spectrum for hydrogen. However, these lines did not have the exact same measurements as those for hydrogen. Instead, they were shifted toward the red end of the visible spectrum (Figure 28.23). This was a puzzle at first, until scientists realized that a red-shifted spectrum meant Sirius was moving away from Earth. They could even determine how fast Sirius was moving away by measuring the amount that the lines had shifted toward red.

Distance from Earth

Figure 28.24: A graph of Hubble’s data.

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The Big Bang theory The Big Bang The Big Bang theory says the universe began as a huge explosion between 10 theory billion and 20 billion years ago (Figure 28.25). According to this theory, all

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matter and energy started in a space smaller than the nucleus of an atom. Suddenly, (no one knows why) a huge explosion occurred that sent everything that makes up the universe spraying out in all directions. In its first moments of existence, the universe was an extremely hot fireball of pure energy that began to expand rapidly. Protons and As the universe expanded, it cooled down as its energy spread out over a neutrons form at larger volume. About four minutes after the Big Bang, the universe had four minutes cooled enough that protons and neutrons could stick together to form the

nuclei of atoms. Because atoms were still flying around with high energy, heavy nuclei were smashed apart. Only one helium atom survived for every 12 hydrogen atoms. Almost no elements heavier than helium survived. When we look at the matter in the universe today, we see this ratio of hydrogen to helium left by the Big Bang, with the exception of elements formed later in stars. Matter and light For approximately the next 700,000 years, the universe was like the inside of decouple in a star—hot ionized hydrogen and helium. At the age of about 700,000 years, 700,000 years the universe had expanded enough to become transparent to light. At this

point, the light from the fireball was freed from constant interaction with hot matter. The light continued to expand separately from matter and became the cosmic background radiation we see today. Stars and When the universe was about 1 billion years old, it had expanded and cooled galaxies form enough that galaxies and stars could form. At this point, the universe probably

began to look similar to how it looks today. The Sun and solar system formed about 4.6 billion years ago, by which time the universe was about 12 billion years old. Unresolved While scientists feel relatively confident about the overall picture, they are questions not confident about the details. For example, recent observations suggest the

Figure 28.25: Big Bang time line.

expansion of the universe is accelerating. This is a puzzle because, if anything, gravity should be slowing the expansion down. 28.3 THEORIES ABOUT THE UNIVERSE

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Evidence for the Big Bang theory Evidence for the When it was first introduced, the Big Bang theory was not widely accepted. Big Bang In fact, the name “Big Bang” was made up by scientists to mock the theory.

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Unfortunately for them, the name stuck. As with any new theory, the Big Bang became more accepted as new scientific tools and discoveries established more evidence. The fact that galaxies are expanding away from each other is a strong argument for the Big Bang. As far as we can look into the universe, we find galaxies are expanding away from each other. We do not see galaxies coming toward each other. More evidence In the 1960s, Arno Penzias and Robert Wilson, two American astrophysicists, for the Big Bang were trying to measure electromagnetic waves given off by the Milky Way.

No matter how they refined their technique, they kept detecting a background noise that interfered with their observations. This noise seemed to be coming from all directions and had little variation in frequency. Cosmic When you light a match, the flame bursts rapidly from the first spark and background then cools as it expands. When the Big Bang exploded, it also created hot radiation radiation. This radiation has been expanding and cooling for 16 billion years.

The radiation is now at a temperature only 2.7°C above absolute zero and it fills the universe. The cosmic background radiation is the “smoke” from the Big Bang that fills the room (that is, the universe), even 16 billion years later. The “noise” that Penzias and Wilson found was the cosmic background radiation predicted by the Big Bang theory (Figure 28.26).

Figure 28.26: The COBE satellite

measured these images of the cosmic background radiation. The upper image includes radiation from the Milky Way. This radiation has been eliminated in the lower image to reveal ripples left over from the Big Bang (NASA).

Elements in the universe 0.1% all other elements 8% helium

Ratios of the We have other evidence that supports the Big Bang theory. The proportion of elements hydrogen to helium is consistent with the physics of the Big Bang

(Figure 28.27). Elements heavier than hydrogen and helium are formed in stars. When stars reach the end of their life cycles, they spread heavy elements such as carbon, oxygen, and iron out into the universe. If the universe were significantly older, there would be more heavy elements present compared with hydrogen and helium.

91.9% hydrogen

Figure 28.27: The percentage of the elements in the universe.

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Planetary systems and how they were formed Other stars have A star with orbiting planets is called a planetary system. Until the last planetary decade, no one knew whether planets were commonly formed with stars or systems whether solar systems like our own were rare. However, as of this writing,

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more than 150 planets have been discovered around nearby stars. Because they give off no light of their own, planets are very hard to see against the brightness of a star. Astronomers had to devise very clever techniques to find them. Scientists now believe that planets are a natural by-product of the formation of stars. Therefore, planets of some type should exist around many (if not most) stars in the universe. How was our The solar system was formed out of the same nebula that created the Sun (see solar system Figure 28.28 on page 730). As the Sun was being formed 4.6 billion years formed? ago, it was surrounded by a cloud of dust and gas. This cloud was made

mostly of hydrogen and helium, but contained smaller amounts of other elements such as carbon, nickel, iron, aluminum, and silicon. As this cloud spun around, it flattened, with the help of gravity, into a disk-shape along the axis of its rotation. This explains why all of the planets formed in the same plane around the Sun, and why they all orbit in the same direction.

Planet formation At the center of the disk, temperatures became hot enough for fusion to begin,

planetary system - a star with orbiting planets.

Why are planets and stars spherical? Planets and stars (and many moons) are spherical because their gravity pulls the matter toward the center of the body. Over long periods of time, the matter gives in to the gravitational pull from its center of gravity. The only way to get all the mass as close as possible to the body’s center of gravity is to form a sphere. With much smaller bodies, like some asteroids, the gravitational pull is too weak to overcome the asteroid’s mechanical strength. As a result, these bodies have irregular shapes. Since gravity pulls toward the center of the planet or star, all of its matter gets pulled down into a sphere. However, planets and stars are not really perfect spheres. Because they rotate, they sometimes bulge out slightly at the equator.

creating the Sun. Farther away from the center, the heaviest molecules began to condense into solid and liquid droplets. These droplets began to collide, forming small clumps—the seeds of planets. Through further collisions, these clumps of material grew larger and larger and eventually gravity formed them into spherical planets.

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The terrestrial Terrestrial planets, like Earth, were formed in the warmer, inner regions of planets the disk. Because the heat drove off the lighter elements such as hydrogen

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and helium, these planets were made mostly of metals and rock. These materials made up less than one percent of the disk, so these planets could not grow very large. Because of their small masses, their gravity could not attract hydrogen and helium and their atmospheres were thin and contained little of these elements. The gas planets The outer regions of the disk were rich in icy materials made of lighter

elements and the planets there grew comparatively large. Because of their large masses, they were able to capture hydrogen and helium through their gravitational force and so form thick atmospheres. These became gas planets, rich in hydrogen and helium with dense, frozen cores. The Kuiper belt Many astronomers believe that Kuiper belt objects are the primitive

remnants from the early formation of the solar system. The inner, dense parts of the disk condensed into the eight major planets. The outer parts were less dense, and thus the formation of bodies was slower and as a result, many smaller bodies were formed. Binary stars

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Many gas clouds have enough swirling matter to form multiple stars with possible planets. A binary star is a system with two stars that are gravitationally tied and orbit each other. Binary stars are common. Mizar, the middle star in the handle of the Big Dipper, was the first binary star discovered, in 1650, by the Italian astronomer Giovanni Riccioli. Modern telescopes show that those two stars are actually four. Both Mizar A and Mizar B are themselves binary stars making this a four-star system. About half of the 60 nearest stars are in binary (or multiple) star systems.

Figure 28.28: The formation of our

solar system. Scientists now believe that this is a common process in the universe.

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CHAPTER 28

Section 28.3 Review 1. What is Doppler shift? Give a common example of how you might experience Doppler shift.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

2. Suppose you are using a spectrometer to analyze the light from a star that is moving away from Earth. Which statement correctly describes what you would see? a. The spectral lines would be shifted toward the blue end of the spectrum. b. The spectral lines would not be shifted, but would appear the same as if the star were not moving at all relative to Earth’s motion. c. The spectral lines would be shifted toward the red end of the spectrum. 3. Is the star in Figure 28.29 moving away from Earth or toward it? Explain your answer. 4. How did astronomers discover that the star Sirius was moving away from Earth? 5. What did Hubble discover about the relationship between a galaxy’s velocity and distance from Earth? 6. According to the Big Bang theory, how large was the universe before it exploded and expanded in all directions? 7. How many years did it take for stars to begin to form after the Big Bang?

Figure 28.29: Use the diagram

8. What evidence for the Big Bang did the scientists Arno Penzias and Robert Wilson discover?

above to answer question 3.

9. The universe is mostly hydrogen with a small amount of helium and tiny amounts of heavier elements. a. Where are heavier elements formed? b. If the universe was significantly older, what proportions of elements would you expect to find? Explain your answer. 10. Why did the terrestrial planets form closer to the Sun while the gas planets formed farther away?

28.3 THEORIES ABOUT THE UNIVERSE

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CHAPTER 28

EXPLORING THE UNIVERSE

Chapter 28 Assessment Vocabulary

13. A(n) _____ is a star with orbiting planets.

Select the correct term to complete the sentences.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

standard candle

refracting telescope

Doppler shift

planetary system

galaxy

black hole

Milky Way galaxy

inverse square law

universe

Big Bang theory

of light

reflecting telescope

telescope

scientific notation

Section 28.1

Concepts Section 28.1

1.

Why are light years used to measure distances to stars instead of kilometers?

2.

What is the difference between a refracting telescope and a reflecting telescope?

3.

Explain the difference between a radio telescope and an infrared telescope.

1.

The ____ includes all matter and energy that exists.

2.

Very large or very small numbers are sometimes expressed in _____.

4.

What are the advantages to placing a telescope on a satellite?

3.

A(n) _____ is a device that makes objects that are far away appear closer.

5.

Explain why astronomers are looking back in time when they observe faraway stars and galaxies.

4.

A(n) _____ uses mirrors to gather light.

5.

A(n) _____ uses lenses to gather light and magnify objects.

Section 28.2

Section 28.2

6.

Name the four shapes used to classify galaxies.

7.

To which galaxy does our sun belong and what shape does our galaxy take?

6.

The ____ is where you live.

7.

A(n) _____ is a group of stars, dust, gas, and other objects held together by gravitational forces.

8.

What is a black hole? Describe the evidence that supports the idea that a large black hole exists at the center of our galaxy.

8.

Scientists believe that a large _____ exists at the very center of our galaxy.

9.

9.

The _____ relates the mathematical relationship between brightness, luminosity, and distance.

Describe the Milky Way galaxy. Refer to: a. the position of our sun, b. the galaxy’s dimensions in light years, and c. the location of a black hole.

10. A(n) _____ is an object, such as a star, whose luminosity is known. Section 28.3

10. What is a standard candle? How is a standard candle used to measure distances to faraway galaxies?

11. The ____ states that the universe began as a huge explosion. 12. A(n) _____ is a change in wavelength of a wave that occurs when an object is moving toward or away from an observer.

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UNIT 9 MATTER AND MOTION IN THE UNIVERSE

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EXPLORING THE UNIVERSE

CHAPTER 28

Section 28.3

Section 28.2

11. What is the Big Bang theory?

4.

Rank the following from smallest to largest in mass. a. Milky Way galaxy b. our sun c. the universe d. Earth e. the black hole at the center of the Milky Way Galaxy.

5.

Rank the following from closest to farthest away from Earth. a. Andromeda galaxy b. our sun c. the Moon d. the star Sirius

12. Describe three pieces of evidence that support the Big Bang theory. 13. According to the Big Bang theory, how old is the universe?

Problems Section 28.1

3.

Section 28.3

Star A

7. 8.

500

600

400

600

Which star is moving toward Earth? Which star is moving away from Earth? Explain your answer in both cases. You are looking at a candle from 3 meters away. By what factor will its apparent brightness decrease if you move to 18 meters away? You are looking at a candle from 20 meters away. By what factor will its apparent brightness increase if you move 10 meters closer to the candle?

CHAPTER 28 ASSESSMENT

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500

686.3

400

Wavelength (nm)

Violet

600

420.0 472.1

500

Violet

400

Star B

Wavelength (nm)

Red

Wavelength (nm)

464.0 516.1

Standing object

Suppose the Sun suddenly burned out. How long would it take, in minutes, before we noticed this had occurred? (Hint: The speed of light is 300,000 km/s and the distance from Earth to the Sun is 150 million km). In 1989, the space probe Voyager 2 reached the planet Neptune and began sending images of the planet back to Earth. Assuming these radio waves had to travel about 4.0 × 109 km, how long did it take, in minutes, before astronomers received the signals from Voyager 2? (Hint: Radio waves travel at the speed of light—300,000 km/s).

The light from two stars (A and B) is analyzed using a spectrometer. The spectral lines for these stars are shown below. Also shown are the spectral lines for hydrogen from a light source that is on Earth.

642.3

6.

Red

2.

Write the following values using scientific notation. a. 156,000,000,000 kilometers b. 18.5 pounds c. 0.000000000000000000000025 centimeter d. 47,000,000,000,000 kilometers e. 0.0027 second f. 1.5 kilograms g. 93,000,000 miles h. 17,000 light years

656.3

1.

434.0 486.1

15. In the forming solar system, why did the terrestrial planets form closer to the Sun while the gas planets formed farther away?

Violet

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

14. As observed from Earth, the light from a distant star is shifted toward the red end of the visible spectrum. What would this indicate to an astronomer?

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CHAPTER 28

EXPLORING THE UNIVERSE

Applying Your Knowledge Section 28.1

1.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

2.

Scientists conduct many experiments onboard the International Space Station that depend on the constant free fall (microgravity) conditions that this environment provides. Use the Internet to find out about one of these experiments. Identify the research question, hypothesis, procedures, and results of the experiment. Develop a poster presentation about the experiment for your class. Some good websites include: www.nasa.gov spaceflight.nasa.gov Search the Internet for satellite images of your community. Find an image taken by each of the following types of electromagnetic radiation: visible light, radio waves, and infrared. What kinds of information does each type of image provide? What are the scientific uses for each type of image? Some good websites include: www.ghcc.msfc.nasa.gov www.ssec.wisc.edu/data mapping.usgs.gov

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Section 28.2

3.

The diagram below shows a group of stars as seen in the night sky. In the diagram, the relative size of each star indicates how bright it appears in the sky (brightness). Next to each star, its distance from Earth, in light years (ly) is shown. Use the diagram and what you know about the relationship between brightness and luminosity to answer the questions below.

a. b. c. d.

Which star has the greatest brightness? Explain your answer. If all of the stars in the diagram were moved to a distance of ten parsecs from Earth, which star would appear the brightest? Which star do you think has the lowest luminosity? Explain your answer. Which star do you think has the highest luminosity? Explain your answer.

Section 28.3

4.

Create a printed catalog or computer presentation about the astronomical objects you learned about in this unit (planets, stars, galaxies, etc. Follow these steps: a. Make a list of all of the astronomical objects you learned about in this unit (planets, stars, etc.). b. Write a definition and description of each type of object. c. Using the Internet, find images of each type of object to use for your catalog or presentation.

UNIT 9 MATTER AND MOTION IN THE UNIVERSE

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A absolute dating – any process that provides the real age of a sample in years.

absorption – what happens when the amplitude of a wave gets smaller and smaller as it passes through a material. acceleration – the rate at which velocity changes.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

acceleration due to gravity – the value of 9.8 m/s2, which is the acceleration in free fall at Earth’s surface, usually represented by the small letter g. accuracy – how close a measurement is to an accepted or true value. acid – a substance that produces hydronium ions when dissolved in water. Acids have pH less than 7. activation energy – energy needed to break chemical bonds in the reactants to start a reaction. air mass - a large body of air with consistent temperature and moisture content throughout. alkali metals – elements in the first group of the periodic table. alloy – a solution of two or more solids. amino acids - a group of smaller molecules that are the building blocks of proteins. amorphous – a random arrangement of atoms or molecules in a solid. ampere – the unit of electric current. amplitude – the amount that a cycle moves away from equilibrium. apparent density – the total mass divided by the total volume of an object that is made up of more than one material including air. aquifer - a underground area of sediment and rocks in which groundwater collects. Archimedes’ principle – states that the buoyant force is equal to the weight of the fluid displaced by an object. asteroid - an object that orbits the Sun but is too small to be considered a planet. asthenosphere - a zone in the mantle below the lithosphere where the combination of heat and pressure cause the mantle rock to be softest and weakest. astronomical unit - equal to 150 million km, or the average distance from Earth to the Sun.

atmospheric pressure - a measurement of the force of air molecules per unit of area in the atmosphere at a given altitude. atom - the smallest particle of an element that retains the chemical identity of the element.

Glossary

absolute zero - lowest possible temperature, at which thermal energy is as close to zero as it can be, approximately –273 degrees Celsius.

atmosphere – a layer of gases that surrounds a planet.

atomic mass – the average mass of all the known isotopes of an element, expressed in amu. atomic mass unit – a unit of mass equal to 1.66 × 10-24 grams. atomic number – the number of protons in the nucleus. The atomic number determines what element the atom represents. aurora - a phenomenon that occurs when the solar wind energizes the protective layers of the atmosphere. average speed – the total distance divided by the total time for a trip. axis – (1) one of two (or more) number lines that form a graph (2) the imaginary line that passes through the center of a planet from pole to pole.

B balanced forces – combined forces that result in a zero net force on an object. barometer – an instrument that measures atmospheric pressure. base – a substance that produces hydroxide ions when dissolved in water. Bases have a pH greater than 7. bathymetric map – a map that shows the depths of a body of water such as a lake or an ocean. battery – a device that transforms chemical energy to electrical energy, and provides electrical force in a circuit. beat - the oscillation between two sounds that are close in frequency. Bernoulli’s principle – a relationship that describes energy conservation in a fluid. Big Bang theory - states that the universe began as a huge explosion. binary compound - a chemical compound that consists of two elements. biomass – organic material from plants and animals. biomes – major climate regions with particular plant and animal communities. Earth has six important biomes. black hole - an object with such strong gravity that its escape velocity equals or exceeds the speed of light. body waves - seismic waves that travel through the interior of Earth.

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boiling point - the temperature at which a substance changes from liquid to gas (boiling) or from gas to liquid (condensation).

cinder cone - a volcano composed of a pile of solid lava pieces that form during a high-gas, low-lava eruption.

