Tennis ball

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A Wilson tennis ball.

A tennis ball is the bouncing ball designed for the sport of tennis, but also used in some other games, such as squash tennis and lotball.

Tennis balls in the early days of tennis were made of leather stuffed with hair or wool. Starting in the 18th century, ¾" strips of wool were wound tightly around a nucleus made by rolling a number of strips into a little ball. String was then tied in many directions around the ball and a white cloth covering sewn around the ball. This type of ball, but with a cork core, is still used for the original game of tennis, today called real tennis. With the introduction of lawn tennis in the 1870s, vulcanised rubber was first used to manufacture balls often in tubes of four with a package with the name of the brand.

The modern tennis ball is comprised of two major parts, the inner core and the outer cloth covering. The inner core is constructed of two half-shell pieces of formed rubber, which are joined together with adhesive to form a single core. Two dumbbell shaped pieces of cloth are attached to the ball core by adhesive to give the tennis ball its classic appearance. The thickness and density of the ball cloth is matched to the court type for which the ball is designed.

The balls currently in use can be subdivided into two categories:

Pressurized balls have a core pressurised with air or nitrogen. These balls lose their pressure, and hence playing properties, over time.
Non-pressurised balls are made from a thicker rubber core, and the pressure within the core is equal to the ambient pressure. These balls tend to hold their playing characteristics for a longer period of time, as it is only the cloth that deteriorates. Most players feel no difference between presurized and presureless balls, but top-level players claim a notable difference and thus prefer the former.

In 1999, the International Tennis Federation (ITF) approved an experiment in which two new types of tennis ball would be permitted for use in tournaments. The two types of ball were designed to have different performance characteristics derived from their differing dynamic and aerodynamic properties. With the introduction of the two new types of tennis balls (type I and III) there are now three types of ball available for play, type I, II and III. The ball construction for all three ball types can be either pressurised or pressureless as they are classified through measurement of the diameter of the ball and a compression test, which measures the forward and return deformation of the ball under an applied load. Type 1 balls are harder than the traditional type II balls and are designed for slow pace courts such as clay. Type III balls are larger in diameter by approximately 6-8%. Research shows that they are slower through the air due to their increased drag properties, and in addition have a steeper rebound angle both giving more time for the receiver to collect the ball.

Balls and racquets for real tennis

Current regulations imposed by the ITF restrict the colour of the ball to green or white and the seams of the tennis ball must be stitchless. Strict limits are also in place for the mass and diameter for each type of tennis ball, and in addition quasi-static tests are used to determine the ball's static stiffness and coefficient of restitution (COR) through a rebound test. Whilst these tests have the advantage of simplicity, (the rebound test was introduced in 1925 and has remained unchanged since) they may not represent how a ball performs under actual playing conditions. Incident ball speeds in the rebound test of 7m/s are far short of those found at the top echelons of the male game.

Even though, as the name suggests, the ball is used primarily in tennis, it can be used as a safe substitute for games where a solid ball is necessary, for example, to replace a cricket ball, which can inflict damage or injury if not used correctly.

The gift of tennis balls offered to Henry in Shakespeare's Henry V is portrayed as the final insult which re-ignites the Hundred Years' War between England and France.

When we have match'd our rackets to these balls,

We will, in France, by God's grace, play a set

Tennis balls are also a preferred cheap dog toys. This is always of the unpresurized type, so as to not injure the dogs or people playing with them. It is recommended that dog owners replace these tennis balls when they become too worn-out.

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