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■ Explain what energy is.■ Describe the forms energy takes.■ Compare and contrast potentialenergy and kinetic energy.Energy causes all the changes thattake place around you.Review Vocabularyspeed: the distance traveled persecond by an objectNew Vocabularyenergykinetic energy•potential energylaw of conservation of energyEnergy ChangesEnergyEnergy is a term you probably use every day. You might saythat eating a plate of spaghetti gives you energy, or that a gymnasthas a lot of energy. Do you realize that a burning fire, abouncing ball, and a tank of gasoline also have energy?What is energy? The word energy comes from the ancientGreek word energos, which means “active.” You probably haveused the word energy in the same way. When you say you have alot of energy, what does this mean? Energy is the ability to causechange. For example, energy can change the temperature of a potof water, or it can change the direction and speed of a baseball.The energy in a thunderstorm, like the one shown in Figure 1,produces lightning that lights up the sky and thunder that canrattle windows. Energy can change the arrangement of atoms inmolecules and cause chemical reactions to occur. You use energywhen you change the speed of a bicycle by pedaling faster orwhen you put on the brakes.What does energy do?Kennan Ward/The Stock Market/CORBISFigure 1 Lightning causesdramatic change as it lights upthe sky.Forms of EnergyIf you ask your friends what comes to mind when theythink of energy, you probably will get many differentanswers. Some might mention candy barsor food. Others might think of the energyneeded to run a car. Energy does come indifferent forms from a variety of sources.Food provides energy in the form of chemicalenergy. Your body converts chemicalenergy in the food you eat into the energyit needs to move, think, and grow. Nuclearpower plants use nuclear energy containedin the center or nucleus of the atom to produceelectricity. What other forms ofenergy can you think of?162