Boyle’s law – in a fixed quantity of a gas, the pressure and volume are inversely related if the mass and temperature are held constant.

cleavage plane – a surface along which a mineral cleanly splits.

brightness – measures the amount of light reaching Earth. brittleness – the tendency to crack or break; the opposite of elasticity. buoyancy – the measure of the upward force a fluid exerts on an object that is submerged.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

C carbohydrates - a group of energy-rich compounds that are made from carbon, hydrogen, and oxygen and that include sugars and starches. catalyst - a molecule added to a chemical reaction that increases the reaction rate without getting used up in the process. Celsius - a temperature scale in which water freezes at 0 degrees and boils at 100 degrees. cementation - the process by which sediment particles are “glued” together to make a sedimentary rock. channel - the path that a river or stream follows. charged - describes an object whose net charge is not zero. Charles’s law – at constant pressure and mass, the volume of a gas increases with increasing temperature and decreases with decreasing temperature. chemical bond - a bond that forms when atoms transfer or share electrons. chemical cycles - sets of processes that recycle elements on Earth. chemical energy - a form of potential energy that is stored in molecules. chemical equation - an expression of a chemical reaction using chemical formulas and symbols. chemical equilibrium - the state at which the rate of the forward reaction equals the rate of the reverse reaction for a chemical reaction. chemical formula - a representation of a compound that includes the symbols and ratios of atoms of each element in the compound. chemical properties – characteristics that can only be observed when one substance changes into a different substance. chemical reaction - the process of breaking chemical bonds in one or more substances and the reforming of the bonds to create new substances. chromosphere - the inner atmosphere of the Sun which consists of a very hot layer of plasma.

climate – the long-term record of temperature, precipitation, and wind for a region. closed circuit – a circuit with the switch in the on position, so there are no breaks and charge can flow. cloud – a group of water droplets or ice crystals that you can see in the atmosphere. CMYK – the subtractive color process using cyan, magenta, yellow, and black to create colors in reflected light. coefficient - a whole number placed in front of a chemical formula in a chemical equation. cold front – a front that occurs when a cold air mass moves in and replaces a warm air mass. colloid - a mixture that contains evenly distributed particles that are 1 to 1,000 nanometers in size. color – the sensation created by the different energies of light falling on your eye. combustion reaction - a chemical reaction which results in a large amount of energy being released when a carbon compound combines with oxygen. comet - an object in space made mostly of ice and dust. commutator – the device that switches the direction of electrical current in the electromagnet of an electric motor. compaction - the process by which sediment is pressed together as more and more layers, or beds, of sediment are deposited on top of one another. composite volcano - a tall, cone-shaped volcano formed by layers of lava and ash. compound - a substance that contains two or more different elements chemically joined and has the same composition throughout. compression –a squeeze or decrease in size. condensation - the process by which a substance in its gaseous phase loses energy and enters its liquid phase. conductor – a material with low electrical resistance, such as copper and aluminum. constant speed – speed that stays the same and does not change. constellation - a group of stars that, when seen from Earth, form a pattern. constructive interference – when waves add up to make a larger amplitude.

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continental drift - the idea that continents move around on Earth’s surface. continental margin - the region around continents that includes the continental shelf, continental slope, and continental rise.

deep-ocean trench - a valley in the ocean created when one tectonic plate subducts under another.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

control variable – a variable that is kept constant (the same) in an experiment.

density – the mass per unit volume of a given material. Units for density are often expressed as g/mL, g/cm3, or kg/m3.

convection – the transfer of heat by the motion of matter, such as by moving air or water.

dependent variable – the variable that you believe is influenced by the independent variable.

convection cells – large wind patterns in Earth’s atmosphere caused by convection.

deposition - the process of depositing sediment after it has been moved by water, wind, ice, or gravity.

convergent boundary - a tectonic plate boundary where two plates come together.

desert – a climate region that averages less than 35 centimeters of rainfall per year.

converging lens – a lens that bends exiting light rays toward the focal point.

destructive interference – when waves add up to make a smaller, or zero, amplitude.

conversion factor – a ratio that has a value of one, and is used when setting up a unit conversion problem. coordinates – values that give the position relative to an origin. core - the center of Earth, it is divided into the solid inner core and the liquid outer core. Coriolis effect – the bending of currents of air or water due to Earth’s rotation. corona - the outermost layer of the Sun’s atmosphere that extends millions of kilometers outward. coulomb – the unit for electric charge. covalent bond - a chemical bond formed by atoms that are sharing one or more electrons. cross bedding - a pattern of inclined beds of sediment that often form as dunes or ripples of sediment are moved by wind and water.

Glossary

contour lines – curved lines on a map that indicate all the points where the elevation or depth is the same.

deep ocean currents - density- and temperature-driven currents that move slowly within the oceans, also called thermohaline currents.

dew point – the temperature at which more water condenses than evaporates in an air mass at a constant atmospheric pressure. diffraction - the process of a wave bending around a corner or passing through an opening. diffuse reflection – “dull” surface reflection, where each incident ray produces many scattered rays. dimensional analysis – a method of using conversion factors and unit canceling to solve a unit conversion problem. direct relationship – a relationship in which one variable increases with an increase in another variable. direction of younging - the order in which sediment is deposited—from larger to finer particles.

crust - the outermost layer of Earth.

dissolution reaction - an endothermic reaction that occurs when an ionic compound dissolves in water to make an ionic solution.

crystalline – an orderly, repeating pattern arrangement of atoms or molecules in a solid.

dissolve – to separate and disperse a solid into individual molecules or ions in the presence of a solvent.

cycle – a unit of motion that repeats.

distance - the amount of space between two points.

cyclone – a low-pressure center surrounded by rotating winds.

divergent boundary - a tectonic plate boundary where two plates move apart.

D

diverging lens – a lens that bends exiting light rays outward, away from the focal point.

decibel - a unit of measure for the intensity or strength of a sound.

DNA - a type of nucleic acid that contains the genetic code for an organism.

decomposition reaction - a chemical reaction in which a compound is broken down into two or more smaller compounds.

Doppler effect – an increase or decrease in frequency caused by the motion of a source of sound.

deduce – to figure something out from known facts using logical thinking.

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Doppler shift - a change in the wavelength of a wave that occurs when an object is moving toward or away from an observer.

element - a pure substance that cannot be broken down into simpler substances by physical or chemical means.

double-displacement reaction - a chemical reaction in which ions from two compounds in solution exchange places to produce two new compounds.

elementary charge – the smallest unit of electric charge that is possible in ordinary matter; represented by the lowercase letter e.

ductility – the ability to bend without breaking.

elevation – the height of an object measured from a reference level.

E earthquake - the movement of Earth’s crust resulting from the release of builtup potential energy along a fault.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

ecosystem - a group of living things and their physical surroundings. efficiency – the ratio of output work divided by input work. Efficiency is often expressed as a percent with a perfect machine having 100 percent efficiency. elasticity – the ability to be stretched or compressed and then return to original size. electric charge – a fundamental property of matter that can be either positive or negative.

endothermic – a reaction that uses more energy than it releases. energy - a quantity that is related the ability of an object to change or cause changes. energy level – one of the discrete allowed energies for electrons in an atom. engineer – a professional who uses scientific knowledge to create or improve inventions that solve problems and meet needs. engineering cycle – a process used to build devices that solve technical problems. English System – measurement system used for everyday measurements in the United States. enzyme - a type of protein used to speed up chemical reactions in living things.

electric circuit – a complete path through which electric current can flow.

epicenter - a point on Earth’s surface right above the focus of an earthquake.

electric current – the flow of electric charge.

equator – an imaginary line around the middle of Earth between the north and south poles.

electric motor – a device that converts electrical energy into mechanical energy. electrical conductor – a material that allows electricity to flow through easily.

equilibrium – (1) the state in which the net force on an object is zero; (2) the state of a solution in which the dissolving rate equals the rate at which molecules come out of solution.

electrical power – the rate at which electrical energy is changed into other forms of energy.

erosion - the process of moving rock and sediment by wind, water, ice, and gravity.

electrically neutral – describes an object that has equal amounts of positive and negative charges.

evaporation - the process by which a substance in its liquid phase gains energy and enters its gaseous phase

electricity – the science of electric charge and current.

exosphere – the region of the atmosphere that begins at about 500 km above Earth and extends into space.

electromagnet – a magnet created by a wire carrying electric current. electromagnetic induction – the process of using a moving magnet to create a current or voltage. electromagnetic spectrum – the entire range of electromagnetic waves including all possible frequencies such as radio waves, microwaves, X-rays, and gamma rays. electromagnetic wave – a wave of electricity and magnetism that travels at the speed of light. Light is an electromagnetic wave.

exothermic – a reaction that releases more energy than it uses. experiment – a situation specifically set up to investigate relationships between variables. experimental technique – the exact procedure that is followed each time an experiment is repeated. experimental variable – the variable you change in an experiment. extension – a stretch or increase in size.

electron – a particle with an electrical charge (-e) found inside of atoms but outside the nucleus.

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F Fahrenheit - a temperature scale in which water freezes at 32 degrees and boils at 212 degrees.

floodplain - flat land alongside a river that tends to flood. A floodplain is usually located at a distance from the headwaters of the river. fluid – any matter that flows when force is applied; liquids and gases are fluids.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

fluorescence – a process that makes light directly from electricity. focus - the point below Earth’s surface where a rock breaks or slips and causes an earthquake. food chain - shows how each member of an ecosystem community gets its food. force - a push or a pull, or any action that involved the interaction of objects and has the ability to change motion. fossil – the remains or traces of a dead animal or plant that has been preserved for a long time. fossil fuels – substances found in Earth’s crust that were formed over millions of years from the remains of dead organisms. free fall – accelerated motion that happens when an object falls with only the force of gravity acting on it. free-body diagram – a diagram showing all the forces acting on an object. frequency – how often something repeats, expressed in hertz. friction – a force that resists motion. front – the border between two different air masses. frost wedging - mechanical weathering that results from freezing water. fundamental - the lowest natural frequency of an oscillator.

G galaxy - a group of stars, dust, gas, and other objects held together by gravitational forces. gas - a phase of matter that flows, does not hold its volume, and can expand or contract to fill a container. gas planets - Jupiter, Saturn, Uranus, and Neptune.

generator – a device that converts kinetic energy into electrical energy using the law of induction. geologic time scaler – a model of Earth’s history. geology – the study of the solid matter that constitutes Earth. geothermal – describes energy from Earth’s internal heat. giant impact theory - a scientific theory that explains how the Moon was formed. glacier - a huge mass of ice that forms on land when snow and ice accumulate faster than they melt.

Glossary

fault - a region on Earth’s surface that is broken and where movement takes place.

gear – a rotating wheel with teeth that transfers motion and forces to other gears or objects.

global climate change - any significant change in Earth’s climate for an extended time period that happens naturally or is human-caused. global warming - the increase of Earth’s average temperature due to increased concentrations of greenhouse gases in the atmosphere. globe – a map of Earth that models its shape, and the locations and relative sizes of oceans and continents. graded bedding - layers of sediment with the largest particles at the bottom and smallest particles on top. graph – a visual representation of data. grasslands – climate regions with too little rainfall to support a forest. gravitational force - the force of attraction between all objects. greenhouse effect - the warming of Earth that results when greenhouse gases trap heat reflecting from the planet’s surface. greenhouse gases - atmospheric gases that trap heat from the Sun so that Earth stays warm. groundwater - water that collects underground. group – a column of the periodic table. gyres - large rotating ocean current systems.

H half-life - a certain length of time after which half the amount of a radioactive element has undergone radioactive decay. halogens – elements in the group containing fluorine, chlorine, and bromine, among others. hardness – a measure of a solid’s resistance to scratching.

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FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

harmonic - one of many natural frequencies of an oscillator.

instantaneous speed – the actual speed of a moving object at any moment.

harmonic motion – motion that repeats in cycles. heat – thermal energy that is moving or is capable of moving.

insulator – a material that slows down or stops the flow of either heat or electricity.

heat conduction – the transfer of heat by the direct contact of particles of matter.

insulator (electrical) – a material with high electrical resistance, such as rubber and plastic.

heat pump system – takes advantage of Earth’s constant shallow ground temperature for seasonal heating and cooling of buildings and homes.

intermolecular forces - forces between atoms or molecules in a substance that determine the phase of matter.

heat transfer – the flow of thermal energy from higher temperature to lower temperature.

international dateline – an imaginary longitude line located 180 degrees from the prime meridian.

hertz – the unit of frequency. One hertz is one cycle per second.

inverse relationship – a relationship in which one variable decreases when another variable increases.

heterogeneous mixture - a mixture in which different samples are not necessarily made up of the same proportions of matter. high-pressure center – a high-pressure area created by sinking cold air. homogeneous mixture - a mixture that is the same throughout. All samples of a homogeneous mixture are the same. horsepower – a unit of power equal to 746 watts. hurricane – a tropical cyclone with wind speeds of at least119 kilometers per hour. hydroelectric – a type of power plant that generates electricity from the energy of falling water. hydrogen bond - an intermolecular force between the hydrogen on one molecule to another atom on another molecule. hypothesis – a possible explanation that can be tested by comparison with scientific evidence.

I incandescence – a process that makes light with heat. independent variable – a variable that you believe might influence another variable. index of refraction – a number that measures how much a material is able to bend light. inertia – the property of an object that resists changes in its motion. inhibitor - a molecule that slows down a chemical reaction. input – forces, energy, or power supplied to make a machine accomplish a task. inquiry – a process of learning that starts with questions and proceeds by seeking the answers to the questions. insoluble – when a solute is unable dissolve in a particular solvent.

inverse square law of light - relates the mathematical relationship between brightness, luminosity, and distance. ion – an atom (or group of atoms) that has an electric charge other than zero, created when an atom (or group of atoms) gains or loses electrons. ionic bond – a bond that transfers an electron from one atom to another resulting in attraction between oppositely charged ions. ionosphere – portions of the atmosphere in the region of the thermosphere where electricity can be transmitted. isobar – a line on a weather map that connects places that have the same atmospheric pressure. isotopes – atoms of the same element that have different numbers of neutrons in the nucleus.

J jet streams – high-altitude, fast-moving winds. joule – a unit of energy. One joule is enough energy to push with a force of 1 newton for a distance of 1 meter.

K Kelvin scale - a temperature scale that starts at absolute zero and has units the same as Celsius degrees. kilowatt-hours – a unit of energy equal to one kilowatt of power used for one hour, equals 3.6 million joules. kinetic energy - energy of motion. Kirchoff’s current law – states that all of the current entering a circuit branch must exit again.

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Kirchoff’s voltage law – the total of all voltage drops in a series circuit must equal the voltage supplied by the battery.

latitude – east-west lines that are north or south of the equator. lava - magma that has erupted onto Earth’s surface and cooled. law of conservation of energy – energy can never be created or destroyed, only transformed into another form. The total amount of energy in the universe is constant.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

law of conservation of mass - a principle that states that the total mass of the reactants equals the total mass of the products in a chemical reaction. law of conservation of momentum - states that as long as interacting objects are not influenced by outside forces, the total amount of momentum is constant. law of universal gravitation - states that the strength of the gravitational force depends on the mass of the objects and the distance between them. legend – a special area on a map that lists the symbols that are used. length – a measured distance. lens – an optical device for bending light rays. lever – a stiff structure that rotates around a fixed point called a fulcrum. Lewis dot diagram - a method for representing an atom’s valence electrons using dots around the element symbol.

luminosity – the total amount of light given off by a star. lunar cycle - the cycle of change in the appearance of the Moon due to the positions of Earth, the Moon, and the Sun. lunar eclipse - an event that occurs when the Moon passes through Earth’s shadow.

M machine – a device with moving parts that work together to accomplish a task. magma - underground melted rock. magma chamber - a location where magma collects inside Earth. magnetic – describes a material that can respond to forces from magnets. magnetic declination – the difference between true north and the direction a compass points. magnetic field – the influence created by a magnet that exerts forces on other magnets and magnetic materials. main sequence star - a stable star in the main sequence category in the H-R diagram. malleability - the ability of a solid to be pounded into thin sheets. mantle - the hot, slow-flowing, solid layer of Earth between the crust and the core.

light - a form of electromagnetic energy that makes things visible.

mantle plume - heated lower mantle rock that rises toward the lithosphere and forms a hot spot on the overlying tectonic plate.

light ray – an imaginary line that represents a beam of light.

map – a representational drawing of a location.

light year - the distance that light travels through space in one year.

mass number – the number of protons plus the number of neutrons in the nucleus.

lightning – a bright spark of light that occurs inside a storm cloud, between a cloud and Earth’s surface, or between two clouds. linear motion – motion that goes from one place to another without repeating. lipids - a group of energy-rich compounds that are made of carbon, hydrogen, and oxygen, and they include fats, waxes, and oils. liquid - a phase of matter that holds its volume, does not hold its shape, and flows. lithosphere - a layer of Earth that includes the crust and the upper mantle, above the asthenosphere.

Glossary

L

low-pressure center – a low-pressure area created by rising warm air.

mass wasting - the downhill movement of large amounts of rock and sediment due to the force of gravity. meanders - S-shaped curves in a river. measurement – a determination of something that typically has a number value and a unit that tells you what the number value means. mechanical advantage – the ratio of output force to input force for a simple machine. mechanical energy - a form of energy that is related to motion or position.

longitude – north-south lines that are east or west of the prime meridian. longitudinal – a wave is longitudinal if its oscillations are in the direction it moves.

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melting point - the temperature at which a substance changes from solid to liquid (melting) or liquid to solid (freezing).

net force – the sum of all forces acting on an object.

mesosphere – a layer of atmosphere that occurs from about 50 km to 80 km above Earth’s surface.

neutron – a particle found in the nucleus with mass similar to the proton but with zero electric charge.

metal – elements that are typically shiny and good conductors of heat and electricity.

newton – the metric unit of force, equal to the force needed to make a 1 kg object accelerate at 1 m/s2.

metamorphic rock - a rock formed when another rock is changed by heat and pressure.

Newton’s first law – a law of motion that states that an object at rest will stay at rest and an object in motion will stay in motion with the same velocity unless acted on by an unbalanced force.

meteor - a chunk of burning rock traveling through Earth’s atmosphere.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

meteorite – a meteor that passes through Earth’s atmosphere and strikes the ground. meter – a basic SI unit of length. mid-ocean ridge - a long chain of undersea mountains. Milky Way galaxy - the galaxy to which our solar system belongs.

neutralization - the reaction of an acid and a base to produce a salt and water.

