chapter 4: energy · chapter 4 chapter organizer 98b ... performance assessment in the science...

Explore Activity: Model how a lightbulb works, p. 99Before You Read, p. 99

Science Online, p. 102MiniLAB: Interpreting Data from aSlingshot, p. 103Math Skills Activity: CalculatingGravitational Potential Energy, p. 104Earth Science Integration, p. 104Activity: Bouncing Balls, p. 106

Visualizing EnergyTransformations, p. 110Earth Science Integration, p. 111MiniLAB: Transforming Energy Usinga Paper Clip, p. 112Science Online, p. 113Activity: Swing Energy, pp. 116–117Science and Society: The ImpossibleDream, pp. 118–119

Chapter Opener

Section 1 The Nature of Energy

3 sessions

2 blocks

1. Distinguish between kinetic and potential energy.2. Recognize different ways that energy can be

stored.

Section 2 Conservation of Energy

4 sessions

2 blocks

1. Describe how energy is conserved when changingfrom one form to another.

2. Apply the law of conservation of energy to familiarsituations.

See p. 37T for aKey to Standards.

National ContentStandards: UCP3,A2, B3 (5–8), B5,B6 (9–12), E2

National ContentStandards: UCP3,A2, B3 (5–8), B5,B6 (9–12), E2,F5 (5–8), F6 (9–12)

Texas

TEKS: 1, 1A, 2, 2A,2B, 2C, 2D, 3, 3A, 4,4B, 6, 6A, 6B

TEKS: 1, 1A, 2, 2A,2B, 2C, 2D, 3, 3A,3C, 3E, 4, 6, 6A, 6H,8, 8A, 8D

National State/Local

Section/Objectives Standards Activities/Features

98A CHAPTER 4 Energy

C H A P T E R E N E R G Y44

Section Focus TransparencyTeaching TransparencyInteractive CD-ROM/DVDGuided Reading Audio

Program

Section Focus TransparencyInteractive CD-ROM/DVDGuided Reading Audio

Program

Chapter Resources BookletFoldables Worksheet, p. 17Note-taking Worksheets,

pp. 31–32

Chapter Resources BookletTransparency Activity, p. 42MiniLAB, p. 3Enrichment, p. 29Reinforcement, p. 27Directed Reading, p. 20Activity Worksheet, pp. 5–6Lab Activity, pp. 9–12Transparency Activity, pp. 45–46

Reading and Writing SkillActivities, p. 35

Chapter Resources BookletTransparency Activity, p. 43MiniLAB, p. 4Enrichment, p. 30Reinforcement, p. 28Directed Reading, pp. 21, 22 Activity Worksheet, pp. 7–8Lab Activity, pp. 13–15

Home and CommunityInvolvement, p. 36

Cultural Diversity, p. 53

PortfolioCurriculum Connection, p. 102PerformanceMiniLAB, p. 103Skill Builder Activities, p. 105ContentSection Assessment, p. 105

PortfolioVisula Learning, p. 114PerformanceMiniLAB, p. 112Skill Builder Activities, p. 115ContentSection Assessment, p. 115

Explore Activity: 2 D-cellbatteries, 2 non-coatedpaper clips, tape, metaltongs, steel wool

MiniLAB: rubber band, nickelActivity: tennis ball, rubberball, balance, meterstick,masking tape, cardboard box

MiniLAB: paper clipActivity: ring stand, test-tube clamp, support-rodclamp (right angle), 30-cmsupport rod, 2-hole, mediumrubber stopper, 1m string,metersticks, graph paper

CHAPTER 4 Chapter Organizer 98B

Activity Materials Reproducible Resources Section Assessment Technology

C H A P T E R O R G A N I Z E R

Need materials? Contact Science Kit at 1-800-828-7777 or www.sciencekit.com on the Internet.

Chapter Resources BookletChapter Review, pp. 35–36Chapter Tests, pp. 37–40

Standardized Test Practice by The Princeton Review, pp. 20–23

MindJogger VideoquizCD-ROM Explorations and QuizzesVocabulary Puzzle MakersExamView Pro Test BankInteractive Lesson PlannerInteractive Teacher’s Edition

Performance Assessment in the Science Classroom (PASC)

End of Chapter Assessment

Blackline Masters Technology Professional Series

http://www.sciencekit.com


Hands-on Activities

Laboratory ActivitiesActivity Worksheets

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Energy 5

Name Date Class

Lab PreviewDirections: Answer these question sbefore your activity begins.

1. Why is it important to drop both balls from the same height?

2. How is the cardboard box used in this activity?

What happens when you drop a ball on to a hard, flat surface? It starts withpotential energy. It bounces up and down until it finally comes to a rest.Where did the energy go?

What You’ll InvestigateHow do balls differ in their bouncing behavior?

Materialstennis ballrubber ballbalancemeterstickcardboard box*shoe box

Goals■ Identify the energy forms observed in a

bouncing ball.■ Infer why the ball stops bouncing.

Procedure 1. Determine the mass of the two balls.2. Have a friend drop one ball from 1 m.

Measure how high the ball bounced.Repeat this two more times so that you cancalculate an average bounce height. Recordyour values on the data table.

3. Repeat step 2 for the other ball.4. Predict whether the balls would bounce

higher or lower if they were dropped ontothe cardboard box. Design an experimentto measure how high the balls wouldbounce off the surface of a cardboard box.

Bouncing Balls

Hand

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Safety Precautions

Data and Observations

4Chapter

Type of ball

Height Ball Bounces off Floor (cm)

Trial 1 Trial 3Trial 2

Rubber ball

Tennis ball

L2

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Energy 9

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The Energy of a Pendulum

When you ride on a playground swing, you have energy. Any moving object has kinetic energy,which is energy due to motion. Kinetic energy depends on the velocity and the mass of the mov-ing object. Increasing the mass on the swing by holding something in your lap or your velocity byswinging faster increases your kinetic energy.

An object at rest may also have energy. When an object is held in a position where it would moveif released, it has energy of position called potential energy. When you begin to swing, a friend maypull your swing back and up. See Figure 1. Before your friend releases the swing, you are at rest andhave potential energy. In this position, you are not moving, so you have no kinetic energy. But youcould move if released, so you have potential energy. As long as the swing is in a position where itcan move, you have potential energy. After your friend releases the swing, you have both potentialenergy and kinetic energy. See figure 2.

LaboratoryActivity11

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If you were to sit in the swing and allow it to hang straight down from its supports, you wouldnot move. You are not held in a position where you can move. With reference only to the swing,you have no potential energy and no kinetic energy. See figure 3.

A swing is one example of a pendulum. Many clocks have a swinging mass, or pendulum, tomove the hands. A pendulum can have both potential energy and kinetic energy, depending on itsposition. How much energy depends also on its mass and velocity. A pendulum hanging straightdown, at rest, has neither potential energy nor kinetic energy.

How do potential energy and kinetic energy change as a pendulum swings? Write your hypoth-esis in the Data and Observations section.

StrategyYou will construct a pendulum.You will explain how a pendulum behaves.You will describe the potential energy and kinetic energy of a pendulum.

Materials ring sinkers, different sizes (2)strings, 20 cm and 30 cm long (2) metric rulerring stand watch with second hand

L2

Hands-on Activities

TransparenciesSection Focus

Energy

Here’s a tough question—what do these three pictures have in common?

They’ve got potential.Section FocusTransparency11

1. What happens as the tennis ball returns to its original shape?

2. What happens between the top and the bottom of a waterfall?

3. How do moose use moss?

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4Chapter

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All living things have something in common. If they don’t getenergy, they die and decay. Plants convert energy from the Sun into aform of chemical energy other living things can use.

Power PlantsSection FocusTransparency22

1. How do people obtain the energy plants store?

2. Name some other ways energy is stored.

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4Chapter

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Transparencies

TeachingAssessment

Energy

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Directions: Carefully review the table and answer the following questions.

Energy

1. What principle is probably being tested in the above experiment?A velocityB nuclear fissionC energy conversionD gravitational potential energy

2. Students conducted an experiment to find which form of exerciseburned the most calories. They collected data from the experimentinto the table above. The experiment could be improved by ___.F having the same person do each activity for the same amount

of timeG recording the time of day each activity was performedH recording the air temperature during each activity

J calculating Person 2’s rate of speed

3. Which person burned more calories than consumed?A Person 1 B Person 2C Person 3D Person 4

AssessmentTransparency 4

Chapter

Person ActivityCaloriesconsumed

Length ofactivity

Caloriesburned

Watching TV

Walking

Running

Playingtennis

400

200

1,000

450

150

180

350

460

2 h

1 h

1/2 h

1 h

1

2

3

4

L2 Energy

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Kinetic EnergyTeachingTransparency11 4

Chapter

100

km/h

100

km/h

80 k

m/h

L2

The following designations will help youdecide which activities are appropriatefor your students.

Level 1 activities should be appropriate for students with learning difficulties.

Level 2 activities should be withinthe ability range of all students.

Level 3 activities are designed forabove-average students.

ELL activities should be within the ability range of EnglishLanguage Learners.

Cooperative Learning activities are designed for small group work.

Multiple Learning Styles logos are used throughout to indicate strategies that address differentlearning styles.

These strategies represent studentproducts that can be placed into a best-work portfolio.

P

LS

COOP LEARN

ELL

L3

L2

L1

Key to Teaching Strategies

This is a representation of keyblackline masters available in theTeacher Classroom Resources. SeeResource Manager boxes within thechapter for additional information.

98C CHAPTER 4 Energy

R E S O U R C E M A N A G E R

Spanish Directed Reading

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Energy 23

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SinopsisEnergía

Instrucciones: Completa el mapa conceptual usando los términos de la siguiente lista.

movimiento conservación energía elástico

energía potencial velocidad destruir química

Ejemplosincluyen

1.

2.

3.

almacenada en un

La energía

cuerpo

es

potencialgravitacional.

posición y elmovimiento

energía mecánica (EM)

energía cinética +energía potential.

es

energía cinética.

una rueda quegira.

un corredorque corre.

la ley de

7. ____________de la energía,

puede crearni

8. ____________.

6. ____________cinética tiene.

cambiar de forma.

la energía puede

mayor

debido a la

e incluye

en

5. ____________potencial.

es

EM equivale a la

De acuerdo con

4. ____________potencial.

Entre más grandees el(la)

la energía no se

Lectura Dirigida para la

Maestría del Contenido

L1

Enrichment

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Energy 29

Transferring Kinetic andPotential Energy

Materialswashers or bolts exactly the same size (2)ring stands (2)strong thread

In this activity you will build twin pendulums. You will use the twin pendulums to observe howkinetic and potential energy can be transferred in a system.

Enrichment11

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Procedure1. Try to duplicate the apparatus shown in the

figure. To build twin pendulums, place thetwo ring stands about 30 cm apart. Tie apiece of thread about one-fourth of the waydown from the top of one ring stand. Attachthe other end of the thread an equal dis-tance from the top of the other ring stand.There should not be any slack in the thread.

2. Cut two 15-cm lengths of thread. Attach awasher to each thread. Tie the other ends ofthese threads to the horizontal thread,about 5cm apart. The washers must hang atexactly the same height.

3. Pull one of the washers upward and back-ward so it is as high as the horizontalstring. Let go of the washer and observewhat happens.

Conclude and Apply1. Describe what happened to the two pendulums after you let go of the washer?

