Posted by on Jul 12, 2015 in Tell Me Why |

# Why Do Tennis Balls Bounce?

Like many other types of balls, tennis balls have a hollow center filled with air. Like all gases, the air inside a ball moves around easily to fill the space it occupies. Being loosely organized, the molecules of gas can expand or contract quite easily.

When a tennis ball hits the ground, the ground exerts a force on the ball, pressing upward and pushing the bottom of the ball inward. This force compresses the gas inside the ball. Immediately, the gas begins to expand again, returning the ball to its normal shape. This action is a bit like a spring that causes the ball to bounce back into the air.

How high a particular tennis ball will bounce depends upon the pressure of the air inside the ball. Scientists use a special equation to determine the amount of pressure: p=r RT, where “p” is the pressure, “r” is the density, “R” is a constant specific to the gas, and “T” is temperature.

Will a ball bounce higher in hot or cold weather?

Higher temperature will lead to a higher pressure. As temperature increases, gas molecules expand which increases energy and they bounce around faster inside the ball. That’s why higher pressure leads to a higher bounce of the ball.

Likewise, a lower temperature will lead to a lower pressure. As the temperature decreases, gas molecules contract and move around more slowly with less energy. Thus, lower pressure leads to a lower bounce of the ball.

That’s why a fully-inflated ball might appear deflated if the temperature drops dramatically. As you probably already know, that partially-deflated ball won’t bounce nearly as high as it would if it were warmer.

Professional athletes and sports teams take temperature into consideration when playing games. They understand that balls act differently in colder weather than they do in warmer weather.

For example, football teams playing in extremely cold weather often have to compensate for the fact that footballs will bounce differently, especially when kicked.

Content for this question contributed by Amy Mescher, resident of Manning, Carroll County, Iowa, USA