Tennis matches fascinate everyone because of their intensity which consistently locks the audience’s eyes to the ball, but it is hard to master even its basic strokes when it comes to playing. This game was originated around the 12th century in the court of Louis X in France. At that time, balls used for playing were made from strips of wool.
Since there has been a tremendous evolution in the tennis balls and now they are made from raw rubber pellets molded into hemispherical shells and glued together with adhesive. The ball is also inflated with pressurized air to achieve the optimum bounce.
The outer layer of the ball is fuzz covered which impacts the ball’s pace and bounce. This fuzzy covering is called ‘nap’ and it is collectively made from wool, cotton, and nylon.
The nap on the ball gives it resistance while moving through the air. If a ball has a smooth surface, there will be very small friction between its surface and air which will make it move at high speed. When a nap is present around the ball, its rough surface creates good required friction (drag force) with the surrounding air thereby slowing down the speed of the ball.
This drag force is known as skin friction drag. Moreover, when the ball moves through the air it tries to knock the air out of its way and turbulent swirls of air are created behind it known as ‘wake’. This wake is a region of low air pressure and the larger its size is, the larger the area of low pressure becomes. The front area of the ball still has a high pressure, and due to this pressure difference in the front and the back of the ball, a drag force acts on the ball in the opposite direction of its movement. Therefore, the speed of the ball is reduced.