That's a good question! It can be surprising how
objects that seem very similar, like two
basketballs that both appear to be fully pumped
up,can behave differently. How high a ball bounces
depends on the elasticity of material it's made
out of and, in the case of balls that need to be
inflated, the elasticity can also depend on how
fully inflated the ball is.
basically the ability of an object to bend without
breaking and then to return to its original shape.
If you were to drop a basketball and a lump of
clay, it is the elasticity of the rubber
basketball that allows it to bounce back while the
clay just lies on the floor. Both objects can
bend without breaking when they hit the ground,
but the clay can't return to its original shape so
it can't bounce back.
The bounciness of a
ball is given by a number called the "coefficient
of restitution", which is just a big scientific
term for how high a ball bounces after you drop
it. A super ball, usually made of highly
compressed synthetic rubber, has a coefficient of
0.9 to 0.95, which means that when you drop the
ball it bounces back to 90% - 95% of the original
height that you dropped it from (almost all the
way back!). A fully inflated basketball, on the
other hand, has a coefficient of about 0.75, which
means it bounces back to 75% of the height that it
started from (3/4 of the way back). When a
basketball has a little less air in it (even if
it's such a small difference that you can't really
see it),the coefficient will go down and the ball
won't bounce as high. This could be the reason
that some basketballs bounce higher than others
even when they both seem to be equally pumped up.
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