For athletes who play sports involving inflatable balls, such as soccer and basketball, the relationship between the amount of air in the ball and its bounce is important. Aside from purposeful inflation and deflation, ambient temperature and general use can lead to fluctuations in the ball's air pressure. Armed with knowledge of how air pressure affects the height of a ball's bounce, you may be able to save a potentially troubled game from an improperly inflated ball.
Bouncing a Ball
Similar to tires, soccer and basketballs are primarily composed of two parts: a hard, outer protective shell and an inner air bladder connected to a valve for inflation. Without air in the ball, nearly all of the potential energy in the ball as it is dropped will be used to mold the ball to the shape of the ground as it hits. In comparison, a slightly inflated ball will store some of this energy in the air inside, with some of it lost to denting as it hits the ground and the rest used to rebound upward.
Proper Inflation
While the outer surface of the ball stores and returns energy poorly, the air inside works much better to help the ball rebound from the ground. With all other factors held constant, a fully inflated ball will bounce higher than a slightly inflated ball. As such, the needs of a sport can be used to determine the extent to which a ball should be inflated. By slightly under-inflating a ball and allowing some of its energy to be lost as it strikes the ground's surface, you can limit the maximum height of its bounce to your sport's needs.
Overinflation
All balls are manufactured to withstand a limited amount of air pressure. Although the relationship between the amount of air in a ball and the height of its bounce is constant, this relationship is restricted by ball's air pressure limit. By filling a ball to or beyond its maximum, you may run the risk of causing tears or slow leaks in its air bladder. While an overinflated ball will initially bounce higher than a properly inflated ball, such slow leaks will gradually reduce the ball's air pressure, leading to inconsistent, ever-decreasing bounce heights as the game goes on.
Outside Influences
Just as the surface of an under-inflated ball absorbs some of its potential energy as it dents while striking the ground, a softer surface will absorb more of a ball's energy than a harder one. Basketball, which traditionally is played inside on a hardwood floor, requires considerably lower air pressure than soccer for a controlled, consistent bounce. As outside air pressure and temperature have little effect on a basketball's bounce, National Basketball Association rules dictate a small, very controlled pressure range between 7.5 and 8.5 pounds per square inch for all regulation balls. To allow for greater bounce height on the soft, outdoor soccer pitch, FIFA's Laws of the Game allow for a higher, more flexible range of ball pressures. To accommodate for the soft pitch, differences in air pressure between stadiums at different altitudes and fluctuating outside temperatures, FIFA balls can be inflated between 8.5 and 15.6 psi.
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