2. Explain why the second pendulum was able to move without your touching it.

3. Why did the pendulums eventually stop swinging?

Thread

Ringstand

Let go ofone washerWashers

4Chapter

L3

Meeting Different Ability LevelsDirected ReadingReinforcementContent Outline

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Energy 31

Energy

Section 1 The Nature of Energy

A. Energy is the ability to cause ___________.

1. Kinetic energy—Energy in the form of ____________

a. The amount of kinetic energy an object has depends on its _________ and its

___________.

b. Kinetic energy = 12 ________ ✕ velocity2

c. __________—The SI unit used to measure energy

2. Potential energy—Energy stored in a ______________ object, giving it the potential to

cause change

3. Elastic potential energy—Energy stored by things that ___________________

4. Chemical potential energy—Energy stored in __________________ between atoms

5. Gravitational potential energy—Energy stored by things that are gravitationally

_________________________

a. The amount of GPE an object has depends on its ___________ , the acceleration

due to _______ , and its _____________________.

b. GPE = mass in kilograms ✕ 9.8 m/s2 ✕ height in meters

Section 2 Conservation of Energy

A. Energy conversions—energy changing from one _________ to another

1. Fuels store energy in the form of _______________________ energy.

2. ______________ energy—the total amount of potential and kinetic energy in a system

B. Law of Conservation of Energy—Energy may change from one form to another, but the

________________ of energy never changes.

1. Example—As a swing moves back and forth, its energy continually converts from

____________ to _____________ and back.

2. If the energy of the swing decreases, then the energy of some other object must

____________ by an equal amount.

3. Friction converts some of the mechanical energy into ___________ energy.

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Note-takingWorksheet

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Energy 27

Directions: Place a plus (+) to the left of the statements that agree with what was said in the textbook. Place aminus(-) to the left of the statements that do not agree with the textbook. Then circle the word or words thatneed to be changed, and write down what they need to be changed t so that the statement is true.

1. Anything that causes change must have energy.

2. Kinetic energy is energy in the form of motion.

3. The joule is the SI unit of energy.

4. According to the law of conservation of energy, energy can be created or destroyed.

5. Energy may change from one form to another, but the total amount of energy neverchanges.

6. Mechanical energy is the total amount of potential and kinetic energy in a system.

7. A rock at the edge of a 200-m high cliff has more potential energy than an equal-sized rock at the edge of a 600-m high cliff.

8. The energy stored in foods, fuels, and dry cells is chemical potential energy.

9. One food Calorie is equivalent to about 2,800 joules.

Directions: Fill in the missing information in the chart below which compares kinetic energy and gravitational potential energy.

The Nature of Energy

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Reinforcement11

Characteristic Kinetic energy Gravitational potential energy

Definition

Units of measure

Quantities in calculation

10.

12.

14.

11.

13.

15.

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Energy 19

OverviewEnergy

Directions: Complete the concept map using the terms in the list below.

motion conservation energy elastic

potential energy velocity destroyed chemical

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Examplesinclude

1.

2.

3.

stored in an

Energy

object

is

gravitational potential.

position and motion

mechanical energy (ME)

kinetic energy +potential energy.

is

kinetic energy.

a spinningwheel.

a sprintingrunner.

the law of

7. ____________of energy,

neither becreated nor

8. ____________.

kinetic

6. ____________it has.

change forms.

energy can

the more

due to

and includes

in

5. ____________potential.

is

ME equals

According to

4. ____________potential.

The greateran object’s

energy can

4ChapterDirected Reading for

Content Mastery

Meeting Different Ability Levels

L2 L2 L1

Chapter Tests

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Energy 37

Chapter Test

Energy

I. Testing ConceptsDirections: Determine whether the italicized term makes each of the following statements true or false. If thestatement is true, write the word “true” in the blank. If the statement is false, write in the blank the term thatmakes the statement true.

1. Energy in the form of motion is potential energy.

2. The greater mass a moving object has, the more kinetic energy it has.

3. A rock at the edge of a cliff has kinetic energy because of its position.

4. Friction causes some mechanical energy to change to thermal energy.

5. Energy that is stored is kinetic energy.

6. Mass is measured in joules.

7. Doubling an object’s velocity will double its kinetic energy.

8. Chemical potential energy is energy stored in chemical bonds.

9. Thermal energy is energy stored by things that stretch or compress.

10. A book and a feather sitting next to each other on a shelf have different potential energies.

11. Two copies of the same book are in a book case. One book is twice ashigh as the other. They have the same potential energy.

12. A toaster uses chemical energy to make toast.

13. Mechanical energy is the total amount of potential and kineticenergy in a system.

14. When a plant falls from a window its thermal energy is transformedinto kinetic energy.

15. The law of conservation of energy states that altough energy canchange forms it can never be created or destroyed.

Directions: In the blank at left, write the letter of the term or phrase that correctly answers each question orbest completes each statement.

16. Which of the following is not used to calculate kinetic energy?a. mass c. heightb. speed d. velocity

17. Which of the following is not used to calculate potential energy?a. mass c. heightb. gravitational acceleration d. velocity

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Chapter ReviewTest Practice Workbook

1 The objects in Group A are different from the objects in Group B because only the objects in Group A —

A are electrical appliances

B have chemical potential energy*

C convert electrical energy to mechanical energy

D are fossil fuels

Group A Group B

20 Energy and Motion

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Name: Date: Class:Chapter Test Chapter 4 Energy

DIRECTIONS

Read each question and choose the best answer. Then fill in the correct answer on your answerdocument.

2 In the diagram above, a roller coaster carstarts from rest at point A and moves along thetrack. At which point does the roller coastercar have the greatest kinetic energy?

F A

G B*

H C

J D

3 Air resistance is a form of friction that makesa moving object slow down. Which of thesedrawings shows a skier whose shape wouldallow him or her to move through the air withthe LEAST resistance?

A

B

C

D

20m 6m 10m 15m

A

B

C

D

L2

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Energy 35

Chapter Review

Energy

Part A. Vocabulary ReviewDirections: Match the description in the first column with the term in the second column by writing the correctletter in the space provided.

1. total amount of kinetic and potential energy in a system

2. the ability to cause change

3. stored energy due to position

4. energy in the form of motion

5. Energy cannot be created or destroyed

6. unit used to measure energy in food

7. energy stored in chemical bonds

8. energy stored by things that stretch or compress

9. energy stored by things that are above earth

10. SI unit of energy

11. causes some mechanical energy to change to thermal energy

Asse

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a. energy

b. friction

c. kinetic energy

d. law of conservation ofenergy

e. gravitational potentialenergy

f. mechanical energy

g. potential energy

h. Calorie

i. elastic potentialenergy

j. chemical potentialenergy

k. joule

Part B. Concept ReviewDirections: Complete the following sentences using the correct terms.

1. The amount of kinetic energy a moving object has depends onits mass and its ______.

2. The potential energy of an object depends on its ______.

3 The energy stored in foods, fuels, and batteries is ______ potential energy.

4. The law of _________________________________ states thatenergy cannot be created or destroyed under ordinary conditions.

5. Nutritionists use the ______ to measure how much energy weget from foods.

6. The conversion of potential energy to kinetic energy followsthe ______.

7. You convert kinetic energy into thermal energy when you rubtwo sticks together because of ______.

4Chapter

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AssessmentAssessment

CHAPTER 4 Resource Manager 98D

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98E CHAPTER 4 Energy

Hooke’s law describes the relationshipbetween stress and strain in a spring. Theamount of force is directly proportional to thestretching of the spring. The amount of poten-tial energy depends on the amount of stretch-ing and the elasticity of the spring.

Without friction, the work done to lift anobject is equal to the object’s gain in potentialenergy. Consider the two equations: Work �Force � Distance and Potential Energy � mass� gravity � height. The force needed to lift anobject is equivalent to the object’s mass �gravity. The distance traveled is the height. Soin this case, these two equations are equivalent.

If you took a one-kilogram mass to a dis-tance from Earth that corresponds to the dis-tance to the Moon, the mass would have apotential energy to Earth of 62,000,000 joulesor 62 mega-joules. This is small compared tothe one-kilogram mass’ potential energy to theSun, which would be 190,000 mega-joules.

The Nature of EnergyWhat is energy?Energy is not matter. Electro-magnetic energy can exist inde-

pendent of matter. Other forms of energy, suchas chemical and kinetic energy, can only existwith matter.

Kinetic EnergyThe equation for kinetic energy states that E �1/2mv2. This means that as an object’s velocitydoubles its kinetic energy quadruples.

Kinetic comes from a Greek word for move-ment. The word cinema—used to describemoving pictures or movies—shares the sameroot word.

Potential EnergyPotential energy isenergy due to anobject’s position or con-dition. A rock on a cliffhas potential energy dueto its position, while theenergy stored in a starchmolecule is due to thecondition of the bondsbetween the atoms in thatmolecule.

11S E C T I O N

Mitochondria are organelles thatconvert chemical energy into formsusable by cells. For this reason, theyare called the powerhouses of thecell. Mitochondria have their ownDNA, separate from the DNA in the nucleus.The mitochondria we have come from only our mothers, not our fathers.

H E L P I N G Y O U P R E PA R E

CHAPTER 4 Helping You Prepare 98F

Conservation of EnergyChanging Forms of EnergyIn our common experiences onEarth, energy is neither created

nor destroyed, but is often transformed fromone form into another. People use these energytransformations to do work. In most energytransformations, heat is produced.

Energy is not recycled in ecosystems likematter is recycled. Much of the energy thatflows through ecosystems is lost to heat. Asenergy flows from organism to organism, moreand more is lost as heat. This flow of energycan be visually represented as food chains. TheSun supplies new energy to plants, which startalmost all food chains.

Conversions Between Kinetic and Potential EnergyAs an object falls, its gravitational potentialenergy is converted into kinetic energy. There-fore, if you know the falling object’s initialpotential energy, you can calculate the velocityit attains just before it hits the ground using theequation PE � mgh. A 0.06 kg tennis balldropped from a height of 2.9 m starts with 1.7 Jof energy. Solving the kinetic energy equationfor v gives 7.54 m/s.

The joule is the SI unit of energy and work.It is in the units kg�m2/s2. In work calculations ajoule is sometimes called a newton-meter. Sincea newton is composed of the units kg�m/s2,multiplying newtons by meters, results inkg�m2/s2, or joules.

The Law of Conservation of EnergyThe law of conservation of energy works formost of our calculations, but Einstein suggestedthat mass could be converted to energy andenergy into mass. Einstein’s famous equation,E�mc2 shows the relationship between massand energy and explains the incredible powerunleashed by atomic bombs. So the law of con-servation of energy should more accurately becalled the law of conservation of energy andmass.

For additional content background on thistopic, go to the Glencoe Science Web siteat science.glencoe.com.

22S E C T I O N

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C H A P T E R 44Energy

Chapter Vocabularykinetic energy, p. 102joule, p. 102potential energy, p. 103elastic potential energy, p. 103 chemical potential energy,

p. 103gravitational potential energy,

p. 104mechanical energy, p. 108law of conservation of energy,

p. 111

What do you think?Science Journal The photograph showsthe filaments in a lightbulb. Electricalenergy has been converted into light andheat.

98

Snowboarding down the side of a mountain is an exhilaratingexperience. With little effort,

you can easily reach speeds well over50 km/h using nothing other than asnowboard, the slope, and a lot ofsnow. How do snowboarders achievesuch high speeds? What supplies theenergy to move them so fast? Theanswers to these questions can befound by studying energy and energy conservation.

What do you think? Science Journal Look at the picturebelow with a classmate. Discuss whatyou think this might be or what ishappening. Here’s a hint: It’s usedevery day and allows people to workand play at any hour. Write youranswer or best guess in your Science Journal.

Energy44

98 CHAPTER 4 Energy

Energy This chapter focuses ondifferent forms of energy andenergy conversions. The law ofconservation of energy isexplained and applied to varioussystems.

6H analyze the effects of heating and coolingprocesses in systems such as weather, living, andmechanical;8A distinguish between physical and chemicalchanges in matter such as oxidation, digestion,changes in states, and stages in the rock cycle; and8D describe types of nuclear reactions such as fis-sion and fusion and their roles in applications suchas medicine and energy production.

Scientific Processes1A, 2A, 2B, 2C, 2D, 3A, 3C, 3ESee the correlation charts starting on page 5T for a complete correla-tion of chapter content to TEKS and to TAKS objectives.

Meeting the TEKSThis chapter covers the following TEKS:

Science ConceptsThe student is expected to4B investigate and describeapplications of Newton’slaws such as in vehiclerestraints, sports activities,geological processes, andsatellite orbits; 6A describe the law of con-servation of energy;6B investigate and demon-strate the movement of heatthrough solids, liquids, andgases by convection, conduc-tion, and radiation;

EXPLOREACTIVITY

Purpose Use the Explore Activ-ity to introduce students to theconversion of electricity to lightand heat.