Newton’s second law – acceleration is force divided by mass. Newton’s third law – for every action force, there is a reaction force equal in strength and opposite in direction. noble gases – elements in the group containing helium, neon, and argon, among others.

mineral – a solid, naturally occurring, crystalline object with a defined chemical composition.

nonmetal – elements that are poor conductors of heat and electricity.

mirror – a surface that reflects light rays.

nonrenewable resource – a natural resource that is not replaced as it is used.

mixture - matter that contains a combination of different elements and/or compounds and can be separated by physical means.

normal force – the perpendicular force that a surface exerts on an object that is pressing on it.

Modified Mercalli scale - a scale that rates how an earthquake is experienced by people and the damage caused to buildings.

nuclear energy - a form of energy that is stored in the nuclei of atoms.

Mohs hardness scale – a scale used to identify minerals based on their hardness or resistance to being scratched.

nonpolar molecule - a molecule that does not have distinctly charged poles.

nuclear fission - a nuclear reaction in which the nuclei of heavier atoms are split to make lighter atoms.

molecule - a group of two or more atoms joined together by chemical bonds.

nuclear fusion - a nuclear reaction in which the nuclei of lighter atoms are combined to make a heavier atoms.

Moment Magnitude scale - a scale that rates the total energy released by earthquakes.

nuclear reaction - a reaction in which the number of protons and/or neutrons is altered in one or more atoms.

momentum – the mass of an object times its velocity.

nucleic acids - compounds made of long, repeating chains of smaller molecules called nucleotides.

moon - a natural satellite orbiting a planet or other body, such as a dwarf planet. multimeter – a measuring instrument for current, voltage, and resistance.

N natural frequency – the frequency at which a system oscillates when disturbed. natural law – a theory that has been tested many times without any contradictions. nebula – a huge cloud of dust and gas from which stars form. negative, positive - the two kinds of electric charge.

nucleus – the tiny core at the center of an atom containing most of the atom’s mass and all of its positive charge.

O objective – describes evidence that documents only what actually happened as exactly as possible. ohm – the unit of measurement for resistance. Ohm’s law – states that the current is directly related to the voltage and inversely related to the resistance.

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open circuit – a circuit with the switch in the off position, so there is a break and charge cannot flow.

origin – the place where the position has a value of zero. oscillator - a physical system that has repeating cycles. output – the forces, energy, or power provided by the machine. oxidation number - a quantity that indicates the charge on an atom when it gains, loses, or shares electrons during bond formation.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

P paleontologist – a scientist who studies and identifies fossils. Pangaea - an ancient, huge landmass composed of earlier forms of today’s continents

pitch - the perception of high or low that you hear at different frequencies of sound. pixel – a single dot that forms part of an image of many dots. planet - a celestial body that (1) is in orbit around the Sun, (2) is nearly round in shape, and (3) has cleared the orbit of other objects. planetary nebula – the expanding outer shell of a sunlike star. This matter is blown away as the core shrinks to become a white dwarf. planetary system - a star with orbiting planets. plasma - a phase of matter in which the matter is heated to such a high temperature that some of the atoms begin to break apart. plate tectonics - a theory explaining how tectonic plates move on Earth’s surface. polar molecule - a molecule that has a negative and a positive end or pole.

parallel circuit – an electric circuit with more than one path or branch.

polyatomic ion - an ion that contains more than one atom.

parsec - An astronomical distance equal to about 3.26 light years.

polymer - a compound that is composed of long chains of smaller molecules.

pascal – the SI unit of pressure equal to one newton of force per square meter of area.

polymerization - the formation of polymers by a series of addition reactions. position – a variable that gives your location relative to an origin.

pendulum – a device that swings back and forth due to the force of gravity.

positive, negative – the two kinds of electric charge.

percolation - the process of water seeping into the ground through soil and rock.

potential energy – stored energy that comes from position.

period – (1) a row of the periodic table; (2) the time it takes for each complete cycle. periodic force – a repetitive force. periodic table – a chart that organizes the elements by their chemical properties and increasing atomic number. periodicity – the repeating pattern of chemical and physical properties of the elements. permanent magnet – a material that retains its magnetic properties, can attract or repel other magnets, and can attract magnetic materials. pH – a measure of the concentration of hydronium ions in a solution. pH scale – the pH scale goes from 1 to 14 with 1 being very acidic and 14 being very basic. Pure water is neutral with a pH of 7. photon – the smallest possible amount of light, like a wave-bundle. photoreceptors - light-sensitive cells on the surface of the retina. photosynthesis - the process that plants use to convert sunlight energy into chemical energy.

Glossary

organic chemistry - a branch of chemistry that specializes in the study of carbon compounds, also known as organic molecules.

physical properties – characteristics that you can observe directly.

potentiometer – a type of variable resistor that can be adjusted to give resistance within a certain range. pound – the English unit of force equal to 4.448 newtons. power – the rate of doing work or moving energy. Power is equal to energy (or work) divided by time. precipitate - a solid that forms and does not dissolve in a reaction mixture. precipitation - condensed water vapor in the atmosphere that falls back to Earth in the form of rain, snow, sleet, or hail. precision – describes how close together or reproducible repeated measurement are. pressure – the amount of force exerted per unit of area. prime meridian – an imaginary line through Greenwich, England that is perpendicular to the equator. prism – a glass shape with flat, polished surfaces that can both bend and reflect light. procedure – a collection of all the techniques you use to do an experiment. product - a new substance formed in a chemical reaction.

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proteins - a group of very large molecules made of carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur. proton – a particle found in the nucleus with a positive charge exactly equal and opposite to the electron. protostar – the first stage in the life cycle of a star. prototype – a working model of a design that can be tested to see if it works.

renewable resource – a natural resource that can be replaced. repeatable – describes evidence that can be seen independently by others if they repeat the same experiment or observation in the same way. reservoir - a protected artificial or natural lake that is used to store water. resistance – determines how much current flows for a given voltage. Higher resistance means less current.

FOR SAMPLE ONLY - NOT FOR CLASSROOM USE

pure substance - matter that cannot be separated into other types of matter by physical means. Includes all elements and compounds.

resistor – a component that uses energy carried by electric current

P-waves - seismic waves that move with a forward-and-backward motion. They are faster than S-waves and can travel through both solids and liquids.

resolution – refers to the smallest interval that can be measured.

Q quantum theory – the theory that describes matter and energy at very small (atomic) sizes.

R radiant energy - a form of energy that is represented by the electromagnetic spectrum.

resistors are often used to control current in a circuit. resonance – an exceptionally large amplitude that develops when a periodic force is applied at the natural frequency. respiration - the process by which living organisms use oxygen to obtain energy from food. RGB color model – a model for tricking the eye into seeing almost any color by mixing proportions of red, green, and blue light. Richter scale - a scale that ranks earthquakes according to the magnitude of the seismic waves. river - a large body of water that flows into an ocean, lake, or another river.

radioactive – a nucleus is radioactive if it spontaneously breaks up, emitting particles or energy in the process.

rock – a naturally formed solid made of one or more minerals.

radioactive isotope – an unstable isotope that loses energy and matter over time.

rotation - the spinning of a planet on its axis.

reactant - a starting ingredient in a chemical reaction. reaction rate - the change in concentration of reactants or products in a chemical reaction over time. red giant – a large star with low temperature and high brightness. reflecting telescope - a telescope that uses mirrors to gather light and a lens to magnify the object. reflection – the process of a wave bouncing off a surface; the reflection of light waves causes an image in a mirror. refracting telescope - a telescope that uses lenses to gather light and magnify objects. refraction – the process of a wave bending as it crosses a boundary between two materials; light refracts passing from air into water or back. relative dating – the process of putting events in the order in which the happened.

rock cycle – the formation and recycling of rocks by geologic processes. rotor – the rotating disk of an electric motor or generator.

S salinity - a term that describes the amount of dissolved salts in water. saturated – describes a solution that has as much solute as the solvent can dissolve under the conditions. saturated fat - a fat in which the carbon atoms are surrounded by as many hydrogen atoms possible. scatterplot – a graph of two variables thought to be related. scientific method – a process of learning that begins with a hypothesis and proceeds to prove or change the hypothesis by comparing it with scientific evidence. scientific notation - an abbreviation in which a number is expressed as a number between 1 and 10 multiplied by a power of ten.

relief – the distance between a high and low place on a map.

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sea-floor spreading - a hypothesis that new sea floor is created at mid-ocean ridges and that, in the process, the continents are pushed apart from each other.

seismograph - an instrument that records seismic waves. seismologist - a scientist who studies earthquakes. semiconductor – a material between conductor and insulator in its ability to carry current.

spectral line – a bright, colored line in a spectroscope. spectrometer – an instrument that separates light into a spectrum. spectroscopy – a method of studying an object by examining the visible light and other electromagnetic waves it creates. spectrum – the characteristic colors of light given off or absorbed by an element.

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series circuit – an electric circuit that has only one path for current.

specular reflection – “shiny” surface reflection, where each incident ray produces only one reflected ray.

shield volcano - a flat and wide volcano that has low-silica magma and lava with low or high levels of dissolved gas.

speed – describes how quickly an object moves, calculated by dividing the distance traveled by the time it takes.

short circuit – a branch in a circuit with zero or very low resistance.

stable – a term that describes an atomic nucleus that stays together.

SI – International System of Units used by most countries for everyday measurement and used by the scientific community worldwide.

standard candle - an object, such as a star, whose luminosity is known. standing wave - a wave that is confined in a space.

significant digits – meaningful digits in a measured quantity.

star – a giant, hot ball of gas held together by gravity.

simple machine – an unpowered mechanical device that accomplishes a task with only one movement.

static electricity – a tiny imbalance between positive and negative charge on an object.

single-displacement reaction - a chemical reaction in which one element replaces a similar element in a compound.

static friction – the friction force that resists the motion between two surfaces that are not moving.

sliding friction – the friction force that resists the motion of an object moving across a surface.

steel – an alloy of iron and carbon.

slope –(1) the ratio of the rise (vertical change) to the run (horizontal change) of a line on a graph, (2) a measure of how steep land is. solar constant - the amount of energy from the Sun that actually reaches the edge of Earth’s atmosphere. solar eclipse - an event that occurs when the Moon’s shadow falls on Earth. solar energy – energy from the Sun. solid - a phase of matter that holds its shape and does not flow. solubility – the amount of solute that can be dissolved under certain conditions. solubility rules - a set of rules used to predict whether an ionic compound will be soluble or insoluble in water. solute – any component of a solution other than the solvent. solution – a mixture of two or more substances that is homogeneous at the molecular level.

Glossary

seismic waves - vibrations that travel through Earth and are caused by events like earthquakes or human-made blasts.

specific heat – the amount of heat needed to raise the temperature of one kilogram of a material by one degree Celsius.

storm cell – a convection cell within a cloud that is associated with a storm. stratosphere – a layer of atmosphere that occurs from about 11 to 50 kilometers above Earth’s surface. stream - a small river. strength – the ability to maintain shape under the application of forces. subduction - a process that involves a tectonic plate sinking into the mantle. sunspot – an area of gas on the Sun that is cooler than the gases around it. Sunspots appear as dark spots on the Sun’s photosphere. supergiant – very large, bright star that may be blue or red, depending on its temperature. supernova – the explosion of a very large star. supersaturated – a concentration greater than the maximum solubility. supersonic – faster than the speed of sound.

solvent – the component of a solution that is present in the greatest amount.

surface ocean currents - wind-driven currents that move at the ocean

sound - a traveling oscillation of atoms or pressure.

surface, often for long distances.

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surface runoff - water that flows over land until it reaches lakes, rivers, and oceans.

thermal conductor – a material that allows heat to flow easily.

surface water - the water found on Earth’s surface in places like oceans, lakes, rivers, and reservoirs.

thermal equilibrium – when two objects are at the same temperature and no heat flows.

surface waves - seismic waves that can travel only along Earth’s surface.

thermal expansion – the tendency of the atoms or molecules in a substance (solid, liquid, or gas) to take up more space as the temperature increases.

suspension - a mixture that contains particles that are greater than 1,000 nanometers. S-waves - seismic waves that move with a side-to-side motion, are slower than P-waves, and can only travel through solids.

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switch – a device for alternately allowing and not allowing charge to flow in a circuit. synthesis reaction - a chemical reaction in which two or more substances combine to form a new compound. system – a group of variables that are related in some way.

T

thermal energy - energy due to temperature.

thermal radiation – electromagnetic waves produced by objects because of their temperature. thermometer - an instrument that measures temperature. thermosphere – a layer of atmosphere that occurs from about 80 km to about 500 km. This layer has a low density of air molecules and a very high temperature. thunder – a sound that occurs when a lightning spark heats air and the air expands. tide - a cycle of rising and falling ocean levels. topographic map – maps that use contour lines to show elevation.

taiga – the largest climate region, found in the higher latitudes; also known as a boreal or coniferous forest.

tornado – a system of rotating winds around a low-pressure center. A tornado is smaller than a hurricane, but has faster winds.

technology – the application of science to meet human needs and solve problems.

transform fault boundary - a tectonic plate boundary where two plates slide by each other.

tectonic plates - large pieces of Earth’s lithosphere that move over the asthenosphere.

translucent – allows light rays through but scatters them in all directions.

telescope - a device that makes objects that are far away appear closer. temperate deciduous forests

transpiration - the process by which plants lose water through tiny pores in their leaves.

temperate deciduous forests – climate regions in the mid-latitudes that have seasons.

transverse – a wave is transverse if its oscillations are not in the direction it moves.

temperate grassland

trial – each time an experiment is tried.

temperature - a quantity that measures the kinetic energy per molecule due to random motion.

tropical rainforests – climate regions found near the equator that have a lot of rainfall and high biodiversity.

tensile strength – a measure of how much pulling, or tension, a material can withstand before breaking.

troposphere – a layer of atmosphere that occurs from 0 to about 11 kilometers above Earth’s surface and where all weather occurs.

tension – a pulling force that acts in a rope, string, or other object. terrestrial planets - Mercury, Venus, Earth, and Mars.

tundra – a climate region located in high latitudes; known as the coldest land biome.

the particles are deposited as flowing water slows down.

Tyndall effect - the scattering of light by the particles in a colloid.

transparent – allows light rays to pass through without scattering.

theory – a scientific explanation supported by much evidence collected over a long period of time. thermal - a small, upward flow of warm air caused by convection.

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U unbalanced forces – forces that result in a net force on an object and can cause changes in motion. universe - everything that exists including all matter and energy. unsaturated- describes a solution with a concentration less than the maximum solubility.

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unsaturated fat - a fat that has fewer hydrogen atoms because double bonds exist among some of the carbon atoms.

V valence electrons - the electrons in the highest, unfilled energy level of an atom. variable – a factor that affects how an experiment. vector – a variable that gives direction information included in its value. velocity – a variable that tells you both speed and direction. viscosity – a measure of a fluid’s resistance to flow. volcano - an erupting vent through which molten rock and other materials reach Earth’s surface, or a mountain built from the products of an eruption.

weather - a term that describes the condition of the atmosphere in terms of temperature, atmospheric pressure, wind, and precipitation. weathering - the process of breaking down rocks and minerals. white dwarf – a small star with a high temperature and low brightness. white light - visible light containing an equal mix of all colors. wind - the horizontal movement of air that occurs as a result of pressure difference between two air masses. wind farm – a collection of wind turbines.

Glossary

unit – a fixed amount of something, like a centimeter (cm) of distance.

wavelength – the distance from any point on a wave to the same point on the next cycle of the wave.

work – a form of energy that comes from force applied over distance. A force of 1 newton does 1 joule of work when the force causes 1 meter of motion in the direction of the force. work input – the work that is done on an object. work output – the work that an object does as a result of work input.

Y year - the amount of time it takes for a planet to complete one revolution around the Sun.

volt – the measurement unit for voltage. voltage – a measure of electric potential energy. voltage drop – the reduction of electrical potential across an electrical device that has current flowing through it.

W warm front – a front that occurs when a warm air mass moves in and replaces a cold air mass. water cycle - a set of processes energized by the Sun that keeps water moving from place to place on Earth, also called the hydrologic cycle. water table - the upper level of water underground water vapor - water in gaseous form. watershed - an area of land that catches precipitation and surface runoff and collects it in a body of water such as a river. watt – a unit of power equal to one joule per second. wave – a traveling oscillation that has properties of frequency, wavelength, and amplitude.

