# CHAPTER 5 Energy And Energy Resources - Weebly

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Changes Between Kineticand Potential EnergyEnergy transformations also occur when you toss a ballupward, as shown in the figure. The ball slows down as itrises and speeds up as it falls. The ball’s speed and heightchange as the energy changes from one form to another.Copyright Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.Kinetic Energyto Potential EnergyIn the figure, noticethat the ball is movingfastest and has themost kinetic energy(KE) as it leaves thegirl’s hands. As the ballmoves upward, itsspeed and kineticenergy decrease. At thesame time, the ball’spotential energy (PE)increases because theball’s height increases.The ball’s kineticenergy is changing topotential energy as theball moves upward. Atthe ball’s highest point,its gravitationalpotential energy isgreatest and its kineticenergy is the EPEBVisual Check2. Compare When is thegravitational potentialenergy the greatest?TotalenergyKE PEKEPETotalenergyEAPotential Energyto Kinetic EnergyAt the ball’s highest point, it has the most potentialenergy because it is farthest from the ground. As the ballmoves downward, its potential energy decreases because itsheight decreases. At the same time, the ball’s kinetic energyincreases because its speed increases. As the ball drops,potential energy changes to kinetic energy. When the ballreaches the boy’s hands, the ball’s kinetic energy is at thehighest value again.Reading Check3. Explain Why does thepotential energy decrease asthe ball falls?Energy changes between kinetic energy and potentialenergy as the ball moves. However, look at the bars in thefigure. The ball’s total energy does not change.Reading EssentialsEnergy and Energy Resources83

Key Concept Check4. Define What is the lawof conservation of energy?The Law of Conservation of EnergyThe total energy in the universe is the sum of all thedifferent forms of energy everywhere. According to the lawof conservation of energy, energy can be transformed from one forminto another or transferred from one region to another, but energycannot be created or destroyed. The total amount of energy inthe universe does not change.Friction and the Law of Conservation of EnergyVisual Check5. Explain Which type ofenergy is constant in thefigure? Why?Sometimes it seems as if the law of conservation ofenergy is not accurate. Imagine riding a bicycle, as shownbelow. The moving bicycle has mechanical energy. Whathappens to this mechanical energy when you apply thebrakes? According to the law of conservation of energy,the bicycle’s mechanical energy is not destroyed, but itis transformed.When you apply the brakes, the bicycle’s mechanicalenergy is transformed into thermal energy, as shown below.The brake pads rub against the bicycle’s wheels. Theadditional thermal energy warms the brakes, wheels, and airaround the bicycle.Coasting Kinetic Thermal Totalenergy energy energy Kinetic Thermal Totalenergy energy energyStopped Kinetic Thermal Totalenergy energy energyFriction When the bicycle’s brake pads rub against theKey Concept Check6. Specify Friction causeswhat energy transformation?84Energy and Energy Resourcesmoving wheels, friction occurs. Friction is a force that resists themotion of two surfaces that are touching. Friction between thebrake pads and the moving wheels changes the bicycle’smechanical energy into thermal energy. The total amount ofenergy never changes.There is always some friction between any two surfacesthat are rubbing against each other. As a result, somemechanical energy is always transformed into thermalenergy when two surfaces rub against each other.Reading EssentialsCopyright Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. Applying brakes

Using Electric EnergyKey Concept Check9. Restate What happensto energy when it is used?Remember that electric energy is the energy carriedby an electric current. Many of the devices you use everyday, such as a handheld video game, an mp3 player, anda hair dryer, use electric energy. Some devices, such ashair dryers, use electric energy from an electrical powerplant. Other devices, such as handheld video games,transform chemical energy stored in batteries intoelectric energy.Waste EnergyWhen energy changes form, some thermal energy isalways released. For example, a lightbulb converts someelectric energy into radiant energy. However, the lightbulbalso transforms some electric energy into thermal energy.This is what makes the lightbulb hot. Some of this thermalenergy moves into the air and cannot be used.Scientists often refer to thermal energy that cannot beused as waste energy. Whenever energy is used, some energyis transformed into useful energy and some is transformedinto waste energy.Visual Check86Energy and Energy ResourcesReading EssentialsCopyright Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.10. Interpret Circle threeareas on the cars where oneform of energy is beingtransformed into wasteenergy.Chemical energy in gasoline makes cars move. However,a car transforms most of the chemical energy in gasolineinto waste energy. The waste energy is thermal energy thatmoves into the air. As shown below, some of this thermalenergy makes the car’s engine hot. Hot gases in the car’sexhaust contain thermal energy produced by burning fuel.Friction between a car’s tires and the road changesmechanical energy to thermal energy.

Mini Glossaryfriction: a force that resists the motion of two surfaces that aretouchinglaw of conservation of energy: energy can be transformedfrom one form into another or transferred from one regionto another, but energy cannot be created or destroyed1. Review the terms and their definitions in the Mini Glossary. Write a sentence thatprovides an example of friction.2. Use what you have learned about energy to complete the table.Energy ChangeKineticto potentialExampleThrow a ball into the air.Electricto thermalCopyright Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.Potentialto kineticEnergy ChangeChemicalto thermalSoundto radiantAn object falls to the ground.Chemicalto electricExampleA call is received on a cell phone.Electricto radiantChemicalto kineticFood is digested to help a personmove.3. Explain one concept you learned from the sentences that you highlighted.What do you thinkReread the statements at the beginning of thelesson. Fill in the After column with an A if youagree with the statement or a D if you disagree.Did you change your mind?Reading EssentialsConnect EDLog on to ConnectED.mcgraw-hill.comand access your textbook to find thislesson’s resources.END OFLESSONEnergy and Energy Resources87

changes to thermal energy. Thermal energy causes the lamp's bulb to become warm to the touch. Using Thermal Energy All forms of energy can be changed into thermal energy. Recall that thermal energy is the energy due to the motion of particles that make up an object. People often use thermal energy to provide warmth or cook food. An electric space

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