KinestheticMaterials 2 D-cell batteries, 2 non-coated paper clips, tape,metal tongs, steel woolTeaching Strategy Inform stu-dents that the steel wool canbecome quite hot.

ObserveThe steel wool will give off light and

heat.

LSCOOP LEARNL1

99

One of the most useful inventions of the nineteenthcentury was the electric lightbulb. Being able to

light up the dark allows for extended work and recre-ation. A lightbulb uses electricity to produce light, butheat also is produced. To observe the conversion of

electricity to light and heat, do the following activity.

Model how a lightbulb works1. Obtain two D-cell batteries, two non-

coated paper clips, tape, metal tongs andsome steel wool. Separate the steel woolinto thin strands and straighten the paperclips.

2. Tape the batteries together and then tapeone end of each paper clip to the batteryterminals as shown in the photograph.

3. While holding the strands of steel wool with the tongs, briefly completethe circuit by placing the steel wool in contact with both paper clip ends.

WARNING: Steel wool can become hot—connect to battery only for a

brief time.

ObserveDescribe in your Science Journal what you saw. Touch the steel wool. Whatchanges are you observing?

EXPLOREACTIVITY

Making a Know-Want-Learn Study Fold Make the following Fold-able to help identify what you already know and what you want toknow about energy.

1. Place a sheet of paper in front of you so the long side isat the top. Fold the paper in half from top to bottom.

2. Fold both sides in to divide the paper into thirds. Unfoldthe paper so three sections show.

3. Through the top thickness of paper, cut along each ofthe fold lines to the top fold, forming three tabs. Labelthe tabs Know, Want, and Learned, as shown.

4. Before you read the chapter, write what you know about energy under the left tab andwhat you want to know under the middle tab.

5. As you read the chapter, write what you learn about energy under the right tab.

FOLDABLESReading & StudySkills

FOLDABLESReading &Study Skills

CHAPTER 4 Energy 99

Dinah Zike Study FoldPurpose This assignment pro-

vides students with an opportunity to review whatthey know about energy and instructs them to listwhat they would like to know about energy.Theirresults can be used as an assessment tool at the endof the chapter to determine what they have learned.

For additional help, see Foldables Worksheet,p.17 in Chapter Resources Booklet, or go to theGlencoe Science Web site at science.glencoe.com.See After You Read in the Study Guide at the end ofthis chapter.



Before You ReadBefore You Read

Content Have students investi-gate how a light bulb works andwrite a paragraph comparing itwith the model they made inthis activity. Use PerformanceAssessment in the ScienceClassroom, p. 157. P

Texas Science Correlations

Correlation to TEKSPage 98: 4Page 99: 1, 1A, 2, 2A, 2C, 2D, 6, 6B


Tie to Prior KnowledgeAsk students to describe how

the word energy is commonlyused. They might mention fuelenergy or energy from the Sun.Explain that in this section theywill learn the scientific defini-tion of energy.

S E C T I O N

11The Nature of Energy

Energy

Here’s a tough question—what do these three pictures have in common?

They’ve got potential.Section FocusTransparency11

1. What happens as the tennis ball returns to its original shape?

2. What happens between the top and the bottom of a waterfall?

3. How do moose use moss?

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4Chapter

100 CHAPTER 4 Energy

The Nature of Energy S E C T I O N

What is energy? Wherever you are sitting as you read this, changes are taking

place—lightbulbs are heating the air around them, the windmight be rustling leaves, or sunlight might be glaring off anearby window. Even you are changing as you breathe, blink, orshift position in your seat.

Every change that occurs—large or small—involves energy.Imagine a baseball flying through the air. It hits a window, caus-ing the glass to break as shown in Figure 1. The windowchanged from a solid sheet of glass to a number of broken pieces.The moving baseball caused this change—a moving baseball hasenergy. Even when you comb your hair or walk from class toclass, energy is involved.

Change Requires Energy When something is able tochange its environment or itself, it has energy. Energy is the abil-ity to cause change. The moving baseball had energy. It certainlycaused the window to change. Anything that causes change musthave energy. You use energy to arrange your hair to look the wayyou want it to. You also use energy when you walk down thehalls of your school between classes or eat your lunch. You evenneed energy to yawn, open a book, and write with a pen.

� Distinguish between kinetic andpotential energy.

� Recognize different ways thatenergy can be stored.

Vocabularykinetic energyjoulepotential energyelastic potential energychemical potential energygravitational potential energy

Understanding energy helps youunderstand how your environment is changing.

Figure 1Each photo showschanges occurring.Describe the changes

that are occurring.

PORTFOLIO

Curriculum Connection, p. 102

PERFORMANCE ASSESSMENT

MiniLAB, p. 103Math Skills Activity, p. 104Skill-Builder Activities, 105See p. 122 for more options.

CONTENT ASSESSMENT

Section, p. 105Challenge, p. 105Chapter, pp. 122–123

Section Planner


Bellringer TransparencyDisplay the Section FocusTransparency for Section 1.Use the accompanying Trans-parency Activity Master.ELL

L2

Different Forms of EnergyTurn on an electric light, and adark room becomes bright. Turnon your CD player, and soundcomes through your headphones.In both situations, energy moves from one place to another.These changes seem to differ from each other and differ from abaseball shattering a window. This is because energy has severaldifferent forms, such as electrical, chemical, and thermal.

Figure 2 shows some examples of everyday situations inwhich you might notice energy. Is the chemical energy stored infood the same as the energy that comes from the Sun or theenergy stored in gasoline? Thermal energy from the Sun travelsa vast distance through space to Earth, warming the planet andproviding energy that enables green plants to grow. When youmake toast in the morning, you are using electrical energy. Inshort, energy plays a role in every activity that you do.

An Energy Analogy Money can be used in an analogy tohelp you understand energy. If you have $100, you could store itin a variety of forms—cash in your wallet, a bank account, trav-elers’ checks, or gold or silver coins. You could transfer thatmoney to different forms. You could deposit your cash into abank account or trade the cash for gold. Regardless of its form,money is money. The same is true for energy. Energy from theSun that warms you and energy from the food that you eat areonly different forms of the same thing.

How is energy like money?

SECTION 1 The Nature of Energy 101

Figure 2Energy can be stored in fuels,or it can travel through theenvironment. Which objects

are storing energy? Where is

movement of energy occurring?

Section 1 The Nature of Energy 101

What is energy?

Caption Answers• Figure 1 The window breaks, hair

is smoothed, and students changelocation.

• Figure 2 Energy is stored in thegasoline and in the food. Energy ismoving from the Sun to Earth.

DiscussionName some objects that

store energy and some exam-ples of energy in motion. Possi-ble answers: stored—springs, muscles inour bodies; motion—bouncing ball,spinning top, baseball flying through theair Linguistic

ExtensionStudents often have difficulty

understanding that sound is aform of energy. Have interestedstudents research this topic andpresent their findings in oralreports to the class.

LinguisticLSL3

LSL1

Different Forms of Energy Have studentsmake a list in their Science Journals of the dif-ferent types of energy mentioned in the text.Have them list several examples of how they useeach form of energy every day.

LinguisticLSL2

Answer When money is transferredfrom one person or place to another itcan change form but it remains money.When energy is transferred, it canchange form but it still remains energy.

Reading Check


Correlation to TEKS0: 6Page 101: 6

Chapter Resources Booklet

Transparency Activity, p. 42Note-taking Worksheets, pp. 31–32

Resource Manager

Kinetic EnergyUsually, when you think of energy, you think of action—or

some sort of motion taking place. Kinetic energy is energy inthe form of motion. A spinning bicycle wheel, a sprinting run-ner, and a football passing through the goalposts all have kineticenergy, but the amounts depend on two quantities—the mass ofthe moving object and its velocity.

The more mass a moving object has, the more kinetic energyit has. Similarly, the greater an object’s velocity is, the morekinetic energy it has. Figure 3 shows a truck and a motorcyclethat are moving at 100 km/h. Which vehicle has more kineticenergy? Although they have the same velocity, the truck hasmore kinetic energy because it has a greater mass than themotorcycle. Figure 3 also shows two motorcycles—one movingat 100 km/h and one moving at 80 km/h. Which motorcycle hasmore kinetic energy? Assuming that the motorcycles have thesame mass, the one moving at 100 km/h has greater kineticenergy than the one moving at 80 km/h.

Calculating Kinetic Energy The kinetic energy of anobject can be calculated using the following relationship.

kinetic energy � �12

� mass � velocity 2

KE (J) � �12

� m (kg) � v 2 (m2/s2)

The joule (JEWL) is the SI unit of energy. It is named after the nineteenth-century British scientist James PrescottJoule. To calculate kinetic energy in joules (J), mass is measuredin kilograms, and velocity is measured in meters per second.

Because velocity is squared in the equation for kinetic energy,increasing the velocity of an object can produce a large change in its kinetic energy. Without changing the mass of an object,doubling its velocity will quadruple its kinetic energy.


Collect Data Visit the Glencoe Science Web site atscience.glencoe.com for more information aboutthe kinetic energy of variousanimals. Communicate toyour class what you learn.

Figure 3The kinetic energy of each vehicleis different because kineticenergy depends on an object’smass and its velocity.

100 km/h

100 km/h80 km/h

Kinetic Energy

Use Science WordsWord Origin Have students lookup the words kinetic and potentialin the dictionary. Kinetic comes fromthe Greek root kinein (to move) andpotential from the Latin root potere (tobe powerful). Ask a volunteer tostate how the words kinetic andpotential reflect the meanings oftheir roots. Possible answer: Kineticenergy is energy of movement. Potentialenergy is stored energy due to position,almost like a powerful force waiting tobe unleashed. Linguistic

Quick DemoShow students two balls, one

heavy and one light. Roll theballs across a table at about thesame speed. Which ball hasgreater kinetic energy? Sincethe velocity of both balls is the same, theball with greater mass has greaterkinetic energy. Next show studentstwo balls with the same mass.Roll the balls across a table, butroll one ball faster than theother. Which ball has greaterkinetic energy? the bal l withgreater speed

Logical-Mathematical

Use an AnalogySuggest to students that

potential energy is analogous tomoney in a savings account. Themoney is not in use now, but it’sready for you to use whenneeded.

LSL1

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Geography On May 18, 1980, Mount St. Helensin the state of Washington erupted in a devas-tating volcanic explosion. The tremendousenergy of the eruption hurled hot ash and rockmore than 16 kilometers. Have students doresearch to discover other geologic events inhistory that have involved large amounts of

energy. Have each student make a table listingthe examples they find and where each eventoccurred. Possible events: earthquakes in 1964 in Alaska,in 1991 in southern California, in 1995 in Kobe, Japan, and in2001 in India; and eruptions of the volcanoes Krakatau in1883 and Mount Vesuvius in 79 A.D. Visual-SpatialP

LSL2

Internet Addresses

Explore the Glencoe Science Web siteat science.glencoe.com to find outmore about topics in this section.



Interpreting Data froma SlingshotProcedure1. Using two fingers, carefully

stretch a rubber band on atable until it has no slack.

2. Place a nickel on the table,slightly touching the mid-point of the rubber band.

3. Push the nickel back 0.5 cmand release. Measure thedistance the nickel travels.

4. Repeat step 3, each timepushing the nickel back anadditional 0.5 cm.

Analysis1. How did the takeoff

speed of the nickel seemto change relative to thedistance that you stretchedthe rubber band?

2. What does this implyabout the kinetic energyof the nickel?

Oxygen Carbon dioxide and waterNatural gas

�

Figure 4As natural gas burns, it combines with oxygen to form carbon dioxide andwater. In this chemical reaction, chemical potential energy is released.


Potential EnergyEnergy doesn’t have to involve motion. Even motionless

objects can have energy. This energy is stored in the object.Therefore, the object has potential to cause change. A hangingapple in a tree has stored energy. When the apple falls to theground, a change occurs. Because the apple has the ability tocause change, it has energy. The hanging apple has energybecause of its position above Earth’s surface. Stored energy dueto position is called potential energy. If the apple stays in thetree, it will keep the stored energy due to its height above theground. If it falls, that stored energy of position is converted toenergy of motion.