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A

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absolute dating . . . . . . . . . . . . . . . . . 453, 454 absolute humidity . . . . . . . . . . . . . . . . . . . 256 absolute zero . . . . . . . . . . . . . . . . . . . . . . 188 absorption . . . . . . . . . . . . . . . . . . . . 616, 646 abyssal plain . . . . . . . . . . . . . . . . . . . . . . 576 AC motor . . . . . . . . . . . . . . . . . . . . . . . . 432 acceleration and direction . . . . . . . . . . . . . . . . . . . . 91 and force . . . . . . . . . . . . . . . . . . . . . . 131 and mass . . . . . . . . . . . . . . . . . . . . . . 132 calculating . . . . . . . . . . . . . . . . . . . . . . 87 constant . . . . . . . . . . . . . . . . . . . . . . . 90 due to gravity . . . . . . . . . . . . . . . . . . . 90 from position vs. time graph . . . . . . . . . 89 from speed vs. time graph . . . . . . . . 86, 89 Newton’s second law . . . . . . . . . . . . . 130 unbalanced forces . . . . . . . . . . . . . . . 115 accuracy . . . . . . . . . . . . . . . . . . . . . . . . . . 10 acid . . . . . . . . . . . . . . . . . . . . . . . . . 546–552 acid rain . . . . . . . . . . . . . . . . . . . . . . . . . 586 acoustics . . . . . . . . . . . . . . . . . . . . . . . . . 622 action-reaction pair . . . . . . . . . . . . . . . . . . 137 action-reaction pairs . . . . . . . . . . . . . . . . . 138 activation energy . . . . . . . . . . . . . . . . . . . 349 adaptation . . . . . . . . . . . . . . . . . . . . . . . . 260 additive color process . . . . . . . . . . . . . . . . 639 additive primary colors . . . . . . . . . . . . . . . 639 air mass . . . . . . . . . . . . . . . . . . . . . . . . . . 253 air pressure . . . . . . . . . . . . . . . . . . . . . . . 248 airfoil . . . . . . . . . . . . . . . . . . . . . . . . . . . 229 Aldrin, Buzz . . . . . . . . . . . . . . . . . . . . . . 711 alkali metals . . . . . . . . . . . . . . . . . . . . . . 294 alloy . . . . . . . . . . . . . . . . . . . . . . . . 300, 536 alpha decay . . . . . . . . . . . . . . . . . . . . . . . 355 alternating current (AC) . . . . . . . . . . . . . . 434 altocumulus cloud . . . . . . . . . . . . . . . . . . 266 altostratus cloud . . . . . . . . . . . . . . . . . . . . 267 Alvin . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237 amino acid . . . . . . . . . . . . . . . . . . . . . . . . 327 amorphous . . . . . . . . . . . . . . . . . . . . . . . . 223 ampere (A) . . . . . . . . . . . . . . . . . . . . . . . 389 Ampere, Andre-Marie . . . . . . . . . . . . . . . . 389

amplitude . . . . . . . . . . . . . . . . . . . . 609, 613 aneroid barometer . . . . . . . . . . . . . . . . . . 249 angle of incidence . . . . . . . . . . . . . . . . . . 648 angle of reflection . . . . . . . . . . . . . . . . . . 648 antinode . . . . . . . . . . . . . . . . . . . . . . . . . 624 apparent density . . . . . . . . . . . . . . . . . . . 238 aquifer . . . . . . . . . . . . . . . . . . . . . . . . . . 566 Archean . . . . . . . . . . . . . . . . . . . . . . . . . 450 Archimedes . . . . . . . . . . . . . . . . . . 235, 241 Archimedes’ principle . . . . . . . . . . . . . . . 235 Armstrong, Neil . . . . . . . . . . . . . . . . . . . .711 Arrhenius, Svante . . . . . . . . . . . . . . 376, 553 asteroid . . . . . . . . . . . . . . . . . . . . . . . . . 681 asteroid belt . . . . . . . . . . . . . . . . . . . . . . 681 asthenosphere . . . . . . . . . . . . . . . . . . . . . 474 astronomical unit (AU) . . . . . . . . . . . . . . 664 at-a-distance force . . . . . . . . . . . . . . . . . . 101 atmosphere . . . . . . . . . . . . . . . . . . . . . . . 302 balance of gases . . . . . . . . . . . . . . . . 375 composition of . . . . . . . . . . . . . . . . . 246 Earth, Venus, Mars . . . . . . . . . . . . . . 247 greenhouse gases . . . . . . . . . . . . . . . 374 layers of . . . . . . . . . . . . . . . . . 250–251 production of oxygen . . . . . . . . . . . . 571 water in . . . . . . . . . . . . . . . . . . . . . . 558 atmospheric pressure . . . . . . . . . . . . . . . . 248 atom and light . . . . . . . . . . . . . . . . . . . . . 633 arrangement in solids . . . . . . . . . . . . 223 definition of . . . . . . . . . . . . . . . . . . . 179 evidence for . . . . . . . . . . . . . . . . . . . 178 magnetism . . . . . . . . . . . . . . . . . . . . 428 models of . . . . . . . . . . . . . . . . . . . . . 279 oscillation . . . . . . . . . . . . . . . . . . . . 620 structure of . . . . . . . . . . . . . . . 278–283 atomic mass . . . . . . . . . . . . . . . . . . . . . . 293 atomic mass unit (amu) . . . . . . . . . . . . . . 293 atomic number . . . . . . . . . . . . . . . . . . . . 282 attract . . . . . . . . . . . . . . . . . . . . . . 278, 419 aurora . . . . . . . . . . . . . . . . . . . . . . . . . . 690 average speed . . . . . . . . . . . . . . . . . . . . . . 76 axial tilt . . . . . . . . . . . . . . . . . . . . . . . . . 671 axis . . . . . . . . . . . . . . . . . . . . . . . . . 54, 666

B balanced forces . . . . . . . . . . . . . . . . . . . . 114 ball bearing . . . . . . . . . . . . . . . . . . . . . . . 110 bar graph . . . . . . . . . . . . . . . . . . . . . . . . . 24 bar scale . . . . . . . . . . . . . . . . . . . . . . . . . . 59 barometer . . . . . . . . . . . . . . . . . . . . . . . . 249 barred spiral galaxy . . . . . . . . . . . . . . . . . 719 base . . . . . . . . . . . . . . . . . . . . . . . . 546–552 bathymetric map . . . . . . . . . . . . . . . . . 66–69 battery . . . . . . . . . . . . . . . . . . 387, 389, 390 beat . . . . . . . . . . . . . . . . . . . . . . . . . . . . 626 Benedictus, Edouard . . . . . . . . . . . . . . . . 183 Bernoulli’s principle . . . . . . . . . . . . . . . . 229 beta decay . . . . . . . . . . . . . . . . . . . . . . . . 355 Big Bang theory . . . . . . . . . . . . . . . 725–728 binary compound . . . . . . . . . . . . . . . . . . . 319 binary star . . . . . . . . . . . . . . . . . . . . . . . . 730 biological compass . . . . . . . . . . . . . . . . . 421 biological weathering . . . . . . . . . . . . 585–587 biomass . . . . . . . . . . . . . . . . . . . . . 364, 440 biome . . . . . . . . . . . . . . . . . . . . . . . 258–261 black hole . . . . . . . . . . . . . . . . . . . . . . . . 720 blueshift . . . . . . . . . . . . . . . . . . . . . . . . . 726 body wave . . . . . . . . . . . . . . . . . . . . . . . 503 Bohr model . . . . . . . . . . . . . . . . . . . . . . . 286 Bohr, Neils . . . . . . . . . . . . . . . . . . . . . . . 286 boiling point . . . . . . . . . . . . . . 192, 298, 533 bonding pair . . . . . . . . . . . . . . . . . . . . . . 530 boreal . . . . . . . . . . . . . . . . . . . . . . . . . . . 259 Boyle’s law . . . . . . . . . . . . . . . . . . . . . . . 230 branch . . . . . . . . . . . . . . . . . . . . . . . . . . 407 brightness . . . . . . . . . . . . . . . . . . . . . . . . 696 British thermal unit (btu) . . . . . . . . . . . . . 201 brittleness . . . . . . . . . . . . . . . . . . . . . . . . 224 Brown, Robert . . . . . . . . . . . . . . . . . . . . . 178 Brownian motion . . . . . . . . . . . . . . . . . . . 178 buoyancy . . . . . . . . . . . . . . . . . . . . 234–237 byte . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

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conservation of momentum . . . . . . . . . . . . 140 constant acceleration . . . . . . . . . . . . . . . . . . 90 constant speed . . . . . . . . . . . . . . . . . . .81, 84 constellation . . . . . . . . . . . . . . . . . . . . . . 658 constructive interference . . . . . . . . . . 618, 626 consumer . . . . . . . . . . . . . . . . . . . . . . . . . 366 contact forces . . . . . . . . . . . . . . . . . . . . . . 101 contact metamorphism . . . . . . . . . . . . . . . 492 continental crust . . . . . . . . . . . . . . . . 474, 475 continental drift . . . . . . . . . . . . . . . . 478, 479 continental margin . . . . . . . . . . . . . . . . . . 575 continental rise . . . . . . . . . . . . . . . . . . . . . 575 continental shelf . . . . . . . . . . . . . . . . . . . . 575 continental slope . . . . . . . . . . . . . . . . . . . 575 contour line . . . . . . . . . . . . . . . . . . . . . 61–63 control variable . . . . . . . . . . . . . . . . . . . . . 40 convection . . . . . . . . . . . . . . . . . . . . 208, 253 convection cell . . . . . . . . . . . . . . . . . 254, 475 convection current . . . . . . . . . . . . . . . . . . 210 convergent boundaries . . . . . . .485, 487, 488 convergent plate boundaries . . . . . . . . . . . 508 converging lens . . . . . . . . . . . . . . . . 645, 650 conversion factor . . . . . . . . . . . . . . . . . . . . 19 converting between temperature scales 184, 188 converting units . . . . . . . . . . . . . . . . . . 17–20 coordinates . . . . . . . . . . . . . . . . . . . . . . . . 54 Copernicus, Nicolas . . . . . . . . . . . . . . . . . 660 core . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 474 Coriolis effect . . . . .254, 255, 265, 269, 573 corona . . . . . . . . . . . . . . . . . . . . . . . . . . . 689 cosmic background radiation . . . . . . . . . . . 728 coulomb . . . . . . . . . . . . . . . . . . . . . . . . . 384 Coulomb, Charles Augustin de . . . . . . . . . 384 covalent bond . . . . . . . . . . . . . . . . . . 308, 317 cross bedding . . . . . . . . . . . . . . . . . . . . . . 600 crust . . . . . . . . . . . . . . . . . . . . . . . . . . . . 474 crystalline . . . . . . . . . . . . . . . . . . . . . . . . 223 crystallization . . . . . . . . . . . . . . . . . . . . . . 520 cumuliform cloud . . . . . . . . . . . . . . . . . . . 266 cumulonimbus cloud . . . . . . . . . . . . . . . . . 266 cumulus cloud . . . . . . . . . . . . . . . . . . . . . 266 curved motion . . . . . . . . . . . . . . . . . . . . . . 92 cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . 606 cyclone . . . . . . . . . . . . . . . . . . . . . . . . . . 269

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calendar . . . . . . . . . . . . . . . . . . . . . . . . . 667 calorie . . . . . . . . . . . . . . . . . . . . . . . . . . 201 carbohydrate . . . . . . . . . . . . . . . . . . . . . . 325 carbon . . . . . . . . . . . . . . . . . . . . . . . . . . 324 carbon cycle . . . . . . . . . . . . . . . . . . . . . . 369 carbon dating . . . . . . . . . . . . . . . . . . . . . 357 carnivore . . . . . . . . . . . . . . . . . . . . . . . . 366 Carver, George Washington . . . . . . . . . . . 347 catalyst . . . . . . . . . . . . . . . . . . . . . . . . . . 351 Celsius scale . . . . . . . . . . . . . . . . . . . . . . 184 cementation . . . . . . . . . . . . . . . . . . . . . . 598 Cenozoic Era . . . . . . . . . . . . . . . . . . . . . 452 center of mass . . . . . . . . . . . . . . . . . . . . . 672 Cepheid star . . . . . . . . . . . . . . . . . . . . . . 723 channel . . . . . . . . . . . . . . . . . . . . . . . . . 593 charged . . . . . . . . . . . . . . . . . . . . . . . . . 384 Charles, Jacques . . . . . . . . . . . . . . . . . . . 239 Charles’s law . . . . . . . . . . . . . . . . . . . . . 239 chemical bond . . . . . . . . . . . . 308, 310, 312 chemical change . . . . . . . . . . . . . . . 222, 334 chemical cycle . . . . . . . . . . . . . . . . . . . . 364 chemical energy . . . . . . . . . . . . . . . . . . . 156 chemical equation . . . . . . . . . . 338, 379, 564 chemical equilibrium . . . . . . . . . . . . . . . . 352 chemical formula . . . . . . . . . . 308, 315–321 chemical properties . . . . . . . . . . . . . . . . . 222 chemical reaction combustion . . . . . . . . . . . . . . . . . . . 346 compared to nuclear reaction . . . . . . . 358 decomposition reaction . . . . . . . . . . . 344 definition of . . . . . . . . . . . . . . . . . . . 335 double replacement . . . . . . . . . . . . . . 345 endothermic . . . . . . . . . . . . . . . 348, 364 exothermic . . . . . . . . . . . . 348, 349, 364 polymerization . . . . . . . . . . . . . . . . . 343 reactants and products . . . . . . . . . . . . 336 single-displacement . . . . . . . . . . . . . 345 synthesis reaction . . . . . . . . . . . . . . . 343 writing . . . . . . . . . . . . . . . . . . . . . . . 338 chemical reactivity . . . . . . . . . . . . . . . . . 310 chemical weathering . . . . . . . . . . . . 583, 586 chlorofluorocarbons (CFCs) . . . . . . . . . . . 379

chlorophyll . . . . . . . . . . . . . . . . . . . . . . . 643 chromosphere . . . . . . . . . . . . . . . . . . . . . 689 cinder cone . . . . . . . . . . . . . . . . . . . . . . . 516 circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . 385 circuit breaker . . . . . . . . . . . . . . . . . 391, 409 circuit diagram . . . . . . . . . . . . . . . . . . . . 386 circular motion . . . . . . . . . . . . . . . . . . . . . 92 circulated solar heating . . . . . . . . . . . . . . . 691 cirrocumulus cloud . . . . . . . . . . . . . . . . . 266 cirrostratus cloud . . . . . . . . . . . . . . . . . . . 267 cirrus cloud . . . . . . . . . . . . . . . . . . . . . . . 267 Clarke Belt . . . . . . . . . . . . . . . . . . . . . . . 251 cleavage plane . . . . . . . . . . . . . . . . . . . . . 463 climate . . . . . . . . . . . . . . . . . . 258, 572, 587 clock . . . . . . . . . . . . . . . . . . . . . . . . . . . 667 closed circuit . . . . . . . . . . . . . . . . . . . . . . 387 cloud . . . . . . . . . . . . . . . . . . . . . . . 266–267 CMYK . . . . . . . . . . . . . . . . . . . . . . . . . . 642 cochlea . . . . . . . . . . . . . . . . . . . . . . . . . . 625 coefficient . . . . . . . . . . . . . . . . . . . . . . . . 339 cold front . . . . . . . . . . . . . . . . . . . . . . . . 263 collision . . . . . . . . . . . . . . . . . . . . . . . . . 140 colloid . . . . . . . . . . . . . . . . . . . . . . . . . . 537 color . . . . . . . . . . . . . . . . . . . . . . . . 634–643 coma . . . . . . . . . . . . . . . . . . . . . . . . . . . 681 combustion . . . . . . . . . . . . . . . . . . . . . . . 375 combustion reaction . . . . . . . . . . . . . . . . . 346 comet . . . . . . . . . . . . . . . . . . . . . . . . . . . 681 commutator . . . . . . . . . . . . . . . . . . . . . . . 431 compact fluorescent lamp (CFL) . . . . . . . . 633 compact fluorescent light (CFL) . . . . . . . . 387 compaction . . . . . . . . . . . . . . . . . . . . . . . 598 compass . . . . . . . . . . . . . . . . . . . . . 421, 422 composite volcano . . . . . . . . . . . . . . 514, 515 compound . . . . . . . . . . . . . . . . . . . . 180, 308 compression . . . . . . . . . . . . . . . . . . . . . . 102 conceptual design . . . . . . . . . . . . . . . . . . . 46 concretion . . . . . . . . . . . . . . . . . . . . . . . . 588 condensation . . . . . . . . . . . . . . . . . . . . . . 565 conductor . . . . . . . . . . . . . . . . 207, 299, 398 cone cell . . . . . . . . . . . . . . . . . . . . . . . . . 638 conglomerate . . . . . . . . . . . . . . . . . . . . . . 599 coniferous forest . . . . . . . . . . . . . . . . . . . 259 conservation of energy . . . . . . . 164, 169, 405

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Dalton, John . . . . . . . . . . . . . . . . . . . . . . 178 damping . . . . . . . . . . . . . . . . . . . . . . . . . 609 Darwin, Charles . . . . . . . . . . . . . . . . . . . . 459 de Coriolis, Gaspard Gustave . . . . . . . . . . 254 de Reaumer, Rene . . . . . . . . . . . . . . . . . . . 39 deceleration . . . . . . . . . . . . . . . . . . . . . . . . 89 decibel (dB) . . . . . . . . . . . . . . . . . . . . . . . 622 decomposer . . . . . . . . . . . . . . . . . . . . . . . 366 decomposition reaction . . . . . . . . . . . . . . . 344 deduce . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 deep ocean currents . . . . . . . . . . . . . . . . . 574 deep-ocean trench . . . . . . . . . . . . . . . . . . . 487 delta . . . . . . . . . . . . . . . . . . . . . . . . . . . . 593 Democritus . . . . . . . . . . . . . . . . . . . . . . . 178 dendrochronology . . . . . . . . . . . . . . . . . . 454 density a property of matter . . . . . . . . . . . . . . 216 and buoyancy . . . . . . . . . . . . . . . . . . 237 and ocean currents . . . . . . . . . . . . . . . 574 apparent density and boats . . . . . . . . . 238 calculating . . . . . . . . . . . . . . . . . . . . . 219 of common materials . . . . . . . . . . . . . 217 of Earth’s materials . . . . . . . . . . . . . . 475 of gases . . . . . . . . . . . . . . . . . . . . . . . 230 of liquids . . . . . . . . . . . . . . . . . . . . . . 218 of minerals . . . . . . . . . . . . . . . . . . . . 467 of solids . . . . . . . . . . . . . . . . . . 218–219 of water . . . . . . . . . . . . . . . . . . . . . . 216 dependent variable . . . . . . . . . . . . . . . . . . . 25 deposition . . . . . . . . . . . . . . . . . . . . 193, 592 destructive interference . . . . . . . . . . . 618, 626 dew . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257 dew point . . . . . . . . . . . . . . . . . . . . 256, 539 diffraction . . . . . . . . . . . . . . . . . . . . . . . . 616 dimensional analysis . . . . . . . . . . . . . . . . . . 19 direct current (DC) . . . . . . . . . . . . . . . . . . 434 direct relationship . . . . . . . . . . . . . . . . 27, 395 direction of younging . . . . . . . . . . . . . . . . 600 directly proportional . . . . . . . . . . . . . . . . . 131 dissociation . . . . . . . . . . . . . . . . . . . . . . . 534 dissociation of water . . . . . . . . . . . . . . . . . 548 dissolution reaction . . . . . . . . . . . . . . . . . 350

dissolve . . . . . . . . . . . . . . . . . . . . . . . . . 538 distance . . . . . . . . . . . . . . . . . . . . . . . 13, 84 divergent boundary . . . . . . . . . . . . . 485, 486 diverging lens . . . . . . . . . . . . . . . . . 645, 650 DNA . . . . . . . . . . . . . . . . . . . . . . . . . . . 328 Doppler effect . . . . . . . . . . . . . . . . . . . . . 626 Doppler radar . . . . . . . . . . . . . . . . . . . . . 627 Doppler shift . . . . . . . . . . . . . . . . . . . . . 725 Doppler, Christian . . . . . . . . . . . . . . . . . . 725 double helix . . . . . . . . . . . . . . . . . . . . . . 328 double-displacement reaction . . . . . . . . . . 345 Douglass, Andrew . . . . . . . . . . . . . . . . . . 454 downdraft . . . . . . . . . . . . . . . . . . . . . . . . 268 ductility . . . . . . . . . . . . . . . . . . . . . . . . . 225 dwarf planet . . . . . . . . . . . . . . . . . . . . . . 674 dwarf star . . . . . . . . . . . . . . . . . . . . . . . . 694

