A professional tennis player can serve a modern tennis ball much faster than a pitcher can throw a baseball, and can use a variety of spins to befuddle an opponent. Many innovations to the tennis ball have occurred over the years that have served to drastically improve the game. The physics of the tennis ball is interesting enough to inspire physicists to write research papers about it.
Fuzziness
A tennis ball is fuzzy for several different reasons. First, its fuzziness provides extra friction, ensuring that when the ball hits the surface, it rolls or skips rather than slides, according to the book "The Physics of Sports" by Angelo Jr. Armenti. Second, the extra friction allows players to more effectively use top spins and back spins. Finally, the tennis ball's fuzzy surface slows it down. Without fuzziness, no one could return a serve, because the ball would be moving too fast.
Composition
Tennis balls are rubber balls with a special kind of felt wrapped around them to provide fuzziness. Two main types are used -- pressurized balls and pressureless balls. Pressurized balls have hollow cores filled with either air or nitrogen. Nitrogen balls stay inflated longer. Pressureless balls, by contrast, have solid cores. Unlike pressurized balls, which go flat about a month after they are removed from their container, pressureless balls can be used indefinitely. The disadvantage of pressureless balls is that the felt wears off faster.
Special Types
Two special types of tennis balls are commonly used. If the container specifies that the balls are regular duty, they are ordinary tennis balls and are most suitable for indoor and clay courts. Extra duty tennis balls are thicker, and are most suited to grass courts and competition tennis courts. They quickly become too fuzzy when used on clay courts. High-altitude balls have lower air pressure than other balls, because ball with standard pressure bounce too high at high elevations.
Specifications
Tennis balls must adhere to certain specifications to be used in competition. According to the study "Dynamic Properties of Tennis Balls" conducted by Rod Cross at the University of Sydney in 1999, a tennis ball dropped from 2.54 m -- 100 inches -- onto a concrete slab must bounce between 53 and 58 inches. It must weigh between 56.7 and 58.7 g, and have a deformation of less than 5.97 cm.
Historical Development
Tennis balls were originally made of leather or cloth, and stuffed with rags or horse hair. In the 1870s India rubber began to be used, and their function was improved by wrapping flannel around their surfaces. Later innovations included using a felt on the exterior, and the use of pressurized balls.
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