I know tennis balls go flat (even if all they do is sit there) because the interior of the ball is actually pressurized above normal atmospheric pressure, and over time some of the air leaks out. The question is, why aren't the balls manufactured with some material lining the interior that's pro...

Two matches I lost recently, I thought I hadn't taken advantage of my opponent's serve. One had a pretty short and dinky with a some weird spin (she had some shoulder problem). The other one had a powerful first serve which I had to block, but her second serve was easy with some kind of spin (...