Why is tennis-ball furry?

The tennis balls are made from synthetic substances and about ten different chemicals. First the sheets are made from these ingredients which are then cut into strips shaped like the numeral 8. Two strips are heated up to a certain temperature in a pressure chamber and their edges are joined with latex like adhesive. Natural atmospheric pressure is 14.7 pounds per square inch whereas the air pressure inside the ball is kept at 13 pounds per square inch. If the internal pressure is same as the external then the ball’s pitching on the court would not absorb the force of its momentum. It would bounce higher than the racket extended above the head of the opposite player, because equal air pressure inside as well as outside the ball would not allow the ball to compress as it hits the court. However, the small difference of 1.7 pounds per square inch between internal and external pressure is not adequate to keep the bounce low. Hence, a coat of furry felt comprising of nylon, wool and Dacron fibers is pasted over the ball.

As the tennis ball pitches on the ground the felt covering is compressed first and then the synthetic material beneath the felt. Both the phenomena ultimately absorb much force of impact. One of the important laws of tennis stipulates that the ball released from the height of 100 inches above the court should not bounce higher than 58 inches. This law is meant to ensure that the bounce of the ball is controlled. Another important purpose served by the furry felt is reduction in the speed of the ball through friction with the air in order to give some more time (even if it is friction of a second) to the player to return fiery service or to hit a volley. One more advantage of felt covering: It is the fibrous surface of the ball that prevents it from slipping on the catgut cord of the racket even if it is hit from the slanting angle. On the other hand playing with a fiber-less smooth ball the players find it difficult to judge where the ball will pitch.

More reading:
Tennis-ball (Wikipedia)

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