Elastic Potential Energy Energy can be stored in otherways, too. If you stretch a rubber band and let it go, it sailsacross the room. As it flies through the air, it has kinetic energydue to its motion. Where did this kinetic energy come from?Just as the apple hanging in the tree had potential energy, thestretched rubber band had energy stored as elastic potentialenergy. Elastic potential energy is energy stored by somethingthat can stretch or compress, such as a rubber band or spring.

Chemical Potential Energy The cereal you eat for break-fast and the sandwich you eat at lunch also contain storedenergy. Gasoline stores energy in the same way as food storesenergy—in the chemical bonds between atoms. Energy stored inchemical bonds is chemical potential energy. Figure 4 shows amolecule of natural gas. Energy is stored in the bonds that holdthe carbon and hydrogen atoms together and is released whenthe gas is burned.

How is elastic potential energy different fromchemical potential energy?


Purpose Students observe therelationship between the elas-tic potential energy andkinetic energy of an object.

KinestheticMaterials nickel, rubber band,meterstickTeaching Strategy Have stu-dents work in pairs and take turns making the measurements.Troubleshooting Be sure stu-dents don’t pull the rubberband back too far. The nickelcan quickly travel a long distance.Analysis1. The farther you stretch the band,

the faster the nickel takes off.2. The greater the speed of the

nickel, the greater its kineticenergy.

LSCOOP LEARNL1

Process Have students predicthow their results would differon a rough surface. Have themtest their hypotheses by repeat-ing the activity on sandpaper.Use Performance Assess-ment in the Science Class-room, p. 93.

Answer Elastic potential energy isenergy stored by things that stretch orcompress. Chemical potential energy isenergy stored in chemical bonds.

Reading Check

MiniLAB


Correlation to TEKSPage 102: 6Page 103: 1, 1A, 2, 2A, 2B, 2C, 2D, 6

Figure 4 What forms of energy are given offwhen natural gas burns? light and heat (thermalenergy)


MiniLAB, p. 3Directed Reading for Content

Mastery, p. 20

Reading and Writing Skill Activities, p. 35

Resource Manager

Potential Energy

Math Skills Activity

Example ProblemA 0.06-kg tennis ball starts to fall from a height of 2.9 m. How much gravita-

tional potential energy does the ball have at that height?

Solution

This is what you know: mass of tennis ball: m � 0.06 kgheight of the tennis ball: h � 2.9 m acceleration of gravity: 9.8 m/s2

This is what you want to find: gravitational potential energy: GPE

This is the equation you use: GPE � m � 9.8 m/s2 � h

Solve the equation by substituting the known values: GPE � 0.06 kg � 9.8 m/s2 � 2.9 m � 1.7 J

Check your answer by substituting it and the known values into the original equation. Do you get the same result?

Calculating Gravitational Potential Energy

For more help, refer to the Math Skill Handbook.

Practice Problem

Bjorn is holding a tennis ball outsidea second-floor window (3.5 m fromthe ground) and Billie Jean is holdingone outside a third-floor window

(6.25 m from the ground). How muchmore gravitational potential energydoes Billie Jean’s tennis ball have? (Eachtennis ball has a mass of 0.06 kg.)

Gravitational Potential Energy Gravity caused the apple tofall from the tree. Anything that can fall has stored energy calledgravitational potential energy. Gravitational potential energy(GPE) is energy stored by objects that are above Earth’s surface.The amount of gravitational potential energy depends on threethings—the mass of the object, the acceleration due to gravity, andthe height above the ground. The acceleration of gravity on Earthis 9.8 m/s2, and the height is measured in meters.

The amount of gravitational potential energy an object hascan be calculated using the following equation.

GPE � mass � 9.8 m/s2 � height

GPE (J) � m (kg) � 9.8 m/s2 � h (m)

Just like kinetic energy, gravitational potential energy is mea-sured in joules. All energy, no matter which form it is in, can bemeasured in joules.


Fast-flowing rivers andslow-moving glaciers havekinetic energy. A rock bal-anced on a hill containspotential energy. What aresome other examples ofkinetic and potentialenergy in nature?

Potential Energy, continued


Quick DemoDemonstrate the idea of

gravitational potential energy.Place three tennis balls on levelsurfaces at different heights.Ask students to compare thegravitational potential energy(GPE) of the balls. GPE increaseswith height. So the ball that is highesthas the greatest GPE and the ball near-est the ground has the lowest GPE.

Logical-MathematicalLSL1

Working with Energy During World WarII, O.S. (Ozzie) Williams became the firstAfrican American aeronautical engineer hiredby Republic Aviation, Inc. Later, his workincluded the application of solar and wind

energy to the needs of Africa. Have studentsfind other scientists who have spent much oftheir careers working with energy. Ask studentsto present their findings in oral reports to theclass. InterpersonalLSL2

Possible answers: Kinetic—wind,ocean waves, avalanches, and erupt-ing volcanoes; potential—water atthe top of a waterfall, acorns hangingfrom a tree

National Math StandardsCorrelation to Mathematics Objectives1, 2, 6, 9

Answers toPractice Problems1. Solve the equations:

0.06 kg � 9.8 m/s2 � 3.5 m � 2.06 J for Bjorn’s tennis ball0.06 kg � 9.8 m/s2 � 6.25 m � 3.68 J for Billie Jean’s tennisball j Billie Jean’s tennis ball has3.68 J � 2.06 J � 1.62 J moreenergy than Bjorn’s.


Correlation to TEKSPage 104: 4, 4B, 6Page 105: 4, 4B, 6

Changing GPE Look at the objects on the bookshelf inFigure 5. Which of these objects has the most gravitationalpotential energy? According to the equation for gravitationalpotential energy, the GPE of an object can be increased byincreasing its height above the ground. If two objects are at thesame height, then the object with the larger mass has more grav-itational potential energy.

In Figure 5, suppose the green vase on the lower shelf andthe blue vase on the upper shelf have the same mass. Then thevase that is on the upper shelf has more gravitational potentialenergy because it is higher above the ground.

Imagine what would happen if the two vases were to fall. Asthey fall and begin moving, they have kinetic energy as well asgravitational potential energy. As the vases get closer to theground, their gravitational potential energy decreases. At thesame time they are moving faster, so their kinetic energyincreases. The vase that initially had more gravitational potentialenergy will be moving faster when it hits the floor.

Do the books on the shelf above the green vase have moregravitational potential energy than the vase? That depends onthe mass of the books. Even though they are twice as high as thevase, their gravitational potential energy also depends on theirmass. If the mass of the books is less than half the mass of thevase, then the books have less gravitational potential energy,even though they are at a greater height.

What does GPE depend on?


Section Assessment

1. Two books with different masses fall off thesame bookshelf. As they fall, which hasmore kinetic energy and why?

2. How can the gravitational potential energyof an object be changed?

3. How is energy stored in food? Is the form ofenergy stored in food different from theform stored in gasoline? Explain.

4. Contrast potential and kinetic energy.

5. Think Critically The food you eat sup-plies energy for your body. Suggest waysyour body might make use of this energy.

6. Comparing and Contrasting Compare andcontrast elastic potential energy, chemical potential energy, and gravitational potentialenergy. For more help, refer to the Science Skill Handbook.

7. Solving One-Step Equations An 80-kg diver jumps off a 10-m platform. Calculate howmuch gravitational potential energy the diverhas at the top of the platform and halfwaydown. For more help, refer to the Math Skill Handbook.

Figure 5An object’s gravitational potential energy increases with increased height. Which

vase has more gravitational poten-

tial energy? Which one will have

more kinetic energy when it

strikes the ground?

Caption AnswerFigure 5 The vase highest off theground has the highest GPE and will alsohave the greatest kinetic energy justbefore it strikes the ground.


ReteachPerform several tasks, such as

clapping your hands, walkingacross the room, tossing a ballacross the room, or turning on alight. Ask students to identifythe energy transformations thatoccur during each task.

Visual-Spatial

ChallengeThe kinetic energy of a falling

object is greatest just before theobject hits the ground. Thekinetic energy of the objectimmediately after falling is zero.What happens to the kineticenergy? It changes into other forms of energy, such as heat or sound.


LSELLL1

Answer height and mass

Reading Check

Process Tell students that a 5 kgbowling ball is on a rack 1.5 mabove the ground. Have themcalculate the GPE of the ball.5 kg � 9.8 m/s2 � 1.5 m � 73.5 J UsePASC, p. 101.

Answers to Section Assessment1. The book with the larger mass;

kinetic energy depends on anobject’s mass as well as its velocity.

2. by changing the height of the object3. in chemical bonds; no, they are both

chemical potential energy4. Potential energy is stored energy due

to an object’s position. Kinetic energyis energy due to motion.

5. Possible answers: for walking, swim-ming, playing

6. All are stored energy due to position.To acquire elastic potential energy,an object is compressed or stretched.Chemical potential energy is due tothe positions of atoms relative to oneanother. Gravitational potential

energy is due to an object’s heightabove the ground.

7. at the top, GPE � 7,840 J; halfwaydown, GPE � 3,920 J


Lab Activity, pp. 9–12Enrichment, p. 29Reinforcement, p. 27

Resource Manager

Meet with three other lab teams and compare average bounce heights for the tennis ball on the floor. Discuss why yourresults might differ. For more help, refer to the Science Skill Handbook.

Bouncing Balls

2. As the balls fall, what happens to their gravi-tational potential energy and their kineticenergy? What happens to their kinetic energywhen they hit the floor?

3. Calculate the average bounce height for thethree trials under each condition. Describeyour observations.

4. How did the bounce heights compare whendropped on a cardboard box instead of thefloor? Why? Hint: Did you observe any move-

ment of the box when the balls bounced?

5. Use elastic potential energy to explain whythe balls bounced to different heights.

What happens when you drop a ball onto ahard, flat surface? It starts with potential

energy. It bounces up and down until it finallycomes to a rest. Where did the energy go?

What You’ll InvestigateHow do balls differ in their bouncing behavior?

Materialstennis ball masking taperubber ball cardboard boxbalance *shoe box

meterstick *Alternate materials

Goals� Identify the forms of energy observed in a

bouncing ball.� Infer why the ball stops bouncing.

Safety Precautions

Procedure1. Measure the mass of the two balls.

2. Have a friend drop one ball from 1 m.Measure how high the ball bounced. Repeatthis two more times so that you can calculatean average bounce height. Record your valueson the data table.

3. Repeat step 2 for the other ball.

4. Predict whether the balls would bouncehigher or lower if they were dropped onto thecardboard box. Design an experiment tomeasure how high the balls would bounce offthe surface of a cardboard box.

Conclude and Apply1. Calculate the gravitational potential energy

of each ball before dropping them.

Type Surface Trial Height of Ball (cm)

Tennis Floor 1 36

Tennis Floor 2 34

Tennis Floor 3 37

Rubber Floor 1 54

Rubber Floor 2 56

Rubber Floor 3 56

Tennis Box 1 29

Bounce Height


Purpose Students observe howthe GPE of a falling ball is con-verted to kinetic energy andelastic potential energy,enabling the ball to bounce.

KinestheticProcess Skills observing andinferring, predicting, compar-ing, recognizing cause and effectTime Required 30 minutesAlternate Materials table tennisball, bookTeaching Strategy Explain that itis only possible to measure theapproximate height of the ball’sbounce.

Conclude and Apply1. Use the formula: GPE � m (kg) �

9.8 m/s2 � h (m).2. GPE decreases; kinetic energy

increases. Most of their kinetic energyis converted to elastic potentialenergy.

3. Average height � sum of heights �number of trials. Answers will vary.

4. The balls don’t bounce as high on thebox. Some of the kinetic energy theball has when it hits the box is trans-ferred to the box, causing the box tovibrate.This energy is then unavail-able to help propel the ball up.

5. When a ball hits the ground, most ofits kinetic energy is converted toelastic potential energy.This becomeskinetic energy as the ball rebounds.Some balls store more elastic poten-tial energy than others.

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L2


Process Demonstrate how the bounce height ofa ball becomes lower and lower each time itbounces. Have students infer why this happens.Each time the ball bounces, part of its energy is converted toother forms of energy, such as thermal energy and sound.Use PASC, p. 89.

