Why are tennis balls fuzzy?

Tennis balls are circular objects made of vulcanized rubber that have a colored coating attached to it. This coating is called the felt. The felt is stitched at certain angles which gives us the characteristic lines on the tennis balls.

Tennis balls come in various forms. They can be pressureless, pressurised, regular duty, extra duty or high altitude balls. Each of them have their own specific function. Based on their function the durability of the core of the tennis ball varies. However, what makes the ball suitable for a match is the felt that is stitched and adhered to it.

The felt is what makes the tennis ball fuzzy. The fuzziness contributes to the aerodynamics of a tennis ball. The ball falls under the category of a “bulky object” that experiences two mechanisms: skin friction and pressure drag. 

When a racquet’s string contacts the tennis ball, the felt is what generates the needed friction for better control of shots. This is called skin friction and it allows the player to experiment with slices, spins, drop shots, smashes, etc when the tennis ball contacts the racquet. Once the ball leaves the racquet, it will travel in the desired direction but will be countered by the air in the opposite direction. This is called pressure drag. The felt allows the pressure drag in a way that the ball can follow a certain parabolic motion that can be appreciated at each stroke in a tennis match. The parabolic path is the result of the ball getting slows down as each particle on the felt acts as an obstacle for the air.

Thus, it is extremely crucial for a tennis ball to have a certain fuzz on it, else it would be difficult for the player to control the ball.

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