At The USTA Training Center (Page 15)

Because of the unpredictable shot making in pro tennis, it was impossible for our cameraman to follow the flight of the ball and at the same time keep the ball in focus well enough to count the revolutions of spin. If we had attempted to film the spin over the course of the flight at the Open, we would have had to devote all our time to get probably just a few good examples!

Once again the team decided that what was needed was a controlled experiment. We were able to set up this second experiment at Key Biscayne at the same time we were using the camera to study the ball/court interaction and the trajectory of the flight.

For the camera to see and track the flight of the ball and its spin, the team needed a higher camera position that allowed us to look at the flight of an oncoming ball from a position above court level. The USTA training center was perfect for this because it includes one of the largest and most famous stadium courts in the world, used for the Lipton Championships every year.

With the support of the USTA and Paul Roetert, we were able to gain access to the stadium and create an ideal vantage point.

The ball machine was placed in the same position as for the ball/court interaction experiments, in the center of the baseline and set to throw the same kind of rally ball along the center service line. Once again we extended this center line all the way to the baseline, to help us judge the angle of the trajectory. Using the same ball machine setting, we filmed 6 different types of spin:

1. Flat or no spin
2. "Low" Topspin
3. "Medium" Topspin
4. "Heavy" Topspin
5. "Medium" Underspin
6. "Heavy" Underspin

Our cameraman Mark followed the ball as it came out of the machine, as it approached the court surface prior to the bounce, and then after the bounce. With our same ball marking system, we were able to see the spin clearly and count the revolutions as the ball left the machine, and also before and after the bounce. Our Principal Investigator Jani Pallis once again determined if a given ball drifted too far to the left or right of our extended service line, while Mark and John counted the number of clean events filmed until we had recorded 10 for each of the spin variations.

Using the exact same experimental set up, we repeated the trials using the "fuzzless" core balls. It was immediately apparent what the effect of the fuzz is in the flight of the ball! When the balls started coming out the machine they took off like rockets! The ball travels much further and bounces much higher. The fuzz allows players to control their shots and keep the ball in the court! We plan to study some of these differences by putting both types of balls--with and without fuzz in a wind tunnel in another exciting part of our project!