Great servers have realized that power and pace are not the end-all and be-all, and that their killer shots must be backed up with a solid return game.

But, of course, serving the ball inbounds is just the first step ... per hour faster than the average female professional tennis player. Now, part of that speed is the result of pure strength.

What are tennis balls made of? Modern tennis balls are made of a hollow rubber core, covered in a wool or nylon shell which is known as the nap. Pressurised air inside the rubber core makes the ball ...