Pressure and Tennis Balls
Tennis balls come in a pressurized can. Once the can is popped open and the balls are exposed to the surrounding air, the internal pressure starts to decrease.
Pressurized tennis balls have better bounce, more spin and travel faster, but they have a short life span and have to be replaced often during the course of a game.
Both the ATP (Association of Tennis Professionals) and WTA (Women’s Tennis Association) require balls to be replaced every 7-9 games, depending on the tournament.