5 SECTION 2 Energy Conversions

NameClassCHAPTER 5DateEnergy and Energy Resources2 Energy ConversionsSECTIONNational ScienceEducation StandardsBEFORE YOU READAfter you read this section, you should be able to answerthese questions:PS 3a, 3f What are energy conversions? How do machines use energy conversions?What Is an Energy Conversion?Think of a book sitting on a shelf. The book has gravitational potential energy when it is on the shelf. What happensif the book falls off the shelf? Its potential energy changes intokinetic energy. This is an example of an energy conversion.An energy conversion is a change from one form ofenergy to another. Any form of energy can change intoany other form of energy. One form of energy can sometimes change into more than one other energy form.STUDY TIPMake a list in your sciencenotebook of the energyconversions discussed in thissection.KINETIC AND POTENTIAL ENERGY CONVERSIONA common energy conversion happens between potential energy and kinetic energy. When the skateboarderin the figure below moves down the half-pipe, he has alot of kinetic energy. As he travels up the half-pipe, hiskinetic energy changes into potential energy.Potential Energy and Kinetic EnergyAt the top of his jump, the skateboarder looks like he has almoststopped moving. Hisis at a maximum.At the bottom of the half-pipe, the skateboarder has a lot ofspeed. Hisis at a maximum.TAKE A LOOK1. Identify Complete thetwo blanks in the figure.Copyright by Holt, Rinehart and Winston. All rights reserved.Interactive Textbook87Energy and Energy Resources

NameSECTION 2ClassDateEnergy Conversions continuedELASTIC POTENTIAL ENERGYREADING CHECK2. Describe How does arubber band gain elasticpotential energy?Another example of potential energy changing intokinetic energy is shown in a rubber band. When youstretch a rubber band, you give it potential energy. Thisenergy is called elastic potential energy. When you let goof the rubber band, it flies across the room. The storedpotential energy in the stretched rubber band is turnedinto kinetic energy.How Do Chemical Energy Conversions Happen?You may have heard that breakfast is the most important meal of the day. Why is eating breakfast so important? Chemical energy comes from the food you eat. Yourbody changes the chemical energy from food into severaldifferent energy forms that it can use. Some of these are: mechanical energy, to move your muscles thermal energy, to keep your body temperature constant electrical energy, to help your brain thinkSo eating breakfast helps your body do all of yourdaily activities.Food has chemical energy.You eat.Your body stores the chemical energy ofthe food.Chemical energy is converted into:TAKE A LOOK3. Identify Fill in the processchart to show how energy isconverted in your body.Copyright by Holt, Rinehart and Winston. All rights reserved.Interactive Textbook88Energy and Energy Resources

NameClassDateEnergy Conversions continuedSECTION 2From Light Energy to Chemical EnergySTANDARDS CHECKLight energyPhotosynthesisLight energyCarbon dioxideSugar Oxygen WaterChlorophyllSugar in foodCarbon dioxidein the airChlorophyll ingreen leavesPS 3f The sun is a major sourceof energy for changes on theearth’s surface. The sun losesenergy by emitting light. A tinyfraction of that light reaches theearth, transferring energy fromthe sun to the earth. The sun’senergy arrives as light with arange of wave lengths, consisting of visible light, infrared, andultraviolet radiation.4. Identify Light energyfrom the sun is convertedinto what kind of energy bygreen leaves?Water in the soilENERGY CONVERSIONS IN PLANTSDid you know the chemical energy in the food youeat comes from the sun’s energy? When you eat fruits,vegetables, or grains, you are taking in chemical energy.Energy from the sun was used to make the chemicalenergy in the food. Many animals also eat plants. If youeat meat from these animals, you are also taking inenergy that comes from the sun.The figure above shows how light energy is usedto make new material that has chemical energy. Whenphotosynthesis happens in plants, light energy from thesun is changed into chemical energy. Photosynthesis isa chemical reaction in plants that changes light energyinto chemical energy. When we eat fruits, vegetables, orgrains, we are eating the chemical energy that is stored inthe plants.The chemical energy from a tree can also be changedinto thermal energy. This change happens when you burna tree’s wood. If you go back far enough, you would seethat the energy from a wood fire comes from the sun.Say ItDiscuss With a partner,describe how light energy fromthe sun becomes chemicalenergy in meat from animals.Copyright by Holt, Rinehart and Winston. All rights reserved.Interactive Textbook89Energy and Energy Resources

NameSECTION 2ClassDateEnergy Conversions continuedEnergy Conversions in a Hair Dryer1The electricalenergy enters thehair dryer. Thisenergy is changedintowhen a smallelectric motor spinsa fan blade.TAKE A LOOK2Electrical energyis changed intoas many wiresin the hair dryerheat up.5. Identify Fill in the blanksin the figure.3The fan moves air acrossthese hot wires. Thisblows hot air out ofthe hair dryer. You hearthatcomes out of the hairdryer.Why Are Energy Conversions Important?Energy conversions happen everywhere. Heating ourhomes and getting energy from food are just a few examples of how we use energy conversions. Machines alsoconvert and use energy. This can be seen from the figureof the hair dryer above. Electrical energy by itself won’tdry your hair. The hair dryer changes electrical energyinto thermal energy. This heat helps dry your hair.ELECTRICAL ENERGY CONVERSIONSYou use electrical energy all of the time. Some examples of when you use electrical energy are listening tothe radio, making toast, and taking a picture. Electricalenergy changes into other kinds of energy easily.Some Conversions of Electrical EnergyTAKE A LOOK6. Identify Look at the table.In each example, think aboutwhat kind of energy conversion happens. Then, fill in thelast column of the table withthe kind (or kinds) of energythat is formed.Alarm ClockElectrical energy ‡Hair dryerElectrical energy ‡Light bulbElectrical energy ‡BlenderElectrical energy ‡Copyright by Holt, Rinehart and Winston. All rights reserved.Interactive Textbook90Energy and Energy Resources

