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Increasing Potential Energy When you raise an objectabove its original position, it has the potential to fall. If it doesfall, it has kinetic energy. To raise an object, you have to transferenergy to the object. The ski lift uses energy when it takes a skierup a hill and transfers some of that energy to the skier. Thisenergy becomes stored as potential energy in the skier. As theskier goes down the hill, the potential energy she had at the topof the hill is converted to kinetic energy.If the skier were lifted higher, her potential energy wouldincrease. The higher an object is lifted above Earth, the greaterits potential energy.Converting Potential and Kinetic EnergyWhen a skier skis down a hill, potential energy is transformedto kinetic energy. Kinetic energy also can be transformedinto potential energy. Suppose you throw a ball straightup into the air. The muscles in your body cause the ball to moveupward when it leaves your hand. Because it is moving, the ballhas kinetic energy. Look at Figure 8. As the ball gets higher andhigher, its potential energy is increasing. At the same time, theball is slowing down and its kinetic energy is decreasing.What happens when the ball reaches its highest point? Theball comes to a stop for an instant before it starts to fall downwardagain. At its highest point, the ball has no more kineticenergy. All the kinetic energy the ball had when it left your handhas been converted to potential energy, and the ball will go nohigher. As the ball falls downward, its potential energy is convertedback into kinetic energy. If you catch the ball at the sameheight above the ground as when you threw it upward, itskinetic energy will be the same as when it left your hand.Comparing KineticEnergy and HeightProcedure:1. Lay a 3-cm-thick layer ofsmooth modeling clay on apiece of cardboard. Placethe cardboard on the floor.2. Drop an object such as abaseball, golf ball, ororange into the clay froma height of 10 cm. Measureand record the depth ofthe hole made by theobject.3. Repeat step 2 from aheight of 50 cm and 1 m.Analysis1. How does the depth of thehole depend on the heightof the ball?2. How does the kineticenergy of the falling balldepend on the distanceit fell?Figure 8 Energy is transformedas a ball rises and falls.KE PE KE PE KE PEAs the ball leaves the person’shand, it is moving thefastest and has maximumkinetic energy.As the ball moves upward, itslows down as its kineticenergy is transformed intopotential energy.As the ball moves downward, itspeeds up as its potential energyis transformed into kineticenergy.SECTION 1 Energy Changes 167