At The USTA Training Center (Page 14)

The team knew from its study of ball speed at the Sybase Open, that in pro tennis the speed of the ball decreases significantly over its flight. A Pete Sampras serve that is traveling about 120mph as it leaves his racket has lost about half its speed, traveling at about 60mph just before the return.

What about the spin? How does it change over the course of the flight? At the Open, our digital camera allowed us to measure the spin of the ball as it comes off the racket. As a result of our work, the tennis world for the first time has extensive data on the incredible rpms generated in pro tennis. (See the section in the web pages on ball spin for how we measured the spin in pro tennis and also for the results.)We know for example, that a so called "flat" first serve traveling at 130mph still is spinning at about 2000rpm. Second serves can spin at rates over double that, 4500rpm or higher. Heavy topspin groundstrokes, for example, the forehands of Sergi Bruguera or Tomas Muster are spinning at 3000 to 3500rpm as they come off the racket.

But those numbers represent the initial spin off the racket--what actually happens to the rate of spin over the course of the flight? If the speed slows down so much, is the same true of the spin? Will it decrease by half as well?