Why Are Tennis Balls Fuzzy?

It’s common to see her racing out the door at lunch time to head to a tennis practice with her team affectionately known as the “Smash Girls.” Watching our CEO maintain health—physical and mental—by slamming fuzzy, fluorescent balls across the tennis court made us wonder about the science of tennis balls.

First of all, why are tennis balls fuzzy?

The simple answer has to do with the aerodynamics of the ball. When the bright yellow felt that covers a tennis ball is fluffed up, even slightly, it has an effect on the ball’s speed as it flies through the air and over the net. Not that there are many folks out there who would be able to tell much of a difference when watching the next US Open. After all, when Serena Williams serves a ball at 122 miles per hour, it can be difficult to imagine any amount of fuzz capable of slowing the ball down.

The fuzz on the ball can also impact the path of the ball as it soars toward your opponent. You could hit the ball with just the right kind of spin and think getting your point is inevitable. But, what if some stray fuzz catches the wind? That slight change may just cause the ball to veer off course, giving the other player the opening he or she needs to send the ball right back to you.

Have you ever noticed how the pros will sometimes examine several tennis balls before settling on the one they ultimately serve across the court? They are looking for the perfect ball. The one ball whose fuzz is lying as flat and as close to the surface of the ball as possible.

The tennis ball has come quite far in its long history. Modern tennis balls have always been made of rubber but, historically, the balls were made from leather, moss, human hair, or even sheep guts. Picture yourself arriving at the tennis court with a freshly opened can of sheep gut tennis balls. Makes you thankful for advances in modern sport science, doesn’t it?

Understanding why tennis balls are fuzzy is one thing but understanding why they bounce is another. One aspect is entropy and another is the chemical composition of the ball. The chemical composition of a ball establishes the elasticity, which determines the ball’s ability to retain energy when deformed and subsequently influences the bounce. With increased elasticity more energy is retained in the rubber and recovered in the bounce. Different rubber materials retain different amounts of energy–all rubber is not created equal. Therefore, the bounce-ability of a tennis ball is largely controlled by the molecular structure of the rubber.

And even though our modern tennis balls have always been made of rubber, the bright yellow fuzz was not always a commonplace look. Early on, tennis players would stitch flannel around the outside of the rubber core. And, depending on the look of the court on which the players played, the balls were typically either black or white in color.

This leads us to another question: why are tennis balls a bright, fluorescent yellow?

Again, we have another simple answer. Because of television. In 1972, the International Tennis Federation introduced yellow tennis balls because studies showed the yellow balls were easier to see during televised tennis tournaments. Not everyone was on board with this change, however. Wimbledon continued to utilize the traditional white tennis ball until 1986.

So, the next time you play a game of tennis, or even watch a couple of pros go at it on TV, see if you can notice if there is a difference between a brand new ball being used versus one that has seen its share of match points. And remember to be grateful for that little yellow ball flying across your screen. If it was still white, there may not be much to watch.

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