E Earth age of . . . . . . . . . . . . . . . . . . . . . . . 453 and the Moon . . . . . . . . . . . . . . . . . . 675 atmosphere . . . . . . . . . . . 246–251, 302 axial tilt of . . . . . . . . . . . . . . . . . . . . 671 climate . . . . . . . . . . . . . . . . . . . . . . 258 composition of . . . . . . . . . . . . . . . . . 302 density of materials . . . . . . . . . . . . . . 475 earliest history . . . . . . . . . . . . . . . . . 450 effects of rotation . . . . . . . . . . . . . . . 254 energy balance . . . . . . . . . . . . . . . . . 374 interior . . . . . . . . . . . . . . . . . . . . . . 473 layers . . . . . . . . . . . . . . . . . . . . . . . 474 magnetic field . . . . . . . . . . . . . . . . . 421 oceans . . . . . . . . . . . . . . . . . . . 570–576 recycling of rocks . . . . . . . . . . . . . . . 465 rotation of . . . . . . . . . . . . . . . . . . . . 671 seismic waves . . . . . . . . . . . . . . . . . 472 shaping of landscape . . . . . . . . . . . . . 591 source of magnetism . . . . . . . . . . . . . 423 source of oxygen . . . . . . . . . . . . . . . 368 surface . . . . . . . . . . . . . . . . . . . . . . . 485 temperature regulation . . . . . . . 203, 572 temperature regulation of . . . . . . . . . 169

water on . . . . . . . . . . . . . . . . . . 558–561 Earth–Moon system . . . . . . . . . . . . . . . . . 675 earthquake activity . . . . . . . . . . . . . . . . . . . . . . . 502 and plate boundaries . . . . . . . . . . . . . 500 locating epicenter . . . . . . . . . . . . . . . 504 measuring . . . . . . . . . . . . . . . . . 505–506 seismic waves . . . . . . . . . . . . . . . . . . 503 stored energy . . . . . . . . . . . . . . . . . . 501 earthquake zone . . . . . . . . . . . . . . . . . . . . 500 echo sounding . . . . . . . . . . . . . . . . . . . . . . 67 echolocation . . . . . . . . . . . . . . . . . . . . . . 626 ecosystem . . . . . . . . . . . . . . . . . . . . 260, 365 efficiency . . . . . . . . . . . . . . . . . . . . 168, 169 Einstein, Albert . . . . . . . . . . . . 133, 178, 692 Einstein’s theory of relativity . . . . . . . . . . 720 elastic energy . . . . . . . . . . . . . . . . . . . . . 157 elasticity . . . . . . . . . . . . . . . . . . . . . . . . . 224 electric charge . . . . . . . . . . . . . . . . . 278, 384 electric circuit . . . . . . . . . . . . . . . . . 385, 393 electric current . . . . 385, 389, 391, 401, 408 electric field . . . . . . . . . . . . . . . . . . . . . . 635 electric motor . . . . . . . . . . . . . . . . . 430–432 electrical conductor . . . . . . . . . . . . . . . . . 299 electrical energy . . . . . . . . . . . . . . . . . . . 156 electrical power . . . . . . . . . . . . . . . . . . . . 442 electrical symbol . . . . . . . . . . . . . . . . . . . 386 electrically neutral . . . . . . . . . . . . . . . . . . 384 electricity . . . . . . . . . . . . . . . . . . . . . . . . 385 from fossil fuels . . . . . . . . . . . . . . . . 437 from nuclear energy . . . . . . . . . . . . . 438 from renewable resources . . . . . . . . . 439 transporting . . . . . . . . . . . . . . . . . . . 436 electrolytes . . . . . . . . . . . . . . . . . . . . . . . 553 electromagnet . . . . . . . . . . . . . 425–428, 431 electromagnetic force . . . . . . . . . . . . . 98, 281 electromagnetic induction . . . . . . . . . . . . . 433 electromagnetic spectrum . . . . . . . . . 157, 636 electromagnetic wave . . . . . . . . 209, 635, 691 electron and chemical bonds . . . . . . . . . . 308–313 bonding pair . . . . . . . . . . . . . . . . . . . 530 electromagnets . . . . . . . . . . . . . . . . . 428 energy levels . . . . . . . . . . . . . . . 285–289

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thermal radiation . . . . . . . . . . . . . . . . 209 transported by ocean currents . . . . . . . 573 energy level . . . . . . . . . . . 286–289, 295, 311 engineer . . . . . . . . . . . . . . . . . . . . . . . . . . 45 engineering cycle . . . . . . . . . . . . . . . . . . . . 46 English System . . . . . . . . . . . . . . . . . . . 7, 19 enzyme . . . . . . . . . . . . . . . . . . . . . . . . . . 327 epicenter . . . . . . . . . . . . . . . . . . . . . 501, 504 equator . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 equilibrium and buoyancy . . . . . . . . . . . . . . . . . . 236 chemical . . . . . . . . . . . . . . . . . . . . . . 352 natural frequency . . . . . . . . . . . . . . . 611 of an oscillator . . . . . . . . . . . . . . . . . 609 of forces . . . . . . . . . . . . . . . . . . . . . . 115 solution . . . . . . . . . . . . . . . . . . . . . . 542 thermal . . . . . . . . . . . . . . . . . . . . . . . 206 erosion . . . . . . . . . . . . . . 561, 582, 588, 590 escape velocity . . . . . . . . . . . . . . . . . . . . 720 evaluation . . . . . . . . . . . . . . . . . . . . . . . . . 46 evaporation . . . . . . . . . . . . . . . . . . . 194, 564 evidence . . . . . . . . . . . . . . . . . . . . . . . 34, 35 exfoliation . . . . . . . . . . . . . . . . . . . . . . . . 585 exosphere . . . . . . . . . . . . . . . . . . . . . . . . 251 exothermic . . . . . . . . . . . . . . . . . . . . . . . 348 exothermic reaction . . . . . . . . . 349, 350, 701 expanding universe . . . . . . . . . . . . . . . . . 726 experiment . . . . . . . . . . . . . . . . . . . . . 40–42 experimental technique . . . . . . . . . . . . . . . . 41 experimental variable . . . . . . . . . . . . . . . . . 40 extension . . . . . . . . . . . . . . . . . . . . . . . . 102 extrusive rock . . . . . . . . . . . . . . . . . . . . . 522

F Fahrenheit scale . . . . . . . . . . . . . . . . . . . . 184 Faraday, Michael . . . . . . . . . . . . . . . . . 42, 47 fault . . . . . . . . . . . . . . . . . . . . . . . . . . . . 501 field electric . . . . . . . . . . . . . . . . . . . . . . . 635 force . . . . . . . . . . . . . . . . . . . . . . . . 101 gravitational . . . . . . . . . . . . . . . . . . . 101 magnetic . . . . . . . . . . . . . . . . . . 420, 423

fire fountain . . . . . . . . . . . . . . . . . . . . . . . 514 fixed resistor . . . . . . . . . . . . . . . . . . . . . . 399 floating . . . . . . . . . . . . . . . . . . . . . . . . . . 236 floodplain . . . . . . . . . . . . . . . . . . . . . . . . 593 fluid properties of . . . . . . . . . . . . . . . 227–232 fluorescence . . . . . . . . . . . . . . . . . . . . . . . 633 focal length . . . . . . . . . . . . . . . . . . . . . . . 650 focal point . . . . . . . . . . . . . . . . . . . . 650, 712 focus . . . . . . . . . . . . . . . . . . . . . . . . . . . . 501 fog . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257 food chain . . . . . . . . . . . . . . . . . . . . . . . . 366 force action-reaction pair . . . . . . . . . . . . . . 138 action-reaction pairs . . . . . . . . . . . . . . 137 and acceleration . . . . . . . . . . . . . . . . . 131 at-a-distance . . . . . . . . . . . . . . . . . . . 101 balanced . . . . . . . . . . . . . . . . . . . . . . 114 buoyancy . . . . . . . . . . . . . . . . . 234–237 contact . . . . . . . . . . . . . . . . . . . . . . . 101 definition of . . . . . . . . . . . . . . . . . . . . . 98 electromagnet . . . . . . . . . . . . . . . . . . 281 elementary . . . . . . . . . . . . . . . . . . . . . 98 equilibrium . . . . . . . . . . . . . . . . . . . . 114 friction . . . . . . . . . . . . . . . . . . . 107–112 gravitational . . . . . . . . . . . . . . . . . . . 661 input and output . . . . . . . . . . . . . . . . . 149 intermolecular . . . . . . . . . . . . . .191, 297 magnetic . . . . . . . . . . . . . . . . . . . . . . 419 net force . . . . . . 114–115, 117, 126, 133 normal force . . . . . . . . . . . . . . . . . . . 116 of gravity . . . . . . . . . . . . . . . . .103, 281 periodic . . . . . . . . . . . . . . . . . . . . . . . 611 pressure . . . . . . . . . . . . . . . . . . 227–230 strong nuclear force . . . . . . . . . . . . . . 281 tension . . . . . . . . . . . . . . . . . . . . . . . 102 unbalanced . . . . . . . . . . . . . . . .127, 130 vector . . . . . . . . . . . . . . . . . . . . . . . . 100 weak force . . . . . . . . . . . . . . . . . . . . . 281 force field . . . . . . . . . . . . . . . . . . . . . . . . 101 forced convection . . . . . . . . . . . . . . . . . . . 208

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evidence for . . . . . . . . . . . . . . . 279–280 lone pair . . . . . . . . . . . . . . . . . . . . . 530 valence . . . . . . . . . . . . . . . . . . . . . . .311 electron cloud . . . . . . . . . . . . . . . . . 280, 288 element atomic number . . . . . . . . . . . . . 282–283 carbon . . . . . . . . . . . . . . . . . . . . . . . 301 definition of . . . . . . . . . . . . . . . . . . . 179 origin of . . . . . . . . . . . . . . . . . . . . . . 701 periodic table . . . . . . . . . . . . . . 291–295 properties of . . . . . . . . . . . . . . . 297–302 ratios in universe . . . . . . . . . . . . . . . 728 reactivity of . . . . . . . . . . . . . . . . . . . 310 elementary charge . . . . . . . . . . . . . . . . . . 278 elementary forces . . . . . . . . . . . . . . . . . . . 98 elevation . . . . . . . . . . . . . . . . . . . . . 61, 261 elliptical galaxy . . . . . . . . . . . . . . . . . . . 719 emissions . . . . . . . . . . . . . . . . . . . . . . . . 369 emissions trading . . . . . . . . . . . . . . . . . . 378 endothermic reaction . . . . . . . . 348, 350, 701 energy activation . . . . . . . . . . . . . . . . . . . . . 349 and chemical bonds . . . . . . . . . . . . . 310 and chemical reactions . . . 344, 348, 364 and friction . . . . . . . . . . . . . . . . . . . .112 and gravity . . . . . . . . . . . . . . . . . . . . 158 and heat . . . . . . . . . . . . . . . . . . . . . . 200 and nuclear reactions . . . . . . . . . . . . 354 and phase change . . . . . . . . . . . . . . . 192 and temperature . . . . . . . . . . . . . . . . 186 and the rock cycle . . . . . . . . . . . . . . . 582 and work . . . . . . . . . . . . . . . . . . . . . 159 carried by carbon . . . . . . . . . . . . . . . 369 carried by waves . . . . . . . . . . . . . . . . 613 conservation of . . . . . 164, 169, 229, 405 definition of . . . . . . . . . . . . . . . . . . . 155 electrical . . . . . . . . . . . . . . . . . . . . . 434 forms of . . . . . . . . . . . . . . . . . . 156–161 kinetic energy . . . . . . . . . . . . . . 161, 164 light . . . . . . . . . . . . . . . . . . . . 632, 634 nuclear . . . . . . . . . . . . . . . . . . . . . . 438 potential energy . . . . . . . . 160, 164, 228 pressure . . . . . . . . . . . . . . . . . . . . . . 229 solar . . . . . . . . . . . . . . . . . . . . 441, 691

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formula acceleration . . . . . . . . . . . . . . . . . . . . . 87 Boyle’s law . . . . . . . . . . . . . . . . . . . . 230 Charles’s law . . . . . . . . . . . . . . . . . . . 239 density . . . . . . . . . . . . . . . . . . . . . . . 219 Einstein’s formula . . . . . . . . . . . . . . . 692 heat equation . . . . . . . . . . . . . . . . . . . 204 inverse square law . . . . . . . . . . . . . . . 722 kinetic energy . . . . . . . . . . . . . . . . . . 161 Kirchhoff’s current law . . . . . . . . . . . 407 Kirchhoff’s voltage law . . . . . . . . . . . 405 Newton’s second law . . . . . . . . . . . . . 132 Ohm’s law . . . . . . . . . . . . . . . . . . . . 395 period and frequency . . . . . . . . . . . . . 607 potential energy . . . . . . . . . . . . . . . . . 160 power . . . . . . . . . . . . . . . . . . . . . . . . 170 resistance in series circuit . . . . . . . . . . 402 speed . . . . . . . . . . . . . . . . . . . . . . . . . 76 speed of wave . . . . . . . . . . . . . . . . . . 614 temperature conversions . . . . . . . . . . . 184 velocity . . . . . . . . . . . . . . . . . . . . . . . . 78 weight . . . . . . . . . . . . . . . . . . . . . . . 104 fossil . . . . . . . . . . . . . . . . . . . . . . . . 457, 599 fossil fuel . . . . . . . . . . . . . . . . . . . . 369, 437 fractional scale . . . . . . . . . . . . . . . . . . . . . . 59 free fall . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 free-body diagram . . . . . . . . . . . . . . . . . . 117 freezing point . . . . . . . . . . . . . . . . . . . . . . 192 frequency and pitch . . . . . . . . . . . . . . . . . . . . . . 621 and wave speed . . . . . . . . . . . . . . . . . 614 definition of . . . . . . . . . . . . . . . . . . . 607 of a wave . . . . . . . . . . . . . . . . . . . . . 613 of light . . . . . . . . . . . . . . . . . . . . . . . 634 frequency spectrum . . . . . . . . . . . . . . . . . 621 friction . . . . . . . . . . . . . . . . . . . . . . . . . . 609 a model . . . . . . . . . . . . . . . . . . . . . . . 109 and energy . . . . . . . . . . . . . . . . 112, 163 efficiency . . . . . . . . . . . . . . . . . . . . . 168 reducing . . . . . . . . . . . . . . . . . . . . . . 110 sliding . . . . . . . . . . . . . . . . . . . . . . . 108 static . . . . . . . . . . . . . . . . . . . . . . . . . 108 useful . . . . . . . . . . . . . . . . . . . . . . . . 111 front . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263

frost . . . . . . . . . . . . . . . . . . . . . . . . . . . . frost wedging . . . . . . . . . . . . . . . . . . . . . fulcrum . . . . . . . . . . . . . . . . . . . . . . . . . fundamental . . . . . . . . . . . . . . . . . . . . . . funnel cloud . . . . . . . . . . . . . . . . . . . . . . fuse . . . . . . . . . . . . . . . . . . . . . . . . 391,

257 584 149 624 270 409

G Gagarin, Yuri . . . . . . . . . . . . . . . . . . . . . 716 galaxy . . . . . . . . . . . . . . . . . . . . . . . . . . 718 Galileo Galilei . . . . . . . . . . . . . 35, 660, 712 gamma decay . . . . . . . . . . . . . . . . . . . . . 355 gas definition of . . . . . . . . . . . . . . . . . . . 190 density of . . . . . . . . . . . . . . . . . . . . . 230 pressure and temperature . . . . . . . . . . 239 pressure and volume . . . . . . . . . . . . . 230 properties of . . . . . . . . . . . . . . . 230–231 solubility . . . . . . . . . . . . . . . . . . . . . 543 sound in . . . . . . . . . . . . . . . . . . . . . . 620 volume and pressure . . . . . . . . . . . . . 239 gas planets . . . . . . . . . . . . . . . 674, 678, 730 gauss . . . . . . . . . . . . . . . . . . . . . . . . . . . 423 Gay-Lussac, Joseph . . . . . . . . . . . . . . . . . 239 gear . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149 Geiger, Hans . . . . . . . . . . . . . . . . . . . . . 279 generator . . . . . . . . . . . . . . . . . . . . 433, 434 geographic poles . . . . . . . . . . . . . . . 421, 422 geologic cycle . . . . . . . . . . . . . . . . . . . . . 465 geologic time scale . . . . . . . . . . . . . . . . . 450 geology . . . . . . . . . . . . . . . . . . . . . . . . . 456 geothermal . . . . . . . . . . . . . . . . . . . 440, 513 geyser . . . . . . . . . . . . . . . . . . . . . . . . . . 568 giant impact theory . . . . . . . . . . . . . . . . . 676 glacial retreat . . . . . . . . . . . . . . . . . . . . . 596 glacier . . . . . . . . . . . . . . . . . . 560, 595–596 global climate change . . . . . . . . . . . 373, 377 global warming . . . . . . . . . . . . . . . . 373, 596 global wind cell . . . . . . . . . . . . . . . . . . . 210 globe . . . . . . . . . . . . . . . . . . . . . . . . . 55, 58 gneiss . . . . . . . . . . . . . . . . . . . . . . 493, 494 Gore, Al . . . . . . . . . . . . . . . . . . . . . . . . . 376

graded bedding . . . . . . . . . . . . . . . . . . . . 592 gradient . . . . . . . . . . . . . . . . . . . . . . . . . . 62 graph definition of . . . . . . . . . . . . . . . . . . . . 24 harmonic motion . . . . . . . . . . . . . . . . 610 making . . . . . . . . . . . . . . . . . . . . . 25–26 of motion . . . . . . . . . . . . . . . . . . . 81–84 reading . . . . . . . . . . . . . . . . . . . . . . . . 28 relationships between variables . . . 27, 82 types of . . . . . . . . . . . . . . . . . . . . . . . 24 gravitational field . . . . . . . . . . . . . . . . . . 101 gravitational force . . . . . . . . . . . . . . . . . . 661 gravitational locking . . . . . . . . . . . . . . . . 675 gravitational potential energy . . . . . . . . . . 160 gravity 90, 98, 103, 104, 152, 158, 281, 563 greenhouse effect . . . . . . . . . . . . . . . . . . . 374 greenhouse gas . . . . . . . . . . . . . . . . . . . . 373 groundwater . . . . . . . . . . . . . . . . . . 560, 567 group . . . . . . . . . . . . . . . . . . . . . . . . . . . 291 Group 2 metals . . . . . . . . . . . . . . . . . . . . 294 Gutenberg, Dr. Beno . . . . . . . . . . . . . . . . 472 gyre . . . . . . . . . . . . . . . . . . . . . . . . . . . . 573