Students can use a computer graphics program to pre-pare a display of their activity results. They should beallowed freedom to make their own design, but thepicture should clearly show how the balls bouncedhigher off the floor than off the box.


Transparency Activity, pp. 45–46Activity Worksheet, pp. 5–6

Resource Manager

Tie to Prior KnowledgeDiscuss the various forms of

energy involved in skateboarding.

Text Question Answeralarm clock—sound; hair styler—

heat or kinetic; toaster—heat; music—sound; video game—light

Caption AnswerFigure 6 Possible answers: heater,stove, iron

Conservation of Energy

SECTION 2 Conservation of Energy 107

Changing Forms of Energy Unless you were talking about potential energy, you proba-

bly wouldn’t think of the book on top of a bookshelf as havingmuch to do with energy—until it fell. You’d be more likely tothink of energy as race cars roar past or as your body usesenergy from food to help it move, or as the Sun warms your skinon a summer day. You might be thankful for electrical energy asyou play a favorite CD. These situations involve energy changingfrom one form to another form. Energy is most noticeable as ittransforms from one type to another.

Transforming Electrical Energy You use many devicesevery day that convert one form of energy to other forms. Forexample, you might be reading this page in a room lit by light-bulbs. The lightbulbs transform electrical energy into light soyou can see. The warmth you feel around the bulb is evidencethat some of that electrical energy is turned into thermal energy,as illustrated in Figure 6. What other devices have you usedtoday that make use of electrical energy? You might have beenawakened by an alarm clock, styled your hair, made toast, lis-tened to music, or played a video game. What form or forms ofenergy is electrical energy converted to in these examples?

� Describe how energy is conservedwhen changing from one form toanother.

� Apply the law of conservation ofenergy to familiar situations.

Vocabularymechanical energylaw of conservation of energy

Conservation of energy is a universalprinciple that can explain howenergy changes occur.

Conservation of EnergyS E C T I O N

Light energy out

Thermal energy out

Electrical energy in

Figure 6A lightbulb is a device that trans-forms electrical energy into lightenergy and thermal energy. What

other devices convert electrical

energy to thermal energy?

PORTFOLIO

Visual Learning, p. 114

PERFORMANCE ASSESSMENT

Try At Home MiniLAB, p. 112Skill-Builder Activities, p. 115See p. 122 for more options.

CONTENT ASSESSMENT

Section, p. 115Challenge, p. 115Chapter, pp. 122–123

Section Planner

Energy

All living things have something in common. If they don’t getenergy, they die and decay. Plants convert energy from the Sun into aform of chemical energy other living things can use.

Power PlantsSection FocusTransparency22

1. How do people obtain the energy plants store?

2. Name some other ways energy is stored.

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Section 2 Conservation of Energy 107

Bellringer TransparencyDisplay the Section FocusTransparency for Section 2.Use the accompanying Trans-parency Activity Master.ELL

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22S E C T I O N


Correlation to TEKSPage 106: 1, 1A, 2, 2A, 2B, 2C, 2D, 3, 3A, 4, 4B,6, 6APage 107: 6, 6A

Transforming ChemicalEnergy Fuel stores energy in theform of chemical potential energy.For example, the car or bus thatmight have brought you to schoolthis morning probably runs ongasoline. The engine transformsthe chemical potential energystored in gasoline into the kineticenergy of a moving car or bus.Several energy conversions occurin this process, as shown in Figure7. An electrical spark ignites asmall amount of fuel. The burningfuel produces thermal energy. Sochemical energy is changed tothermal energy. The thermalenergy causes gases to expand andmove parts of the car, producingkinetic energy.

Some energy transformationsare less obvious because they do not result in visible motion,sound, heat, or light. Every green plant you see converts lightenergy from the Sun into energy stored in chemical bonds in theplant. If you eat an ear of corn, the chemical potential energy inthe corn is transformed yet again when it is in your body.

Conversions Between Kinetic and Potential Energy

You have experienced many situations that involve conver-sions between potential and kinetic energy. Bicycles, roller coast-ers, and swings can be described in terms of potential andkinetic energy. Even something as simple as launching a rubberband or using a bow and arrow involves energy conversions. Tounderstand the energy conversions in these activities, it is help-ful to identify the mechanical energy of a system. Mechanicalenergy is the total amount of potential and kinetic energy in asystem and can be expressed by this equation.

mechanical energy � potential energy � kinetic energy

In other words, mechanical energy is energy due to the posi-tion and the motion of an object. What happens to the mechan-ical energy of an object as potential and kinetic energy areconverted into each other?


Spark plug fires Gases expand

Figure 7In a car, a spark plug fires,

initiating the conversion ofchemical potential energy intothermal energy.

As the hot gases expand,thermal energy is convertedinto kinetic energy.


Changing Forms ofEnergy

Figure 7 Review the energy con-versions at work in an internalcombustion engine. Then dis-cuss how a diesel engine works.In a diesel engine, the air in thecylinder is compressed to a highpressure and becomes very hot.When the fuel is sprayed intothe cylinder, it ignites in the hotair without the need of a sparkplug. What energy conver-sions take place in a dieselengine? Chemical potential energy isconverted to thermal energy and thento kinetic energy.


Conversions BetweenKinetic and PotentialEnergy

Make a ModelHave students work in groups

to make models that show theconversion from potentialenergy to kinetic energy. Theymight choose to use a spring,windup car, or ball to demon-strate the idea.

Kinesthetic

ExtensionHave students research the

imaginary inventions of car-toonist Rube Goldberg. Havethem bring a picture of oneinvention they find to class anddiscuss the energy conversionsillustrated by the contraption.

Visual-SpatialLSL2

LSCOOP LEARNL1

Gifted Remind students that work is the transferof energy, is measured in the same units asenergy, and can be calculated using the formulaW � F � d. Provide students the following scenario: The kinetic energy of a hockey puck is 20 J as it moves from ice onto the cement surrounding the rink. By how much is itsenergy decreased if it stops on the cement?

20 J If the cement causes a frictional force of10 N on the puck, how far does it slide? �10N · d � �20 J, therefore d � 2.0 m What happens tothis energy? It is converted into heat.

MathematicalLSL3


Correlation to TEKSPage 108: 4, 6, 6APage 109: 4, 6, 6A

High KELow GPE

Low KEHigh GPE

High KELow GPE

Figure 9A ball hit into the air illustrateshow kinetic energy and gravi-tational potential energy areconverted into each other.

Falling Objects Standing under an apple tree can be haz-ardous. Here is an explanation of why this is true using energyterms. An apple on a tree, like the one in Figure 8, has gravita-tional potential energy due to Earth pulling down on it. Theapple does not have kinetic energy while it hangs from the tree.However, the instant the apple comes loose from the tree, itaccelerates due to gravity. As it falls, it loses height so its gravita-tional potential energy decreases. This potential energy is notlost. Rather, it is transformed into kinetic energy as the velocityof the apple increases.

Look back at the equation for mechanical energy. If the poten-tial energy is being converted into kinetic energy, then themechanical energy of the apple doesn’t change as it falls. Thepotential energy that the apple loses is gained back as kineticenergy. The form of energy changes, but the total amount ofenergy remains the same.

What happens to the mechanical energy of theapple as it falls from the tree?

Energy transformation also occurs when a baseball is hit intothe air. Look at Figure 9. When the ball leaves the bat, it hasmostly kinetic energy. As the ball rises, its velocity decreases, soits kinetic energy must decrease, too. However, the ball’s gravita-tional potential energy increases as it goes higher. At its highestpoint, the baseball has the maximum amount of gravitationalpotential energy. The only kinetic energy it has at this point isdue to its forward motion. Then, as the baseball falls, gravita-tional potential energy decreases while kinetic energy increasesas the ball moves faster. Once again, the mechanical energy ofthe ball remains constant as it rises and falls.


Figure 8Objects that can fall have gravitational potential energy.What objects around you have

gravitational potential energy?

Earth pulls anapple down


Answer Potential energy decreases;kinetic energy increases; total mechani-cal energy remains constant.

Caption AnswerFigure 8 Any objects that are elevatedhave GPE.

DiscussionYou are riding in an elevator.

How do your kinetic andpotential energy relative tothe elevator change as you goup? Neither changes. L1

Reading Check

If there is no air resistance,then two objects that startfalling at the same time fromthe same height will hit theground at the same time. Therate of free fall does notdepend on mass. But an objectwith larger mass has moreGPE before it falls and hasmore kinetic energy as it falls.In other words, it will hurtmore when it hits your head.

Some students may not realizethat when the bob of a pendu-lum reaches its maximumheight, it momentarily stops,and when it is at its lowest partof its swing, its velocity ishighest. Sketch a pendulum onthe board and use arrows toshow movement. Explain thatthe bob must briefly stop tochange directions. Because ithas no velocity, it has nokinetic energy at this point.

History Students have probably heard the tale ofIsaac Newton discovering gravity when an applefell from a tree onto his head. Have studentsinvestigate this story to determine if it is a mythor a true occurrence. Have students share theirfindings with the class. Newton is purported to havesaid himself that the fall of the apple “occasioned” his “notionof gravitation.” InterpersonalLSL3


Directed Reading for Content Mastery,pp. 21, 22

Transparency Activity, p. 43


Resource Manager

Visualizing EnergyTransformations

Have students examine the pic-tures and read the captions. Thenask the following questions.• As the student goes from

point A to B, why is herkinetic energy increasing?because her velocity is increasing

• What force accelerates thestudent as she goes frompoint A to the lowest pointand slows down the studentas she goes from the lowestpoint to point D? gravity

ActivityThe movement of the swing is

similar to the movement of apendulum. Provide studentswith a 1-meter piece of stringwith a large washer tied to theend of it. Ask students to simu-late the movement of the swingor a pendulum using the stringand washer. Have studentsexperiment to see if the lengthof the string has any relation-ship to the time it takes thewasher to make one completeperiod, going from point A onthe diagram to point D and backto point A again.

ExtensionChallenge students to learn

how a pendulum clock worksand prepare posters diagram-ming what they find.

Figure 10

A ride on a swing illustrates how kineticenergy changes to potential energyand back to kinetic energy again. The

diagram at right shows four stages of theswing’s motion. Although it changes from one form to another, the total energy remains the same.

At the rider’shighest point, herpotential energyis at a maximumand her kineticenergy is zero.

As she falls toward thebottom of the path, therider accelerates and gainskinetic energy. Because therider is not as high abovethe ground, her potentialenergy decreases.

The rider, rising toward the opposite side, begins to slow down and lose kinetic energy. As she gainsheight, her potential energy increases.

KE increasingPE decreasing

KE decreasing

PE increasing

VISUALIZING ENERGYTRANSFORMATIONS

B

CA

B

CD

PE = MinimumKE = Maximum

KE = Kinetic EnergyPE = Potential Energy

PE = MaximumKE = 0

PE = MaximumKE = 0

At the highest point on thisside of the swing, her potentialenergy again is at a maximum,and her kinetic energy is zero.

D

A

C

B

D

A

110 CHAPTER 4


LAB DEMONSTRATIONLAB DEMONSTRATIONPurpose to demonstrate the conservationof mechanical energyMaterials 1-m plastic tubing, 2 ring standswith clamps, marblePreparation Form a U-shaped tunnel byclamping each end of the tubing to a ringstand. The ends should be at identicalheights.

Procedure Hold a marble slightly aboveone end of the tubing. Have students pre-dict the height the marble will reach onthe opposite side. Release and discuss theresult. Rearrange the tubing to form vari-ous shaped tunnels and repeat the activity.Expected Outcome There should be a slightloss in mechanical energy.

How was the mechanical energyaffected as the marble traveled alongthe tubing? The mechanical energy decreased.What are possible causes of this? airresistance and friction from the tubing


Swinging Along When you ride on a swing, like the oneshown in Figure 10, part of the fun is the feeling of almostfalling as you drop from the highest point to the lowest point ofthe swing’s path. Think about energy conservation to analyzesuch a ride.

