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Tension and control

Q: Does a tighter string tension mean less control because it bounces off faster? And does a looser string tension mean more control because it stays on the string longer?

A: No. In fact, just the opposite seems to be true.

Although everyone thinks he knows what he means when he says “control,” it is actually a difficult word to describe accurately. For the purposes of this question, let’s assume that for there to be “control,” the bounce of the ball off the strings must be as similar as possible to what it would be if it were obeying the Law of Reflection, that is, where the angle of reflection equals the angle of incidence. The more deviation between the actual bounce and the bounce as described by the Law of Reflection, the less control you have.

It used to be thought that to control the ball better, you wanted the ball to stay on the strings longer, so you used looser tension. As Brody, Cross, and Lindsey point out in the best-selling The Physics and Technology of Tennis, which is available for purchase on-line, we now think we know better.

In the case of on-center hits, the longer the ball is on the strings, the longer the racquet has to rotate out of position due to the natural movement caused by the impact of the ball. In the case of off-center hits, the stringbed deforms asymmetrically (with a higher angle where the ball is closer to the frame, and a lower angle where the ball is farther away). The looser the stringbed is, the greater the angular difference during off-center impacts. In each of these two cases, there is a loss of control.

As Rod Cross has pointed out, contact time decreases if the stiffness of the string plane increases (Dwell Time, by Rod Cross). Therefore, tighter string tension gives you a stiffer stringbed, less contact time, and more control. Looser string tension gives you a softer stringbed, more contact time, and less control.

From the August 2008 issue
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