What happened? It suddenly got a lot chillier, even here in Houston. So let's talk about how that affects your tennis balls. And, before we go much further, let me make clear – I'm talking about the tennis balls that come in cans and that we hit over the net with our racquets. I'm not talking about any part of anyone's anatomy.
But I am talking physics. If you're playing with pressurized tennis balls (and I'm sure you are), then your ball has a hollow core filled with pressurized air or nitrogen. As I'm sure you can imagine, the higher the pressure inside the ball, the more bouncy it is (if you can't imagine this, trust me – it's true). So, when you first open a vacuum-sealed can of tennis balls, the balls are fully pressurized and are nice and bouncy. Over time, they lose their pressure and become less and less bouncy.
One way to get a dead ball to become bouncy again is to warm it up. When the temperature of a ball increases, the air or gas molecules inside the ball move around faster, increasing the pressure. So balls will bounce higher on a hot day because their pressure is higher. In fact, some people think you can revive worn-out tennis balls by heating them in your dryer. (Personally, I'm guessing the dryer effect might last for a little while but certainly not long enough that you can show up with these balls at your next match.)
What about cold balls? As you may have guessed by now, cold balls have less energetic molecules inside them and therefore less pressure. This makes them less bouncy.
What does all of this mean for your tennis game? Well, when you're playing tennis on a cold day, you can expect your tennis balls to be less bouncy, dead even. These “dead” balls will have to be hit harder than usual if you want them to go deep or have any pace.
Bottom line? Expect to work harder on cold days and be ready for those cold balls to react a little differently than they would on a warmer day.