H hail . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268 half-life . . . . . . . . . . . . . . . . . . . . . . . . . . 357 halogens . . . . . . . . . . . . . . . . . . . . . . . . . 294 hardness . . . . . . . . . . . . . . . . . . . . . 224, 464 harmonic motion . . . . . . . . . . . . . . . 606–611 harmonics . . . . . . . . . . . . . . . . . . . . . . . . 624 heat . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200 heat conduction . . . . . . . . . . . . . . . . 206, 207 heat equation . . . . . . . . . . . . . . . . . . . . . . 204 heat pump system . . . . . . . . . . . . . . . . . . 440 heat transfer . . . . . . . . . . . . . . . . . . . . . . 206 Heisenberg, Werner . . . . . . . . . . . . . . . . . 287 herbivore . . . . . . . . . . . . . . . . . . . . . . . . 366 hertz (Hz) . . . . . . . . . . . . . . . . . . . . 607, 613 Hertzsprung, Ejnar . . . . . . . . . . . . . . . . . . 697 Hertzsprung-Russell (H-R) diagram . 697, 723 Hess, Harry . . . . . . . . . . . . . . . . . . . 479, 480 heterogeneous mixture . . . . . . . . . . . 181, 536

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I igneous rock . . . . . . . . . . . . . . 466, 518–522 incandescence . . . . . . . . . . . . . . . . . . . . . 633 incident ray . . . . . . . . . . . . . . . . . . . . . . 648 inclusion . . . . . . . . . . . . . . . . . . . . . . . . 459 independent variable . . . . . . . . . . . . . . . . . 25 index of refraction . . . . . . . . . . . . . . . . . . 649 Industrial Revolution . . . . . . . . . . . . . . . . 375 inertia . . . . . . . . . . . . . . . . . . . . . . 127, 662 infrared telescope . . . . . . . . . . . . . . . . . . 714 inhibitor . . . . . . . . . . . . . . . . . . . . . . . . . 351 inner planets . . . . . . . . . . . . . . . . . . . . . . 663 input . . . . . . . . . . . . . . . . . . . . . . . . . . . 148 input arm . . . . . . . . . . . . . . . . . . . . . . . . 151 input force . . . . . . . . . . . . . . . . . . . . . . . 149 input work . . . . . . . . . . . . . . . . . . . . . . . 167 inquiry . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 insoluble . . . . . . . . . . . . . . . . . . . . . . . . 539 instantaneous speed . . . . . . . . . . . . . . . . . . 76

insulator . . . . . . . . . . . . . . . . . 207, 299, 398 intensity . . . . . . . . . . . . . . . . . . . . . . . . . 638 Intergovernmental Panel on Climate Change (IPCC) . . . . . . . . . . . . . . . . . 376 intermolecular force . . . . . . . . . . . . . 191, 297 International Astronomical Union (IAU) . . 674 international dateline . . . . . . . . . . . . . . . . . 57 International System of Units . . . . . . . . . . . . 7 intrusive rock . . . . . . . . . . . . . . . . . . . . . 522 inverse relationship . . . . . . 27, 395, 607, 634 inverse square law . . . . . . . . . . . . . . 696, 722 inversely proportional . . . . . . . . . . . . . . . 132 ion . . . . . . . . . . . . . . . . . . . . . 282, 309, 544 ionic bond . . . . . . . . . . . . . . . . 309, 313, 317 ionosphere . . . . . . . . . . . . . . . . . . . . . . . 251 irregular galaxy . . . . . . . . . . . . . . . . . . . . 719 island arc . . . . . . . . . . . . . . . . . . . . . . . . 487 isobar . . . . . . . . . . . . . . . . . . . . . . . . . . . 265 isotope . . . . . . . . . . . . . . . . . . 283, 293, 453

J jet stream . . . . . . . . . . . . . . . . . . . . . . . . 264 Joliot-Curie, Irene . . . . . . . . . . . . . . . . . . 359 joule (J) . . . . . . . . . . . . . . . . . . . . . 155, 201 Joule, James . . . . . . . . . . . . . . . . . . . . . . . 37 Julius Caesar . . . . . . . . . . . . . . . . . . . . . . 667 Jupiter . . . . . . . . . . . . . . . . . . . . . . . . . . 678

K Keeling, Charles . . . . . . . . . . . . . . . . . . . 376 Keller, Friedrich . . . . . . . . . . . . . . . . . . . . 39 Kelvin (K) . . . . . . . . . . . . . . . . . . . . . . . . 188 Kelvin scale . . . . . . . . . . . . . . . . . . 188, 240 Kepler, Johannes . . . . . . . . . . . . . . . . . . . 662 kettle hole . . . . . . . . . . . . . . . . . . . . . . . . 596 kilocalorie . . . . . . . . . . . . . . . . . . . . . . . . 201 kilowatt-hours (kWh) . . . . . . . . . . . . . . . . 442 kinetic energy . . . . . . . . . . . . . . . . . 161, 164 kinetic molecular theory . . . . . . . . . . . . . . 351 Kirchhoff, Gustav Robert . . . . . . . . . . . . . 405 Kirchhoff’s current law . . . . . . . . . . . . . . 407

Kirchhoff’s voltage law . . . . . . . . . . . . . . . 405 Krafft, Katia and Maurice . . . . . . . . . . . . . 517 Kuiper Belt . . . . . . . . . . . . . . . . . . . . . . . 680 Kuiper belt object . . . . . . . . . . . . . . . . . . . 730 Kyoto Treaty . . . . . . . . . . . . . . . . . . . . . . 376

L lab report . . . . . . . . . . . . . . . . . . . . . . . . . . 41 lahar . . . . . . . . . . . . . . . . . . . . . . . . . . . . 589 land breeze . . . . . . . . . . . . . . . . . . . . . . . 253 landslide . . . . . . . . . . . . . . . . . . . . . . . . . 589 Latimer, Lewis . . . . . . . . . . . . . . . . . . . . . 411 latitude . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 lava . . . . . . . . . . . . . . . . . . . . . . . . . 482, 509 Lavoisier, Antoine Laurent . . . . . . . . . . . . 337 law of conservation of energy . .164, 229, 405 law of conservation of momentum . . . . . . . 140 law of lateral continuity . . . . . . . . . . . . . . 458 law of original horizontality . . . . . . . . . . . 458 law of reflection . . . . . . . . . . . . . . . . . . . . 648 law of superposition . . . . . . . . . . . . . . . . . 458 law of universal gravitation, formula for . . . 661 Le Chatelier’s principle . . . . . . . . . . . . . . . 352 leap year . . . . . . . . . . . . . . . . . . . . . . . . . 667 Leavitt, Henrietta . . . . . . . . . . . . . . . . . . . 723 legend . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 length . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 lens . . . . . . . . . . . . . . . . . . . . . . . . . 645, 650 lenticular galaxy . . . . . . . . . . . . . . . . . . . . 719 Leucippus . . . . . . . . . . . . . . . . . . . . . . . . 178 lever . . . . . . . . . . . . . . . . . . . . . . . . 149, 151 Lewis dot diagram . . . . . . . . . . . . . . . . . . 313 light and vision . . . . . . . . . . . . . . . . . . . . . 638 energy . . . . . . . . . . . . . . . . . . . . . . . . 632 interactions with matter . . . . . . . 646–649 properties of . . . . . . . . . . . . . . . 632–636 seeing color . . . . . . . . . . . . . . . . . . . . 639 light intensity . . . . . . . . . . . . . . . . . . . . . . 696 light ray . . . . . . . . . . . . . . . . . . . . . . . . . . 647 light year . . . . . . . . . . . . . . . . . . . . . .15, 709 lightning . . . . . . . . . . . . . . . . . . . . . 268, 388

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Hiero II . . . . . . . . . . . . . . . . . . . . . . . . . 241 high-grade metamorphism . . . . . . . . . . . . 493 high-pressure center . . . . . . . . . . . . . . . . 265 homogeneous mixture . . . . . . . . . . . 181, 536 horsepower (hp) . . . . . . . . . . . . . . . . . . . 170 hot spot . . . . . . . . . . . . . . . . . . . . . . . . . 513 hot spring . . . . . . . . . . . . . . . . . . . . . . . . 568 Hubble Space Telescope . . . . . . . . . 715, 719 Hubble, Edwin . . . . . . . . . . . . 715, 719, 726 Huggins, Sir William . . . . . . . . . . . . . . . . 702 human hearing . . . . . . . . . . . . . . . . . . . . 625 humidity . . . . . . . . . . . . . . . . . . . . . . . . . 256 hurricane . . . . . . . . . . . . . . . . . . . . . . . . 269 Hutton, James . . . . . . . . . . . . . . . . . 457, 459 hydroelectric plant . . . . . . . . . . . . . 436, 439 hydrogen . . . . . . . . . . . . . . . . . . . . . . . . .311 hydrogen bond . . . . . . . . . . . . . . . . . . . . 532 hydrologic cycle . . . . . . . . . . . . . . . . . . . 563 hydronium ion . . . . . . . . . . . . . . . . 546, 548 hydrosphere . . . . . . . . . . . . . . . . . . . . . . 558 hydroxide ion . . . . . . . . . . . . . . . . . 547, 548 hypothesis . . . . . . . . . . . . . . . . . . . . . 37, 38

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line graph . . . . . . . . . . . . . . . . . . . . . . . . . 24 linear motion . . . . . . . . . . . . . . . . . . . . . . 606 lipid . . . . . . . . . . . . . . . . . . . . . . . . . . . . 326 Lippershey, Hans . . . . . . . . . . . . . . . . . . . 712 liquid definition of . . . . . . . . . . . . . . . . . . . 190 density of . . . . . . . . . . . . . . . . . . . . . 218 properties of . . . . . . . . . . . . . . . 227–229 solubility . . . . . . . . . . . . . . . . . . . . . . 543 sound in . . . . . . . . . . . . . . . . . . . . . . 620 viscosity . . . . . . . . . . . . . . . . . . . . . . 232 water . . . . . . . . . . . . . . . . . . . . . . . . 561 lithosphere . . . . . . . . . . . . . . . . . . . . . . . . 474 Local Group . . . . . . . . . . . . . . . . . . . . . . 721 Lockyer, Sir Joseph Norman . . . . . . . . . . . 702 loess . . . . . . . . . . . . . . . . . . . . . . . . . . . . 588 logarithmic scale . . . . . . . . . . . . . . . . . . . 622 lone pair . . . . . . . . . . . . . . . . . . . . . . . . . 530 longitude . . . . . . . . . . . . . . . . . . . . . . . . . . 57 longitudinal wave . . . . . . . . . . . . . . . . . . . 617 low-grade metamorphism . . . . . . . . . . . . . 493 low-pressure center . . . . . . . . . . . . . . . . . . 265 lubricant . . . . . . . . . . . . . . . . . . . . . . . . . 110 luminosity . . . . . . . . . . . . . . . . . . . . 696, 723 lunar cycle . . . . . . . . . . . . . . . . . . . . . . . . 668 lunar eclipse . . . . . . . . . . . . . . . . . . 668, 669 luster . . . . . . . . . . . . . . . . . . . . . . . . . . . . 467 Lyell, Charles . . . . . . . . . . . . . . . . . . . . . 459

M machine . . . . . . . . . . . . . . . . . . . . . . . . . . 148 macronutrient . . . . . . . . . . . . . . . . . . . . . . 364 maglev train . . . . . . . . . . . . . . . . 47, 110, 426 magma . . . . . . . . . . . . . . . . . . 482, 509–522 magma chamber . . . . . . . . . . . . . . . . . . . . 509 magnet . . . . . . . . . . . . . . . . . . . . . . . . . . 430 magnetic . . . . . . . . . . . . . . . . . . . . . . . . . 418 magnetic declination . . . . . . . . . . . . . . . . . 422 magnetic field . . . . . . . . . . . . . . . . . 420, 423 magnetic field line . . . . . . . . . . . . . . . . . . 420 magnetic force . . . . . . . . . . . . . . . . . . . . . 419 magnetic pole . . . . . . . . . . . . . . . . . 418, 422

magnetic reversal pattern . . . . . . . . . . . . . 480 magnetic storm . . . . . . . . . . . . . . . . . . . . 690 main group elements . . . . . . . . . . . . . . . . 291 main sequence stars . . . . . . . . . 697, 699, 723 malleability . . . . . . . . . . . . . . . . . . . . . . 225 manipulated variable . . . . . . . . . . . . . . . . . 25 mantle . . . . . . . . . . . . . . . . . . . . . . . . . . 474 mantle plume . . . . . . . . . . . . . . . . . 483, 513 map bathymetric . . . . . . . . . . . . . . . . . 66–69 definition of . . . . . . . . . . . . . . . . . . . . 54 distortion of . . . . . . . . . . . . . . . . . . . . 58 scale . . . . . . . . . . . . . . . . . . . . . . . . . 59 topographic . . . . . . . . . . . . . . . . . 61–64 Mariana Trench . . . . . . . . . . . . . . . . . . . 576 Mars . . . . . . . . . . . . . . . . . . . . . . . . . . . 677 Marsden, Ernest . . . . . . . . . . . . . . . . . . . 279 mass . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 and acceleration . . . . . . . . . . . . . . . . 132 and inertia . . . . . . . . . . . . . . . . . . . . 127 vs. weight . . . . . . . . . . . . . . . . 103, 234 mass number . . . . . . . . . . . . . . . . . . . . . 283 mass wasting . . . . . . . . . . . . . . . . . . . . . 589 mass-percent . . . . . . . . . . . . . . . . . . . . . 540 matter . . . . . . . . . . . . . . . . . . . . . . 178, 222 Mayer, Julius . . . . . . . . . . . . . . . . . . . . . . 37 meanders . . . . . . . . . . . . . . . . . . . . . . . . 594 measurement and graphing . . . . . . . . . . . . . . . . . . . 24 definition of . . . . . . . . . . . . . . . . . . . . . 6 of density . . . . . . . . . . . . . . . . . . . . . 217 of distance . . . . . . . . . . . . . . . . . . . . . 13 of time . . . . . . . . . . . . . . . . . . . . . . . . 12 uncertainty . . . . . . . . . . . . . . . . . . . . . 21 mechanical advantage . . . . . . . . . . . . . . . 150 mechanical energy . . . . . . . . . . . . . . . . . 156 mechanical weathering . . . . . . . . . . 583–585 melting point . . . . . . . . . . . . . . . . . 192, 298 Mercator projection . . . . . . . . . . . . . . . . . . 58 Mercury . . . . . . . . . . . . . . . . . . . . . . . . . 677 mercury barometer . . . . . . . . . . . . . . . . . 249 mesosphere . . . . . . . . . . . . . . . . . . . . . . 250 Mesozoic Era . . . . . . . . . . . . . . . . . . . . . 452 metal . . . . . . . . . . . . . . . . . . . 292, 299, 300

metalloid . . . . . . . . . . . . . . . . . . . . . . . . . 292 metamorphic grade . . . . . . . . . . . . . . . . . 493 metamorphic rock . . . . . . . . . . 466, 492–494 meteor . . . . . . . . . . . . . . . . . . . . . . . . . . 682 meteor shower . . . . . . . . . . . . . . . . . . . . . 682 meteorite . . . . . . . . . . . . . . . . . . . . . . . . . 682 meteorologist . . . . . . . . . . . . . . . . . . . . . 263 meter . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Metric System . . . . . . . . . . . . . . . . . . . . . . . 7 micronutrient . . . . . . . . . . . . . . . . . . . . . . 364 mid-ocean ridge . . . . . . . . . . . . 479, 480, 512 Milky Way galaxy . . . . . . . . . . . . . . . . . . 718 mineral . . . . . . . . . . . . . . 462–464, 467, 587 mirror . . . . . . . . . . . . . . . . . . . . . . . 645, 647 mixture . . . . . . . . . . . . . . . . . . 180, 181, 537 Modified Mercalli scale . . . . . . . . . . . . . . 506 Mohs hardness scale . . . . . . . . . . . . . . . . 464 Mohs, Friedrick . . . . . . . . . . . . . . . . . . . . 464 molecule . . . . . . . . . . . . . . . . . . . . . . . . . 180 biological . . . . . . . . . . . . . . . . . . . . . 325 covalent bonds . . . . . . . . . . . . . . . . . 308 nonpolar . . . . . . . . . . . . . . . . . . . . . . 531 organic . . . . . . . . . . . . . . . . . . . . . . . 324 polar . . . . . . . . . . . . . . . . . . . . . . . . 531 structural diagram . . . . . . . . . . . . . . . 323 Moment Magnitude scale . . . . . . . . . . . . . 505 momentum . . . . . . . . . . . . . . . . . . . . . . . 140 Moon eclipse . . . . . . . . . . . . . . . . . . . . . . . 669 formation of . . . . . . . . . . . . . . . . . . . 676 lunar cycle . . . . . . . . . . . . . . . . . . . . 668 orbit around Earth . . . . . . . . . . . . . . . 663 phases of . . . . . . . . . . . . . . . . . . . . . 668 moon . . . . . . . . . . . . . . . . . . . . . . . . . . . 674 motion and forces . . . . . . . . . . . . . . . . . . 98, 126 and the solar system . . . . . . . . . . . . . 658 circular . . . . . . . . . . . . . . . . . . . . . . . . 92 curved . . . . . . . . . . . . . . . . . . . . . . . . 92 graphs of . . . . . . . . . . . . . . . . . . . 81–84 harmonic . . . . . . . . . . . . . . . . . 606–611 kinetic energy . . . . . . . . . . . . . . . . . . 161 linear . . . . . . . . . . . . . . . . . . . . . . . . 606 of atoms . . . . . . . . . . . . . . . . . . . . . . 186

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mountain . . . . . . . . . . . . . . . . . . . . 488, 494 mudflow . . . . . . . . . . . . . . . . . . . . . . . . . 589 mudstone . . . . . . . . . . . . . . . . . . . . . . . . 599 multimeter . . . . . . . . . . . . . . . . . . . 390, 394

