Originally Posted by daved
Have people not been paying attention to the little bit of actual research done on the subject by Lindsey, Cross, et al.?
Poly strings slide easily against each other. According to research to date, there is an actual "slingshot" effect with the strings flexing and snapping back during the ball's dwell time on the stringbed, thus helping the player put more spin on the ball. While this happens with any string type, it is much amplified with poly (or any strings sliding easily against each other...hence the silicone spray thread here).
Yes, use of poly may affect spin production in other ways -- if the string is less elastic and less powerful, the player may feel more free to swing out hard on every shot.
But the "slingshot" effect appears to be the crucial difference. Try poly at 30 pounds in an open stringbed and you'll feel it.
FYI, in the above experiments, the racquet was stationary and not moving at all.
"In these movies, the racquet was clamped into a secured holding device."
That is completely different from what happens when the racquet is swung vertically at a very high rate of speed. The direction and magnitude of the forces on the strings will be completely different. There would be much more force in pulling the strings aside on impact so the strings will move more (assuming a slippery poly) but the ball would likely have already left the stringbed by the time the strings fully snap back.
Take a poly stringbed and use your fingers to pull the main strings to one side as far as you can. Now time how long it takes for the strings to snap back. Is it longer than 0.005 seconds? Because according to Cross and Lindsey (in the book Technical Tennis
, page 82), the ball only stays on the strings for 0.005 seconds.