The ride starts with a push that gets you moving, giving you some kinetic energy. As the swing rises, you lose speed but gain height. In energy terms, kinetic energy changes to gravita-tional potential energy. At the top of your path, potential energyis at its greatest. Then, as the swing accelerates downward, poten-tial energy changes to kinetic energy. At the bottom of each swing, the kinetic energy is at its greatest and the poten-tial energy is at its minimum. As you swing back and forth,energy continually converts from kinetic to potential and back tokinetic. What happens to your mechanical energy as you swing?

The Law of Conservation of EnergyWhen a ball is thrown into the air or a swing moves back

and forth, kinetic and potential energy are constantly changingas the object speeds up and slows down. However, mechanicalenergy stays constant. Kinetic and potential energy simplychange forms and no energy is destroyed.

This is always true. Energy can change from one form toanother, but the total amount of energy never changes. Evenwhen energy changes form from electrical to thermal and otherenergy forms as in the hair dryer shown in Figure 11, energy isnever destroyed. Another way to say this is that energy is con-served. This principle is recognized as a law of nature. The lawof conservation of energy states that energy cannot be createdor destroyed. On a large scale, this law means that the totalamount of energy in the universe remains constant.

What law states that the total amount ofenergy never changes?

You might have heard about energyconservation or been told to conserveenergy. These ideas are related to reducingthe demand for electricity and gasoline,which lowers the consumption of energyresources such as coal and fuel oil. Thelaw of conservation of energy, on theother hand, is a universal principle thatdescribes what happens to energy as it istransferred from one object to another oras it is transformed.

Thermal EnergyKinetic EnergySound Energy

=ElectricalEnergy

Energy In = Energy Out

Figure 11The law of conservation ofenergy requires that the totalamount of energy going into ahair dryer must equal the totalamount of energy coming out ofthe hair dryer.

One way energy entersecosystems is when greenplants transform radiantenergy from the Sun intochemical potential energyin the form of food. Energymoves through the foodchain as animals that eatplants are eaten by otheranimals. Some energyleaves the food chain, suchas when living organismsrelease thermal energy tothe environment. Diagrama simple biological foodchain showing energy conservation.


In a food chain, arrows showthe direction in which energymoves from one organism tothe next. Possible food chain: grass→ rabbit → fox

Use Science WordsWord Meaning The word conser-vation means to keep from beinglost or wasted. Discuss why thisis an appropriate word to use forthe principle of conservation ofenergy. Possible answer: It is appropri-ate because energy is never lost. It is notappropriate because some forms ofenergy are more valuable than others.

Linguistic

The Law of Conservation of Energy

ExtensionUse a yo-yo to show the con-

servation of energy. The initialGPE changes to rotationalkinetic energy (and translationalkinetic energy) as the yo-yofalls. At the lowest point, theenergy begins to change back togravitational potential energy.Have students investigate theenergy of a yo-yo and use com-puter graphics software to pre-sent their results.

Visual-SpatialLSL2

LSL2


Lab Activity, pp. 13–15Enrichment, p. 30

Home and Community Involvement, p. 36

Resource Manager


Correlation to TEKSPage 110: 4, 6, 6APage 111: 6, 6A

Answer the law of conservation ofenergy

Reading Check

The Law of Conservation ofEnergy, continued


Figure 12In a swing, mechanical energy istransformed into thermal energybecause of friction and air resistance. Friction

Airresistance

Motion

Friction and the Law of Conservation of Energy Youmight be able to think of situations where it seems as thoughenergy is not conserved. For example, while coasting along a flatroad on a bicycle, you know that you will eventually stop if youdon’t pedal. If energy is conserved, why wouldn’t your kineticenergy stay constant so that you would coast forever? In manysituations, it might seem that energy is destroyed or created. Some-times it is hard to see the law of conservation of energy at work.

Following Energy’s Trail You know from experience that ifyou don’t continue to pump a swing or be pushed by somebodyelse, your arcs will become lower and you eventually will stopswinging. In other words, the mechanical (kinetic and potential)energy of the swing seems to decrease, as if the energy were beingdestroyed. Is this a violation of the law of conservation of energy?

It can’t be—it’s the law! If the energy of the swing decreases,then the energy of some other object must increase by an equalamount to keep the total amount of energy the same. Whatcould this other object be that experiences an energy increase? Toanswer this, you need to think about friction. With every move-ment, the swing’s ropes or chains rub on their hooks and airpushes on the rider, as illustrated in Figure 12. Friction and airresistance cause some of the mechanical energy of the swing tochange to thermal energy. With every pass of the swing, the tem-perature of the hooks and the air increases a little, so themechanical energy of the swing is not destroyed. Rather, it istransformed into thermal energy. The total amount of energyalways stays the same.

Transforming EnergyUsing a Paper ClipProcedure1. Straighten a paper clip.

While holding the ends,touch the paper clip to theskin just below your lowerlip. Note whether the paperclip feels warm, cool, orabout room temperature.

2. Quickly bend the paper clipback and forth five times.Touch it below your lowerlip again. Note whether thepaper clip feels warmer orcooler than before.

Analysis1. What happened to the

temperature of the paperclip? Why?

2. As you bend the paper clip,explain all the energy con-versions that take place.


TRY AT HOME

Purpose Students observe howkinetic energy can change intothermal energy.

IntrapersonalMaterials paper clipTeaching Strategy Have stu-dents use uncoated clips thatare not too thick or brittle toeasily bend.S afety Prec aution Studentsshould be careful of the sharpends of the paper clip whenbending it.Analysis1. It went up. Some mechanical

energy from the paper clip wasconverted to thermal energy.

2. Chemical energy from the body isconverted to kinetic energy that istransferred to the paper clip.Mechanical energy is converted tothermal energy by collisions of themolecules.

LSL1

MiniLAB

Oral Have students discussother examples of the processmodeled by this activity. Possi-ble answer: bicycle or car tires heat upas they roll along the road. UsePASC, p. 89.

Many people have tried to develop a perpetual motionmachine, a device which, once set in motion, would for-ever make more energy than it uses. Conservation ofenergy means that such a machine is impossible.

Learning Disabled To help students see how fric-tion affects the velocity and therefore thekinetic energy of objects, have them roll mar-bles across a smooth table and then across apiece of carpet. Explain that the marbles movemore slowly on the carpet because they losekinetic energy to friction. KinestheticLSL1


Research Visit the Glencoe Science Web site atscience.glencoe.com formore information about therole of friction in the design ofautomobiles. Communicate toyour class what you learn.

In this fusion reaction, thecombined mass of the two hydro-gen nuclei, H, is greater than themass of the helium nucleus, He,and the neutron.

Figure 13Mass is converted to energy in theprocesses of fusion and fission.

Radiantenergy Radiant

energy

UHe

HH

Xe

Nuclear fissionNuclear fusion

Mass H + Mass H > Mass He +Mass neutron Mass U + Mass neutron � Mass Xe + Mass Sr + Mass neutrons

Sr

In nuclear fission, the mass of thelarge nucleus on the left is greater thanthe combined mass of the other twonuclei and the neutrons. Why aren’t the

masses equal?

Converting Mass into Energy You might have wonderedhow the Sun unleashes enough energy to light and warm Earthfrom so far away. A special kind of energy conversion—nuclearfusion—takes place in the Sun and other stars. During this processa small amount of mass is transformed into a tremendous amountof energy. An example of a nuclear fusion reaction involvinghydrogen nuclei is shown in Figure 13A.

Nuclear Fission Another process involving the nuclei ofatoms, called nuclear fission, converts a small amount of massinto enormous quantities of energy. In this process, nuclei donot fuse—they are broken apart, as shown in Figure 13B. Ineither process, fusion or fission, mass is converted to energy. Youmust think of mass as energy when applying the law of conser-vation of energy to processes involving nuclear reactions. Here,as in all cases, the total amount of mass and energy is conserved.The process of nuclear fission is used by nuclear power plants togenerate electrical energy. The fission process occurs in anuclear reactor, and the heat released changes water to steam.The steam is used to spin an electric generator.


In the process of fission, neu-trons are released. They initi-ate further fission, beginning achain reaction. For the chainreaction to continue, sufficientfissionable material must bepresent. The amount of mate-rial to sustain a chain reactionis known as the critical mass.

Use Science WordsWord Meaning Have students usea dictionary to look up thewords fusion and fission. Askthem to explain why these areappropriate terms for thenuclear processes discussed inthis section. Fusion is combining ofthings—in nuclear fusion, nuclei com-bine. Fiss ion is spl i t t ing apar t ofthings—in nuclear fission, nuclei splitapart. Linguistic

Caption AnswerFigure 13B Some of the mass has beenconverted to energy.

LSL1

Internet Addresses

Explore the Glencoe Science Web site at science.glencoe.comto find out more about topics in this section.


Correlation to TEKSPage 112: 1, 1A, 2, 2B, 2C, 2D, 6, 6APage 113: 6, 6A, 8, 8D


MiniLAB, p. 4

Physical Science Critical Thinking/Problem Solving, p. 17


Resource Manager



The Human Body—Balancing the EnergyEquation

The Human Body—Balancing theEnergy Equation

What forms of energy discussed in this chapter can you findin the human body? With your right hand, reach up and feelyour left shoulder. With that simple action, stored potentialenergy within your body was converted to the kinetic energy ofyour moving arm. Did your shoulder feel warm to your hand?Some of the potential energy stored in your body is used tomaintain a nearly constant internal temperature. A portion ofthis energy also is converted to the excess heat that your bodygives off to its surroundings. Even the people shown standing inFigure 14 require energy conversions to stand still.

Energy Conversions in Your Body The complex chemicaland physical processes going on in your body also obey the lawof conservation of energy. Your body stores energy in the formof fat and other chemical compounds. This chemical potentialenergy is used to fuel the processes that keep you alive, such asmaking your heart beat and digesting the food you eat. Yourbody also converts this energy to heat that is transferred to yoursurroundings, and you use this energy to make your body move.Table 1 shows the amount of energy used in doing various activ-ities. To maintain a healthy weight, you must have a properbalance between energy contained in the food you eat and theenergy your body uses.

114 CHAPTER 4

Figure 14The runners convert the energystored in their bodies morerapidly than the spectators do.Use Table 1 to calculate how long

a person would need to stand to

burn as much energy as a runner

burns in 1 h.


Students may confuse energytransformations with changesin matter. Some may state thatfood is converted into energyin the body. During digestion,chemical compounds in foodare converted into compoundsthat muscle cells use to enablemuscles to move.

Use Science WordsWord Origin The word calorieoriginates from the eighteenth-century word caloric, which wasa hypothetical weightless fluidthat scientists thought flowedfrom hot objects to cold objects.Ask students to find out howcaloric theory contributed to theidea of conservation of energy.Scientists realized that caloric was nei-ther gained nor lost during experiments.They gradually realized that caloric wasthe flow of energy. Linguistic

Caption AnswerFigure 14 7 to 8 hours depending onbody type

LSL2

Table 1 Have students thinkback over the past 24 hours andmake a list of the things theydid. Have them use the table tofind out about how many Calo-ries of energy they used. P

Energy in Martial Arts Karate, whichmeans “empty hand,” originated on Okinawa inthe 17th century. A trained karateka can break athin concrete block with his or her hand. Havestudents research the meanings of the names ofother forms of martial arts and where they orig-inated. Possible martial arts include judo, aikido, and tae kwon do. IntrapersonalLSL2

Ac tive ReadingLearning Journal Have students draw a verticalline down each page of a Learning Journal andrecord research notes, lecture notes, or vocabu-lary terms in the left column. In the right col-umn, they respond to, interpret, question, oranalyze the left column entries. Students canwrite a Learning Journal while reading aboutconservation of energy.


Correlation to TEKSPage 114: 6, 6A, 6H, 8, 8APage 115: 2D, 6, 6H, 8, 8A

Food—YourChemica lPotent i a l

Energy Your body has been busybreaking down your breakfast into mol-ecules that can be used as fuel. These fuelmolecules, such as sugar, supply all thecells in your body with the energy theyneed to function. If you did not eatbreakfast this morning, your body willconvert energy stored in fat for its imme-diate needs until you eat again. The foodCalorie (C) is a unit used by nutritioniststo measure how much energy you getfrom various foods—1 C is equivalent toabout 4,184 J. Every gram of fat a personconsumes can supply 9 C of energy. Carbo-hydrates and proteins each supply about4 C of energy per gram. The next time you go grocery shopping,look on the packages and notice how much energy each producteventually will supply to you.