N

O objective . . . . . . . . . . . . . . . . . . . . . . . . . . 35 obsidian . . . . . . . . . . . . . . . . . . . . . . . . . 516 ocean current . . . . . . . . . . . . . . . . . . . . . . 210 oceanic crust . . . . . . . . . . . . . . 474, 475, 481 oceans . . . . . . . . . . . . . . . . . . . . . . 570–576 ohm (Ω) . . . . . . . . . . . . . . . . . . . . . . . . . 394 Ohm’s law . . . . . . . 395, 397, 402, 405, 406 omnivore . . . . . . . . . . . . . . . . . . . . . . . . 366 open circuit . . . . . . . . . . . . . . . . . . . . . . . 387 optics . . . . . . . . . . . . . . . . . . . . . . . . . . . 645 orbit . . . . . . . . . . . . . . . . . . . . . . . . . . . . 662 organic chemistry . . . . . . . . . . . . . . 301, 324 origin . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 oscillator . . . . . . . . . . . . . . . . . 607–611, 630 outer planets . . . . . . . . . . . . . . . . . . . . . . 663 output . . . . . . . . . . . . . . . . . . . . . . . . . . . 148 output arm . . . . . . . . . . . . . . . . . . . . . . . . 151 output force . . . . . . . . . . . . . . . . . . . . . . . 149 output work . . . . . . . . . . . . . . . . . . . . . . . 167 oxbow lake . . . . . . . . . . . . . . . . . . . . . . . 594 oxidation . . . . . . . . . . . . . . . . . . . . . . . . . 586 oxidation number . . . . . . . . . . . 315, 316, 318 oxygen cycle . . . . . . . . . . . . . . . . . . . . . . 368 Øersted, Hans Christian . . . . . . . . . . . . . . 425

P paleontologist . . . . . . . . . . . . . . . . . . . . . 457 Paleozoic Era . . . . . . . . . . . . . . . . . . . . . 450 Pangaea . . . . . . . . . . . . . . . . . 450, 460, 478 parabola . . . . . . . . . . . . . . . . . . . . . . . . . . 92 parallax . . . . . . . . . . . . . . . . . . . . . . . . . . 710 parallel circuit . . . . . . . . . . . . . . . . . . . . . 410 parsec . . . . . . . . . . . . . . . . . . . . . . . . 15, 709 parts per billion (ppb) . . . . . . . . . . . . . . . . 540 parts per million (ppm) . . . . . . . . . . . . . . . 540 parts per trillion (ppt) . . . . . . . . . . . . . . . . 540

pascal (Pa) . . . . . . . . . . . . . . . . . . . . . . . . 227 passive solar heating . . . . . . . . . . . . . . . . . 691 Pathfinder . . . . . . . . . . . . . . . . . . . . . . . . . 53 pendulum . . . . . . . . . . . . . . . . . . . . . . . . 606 Penzias, Arno . . . . . . . . . . . . . . . . . . . . . . 728 percolation . . . . . . . . . . . . . . . . . . . . . . . . 566 period . . . . . . . . . . . . . . . . . . . . . . . 291, 607 periodic force . . . . . . . . . . . . . . . . . . . . . . 611 periodic table and chemical bonding . . . . . . . . . . . . . 317 and valence electrons . . . . . . . . . . . . . 312 diagram . . . . . . . . . . . . . . . . . . . . . . . 292 energy levels . . . . . . . . . . . . . . . . . . . 295 groups . . . . . . . . . . . . . . . . . . . . . . . . 294 organization of . . . . . . . . . . . . . . . . . . 291 oxidation numbers . . . . . . . . . . . . . . . 316 periodicity . . . . . . . . . . . . . . . . . . . . . . . . 298 permafrost . . . . . . . . . . . . . . . . . . . . . . . . 596 permanent magnet . . . . . . . . . . . . . . 418, 428 pH . . . . . . . . . . . . . . . . . . . . . . . . . 549–552 pH indicators . . . . . . . . . . . . . . . . . . . . . . 549 pH scale . . . . . . . . . . . . . . . . . . . . . . . . . 549 Phanerozoic Eon . . . . . . . . . . . . . . . . . . . 450 phase change . . . . . . . . . . . . . . . . . . . . . . 192 phases of matter . . . . . . . . . . . . . . . . . . . . 190 phosphorus cycle . . . . . . . . . . . . . . . . . . . 370 photon . . . . . . . . . . . . . . . . . . . . . . . 286, 633 photoreceptor . . . . . . . . . . . . . . . . . . . . . . 638 photosphere . . . . . . . . . . . . . . . . . . . . . . . 689 photosynthesis 247, 348, 365, 368, 450, 543, 643, 692 photovoltaic (or PV) cells . . . . . . . . . . . . . 691 physical change . . . . . . . . . . . . . . . . 222, 334 physical properties . . . . . . . . . . . . . . . . . . 222 pie graph . . . . . . . . . . . . . . . . . . . . . . . . . . 24 pigment . . . . . . . . . . . . . . . . . . . . . . 641, 642 pillow lava . . . . . . . . . . . . . . . . . . . . 486, 512 pitch . . . . . . . . . . . . . . . . . . . . . . . . . . . . 621 pixel . . . . . . . . . . . . . . . . . . . . . . . . . . . . 640 planet . . . . . . . . . . . . . . . . . . . . . . . 659, 674 planetary nebula . . . . . . . . . . . . . . . . . . . . 700 planetary system . . . . . . . . . . . . . . . . . . . . 729 plasma . . . . . . . . . . . . . . . . . . . . . . . 188, 193 plastic . . . . . . . . . . . . . . . . . . . . . . . . . . . 595

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National Aeronautics and Space Administration (NASA) . . . . . . . . . . . . . . . . . . . 42, 714 National Map Accuracy Standards . . . . . . . 62 natural convection . . . . . . . . . . . . . . . . . . 208 natural frequency . . . . . . . . . . . . . . 611, 624 natural law . . . . . . . . . . . . . . . . . . . . . 34, 36 nautical charts . . . . . . . . . . . . . . . . . . . . . . 67 nebula . . . . . . . . . . . . . . . . . . . . . . . . . . 699 negative . . . . . . . . . . . . . . . . . . . . . . . . . 384 negative, positive charge . . . . . . . . . . . . . 278 Neptune . . . . . . . . . . . . . . . . . . . . . . . . . 678 net force . . . . . . . . . .114–115, 117, 126, 133 neutral solution . . . . . . . . . . . . . . . . . . . . 549 neutralization . . . . . . . . . . . . . . . . . . . . . 552 neutron . . . . . . . . . . . . . . . . . . . . . . . . . . 280 neutron star . . . . . . . . . . . . . . . . . . 694, 701 newton (N) . . . . . . . . . . . . . . . . . . . . 99, 130 Newton, Sir Isaac . . 126, 133, 661, 662, 712 Newton’s first law . . . . . . . . . . . . . . 126–129 Newton’s second law . . . . . . . . 130–133, 611 Newton’s third law . . . . . . . . . 136–140, 228 nimbostratus cloud . . . . . . . . . . . . . . . . . 267 nitrogen cycle . . . . . . . . . . . . . . . . . . . . . 370 nitrogen fixation . . . . . . . . . . . . . . . . . . . 370 noble gases . . . . . . . . . . . . . . . . . . . 294, 310 node . . . . . . . . . . . . . . . . . . . . . . . . . . . . 624 nonmetals . . . . . . . . . . . . . . . . . . . . 292, 299 nonpolar molecule . . . . . . . . . . . . . . . . . . 531 nonrenewable resource . . . . . . . . . . . . . . 437 normal force . . . . . . . . . . . . . . . . . . . . . . .116 normal line . . . . . . . . . . . . . . . . . . . . . . . 648 north pole . . . . . . . . . . . . . . . . 418, 421, 425 nuclear energy . . . . . . . . . . . . . . . . 157, 438 nuclear fission . . . . . . . . . . . . . . . . . . . . 356 nuclear fusion . . . . . . . . . . . . . . . . . . . . . 356 nuclear reaction . . . . . . . . . . . . . . . 354–358

nucleic acid . . . . . . . . . . . . . . . . . . . . . . . 328 nucleotide . . . . . . . . . . . . . . . . . . . . . . . . 328 nucleus . . . . . . . . . . . . . . . . . . . . . . 279, 681

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plate tectonics . . . . . . . . . . . . . . . . . . . . . 481 Pluto . . . . . . . . . . . . . . . . . . . . . . . . . . . . 680 point bar . . . . . . . . . . . . . . . . . . . . . . . . . 594 polar easterlies . . . . . . . . . . . . . . . . . . . . . 255 polar front . . . . . . . . . . . . . . . . . . . . . . . . 255 polar molecule . . . . . . . . . . . . . . . . . . . . . 531 pollution . . . . . . . . . . . . . . . . . . . . . . . . . 367 polyatomic ion . . . . . . . . . . . . . . . . . . . . . 320 polymer . . . . . . . . . . . . . . . . . . . . . . . . . . 324 polymerization . . . . . . . . . . . . . . . . . . . . . 343 position . . . . . . . . . . . . . . . . . . . . . 52–54, 78 position vs. time graph . . . . . . . . . . . . . 81–83 positive . . . . . . . . . . . . . . . . . . . . . . . . . . 384 positive, negative charge . . . . . . . . . . . . . . 278 potential energy . . . . . . . . . . . . 160, 164, 228 potentiometer . . . . . . . . . . . . . . . . . . . . . . 399 pound (lb) . . . . . . . . . . . . . . . . . . . . . . . . . 99 power calculating . . . . . . . . . . . . . . . . . . . . . 170 definition of . . . . . . . . . . . . . . . . . . . 170 electrical . . . . . . . . . . . . . . . . . . . . . . 442 power plant . . . . . . . . . . . . . . . . . . . . . . . 436 Precambrian . . . . . . . . . . . . . . . . . . . . . . . 450 precipitate . . . . . . . . . . . . . . . . . . . . . . . . 335 precipitation . . . . . . . . . . . . . . . 257, 565, 599 precision . . . . . . . . . . . . . . . . . . . . . . . . . . 10 pressure . . . . . . . . . . 227–230, 248–249, 543 pressure energy . . . . . . . . . . . . . . . . 156, 229 prevailing westerlies . . . . . . . . . . . . . . . . . 255 prime meridian . . . . . . . . . . . . . . . . . . . . . . 57 principle of cross-cutting relationships . . . . 459 principle of fossil succession . . . . . . . . . . . 459 prism . . . . . . . . . . . . . . . . . . . . . . . . . . . . 645 procedure . . . . . . . . . . . . . . . . . . . . . . . . . 41 producer . . . . . . . . . . . . . . . . . . . . . . . . . 366 product . . . . . . . . . . . . . . . . . . . . . . . . . . 336 projectile . . . . . . . . . . . . . . . . . . . . . . . . . . 92 projection . . . . . . . . . . . . . . . . . . . . . . . . . 58 protein . . . . . . . . . . . . . . . . . . . . . . . . . . . 327 Proterozoic . . . . . . . . . . . . . . . . . . . . . . . 450 proton . . . . . . . . . . . . . . . . . . . . . . . . . . . 280 protostar . . . . . . . . . . . . . . . . . . . . . . . . . 699 prototype . . . . . . . . . . . . . . . . . . . . . . . . . . 46 Ptolemy . . . . . . . . . . . . . . . . . . . . . . 659, 660

pure substance . . . . . . . . . . . . . . . . . . . . 181 P-wave . . . . . . . . . . . . . . . . . . . . . . . . . . 472

Q quantum mechanics . . . . . . . . . . . . . . . . . 288 quantum theory . . . . . . . . . . . . . . . . . . . . 287

R radiant energy . . . . . . . . . . . . . . . . . . . . . 157 radio telescope . . . . . . . . . . . . . . . . . . . . 714 radioactive . . . . . . . . . . . . . . . . . . . . . . . 355 radioactive dating . . . . . . . . . . . . . . . . . . 357 radioactive isotope . . . . . . . . . . . . . 357, 453 radiometric dating . . . . . . . . . . . . . . . . . . 453 rain . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257 reactant . . . . . . . . . . . . . . . . . . . . . . . . . 336 reaction rate . . . . . . . . . . . . . . . . . . . . . . 351 red giant star . . . . . . . . . . . . . . . . . . 697, 700 redshift . . . . . . . . . . . . . . . . . . . . . . . . . 726 reflected ray . . . . . . . . . . . . . . . . . . . . . . 648 reflecting telescope . . . . . . . . . . . . . 712, 713 reflection . . . . . . . . . . . . 616, 646, 647, 648 refracting telescope . . . . . . . . . . . . . 712, 713 refraction . . . . . . . . . . . . . . . . 616, 647, 649 regional metamorphism . . . . . . . . . . . . . . 492 relationship . . . . . . . . . . . . . . . . . . . . . . . 27 relative dating . . . . . . . . . . . . . . . . . 456–460 relative humidity . . . . . . . . . . . . . . . . . . . 256 relief . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 renewable resource . . . . . . . . . . . . . . . . . 439 repeatable . . . . . . . . . . . . . . . . . . . . . . . . . 35 repel . . . . . . . . . . . . . . . . . . . . . . . 278, 419 reservoir . . . . . . . . . . . . . . . . . . . . . . . . . 560 residence time . . . . . . . . . . . . . . . . . . . . . 566 resistance definition of . . . . . . . . . . . . . . . . . . . 393 in series circuits . . . . . . . . . . . . . . . . 402 measuring . . . . . . . . . . . . . . . . . . . . 394 parallel circuit . . . . . . . . . . . . . . . . . 409 resistor . . . . . . . . . . . . . . . . . . . . . . 386, 399 resolution . . . . . . . . . . . . . . . . . . . . . . . . . 10

resonance . . . . . . . . . . . . . . . . . . . . . . . . 611 respiration . . . . . . . . . . . . . . . . . . . . . . . . 368 responding variable . . . . . . . . . . . . . . . . . . 25 Revelle, Roger . . . . . . . . . . . . . . . . . . . . . 376 revolution . . . . . . . . . . . . . . . . . . . . . . . . 666 RGB color model . . . . . . . . . . . . . . . . . . . 640 Riccioli, Giovanni . . . . . . . . . . . . . . . . . . 730 Richter scale . . . . . . . . . . . . . . . . . . 472, 505 Richter, Charles . . . . . . . . . . . . . . . . . . . . 472 right hand rule . . . . . . . . . . . . . . . . . . . . . 425 Ring of Fire . . . . . . . . . . . . . . . . . . . . . . . 508 river . . . . . . . . . . . . . . . . . . . . . . . . . . . . 593 river valley . . . . . . . . . . . . . . . . . . . . . . . 593 rock composition of . . . . . . . . . . . . . . . . . 462 conditions for melting . . . . . . . . . . . . 510 groups . . . . . . . . . . . . . . . . . . . . . . . 465 igneous . . . . . . . . . . . . . . . . . . 518–522 metamorphic . . . . . . . . . . . . . . . 492–494 sedimentary . . . . . . . . . . . . . . . 598–601 weathering and erosion . . . . . . . 582–590 rock cycle . . . . . . . . . . . . 465, 466, 582, 598 rock outcrop . . . . . . . . . . . . . . . . . . . . . . 589 rockfall . . . . . . . . . . . . . . . . . . . . . . . . . . 589 rod cell . . . . . . . . . . . . . . . . . . . . . . . . . . 638 root wedging . . . . . . . . . . . . . . . . . . . . . . 585 rotation . . . . . . . . . . . . . . . . . . . . . . . . . . 666 rotor . . . . . . . . . . . . . . . . . . . . . . . . . . . . 430 Russell, Henry . . . . . . . . . . . . . . . . . . . . . 697 Rutherford, Ernest . . . . . . . . . . . . . . . . . . 279

S Saffir-Simpson Hurricane Scale . . . . . . . . salinity . . . . . . . . . . . . . . . . . . . . . . . . . . salt crystal weathering . . . . . . . . . . . . . . . San Andreas Fault . . . . . . . . . . 489, 500, sandstone . . . . . . . . . . . . . . . . . . . . . . . . satellite . . . . . . . . . . . . . . . . . . 251, 674, saturated fat . . . . . . . . . . . . . . . . . . . . . . saturation . . . . . . . . . . . . . . . . . . . . 257, Saturn . . . . . . . . . . . . . . . . . . . . . . . . . . . scale

