Hey Bug! Natalie K. from Illinois wants to know: What makes a bouncy ball bounce?

When you drop a ball, the ball pushes down on the floor and the floor pushes back up on the ball. (Weird!) In slow motion you would see that the side of the ball squishes or dents when it hits the floor. According to physics professor Lou Bloomfield, the energy of the falling ball is now stored in the dented ball. The ball then uses that energy to push back on the floor. It undents—and bounces.

The ball doesn't bounce back as high as it fell because it cannot store all the energy it had when it hit the ground. Some of that energy is lost to heat. That's why a basketball warms up when you dribble it. Bounciness depends upon what a ball is made of and how it's put together. In a “Bounciness Olympics,” superballs would take the gold. Made from a special hard rubber, superballs return to their original shape when dented without losing too much energy. Most hard surfaces store and release energy better than soft ones. That's why beanbags don't bounce very well and why rubber balls bounce higher on cement than on carpet. Now, when you're told the living room is a bad place to play ball, you'll know why.

Activity

1. Why does a superball have more bounciness than a foam ball?
[anno: A superball has more bounciness than a foam ball because the rubber in a superball is harder and dents less than foam when the superball hits the floor, thus more energy is conserved.]
2. You want a ball to bounce as long as possible. What kind of floor do you bounce the ball against? Why?
[anno: You bounce the ball against a hard floor, like cement, because the harder a floor is, the less energy it will take away from the ball that bounces against it.]
3. Imagine that you are going to play tennis with a friend. There are three tennis courts available. One court has a dry clay floor. The second court has a grass floor. The third court has a cement floor. Which court do you choose? Why?
[anno: Answers will vary but could include that the student chooses the clay or cement court because the tennis balls will bounce farther on these courts.]