Two important factors that determine how high a
basketball bounces are the force with which it is
bounced and the height from which it is released.
The higher you release it from and the more force
you apply, the higher it will bounce.
Additionally, the height a basket ball (or any
other ball) bounces has to do with the elasticity
of the collision between the ball and the floor.
In an elastic collision, kinetic energy and
momentum are conserved. In an inelastic collision,
kinetic energy is not conserved. Energy can be
lost to friction, sound, and heat.
When you drop a ball from a stationary
position, it starts with all potential energy. As
it falls, it gains speed and kinetic energy, but
it still has the same amount of total energy. When
it hits the floor in an inelastic collision, it
loses some of its kinetic energy. As it bounces
back upward, it exchanges its kinetic energy for
potential energy, but it does not bounce as high
as before because overall, it has less energy.
a picture here
A collision between the basketball and floor will
never be perfectly elastic (ideal). The closer a
collision is to being perfectly elastic, the
higher the ball will bounce.
So what makes the basketball behave more
ideally? The less energy that it loses during the
collision, the more kinetic energy will remain.
One important factor is the type of rubber the
ball is made out of. Rubber has two important
properties – it is highly extensible (stretchy)
and it returns to its original shape after
deformation. When the rubber hits the ground, it
is deformed; the side of the ball hitting the
ground is squashed. When it returns to its
original shape, the ball bounces back upward. The
better the rubber is at snapping back to its
original shape without losing energy, the higher
the ball will bounce.
Another important factor is the air pressure
inside the ball. When the ball is deformed, the
volume inside of it changes and the air is
compressed. The extra pressure from the compressed
air helps it to return to its original shape and
bounce up. If there is not much air in the ball to
begin with and the pressure is low, the ball will
not bounce well. However, if there is a lot of
air, the pressure is high and gets even higher
when the ball hits the floor. The compressed air
expands and helps the ball quickly recover from
the deformation and bounce higher. (If there is
too much pressure, the basketball will explode).
The temperature of the ball will affect both
the properties of the rubber and the pressure of
the air inside the ball. Cooling a basketball will
make it bounce less high.
For another explanation from a different
perspective, this website may be helpful:
here to see
McCrum, N. G., C. P. Buckley, and C. B. Bucknall.
Principles of Polymer Engineering. Oxford: Oxford
UP, 1997. Print.
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