Question: How can you tell whether a tennis ball is still good?
Answer: The rules of tennis say that a ball must bounce to a height between 53 and 58 inches when dropped from 100 inches. The crude version of this is to drop the ball from the top of your forehead, and if it bounces at least to your belly button, it's good, assuming it still has a decent coat of felt. Experienced players can often just give a ball a good squeeze and judge its fitness by its firmness.
