The tennis ball has evolved from a leather bag filled with rags or horse hair to the modern, aerodynamic implement used today. Several different types of tennis balls are manufactured. They vary according to the type of surface they are designed to be used on, the altitude of the court and the length of time they will be used before being discarded.
Fuzziness
Tennis balls are wrapped with an outer layer of felt. The felt makes the ball fuzzy, changing its behavior on the court. A fuzzy ball hits the court with more friction, preventing it from sliding. Instead, the ball will either roll or skip if it doesn't hit the court hard enough to bounce, according to the book "The Physics of Sports" by Angelo Jr. Armenti. The friction makes tricky spins possible, enhancing the competitiveness of the game. The fuzzy surface also slows down the ball, preventing it from being served too fast for the opposing player to return it.
Inflation
Two types of tennis balls are manufactured -- solid and hollow. Competitive tennis games use hollow balls almost exclusively. The problem with hollow balls is that they go flat within about a month of being removed from their pressurized cans, so they don't bounce anymore. Hollow balls are used in competition because the felt doesn't wear off as fast. Hollow balls are filled with either air or nitrogen. Nitrogen balls are more expensive to manufacture, but they stay inflated longer.
Bounce
How high a tennis ball bounces is a function of its weight, its deformation and the speed at which it hits the court. Competition tennis balls are manufactured according to certain standards -- they must bounce between 134.62 and 147.32 cm when dropped from a height of 254 cm onto a rigid surface, according to the study "Dynamic Properties of Tennis Balls" conducted by Rod Cross at the University of Sydney in 1999. Competitive tennis balls must weigh between 56.7 and 58.7 g, and they must have deformation of less than 5.97cm.
Extra Duty Balls
Tennis balls interact with the court in ways that can change the game. Four types of courts are normally used -- indoor, clay, grass and competition tennis courts. Ordinary tennis balls are used for indoor and clay courts. Extra duty balls are designed for grass courts and competition tennis courts. Extra duty felt is denser, because ordinary tennis balls become too fuzzy when used on these surfaces.
High Altitude Balls
The inflation of a pressurized tennis ball is a function of the relationship between the air pressure inside the ball and the air pressure outside. At high elevations such as Denver, Colorado, the outside air pressure is lower, making ordinary tennis balls bounce too high for competitive play. For this reason, high-altitude balls were created with lower air pressure in their core. A high-altitude ball will not bounce high enough at sea level.
References
- Reader's Digest Asia: Why Are Tennis Balls Fuzzy?
- Manchester District Tennis League: Nine Facts About the Tennis Ball
- E-tennis.org: Tennis Balls
- University of Sydney Physics Department: Dynamic Properties of Tennis Balls
- University of Illinois Department of Physics: Tennis Ball Facts
- ITF Tennis: Ball History
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