NameSECTION 2ClassDateEnergy Conversions continuedHow Do Machines Use Energy?You have seen how energy can change into differentforms. Another way to look at energy is to see how machinesuse energy. Remember that a machine can make work easier.It does this by changing the size or direction (or both) of theforce that does the work. The machine converts the energyyou put into the machine into work.There is another way that machines can help you useenergy. They can convert energy into a form that you need,such as a stove using electrical energy to cook food.An example of how energy is used by a machine isshown in the figure below. The biker puts a force on thepedals. This transfers kinetic energy from the biker intokinetic energy to move the pedals. This energy moves toother parts of the bike. The bike lets the biker use lessforce over a greater distance. This makes his work easier.READING CHECK7. Describe What are twoways a machine convertsenergy?Energy Conversions in a BicycleFor your bike to start and keepmoving, energy must be transferredand converted.1 Your body storesenergy.This energy is changedinto kinetic energy whenyour muscles contractand relax.2 Your legs transferenergyto the pedals by pushingthem in a circle.TAKE A LOOK8. Identify Complete theblanks in the figure.4 The chain moves and transferskinetic energy to the back wheel.This gets youand keeps you moving.3 The pedals transferenergy to the wheel and then to thechain.Copyright by Holt, Rinehart and Winston. All rights reserved.Interactive Textbook91Energy and Energy Resources

NameClassSection 2 ReviewDateNSESPS 3a, 3fSECTION VOCABULARYenergy conversion a change from one form ofenergy to another1. Identify Suppose a skier is standing still at the top of a hill. What kind of energydoes the skier have?2. Explain What happens to the energy of the skier in Question 1 if he goes downthe hill?3. Describe How does your body get the energy that it needs to do all of its dailyactivities? Describe the energy conversions that take place.4. Explain What energy conversion happens when green plants use energy from thesun to make sugar?5. Analyze A vacuum cleaner is a machine that uses electrical energy. What are threeforms of energy that the electrical energy changes into in the vacuum cleaner?6. Compare How are the energy conversions of a machine similar to the energy con-versions in your body?Copyright by Holt, Rinehart and Winston. All rights reserved.Interactive Textbook92Energy and Energy Resources

MForces, Motion, and Energy Answer Key continuedChapter 5 Energy andEnergy Resources6. Nuclear fusion is more important becausethe sun produces energy by this reaction.Without energy from the sun, there would beno life on Earth.SECTION 1 WHAT IS ENERGY?1. energy2. Energy moves from the tennis player to theSECTION 2 ENERGY CONVERSIONS1. 1) potential energyracket.The tennis racket does work on the ball.Energy moves from the tennis player to theball.3. moving2) kinetic energy2. by stretching it3. Food has chemical energy.mv4. kinetic energy 25.6.7.8.9.10.11.12.13.14.15.16.20.50kg (10 m/s)2kinetic energy 2kinetic energy 25 Jits positionPull back farther on the bow string.GPE weight heightGPE 300 N 100 m 30,000 Jkinetic and potential energyPin B should be circled.the kinetic energy from the movement of theparticles in an objectpotential energyThe electrons in the wires move to theamplifier. The moving electrons do work.electrical energy for the amplifier, soundenergy for the guitarlight energyIn nuclear fusion, nuclei join; in fission,nuclei split apart.nuclear fusion4.5.6.7.8.You eat food.Your body stores the chemical energy of thefood.Chemical energy is converted into1) mechanical energy2) thermal energy3) electrical energychemical1) kinetic energy, 2) thermal energy,3) sound energyAlarm clock: light, sound, thermalHair dryer: thermal, soundLight bulb: light, thermalBlender: kinetic, sound, thermalIt converts energy into work and energy intoa different form.1) chemical, 2) kinetic, 3) kinetic, 4) movingReview1. gravitational potential energy2. The potential energy is converted into3.Review1. the object’s mass and the object’s speed2. GPE weight heightGPE 16 N 2.5 m 40 Jmv23. kinetic energy 22,000kg (25 m/s)2kinetic energy 2kinetic energy 625,000 J4. Gravitational potential energy; as her heightincreases, her potential energy, or storedenergy, increases. At the top of her jump,she is not moving, so all of her kineticenergy has become potential energy.5. They both cause molecules to vibrate so thatthe energy can travel.4.5.6.kinetic energy.You get energy from the food you eat. Thebody converts the chemical energy from thefood into chemical energy it can use. Thischemical energy can then be converted intokinetic energy to do any activity.Plants change light energy from the sun intochemical energy.kinetic energy to move the motor in thevacuum, sound energy, thermal energy asvacuum warms upA machine changes the energy that is putinto it into other forms of energy. Yourbody changes the food put into it into otherenergy forms.Copyright by Holt, Rinehart and Winston. All rights reserved.Interactive Textbook Answer Key87Forces, Motion, and Energy

An energy conversion is a change from one form of energy to another. Any form of energy can change into . energy for the guitar 14. light energy 15. In nuclear fusion, nuclei join; in fission, nuclei split apart. . SECTION 2 ENERGY CONVERSIONS 1. 1) potential energy 2) kinetic energy 2. by st