You may need new sneakers, a restringing and the latest court couture to be at the top of your game, but the fuzzy yellow balls still sitting at the bottom of your gear bag in their pristine packaging are probably OK. Tennis balls are packed in cans pressurized to the exact same degree as the inside of the balls to preserve the springy bounce until you open the can to use them.
There's a reason a new can of tennis balls makes that little whoosh or pop when you crack the lid. The can itself is under pressure to protect the balls inside from deflating. Tennis balls bounce because the pressure inside the ball is greater than the pressure outside it. Once you open a can, the pressurized air inside begins to escape. When you whack the balls across the net, the pounding forces microscopic amounts of air through the skin of the ball and the inside pressure itself pushes some air out of the ball.
Tennis Ball Technology
Two hollow rubber hemispheres are glued together to form the base of the ball. The ball interior is filled with pressurized air, the rubber sphere gets a thin coat of adhesive and then a fuzzy layer of yellow felt is applied and sealed with liquid rubber seams. Play wears away the felt and pushes some pressurized air out of the ball. Extreme heat causes the rubber molecules to separate, also allowing pressure to escape. Even ball-can construction affects the bounce factor. Containers made from recycled plastic can leak pressure, causing new balls to go flat. Virgin plastic cans are more impermeable, according to a Wilson Racquet Sports official quoted in "The New York Times."
Once a high-pressure ball is in use in lower-pressure atmosphere, it's good for about two weeks, says Tennis Express. That's for casual play -- most pros change balls during tournaments every nine games to ensure the bounce remains uniform. At Wimbledon, balls are changed alternately every seven and nine games and new balls are stored courtside in refrigerated containers so their pressure will not be affected by the heat. The BBC reports that, in general, three hours of actual play is the max for optimum tennis ball bounce. Keep track of your bounce, if you are a frequent player, by marking the date on tennis balls when you open the can -- or just replace them when the "thwack" begins to sound like a "thud."
Life After Death
When your tennis balls have lost their bounce, they can still contribute to your fitness program. Punch a hole in a dead ball, suspend it on a thin cord and use it for forehand and backhand practice in your garage or backyard. Squeeze tennis balls as hard as you can to build grip strength in your hands. Massage your post-match feet by rolling a used tennis ball under the arch of your foot. Take the dog out for a brisk walk and toss an old tennis ball for a vigorous game of fetch. Dead tennis balls are also handy for fluffing post-match towels and socks in the dryer.
- The New York Times: A Future for the Used-Up Tools of the Tennis Trade
- University of Illinois Department of Physics: Why Do Tennis Balls Lose Their Bounce?
- Tennis Planet: Tennis Balls: Pick the Correct Tennis Ball for Training
- University of Illinois Department of Physics: Tennis Ball Facts
- Tennis Express: Tennis Balls
- BBC: Having a Ball at Wimbledon!
- PhysioAdvisor.com: Hand Strengthening Exercises
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