Health


Section Assessment

1. Define the term mechanical energy.

Describe the mechanical energy of a roller-coaster car immediately before it beginstraveling down a long track.

2. What is the law of conservation of energy?

3. Applying bicycle brakes as you ride down along hill causes the brake pads and thewheel rims to feel warm. Explain.

4. What is the source of the large amounts ofenergy released in nuclear reactors and inthe Sun? Are the same processes occurringin the Sun and in reactors? Explain.

5. Think Critically Much discussion hasfocused on the need to drive more efficientcars and use less electricity. If the law ofconservation of energy is true, why arepeople concerned about energy usage?

6. Communicating Suppose you drop a tennisball out of a second-floor window. The firstbounce will be the highest. Each bounce afterthat will be lower until the ball stops bouncing.Write a description of the energy conversionsthat take place, starting with dropping the ball.Accompany your description with an appropri-ate illustration. For more help, refer to the Science Skill Handbook.

7. Communicating Your body used energy asyou walked into your school today. Where didthis energy come from? In your Science Journal,write a paragraph describing where youacquired this energy. Trace it back through asmany transformations as you can. For morehelp, refer to the Science Skill Handbook.

Table 1 Calories Used in 1 h

Body Frames

Small Medium Large

Sleeping 48 56 64

Sitting 72 84 96

Eating 84 98 112

Standing 96 112 123

Walking 180 210 240

Playing tennis 380 420 460

Bicycling (fast) 500 600 700

Running 700 850 1,000

Type of Activity


ReteachShow students pictures of

people performing various activ-ities, such as those listed inTable 1. Ask students to orderthe pictures according to howquickly they burn Calories. Stu-dents should also identify typesof energy conversion in eachactivity. Visual-Spatial

ChallengeHave students use models to

demonstrate nuclear fission andnuclear fusion. Students could usemarbles for neutrons and protons,with clay to hold them together.

KinestheticLSL2

LSL1

Process Have students draw dia-grams illustrating some of thechanging forms of energyinvolved in bouncing a basket-ball. Chemical energy from the bodychanges to kinetic energy to lift the ball.This energy is transferred to the ball aspotential energy. As the ball falls, thischanges to kinetic energy. As the ballhits the floor, part of the energy changesto sound, part is transferred to the floor,and most is returned to the ball as elas-tic potential energy, enabling the ball tob o u n ce. Use PerformanceAssessment in the ScienceClassroom, p. 127.

Answers to Section Assessment1. the sum of potential and kinetic

energy in a system; mostly potentialenergy

2. Energy cannot be created ordestroyed.

3. Because of friction, kinetic energy isconverted to thermal energy.

4. Mass changes to energy; no, nuclearfusion in the Sun, fission in reactors.

5. Much of the energy we use is con-verted to non-reusable forms.

6. The initial potential energy changesto kinetic during the fall. At theground, kinetic energy becomeselastic potential energy, sound, ther-mal energy, and kinetic energy inthe ground.This lost energy means

the ball won’t bounce as high eachtime.

7. Possible answers: conversion of radi-ant energy from the Sun to chemicalenergy in plants, conversion ofchemical energy to mechanicalenergy for walking


Activity Worksheet, pp. 7–8Reinforcement, p. 28

Resource Manager

Recognize the Problem

PurposeConstruct a pendulum to com-pare the exchange of potentialand kinetic energy.

Kinesthetic

Process Skillsmeasuring, collecting and orga-nizing data, observing and infer-ring, communicating, makingand using tables, comparing andcontrasting, recognizing causeand effect, forming a hypothesis,designing an experiment, usingnumbers, separating and con-trolling variables

Time Requiredone class period

MaterialsHave additional materials avail-able (string, extra ring stands,banner paper, masking tape).

Safety PrecautionsStudents should wear safetygoggles when swinging thestoppers.

Form a Hypothesis

Possible HypothesisStudents may suggest that thecrossarm’s interference halfwayup the length of the string willcause the maximum height todecrease by one half. In fact, theshape of the pendulum’s pathwill change, but the height onthe opposite end should still beclose to the original height.

LSCOOP LEARN

L2

Imagine yourself swinging on a swing. What would happen if a friend grabbed theswing’s chains as you passed the lowest point? Would you come to a complete stop

or continue rising to your previous maximum height?

Recognize the ProblemHow does the motion and maximum height reached by a swing change if the swing isinterrupted?

Form a HypothesisExamine the diagram on this page. How is it similar to the situation in the introduc-tory paragraph? An object that is suspended so that it can swing back and forth alsois called a pendulum. Hypothesize what will happen to the pendulum’s motion andfinal height if its swing is interrupted.

Swinging Energy

Goals� Construct a pendulum to com-

pare the exchange of potential andkinetic energy when a swing isinterrupted.

� Measure the starting and endingheights of the pendulum.

Possible Materialstest-tube clampring standsupport-rod clamp, right angle30-cm support rod 2-hole, medium rubber stopperstring (1 m)metersticksgraph paper

Safety Precautions Be sure the base is heavy enough or well anchored so that the apparatus will not tip over.



Data Table

Trial 1 Trial 2 Trial 3

Initial Height

Height with crossarm

Gifted Have students determine the loss ofenergy from friction after the pendulum hasswung 10 times. Have them measure the massof the stopper, calculate its initial potentialenergy, using its initial height, and calculate itsending potential energy using the height after

10 swings. The difference is the amount ofenergy lost. Have them do this exercise bothwith and without cross-arm interference.

KinestheticLSL3

Test Your Hypothesis

Analyze Your Data

Draw Conclusions

6. Be sure you test your swing,starting it above and below the height of the cross arm.How many times should you repeat each starting point?

Do1. Make sure your teacher approves

your plan before you start.

2. Carry out the approved experimentas planned.

3. While the experiment is going on,write any observations that youmake and complete the data table in your Science Journal.

Plan1. As a group, write your hypothesis

and list the steps that you will taketo test it. Be specific. Also list thematerials you will need.

2. Design a data table and place it inyour Science Journal.

3. Set up an apparatus similar to theone shown in the diagram.

4. Devise a way to measure the start-ing and ending heights of the stop-per. Record your starting andending heights in a data table. Thiswill be your control.

5. Decide how to release the stopperfrom the same height each time.

2. Analyze the energy transfers. Atwhat point along a single swingdoes the stopper have the greatestkinetic energy? The greatest poten-tial energy?

1. When the stopper is released fromthe same height as the cross arm, isthe ending height of the stopperexactly the same as its startingheight? Use your data to supportyour answer.

4. What happens if the mass of thestopper is increased? Test it.

1. Do the results support your hypothesis? Explain.

2. Compare the starting heights tothe ending heights of the stopper. Isthere a pattern? Can you accountfor the observed behavior?

3. Do your results support the law ofconservation of energy? Why orwhy not?

ACTIVITY 117

Compare your conclusions with those of theother lab teams in your class. For more help,refer to the Science Skill Handbook.

Test Your Hypothesis

Possible ProceduresSet up the pendulum and start itmoving. Measure the height atwhich the stopper was releasedto start the pendulum. Whenthe pendulum is on the far sideof its swing, insert the crossarm.Measure the height to which thependulum swings after it hitsthe crossarm.

Teaching StrategiesTape white paper to a wallbehind the pendulum for mark-ing stopper height.

TroubleshootingThe swing of the pendulum willbe irregular if the crossarminhibits movement of only oneside of the pendulum’s swing.Suggest students find a way tohave the cross arm limit swingin both directions.

Expected OutcomeStudents will observe that evenwith the crossarm, the approxi-mate original height is reached.

Analyze Your Data1. no2. Kinetic is greatest at the bottom;

potential is greatest at the top.

Draw Conclusions1. Answers will vary with results.2. Ending heights are lower. Friction

slows the stopper and removes someenergy from the system.

3. Yes; the apparent loss of energy isdue to friction.

4. Kinetic and potential energyincrease; the person must pull harderto stop the swing.

ACTIVITY 117

Have students use a word processing program to writea short description of their experiment. They may wishto use a computer graphics program to make sketchesthat help explain the results.

Process When started from the same height, apendulum without interference from a crossarmwill remain in motion longer than a pendulumwith an arm. Ask students to discuss and explainthis. Some energy transfers to the crossarm. Use Performance Assessment in the ScienceClassroom, p. 89. InterpersonalLSL2


Correlation to TEKSPage 116: 1, 1A, 2, 2A, 3, 3A, 6, 6APage 117: 1, 1A, 2, 2A, 2B, 2C, 2D, 3, 3A, 6, 6A

118

SCIENCEAND

HISTORYSCIENCE

CAN CHANGETHE COURSEOF HISTORY!

The Impossible DreamA machine that keeps on going? It has been tried for hundreds of years.

Science is a bit like an easygoing

parent—it doesn’t lay down a lot of

laws. Those laws that do exist, how-

ever, are hard to get around. Just ask the

hundreds of people who have tried through-

out history—and failed—to build perpetual-

motion machines.

In theory, a perpetual-motion machine

would run forever and do work without a

continual source of energy. You can think of it

as a car that you could fill up once with gas,

and with that single tankful, the car would

run forever. Sound impossible? It is!

Artist M.C. Escher drew this never-endingstaircase. You could walk on it perpetually!

Visitors look at the Keely Motor,the most famous perpetual-motionmachine fraud of the late 1800s.


Content Background

The 1st and 2nd Laws of Ther-modynamics preclude the cre-ation of perpetual motionmachines. Currently acceptedpractices of applied science arebased on the conservation ofmatter and energy and theinevitable increase in theentropy of a closed system.Specifically, the first lawassumes that the quantities ofmatter and energy in the uni-verse are fixed and cannot becreated or destroyed only trans-formed. The second claims thatwithout external input the totalenergy in a system will deterio-rate from coherent, i.e. useful,energy to unusable chaoticenergy ultimately depriving thesystem of its ability to do work.Early clockmakers and scientistsattempted to create mechanismsthat would utilize natural phe-nomena so efficiently that theeffort to set them in motionwould be sufficient to enablethem continue operating for-ever. Most attempts have faileddue to the loss caused by fric-tion and many were simplyfrauds. The U.S. Patent Officewill no longer accept applica-tions claiming the invention of aperpetual motion device. Themodern quest for infinite energysources has turned from thepurely mechanical to the electri-cal and chemical fields. In mod-ern times, the perpetual motionmachine has been replaced bycold-fusion schemes and over-unity devices. These devices andprocesses theoretically require aconstant input of energy, butproduce more than they use.

SCIENCEAND

HISTORY

“Exploiting Zero-Point Energy”, by Philip Yam.Scientific American, (December 1997).

Perpetual Motion: The History of An Obsession. byArthur W.J.G. OrdHume. Barnes and NobleBooks 1998.

Resources for Teachers and Students

TIME SCIENCE AND HISTORY 119

DiscussionWhat are the two laws of

energy that make perpetualmotioin machines impossible?Energy cannot be created or destroyed; itcan only change form. Heat will onlyflow from a warm object to a cold object.

Historical SignificanceDivide students into four or

five groups and give each groupa marble, a foam cup, a groovedruler, a tongue depressor, and apaper and pencil.

Assign students the task ofusing their materials to transferenergy in such a way that theirmarble moves the greatest dis-tance when they release it froma designated starting point.Inform them that throwing themarble or pushing it along thecourse is not permitted. Theymust simply release it from thestarting point, and, using asmany energy transfers as possi-ble, cause it to travel as far aspossible before stopping on itsown.

After all groups have com-pleted this task, a “play-off” maybe held between groups todetermine the best overall classset-up. Invite the winning groupto explain the energy transfersinvolved in their set-up.

CONNECTIONS Ask students to thinkabout how perpetual motion machines might behelpful to science and technology if the laws ofthermodynamics did not exist.Start a dialogueaddressing the thousands of scam artists whohave tried in vain to sell their perpetual motionmachines.

