This Week's Experiment - #479 High Bounce

Be sure to try this science experiment outside! It will save you the work of cleaning up the pieces of broken lamps and shattered windows.

For this experiment you will need:

a basketball or soccer ball
a tennis ball
duct or masking tape
a flat, hard surface, outside

Hold the basket ball about shoulder high in one hand and the tennis ball at the same height with the other. Drop both at the same time. If both are fairly new and fully inflated, they should bounce about the same height. OK, nothing strange about that.

Next, use the tape to make a round, raised collar on the basketball. This is going to help you balance the tennis ball on top of the basketball. It does not have to be fancy. Just a ridge of tape in a circle that will fit the bottom of the tennis ball.

Hold the basketball out at the same height as before, with the tape ring at the top. Place the tennis ball into the tape ring. It should balance there. Now, before you drop it, think about what you expect to happen. Then drop the balls.

Understanding the Science

What happened? The tennis ball bounced VERY high. Why did that happen?

When you were holding the basketball and the tennis ball, they had potential energy, the energy of position. When you released them, that potential energy was changed into the energy of motion. In other words, they fell. When the basketball hit the ground, its momentum compressed it, flattening the bottom. The same thing happened when the tennis ball hit the basketball. Their energy of motion was changed into compressed mechanical energy, much like squeezing a spring.

Then the compressed mechanical energy was changed back into the energy of motion. As the basket ball bounced, it bumped into the tennis. That impact transferred some of the energy of motion from the basketball to the tennis ball. The basketball was left with less energy of motion, so it did not bounce as high as it did the first time. The tennis ball wound up with a lot more energy of motion, so it bounced very high.

What do you think would happen if you reversed the two balls, putting the basketball on the top? How much higher would the extra energy from the tennis ball lift it. What if you used a heavier ball instead of the basketball? Or a ping pong ball on the top? There are all sorts of combinations to try, and you will be surprised how much you learn while you are having fun.

Have a wonder-filled week!