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Q & A: Bouncing on Floor Surfaces

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Q:
does the density of a floor surface have an effect on the ability of a basketball to bounce? what is the best surface to bounce a basketball on?
- Michael Myers (age 13)
Aston PA
A:
Michael -

How high a ball will bounce depends on how much of the ball's energy is left after it's done hitting the ground. Let me explain... The ball starts with some energy when you let go of it. The higher up it is when you let go, and the harder you push it towards the ground, the more energy it has. When it hits the ground, the ball and the surface both squash some, storing some energy the same way energy is stored in a compressed spring. As they spring back, some of that energy goes back into the ball's upward motion. How high the ball will bounce depends on how much of the energy trickled away into internal vibrations in the ball and the floor and the air and how much was left for the ball's upward movement.

Basketballs are designed to be very "elastic", meaning that not much of their stored energy trickles away. Unless a floor happens to also be very elastic, the ball will bounce highest if the energy goes into the ball squashing, not the floor. So you want the floor to be very rigid. That's not quite the same as "dense", but we think that's what you're thinking of.

Most gym floors are made out of wood or rubber, which squash a little, but not as much as the basketball. So your basketball will bounce pretty well, but not as well as on, say, concrete. Gym floors are designed with a bit of give in them for your protection. If you fall on the ground and it doesn't absorb any of the energy of your fall, you could be hurt much worse than if the ground takes part of the impact.

-Tamara and Mike W.

(republished on 07/11/06)

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