Science Puts Its Foot DownFor hundreds of years, people have tried

to create perpetual-motion machines. But

these machines won’t work because they

violate two of nature’s laws. The first law is

the law of conservation of energy, which

states that energy cannot be created or

destroyed. It can change form—say, from

mechanical energy to electrical energy—but

you always end up with the same amount of

energy that you started with.

How does that apply to perpetual-motion

machines? When a machine does work on an

object, the machine transfers energy to the

object. Unless that machine gets more energy

from somewhere else, it can’t keep doing

work. If it did, it would be creating energy.

The second law states that heat by itself

always flows from a warm object to a cold

object. Heat will only flow from a cold object

to a warm object if work is done. In the

process, some heat always escapes. The hood

of a car, for instance, feels hot when the car is

running. That’s because heat, or thermal

energy has escaped from the car’s engine.

To make up for these energy losses,

energy constantly needs to be transferred to

the machine. Otherwise, it stops. No perpet-

ual motion. No free electricity. No devices

that generate more energy than they use. No

engine motors that run forever without fuel.

No lights that shine or ships that sail without

a continual source of energy. Some laws just

can’t be broken.

Losing BattlesFor more than 300 years, people havetried to build a perpetual-motion machinethat works. Nobody has ever succeeded.In fact, the U.S. Patent Office, which stud-ies inventions to see if they work beforethey grant a patent, refuses to even lookat machines that their inventors claim areperpetual-motion machines.

CONNECTIONS Analyze Using your school or public library resources,locate a picture or diagram of a perpetual-motion machine. Figure out why it won’t run forever. Explain to the class what the problem is. For more information, visit

science.glencoe.com

Some laws just can’t be broken.


Correlation to TEKSPage 118: 3C, 3E, 6, 6APage 119: 3C, 3E, 6, 6A

Internet Addresses

Explore the Glencoe Science Web site at science.glencoe.comto find out more about topics in this feature.



ChapterStudy Guide

44 44

120 CHAPTER STUDY GUIDE

PreviewStudents can answer the ques-

tions in their Science Journals.Discuss the answers as you gothrough the chapter. Linguistic

ReviewStudents can write their

answers, then compare themwith those of other students.

Interpersonal

ReteachStudents can look at the illus-

trations and describe details thatsupport the main ideas of thechapter. Visual-Spatial

Answers toChapter ReviewSECTION 12. Radiant energy from the Sun,

mechanical energy of the windmill,chemical potential energy in the grass

4. As it fell, its potential energy woulddecrease as it changed to kineticenergy.

SECTION 23. Potential energy is being converted

to kinetic energy and to thermalenergy from friction; energy is alwaysconserved.

LS

LS

LS

After students have read the chapter and completed

the Foldable described in Before You Read, havethem do the activity on the student page.



After You ReadAfter You Read

120 CHAPTER STUDY GUIDE

Section 2 Conservation of Energy1. Energy can change from one form to

another. You observe many energy transfor-mations every day.

2. The law of conservation of energy statesthat energy never can be created ordestroyed. Because of friction, energy mightseem to be lost, but it has changed intothermal energy.

3. Falling, flying, and swinging objects allinvolve transformations between potentialand kinetic energy. The total amount ofpotential and kinetic energy is calledmechanical energy. What energy transfor-mations are taking place in the figure below?Is energy being conserved?

Section 1 The Nature of Energy1. Energy is the ability of something to

cause change.

2. Energy can take a variety of different forms.What are some of the forms of energy illus-trated in the photograph below?

3. Moving objects have kinetic energy thatdepends on the mass of the object and thevelocity of the object.

4. Potential energy is stored energy.Objects that can fall have gravitationalpotential energy—the amount depends on their weight and height above the ground.If Balanced Rock, shown in the photographbelow, fell, how would its gravitationalpotential energy change?

4. Mass can be converted into energy innuclear fusion and fission reactions. Fusionand fission involve atomic nuclei and releasetremendous amounts of energy.

To help review whatyou’ve learned aboutenergy and energy conser-

vation, use the Foldable you made at thebeginning of the chapter.

After You ReadFOLDABLESReading & StudySkills

FOLDABLESReading & Study Skills

Study GuideChapter 44

Using Vocabulary 1. mechanical energy2. elastic potential energy3. gravitational potential energy4. law of conservation of energy5. kinetic energy

See student page.

ChapterStudy Guide

CHAPTER STUDY GUIDE 121

Vocabulary Wordsa. chemical potential energyb. elastic potential energyc. gravitational potential energy d. joule e. kinetic energyf. law of conservation of energyg. mechanical energyh. potential energy

Using VocabularyUsing the list of vocabulary words, replace the

underlined words with the correct science term.

1. In describing the energy changes of abouncing ball, the total amount of kineticand potential energy must be conserved.

2. The energy due to stretching of a bow canbe used to propel an arrow forward.

3. Snow on the side of a mountain has energydue to Earth pulling down on it.

4. The fact that energy cannot be createdmeans that dynamite does not create energywhen it explodes.

5. The muscles of a runner transform chemi-cal potential energy into energy of motion.

Be a teacher! Get together a group of friends andassign each person a section of the chapter toteach. When you teach you remember andunderstand information thoroughly.

Study Tip

Energy

states that energycan’t be created

or destroyed

energy inthe formof motion

Law of conservation

of energymechanical energyconverts to thermal

energy

stored energy, due to position

mass convertsto energy

Nuclearfusion/fission

Potential energy

Friction

Joulesmeasured in

Kinetic energy

Study GuideChapter 44

Complete the concept map below using the following terms: nuclear fusion/fission, potentialenergy, friction, joules, kinetic energy.

CHAPTER STUDY GUIDE 121

44


Correlation to TEKSPage 120: 3, 4, 6, 6APage 121: 3, 4, 6, 6A

11. At the highest point, a pendulumhas only potential energy. As it fallsthis changes to kinetic energy. Atthe lowest point, the pendulum hasonly kinetic energy. Friction slowsthe pendulum by convertingmechanical energy to thermalenergy.

12. Elastic potential energy is stored inthe stretched spring.This energy isconverted into kinetic energy whenthe spring contracts.

13. Potential and kinetic energy areexchanged as the rider moves upand down along the roller coaster.

14. Under certain conditions, mass canbe converted to energy and energycan be converted to mass.

15. 812.5 J

1. D2. A3. A4. A5. C6. C7. D8. A9. B

10. B

ChapterAssessment

11

Choose the word or phrase that best answersthe question.

1. When energy is transferred from one objectto another, what must occur?A) an explosion C) nuclear fusionB) a chemical reaction D) a change

2. Which has more kinetic energy, a large dogsitting on a sidewalk or a small cat runningdown the street?A) the large dogB) the small catC) Both have the same kinetic energy.D) need more information to answer

3. What energy transformations occur when alump of clay is dropped?A) GPE � KE � thermal energyB) KE � chem PE � thermal energyC) KE � GPE � thermal energyD) GPE � KE � elastic PE

4. Suppose a juggler is juggling oranges. At anorange’s highest point, what form of energydoes it have?A) mostly potential energyB) mostly kinetic energyC) no potential or kinetic energyD) equal amounts of both

5. The gravitational potential energy of anobject depends on which of the following?A) velocity and heightB) velocity and weightC) weight and heightD) weight and acceleration

6. Which idea is central to the law of conser-vation of energy?A) Friction produces thermal energy.B) People must conserve energy.C) The total amount of energy is constant.D) Energy is the ability to cause change.

7. To what property of an object is kineticenergy directly related?A) volume C) positionB) height D) mass

8. Friction frequently causes some of anobject’s mechanical energy to be changed towhich of the following forms?A) thermal energyB) nuclear energyC) gravitational potential energyD) chemical potential energy

9. What is the process of breaking apart largeatomic nuclei into smaller nuclei called? A) nuclear fusion C) atomic fractureB) nuclear fission D) transformation

122 CHAPTER ASSESSMENT

10. Green plants store energy from the Sun inwhat form?A) light energyB) chemical potential energyC) gravitational potential energyD) electrical energy

11. Briefly describe the energy changes in aswinging pendulum. Explain how energy isconserved, even as a pendulum slows.

12. How is energy transformed when one endof a stretched spring is released?

13. Describe the energyconversions that takeplace during a roller-coaster ride.

14. Explain why the law ofconservation of energymust include mass.

15. A 15-kg bicycle carrying a 50-kg boy is trav-eling at a speed of 5 m/s. What is the kineticenergy of the bicycle (including the boy)?

AssessmentChapter 44

122 CHAPTER ASSESSMENT

Portfolio Encourage students to place in theirportfolios one or two items of what they con-sider to be their best work. Examples include:• Curriculum Connection, p. 102• Visual Learning, p. 114

Performance Additional performance assess-ments, Performance Task Assessment Lists, andrubrics for evaluating these activities can befound in Glencoe’s Performance Assessmentin the Science Classroom.

Chapter Planner

44


Correlation to TEKSPage 122: 4, 6, 6APage 123: 1B, 2D, 4, 6, 6A

The Test-Taking Tip was writtenby The Princeton Review, thenation’s leader in test preparation.1. C2. H

18. Possible answers: walking (potentialenergy changes to kinetic energyand this changes to elastic potentialenergy); swimming (chemicalpotential energy in the swimmerchanges to kinetic energy and ther-mal energy); cooking (electricalenergy changes to thermal energy).Use PASC, p. 145.

19. Presentations should include alter-native fuels, and their advantagesand disadvantages. Use PASC,p. 143.

16. (Kinetic energy in joules) 0, 0.5, 2,4.5, 8, 12.5, 18, 24.5, 32, 40.5, 50

17. It is an increasing curve. A straightline would increase at a steady rate.This curve increases slowly at first,then very fast.

ChapterAssessment

11

CHAPTER ASSESSMENT 123

16. Making and Using Tables Make a table that reports the kinetic energy of a 1-kgobject moving at various speeds. Computethe kinetic energy at speed increments of1 m/s, from 0 m/s to 10 m/s.

17. Making and Using Graphs Make a graph toshow how kinetic energy changes as speedincreases. Using the data from question 16,plot speed on the x-axis and kinetic energyon the y-axis. Describe the shape of theplotted line. How is the shape of this linedifferent from a straight line?

18. Poster Make an educational poster thathighlights the law of conservation ofenergy. Include examples of energy conser-vation in your daily life.

19. Oral Presentation Research one type ofalternative fuel. Find out the advantagesand disadvantages of using the fuel. Presentyour findings to your class.

Mass (kg) Speed (m/s) KE (J)

1 0 0

1 1 1

1 2 4

1 10 100

Energy of a Moving Object

Go to the Glencoe Science Web site at science.glencoe.com or use the Glencoe Science CD-ROM for additionalchapter assessment.

TECHNOLOGY

AssessmentChapter 44

Test Practice

A team of students conducted anexperiment in energy conversion and collected their data in a table.

Study the experiment and the tableabove and answer the following questions.

1. The illustration above shows how thesedata were collected. Recording whichone of the following would improvethe experiment?A) owner of the toy carsB) weather conditionsC) height of the rampsD) brand of the toy cars

2. At the beginning of the experiment,a toy car is at rest at the top of a ramp.In this position, what form of energy is stored in the car?F) kinetic energyG) fissionH) potential energyJ) mass

TrialMass of

Toy Car (kg)Distance

Traveled (m)Time to

Travel Ramp (s)Speed(m/s)

12

0.51

0.050.050.050.05

1

2

3.14.42.23.1

0.320.450.220.32

CHAPTER ASSESSMENT 123

44

Reproducible Masters

Chapter Resources BookletChapter Review, pp. 35–36Chapter Tests, pp. 37–40Assessment Transparency Activity, p. 47

Glencoe Science Web siteInteractive TutorChapter Quizzess

Glencoe Technology

Assessment TransparencyInteractive CD-ROM Chapter QuizzesExamView Pro Test BankVocabulary PuzzleMaker SoftwareMindJogger Videoquiz DVD/VHS

Resources

Multimedia resources are availablefrom Glencoe for TAKS preparationand test practice.


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