Serve 'em "Up"

The physics of the serve dictate that the ball must be hit up, not down, in order for it to go into the service box across the net -- unless your are more than seven feet tall!

To demonstrate this to your players, have your tallest player tie one end of a long piece of string to the center of his racquet. Have the player stand at the baseline and hold his racquet as high as he can, simulating racquet/ball contact point on a serve.

Take the other end of the string and bring it toward the opposite service box. Your players will immediately see that the string cannot make it into the opposite service box without going through the net. If you lift the string over the net, it will not go into the service box, unless you bend the string down over the net.

That's right -- when you see pros hitting serves at more than 140 mph, they are actually hitting the ball up. This is possible because of the immense amount of spin that is put on a correctly hit ball which brings it back down into the court.

The article goes on to discuss how to use this knowledge to improve your players' serves.