## Which Bounces Higher?

By : Tony Helies

Roll a piece of clay into a smooth ball the size of a marble. Drop it onto a hard floor. Also drop a marble (or any hard object, like a penny or a paper clip). Which bounces higher? Why?

Hint: Does the clay ball have a flat spot where it hit the floor?

Explanation: Falling objects have energy. When they hit a hard surface, like the floor, they lose some of that energy. Where does the energy go? The impact jiggles the atoms in the object and in the floor. That raises (very slightly) the temperature of both the object and the floor. So the motion energy is turned into heat energy.

It takes several bounces for the marble to lose all of its motion energy to heat, each time jiggling the atoms a little more, and bouncing a little lower. But the clay ball hardly bounces at all. Why does the clay ball lose energy so quickly? Because the clay is soft, its atoms can be moved more easily. Most of the clay ball's motion energy is quickly converted to heat by the work it takes to flatten the side of the ball that hits the floor.

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