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
-Tamara and Mike W.
(republished on 07/11/06)