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Tennis racquet string tension and ball speed Featured science projectScience project video

Abstract

This science fair project was carried out to understand how the string tension level of a tennis racquet will affect the speed of the ball during play. The experiment was performed using 2 different levels of tension.

Hypothesis

The racquet with the lower tension level will make the ball travel faster.
 

Scientific Terms

Stiffness, tension, potential power

Background

Tennis racquet and ball speed

The speed that a tennis ball travels at after being hit by the racquet is determined by the power/strength of the player and the speed   with which the racquet is swung. As different parts of the racquet will be traveling at different speeds during the swing, the location at which the ball hits the racquet also   affects the resultant ball speed.

The power of the racquet  is determined by its weight, the stiffness of its frame  and the tension of the strings. The weight of the racquet is important in determining the potential power: the heavier the racquet, the higher its potential power.   It is also most powerful at the balance point of the racquet, also called the “sweet spot” and normally located about 75mm above the neck of the racquet. Hitting the ball at other spots will cause the racquet to spin or recoil upon impact.

A racquet frame that lacks stiffness can cause the racquet to bend or twist upon contact with the ball. This will result in loss of power due to the bending action - if the racquet does not spring back  in time, the ball would not have launched with maximum speed and power.

 If the string tension of the racquet is too high, it will cause the shape of the ball to deform upon impact. In the centre of the string bed, the strings are longer and able to provide more cushioning, resulting in less ball deformation and less energy loss. If the tension of the strings is too high, or the ball is hit  off-centre (where the strings are shorter), ball deformation will cause the tennis ball to lose up to half of its energy.
 

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Complexity level:
8
Project cost ($):
120
Time required:
1 hour to prepare, 6 hours for this science project experiment
Material availability:
You will need a radar gun. Their prices vary tremendously (some cost a few hundred dollars), but a fairly cheap and effective model is the Bushnell Speedster II - it should cost less than $100
Safety concerns:

Basic safety requirements