# Q & A: Tennis Ball Facts

Q:
I need to know what a tennis ball is made out of, the amoumt of pressure in a tennis ball, and amout of air inside the ball. Thanks,Andrea
- Andrea (age 14)
San Benito High School, San Benito, TX, USA
A:
ndrea -

Tennis balls are made of a layer of rubber surrounding a hollow center. Then they put a thin layer of adhesive on the rubber and cover it with a layer of felt (usually yellow). The letters that you may see on the felt are just black ink.

The air pressure inside the ball is 12 psi (pounds per square inch) greater than ambient air pressure at sea level (the 'normal' air pressure all around you). The ambient air pressure is 14.7 psi, so all together, the pressure inside the ball is 26.7 psi.

I'm not quite sure what you mean by the 'amount of air inside the ball,' but you can figure out how much space is in the ball using the equation for the volume of a sphere (4/3*pi*r^3). A tennis ball that I have here is 2 1/4 inches across, with 1/8 inch thick rubber all around. So the open space inside is 2 inches across (the diameter is 2 inches). The radius (r) is half of that, so r=1 inch. So the volume of the inside of the ball is 4/3*pi (pi=3.14) inches^3 = 4.2 inches^3. (You would say this as 4.2 cubic inches of open space.)

Thanks again to the for their help with this question.

-Tamara

(published on 10/22/2007)