Learn more physics!
Do the standard tennis balls of all tennis brands have the same amount of air pressure inside their tennis balls?
Walnut, CA, US
No. The USTA regulations only specify the pressure for special "pressure-less"balls, which use more rigid skins rather than air pressure. The rules say that that type of ball must have less than or equal to 1 psi (7 kPa) pressure (above atmospheric pressure). There are a number of other rules, for example, a ball dropped from a height of 100 inches must rebound between 53 and 58 inches, which apply to all tennis balls.
For all the gory details see Appendix I at the USTA site: http://www.usta.com/2011_tennis_ball_specifications/
LeeH (mods by mbw)
(published on 01/04/2008)
Follow-up on this answer.