Step 2

This time put the tennis ball on top of the basketball and drop them at the same time. Make sure the tennis ball stays on top of the basketball as it falls. What happened? Did the tennis ball bounce higher than in step one?

How does it work?
It took energy to lift the basketball and tennis ball into the air. As you held the balls, they had potential energy. Potential energy is stored energy. When you let go, the balls now had kinetic energy. Kinetic energy is moving energy.

So which ball had more potential energy? The basketball, because it was heavier and took more energy to lift.

So why did the tennis ball bounce so high? The large kinetic energy from the basketball was transferred to the small tennis ball, causing it to bounce much higher than it would have alone. You might think of it as getting an extra "push" from the basketball.

Try this:
Bounce the basketball by itself near a wall and have someone mark how high it went. Next, put the tennis ball on top of the basketball and let them drop (like in step two of the experiment). Again, have someone mark how high the basketball went. You probably found that the basketball did not bounce as high. This is because it lost some of its energy to the tennis ball and therefore didn't have as much energy to bounce as high.