269 570 584 502 599 715 326 539 678

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Sojourner . . . . . . . . . . . . . . . . . . . . . . 53, 54 Solar America Initiative (SAI) . . . . . . . . . 441 solar cell . . . . . . . . . . . . . . . . . . . . . . . . . 691 solar constant . . . . . . . . . . . . . . . . . . . . . 692 solar eclipse . . . . . . . . . . . . . . . . . . . . . . 670 solar energy . . . . . . . . . . . . . . . . . . . 441, 691 solar flare . . . . . . . . . . . . . . . . . . . . . . . . 690 solar prominence . . . . . . . . . . . . . . . . . . . 690 solar system ancient models . . . . . . . . . . . . . 658–660 current model . . . . . . . . . . . . . . . . . . 663 relative sizes . . . . . . . . . . . . . . . . . . . 664 solar wind . . . . . . . . . . . . . . . . . . . . . . . . 690 solid arrangement of atoms . . . . . . . . . . . . 223 definition of . . . . . . . . . . . . . . . . . . . 190 density of . . . . . . . . . . . . . . . . . 218–219 properties of . . . . . . . . . . . . . . . 222–226 solution . . . . . . . . . . . . . . . . . . . . . . 536 sound in . . . . . . . . . . . . . . . . . . . . . . 620 solubility . . . . . . . . . . . . . . . . . . . . . 539, 541 solubility curve . . . . . . . . . . . . . . . . . . . . 541 solubility rules . . . . . . . . . . . . . . . . . . . . . 544 solute . . . . . . . . . . . . . . . . . . . . . . . . . . . 538 solution . . . . . . . . . . . . . . . . . . . . . . . . . . 536 solvent . . . . . . . . . . . . . . . . . . . . . . . . . . 538 sonar . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 sound definition of . . . . . . . . . . . . . . . . . . . 620 Doppler effect . . . . . . . . . . . . . . . . . . 626 frequency and pitch . . . . . . . . . . . . . . 621 how we hear . . . . . . . . . . . . . . . . . . . 625 loudness and intensity . . . . . . . . . . . . 622 speed of . . . . . . . . . . . . . . . . . . . . . . 623 wavelength of . . . . . . . . . . . . . . . . . . 624 south pole . . . . . . . . . . . . . . . . 418, 421, 425 space probes . . . . . . . . . . . . . . . . . . . . . . 716 space shuttle . . . . . . . . . . . . . . . . . . . 42, 716 space station . . . . . . . . . . . . . . . . . . . . . . 716 specific heat . . . . . . 202, 203, 261, 533, 572 spectral line . . . . . . . . . . . . . . . . . . . . . . . 285 spectrometer . . . . . . . . . . . . . . . . . . 285, 702 spectroscopy . . . . . . . . . . . . . . . . . . . . . . 702 spectrum . . . . . . . . . . . . . . . . . 285, 286, 702

specular reflection . . . . . . . . . . . . . . . . . . 648 speed average . . . . . . . . . . . . . . . . . . . . . . . . 76 calculating . . . . . . . . . . . . . . . . . . .76, 81 calculating for a wave . . . . . . . . . . . . . 614 compared to velocity . . . . . . . . . . . . . . 78 constant . . . . . . . . . . . . . . . . . . . .81, 84 during constant acceleration . . . . . . . . . 90 from position vs. time graph . . . . . . . . . 83 instantaneous . . . . . . . . . . . . . . . . . . . . 76 speed of light . . . . . . . .15, 77, 420, 614, 632 speed vs. time graph . . . . . . . . . . . . . . . . . . 84 spiral galaxy . . . . . . . . . . . . . . . . . . . . . . 719 spring . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 stable . . . . . . . . . . . . . . . . . . . . . . . . . . . 355 standard candle . . . . . . . . . . . . . . . . . . . . 723 standing wave . . . . . . . . . . . . . . . . . . . . . 624 star brightness and luminosity . . . . . . . . . . 696 classifying . . . . . . . . . . . . . . . . . . . . . 694 color and temperature . . . . . . . . . . . . . 695 examining light from . . . . . . . . . . . . . 702 life cycle of . . . . . . . . . . . . . . . . . . . . 699 old age of . . . . . . . . . . . . . . . . . . . . . 700 the Sun . . . . . . . . . . . . . . . . . . . . . . . 688 static electricity . . . . . . . . . . . . . . . . . . . . 384 static friction . . . . . . . . . . . . . . . . . . . . . . 108 steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300 Steno, Nicolas . . . . . . . . . . . . . . . . . 456–458 stick-slip motion . . . . . . . . . . . . . . . . . . . . 501 storm cell . . . . . . . . . . . . . . . . . . . . . . . . . 268 stratocumulus cloud . . . . . . . . . . . . . . . . . 267 stratosphere . . . . . . . . . . . . . . . . . . . . . . . 250 stratus cloud . . . . . . . . . . . . . . . . . . . . . . . 267 streak plate test . . . . . . . . . . . . . . . . . . . . . 464 stream . . . . . . . . . . . . . . . . . . . . . . . . . . . 593 streamline . . . . . . . . . . . . . . . . . . . . . . . . 229 strength . . . . . . . . . . . . . . . . . . . . . . . . . . 224 strong nuclear force . . . . . . . . . . . . . .98, 281 subduction . . . . . . . . . . . . . . . . . . . . 482, 487 sublimation . . . . . . . . . . . . . . . . . . . . . . . 193 subsonic . . . . . . . . . . . . . . . . . . . . . . . . . 623 subtractive color process . . . . . . . . . . 641, 642 subtractive primary colors . . . . . . . . . . . . . 641

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decibel . . . . . . . . . . . . . . . . . . . . . . . 622 of graphs . . . . . . . . . . . . . . . . . . . . . . 25 of maps . . . . . . . . . . . . . . . . . . . . . . . 59 of vectors . . . . . . . . . . . . . . . . . . 91, 100 pH . . . . . . . . . . . . . . . . . . . . . . . . . . 549 temperature . . . . . . . . . . . . . . . . . . . 184 scattered reflection . . . . . . . . . . . . . . . . . 648 scatterplot . . . . . . . . . . . . . . . . . . . . . . . . . 24 scientific evidence . . . . . . . . . . . . . . . . . . . 35 scientific journal . . . . . . . . . . . . . . . . . . . . 44 scientific method . . . . . . . . . . . . . . . . . . . . 38 scientific notation . . . . . . . . . . . . . . . . . . 708 scientific theory . . . . . . . . . . . . . . . . . 34–38 sea breeze . . . . . . . . . . . . . . . . . . . . . . . . 253 sea level . . . . . . . . . . . . . . . . . . . . . . . . . . 61 sea-floor spreading . . . . . . . . . . . . . . . . . 480 seamount . . . . . . . . . . . . . . . . . . . . . . . . 576 seasons . . . . . . . . . . . . . . . . . . . . . . . . . . 671 secondary carnivore . . . . . . . . . . . . . . . . 367 sediment . . . . . . . . . . . . . . . . . . . . . 591, 598 sedimentary rock . . . . . . . . . . . 466, 598–601 seismic wave . . . . . . . . . . . . . . . . . . . . . 472 seismograph . . . . . . . . . . . . . . . . . . . . . . 503 seismologist . . . . . . . . . . . . . . . . . . . . . . 472 semiconductor . . . . . . . . . . . . . . . . 301, 398 series circuit . . . . . . . . . . . . . . . . . . 401–406 shark’s teeth . . . . . . . . . . . . . . . . . . . . . . 456 Shepard, Alan . . . . . . . . . . . . . . . . . . . . . 716 shield volcano . . . . . . . . . . . . . . . . . . . . . 514 short circuit . . . . . . . . . . . . . . . . . . . . . . 409 SI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7–9 SI prefixes . . . . . . . . . . . . . . . . . . . . . . 9, 13 significant digits . . . . . . . . . . . . . . . . . . . . 21 simple machine . . . . . . . . . . . . . . . . 149–154 single-displacement reaction . . . . . . . . . . 345 sinking . . . . . . . . . . . . . . . . . . . . . . . . . . 236 sliding friction . . . . . . . . . . . . . . . . . . . . 108 slope of a line . . . . . . . . . . . . . . . . . . . . . . . 83 of land . . . . . . . . . . . . . . . . . . . . . . . . 62 slumping . . . . . . . . . . . . . . . . . . . . . . . . 589 snow . . . . . . . . . . . . . . . . . . . . . . . . . . . 257 Society of Automotive Engineers (SAE) . . 233 soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . 583

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a star . . . . . . . . . . . . . . . . . . . . . . . . . 688 anatomy of . . . . . . . . . . . . . . . . . . . . 689 and the solar system . . . . . . . . . . . . . . 660 and the water cycle . . . . . . . . . . . . . . 563 as a source of energy . . . . . . . . . . . . . 158 eclipse . . . . . . . . . . . . . . . . . . . . . . . 670 effect on climate . . . . . . . . . . . . . . . . 261 energy of . . . . . . . . . . . . . . . . . . . . . . 692 energy source for ecosystems . . . . . . . 365 heating Earth’s oceans . . . . . . . . . . . . 572 life span of . . . . . . . . . . . . . . . . . . . . 699 sundial . . . . . . . . . . . . . . . . . . . . . . . . . . 667 sunspot . . . . . . . . . . . . . . . . . . . . . . . . . . 689 sunspot cycle . . . . . . . . . . . . . . . . . . . . . . 692 superconductor . . . . . . . . . . . . . . . . . . . . . 396 supergiant . . . . . . . . . . . . . . . . . . . . . . . . 697 supernova . . . . . . . . . . . . . . . . . . . . . . . . 701 superposition principle . . . . . . . . . . . . . . . 626 supersaturation . . . . . . . . . . . . . . . . . 539, 542 supersonic . . . . . . . . . . . . . . . . . . . . . . . . 623 surface area . . . . . . . . . . . . . . . . . . . 538, 587 surface ocean currents . . . . . . . . . . . . . . . . 573 surface runoff . . . . . . . . . . . . . . . . . . . . . 566 surface water . . . . . . . . . . . . . . . . . . . . . . 560 surface wave . . . . . . . . . . . . . . . . . . . . . . 503 suspension . . . . . . . . . . . . . . . . . . . . . . . . 537 S-wave . . . . . . . . . . . . . . . . . . . . . . . . . . 472 S-wave shadow zone . . . . . . . . . . . . . . . . 473 switch . . . . . . . . . . . . . . . . . . . . . . . . . . . 387 symmetry . . . . . . . . . . . . . . . . . . . . . . . . 433 synthesis reaction . . . . . . . . . . . . . . . . . . . 343 system . . . . . . . . . . . . . . . . . . . . . . . . 40, 337

T taiga . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259 tail . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 681 technology . . . . . . . . . . . . . . . . . . . . . 45, 148 tectonic plate . . . . . . . . . . . . . . 481, 501, 502 telescope . . . . . . . . . . . . . . . . . 660, 712–715 temperate rainforest . . . . . . . . . . . . . . . . . 259 temperature . . . . . . . . . . . . . . . 186, 538, 543

tensile strength . . . . . . . . . . . . . . . . . . . . 224 tension . . . . . . . . . . . . . . . . . . . . . . . . . . 102 terrestrial planets . . . . . . . . . . . . . . . 674, 730 theory . . . . . . . . . . . . . . . . . . . . . . . . 34–38 thermal . . . . . . . . . . . . . . . . . . . . . 210, 253 thermal conductor . . . . . . . . . . . . . . 207, 299 thermal energy . . . . . . . . . . . . . . . . 186, 200 thermal equilibrium . . . . . . . . . . . . . . . . . 206 thermal expansion . . . . . . . . . . . . . . . . . . 225 thermal insulator . . . . . . . . . . . . . . . . . . . 207 thermal radiation . . . . . . . . . . . . . . . . . . . 209 thermistor . . . . . . . . . . . . . . . . . . . . . . . . 187 thermohaline current . . . . . . . . . . . . . . . . 574 thermometer . . . . . . . . . . . . . . . . . . . . . . 187 thermosphere . . . . . . . . . . . . . . . . . . . . . 251 Thomson, J. J. . . . . . . . . . . . . . . . . . . . . . 279 thunder . . . . . . . . . . . . . . . . . . . . . . . . . 268 thunderstorm . . . . . . . . . . . . . . . . . . . . . 268 tide . . . . . . . . . . . . . . . . . . . . . . . . . . . . 672 time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 time zone . . . . . . . . . . . . . . . . . . . . . . . . . 57 Tombaugh, Clyde . . . . . . . . . . . . . . . . . . 680 tongue stone . . . . . . . . . . . . . . . . . . . . . . 456 topographic map . . . . . . . . . . . . . . . . . 61–64 tornado . . . . . . . . . . . . . . . . . . . . . . . . . 270 toxin . . . . . . . . . . . . . . . . . . . . . . . . . . . 367 trade wind . . . . . . . . . . . . . . . . . . . . . . . 255 transform fault boundary . . . . . . . . . 485, 489 transform plate boundary . . . . . . . . . . . . . 502 transition elements . . . . . . . . . . . . . . . . . 291 transition metals . . . . . . . . . . . . . . . . . . . 294 translucent . . . . . . . . . . . . . . . . . . . . . . . 646 transparent . . . . . . . . . . . . . . . . . . . . . . . 646 transpiration . . . . . . . . . . . . . . . . . . . . . . 564 transverse wave . . . . . . . . . . . . . . . . . . . 617 tree-ring dating . . . . . . . . . . . . . . . . . . . . 454 trial . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 Triton . . . . . . . . . . . . . . . . . . . . . . . . . . 680 tropical rainforest . . . . . . . . . . . . . . . . . . 259 troposphere . . . . . . . . . . . . . . 250, 256, 264 true north . . . . . . . . . . . . . . . . . . . . . . . . 422 tundra . . . . . . . . . . . . . . . . . . . . . . . . . . 259 Tyndall effect . . . . . . . . . . . . . . . . . . . . . 537

U unbalanced forces . . . . . . . . . . . . . . 127, 130 uncertainty principle . . . . . . . . . . . . . . . . 287 uniformitarianism . . . . . . . . . . . . . . . . . . 459 unit conversions . . . . . . . . . . . . . . . . . 17–20 definition of . . . . . . . . . . . . . . . . . . . . . 6 United States Geological Survey (USGS) 62, 64 universal solvent . . . . . . . . . . . . . . . . . . . 534 universe . . . . . . . . . . . . . . . . . . . . . 708, 727 unloading . . . . . . . . . . . . . . . . . . . . . . . . 585 unsaturated . . . . . . . . . . . . . . . . . . . . . . . 542 unsaturated fat . . . . . . . . . . . . . . . . . . . . . 326 updraft . . . . . . . . . . . . . . . . . . . . . . . . . . 268 uranium . . . . . . . . . . . . . . . . . . . . . 438, 453 Uranus . . . . . . . . . . . . . . . . . . . . . . . . . . 678

V vacuum . . . . . . . . . . . . . . . . . . . . . . . . . . 207 valence electron . . . . . . . . . . . . 311, 312, 316 variable . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 control . . . . . . . . . . . . . . . . . . . . . . . . 40 definition of . . . . . . . . . . . . . . . . . . . . 40 dependent . . . . . . . . . . . . . . . . . . . . . . 25 experimental . . . . . . . . . . . . . . . . . . . . 40 graphing relationship . . . . . . . . . . . . . . 27 independent . . . . . . . . . . . . . . . . . . . . 25 manipulated . . . . . . . . . . . . . . . . . . . . 25 position . . . . . . . . . . . . . . . . . . . . . . . 52 relationship between . . . . . . . . . . . . . . 82 responding . . . . . . . . . . . . . . . . . . . . . 25 variable resistor . . . . . . . . . . . . . . . . . . . . 399 vector force . . . . . . . . . . . . . . . . . . . . . . . . 100 position . . . . . . . . . . . . . . . . . . . . . . . 53 velocity . . . . . . . . . . . . . . . . . . . . 78, 91 velocity . . . . . . . . . . . . . . . . . . . . . . . . 78, 86 Venus . . . . . . . . . . . . . . . . . . . . . . . . . . . 677 verbal scale . . . . . . . . . . . . . . . . . . . . . . . . 59 Verne, Jules . . . . . . . . . . . . . . . . . . . . . . 477 viscosity . . . . . . . . . . . . . . . . . . . . . 232, 511 vision . . . . . . . . . . . . . . . . . . . . . . . . . . . 638

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W Walker, Arthur . . . . . . . . . . . . . . . . . . . . 715 waning . . . . . . . . . . . . . . . . . . . . . . . . . . 668 warm front . . . . . . . . . . . . . . . . . . . . . . . 264 water and solutions . . . . . . . . . . . . . . . . . . 530 and weathering . . . . . . . . . . . . . . . . . 586 density of . . . . . . . . . . . . . . . . . . . . . 216 dissociation of . . . . . . . . . . . . . . . . . 548 hydrogen bonds . . . . . . . . . . . . . . . . 532 in the atmosphere . . . . . . . . . . . . . . . 256 moving sediment . . . . . . . . . . . 591–596 oceans . . . . . . . . . . . . . . . . . . . 570–576 on Earth’s surface . . . . . . . . . . . 558–561 pH of . . . . . . . . . . . . . . . . . . . . . . . . 549 properties of . . . . . . . . . . . . . . . . . . . 533 structure of ice . . . . . . . . . . . . . . . . . 532 the universal solvent . . . . . . . . . . . . . 534 water cycle . . . . . . . . . . . 368, 558, 563–568 water molecule . . . . . . . . . . . . . . . . 530, 564 water table . . . . . . . . . . . . . . . . . . . . . . . 560 water vapor . . . . . . . . . . . . . . . . . . 257, 564 watershed . . . . . . . . . . . . . . . . . . . . . . . . 567 watt (W) . . . . . . . . . . . . . . . . . . . . . 170, 442

Watt, James . . . . . . . . . . . . . . . . . . . . . . . 170 wave definition of . . . . . . . . . . . . . . . . . . . 613 electromagnetic . . . . . . . . . . . . . . . . . 635 interactions of . . . . . . . . . . . . . . . . . . 616 interference . . . . . . . . . . . . . . . . . . . . 618 sound . . . . . . . . . . . . . . . . . . . . . . . . 620 speed of . . . . . . . . . . . . . . . . . . . . . . 614 transverse and longitudinal . . . . . . . . . 617 wave pulse . . . . . . . . . . . . . . . . . . . . . . . 617 wavelength . . . . . . . . . . . . . . . . . . . . . . . 613 waxing . . . . . . . . . . . . . . . . . . . . . . . . . . 668 weak force . . . . . . . . . . . . . . . . . . . . 98, 281 weather . . . . . . . . . . . . . . . . . . 253–257, 563 weather pattern . . . . . . . . . . . . . . . . . . . . 263 weathering . . . . . . . . . . . . . . . . . . . 561, 582 Wegener, Alfred . . . . . . . . . . . . . . . 478–480 weight . . . . . . . . . . . . . . . . . . . . . . . . . . 661 and buoyancy . . . . . . . . . . . . . . 234–236 calculating . . . . . . . . . . . . . . . . . . . . 104 vs. mass . . . . . . . . . . . . . . . . . . . . . . 103 white dwarf star . . . . . . . . . . . . . . . . 697, 700 white light . . . . . . . . . . . . . . . . . . . . . . . . 634 Wilson, Robert . . . . . . . . . . . . . . . . . . . . 728 wind . . . . . . . . . . . . . . . . . . . . . . . . 210, 253 wind energy . . . . . . . . . . . . . . . . . . . . . . 441 wind farm . . . . . . . . . . . . . . . . . . . . . . . . 441 work and energy . . . . . . . . . . . . . . . . . . . . 159 and gravity . . . . . . . . . . . . . . . . . . . . 152 and heat . . . . . . . . . . . . . . . . . . . . . . 201 calculating . . . . . . . . . . . . . . . . . . . . 152 input and output . . . . . . . . . . . . 148, 167

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volcanic island chains . . . . . . . . . . . . . . . 513 volcano and the water cycle . . . . . . . . . . . . . . 568 cinder cone . . . . . . . . . . . . . . . . . . . 516 composite . . . . . . . . . . . . . . . . 514, 515 locating . . . . . . . . . . . . . . . . . . . . . . 508 mid-ocean ridge . . . . . . . . . . . . . . . . 512 parts of . . . . . . . . . . . . . . . . . . . . . . 509 shape and type of eruption . . . . . . . . . .511 shield . . . . . . . . . . . . . . . . . . . . . . . 514 volt (V) . . . . . . . . . . . . . . . . . . . . . . . . . 390 voltage in parallel circuits . . . . . . . . . . . . . . . 408 in series circuits . . . . . . . . . . . . . . . . 404 measuring . . . . . . . . . . . . . . . . . . . . 390 voltage drop . . . . . . . . . . . . . . 404, 405, 406 voltmeter . . . . . . . . . . . . . . . . . . . . . . . . 390

X X-ray telescope . . . . . . . . . . . . . . . . . . . . 714 XY graph . . . . . . . . . . . . . . . . . . . . . . . . . 24

Y year . . . . . . . . . . . . . . . . . . . . . . . . . . . . 666

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