'Feel' in relation to the dynamic characteristics of tennis balls

The quantification of 'feel' in any sport is a difficult objective to obtain because of the number of variables involved. Previous researchers have considered vibration, sound frequency, visual information and force. This paper attempts to define the feel of tennis balls using the coefficient of restitution and contact time on a hard surface. Six types of tennis balls impacted with a force platform at velocities between 2 and 30 ms-1 (5 and 67mph) and the impact and rebound speeds recorded using light gates. The coefficient of restitution decreased with velocity for all balls and the removal of internal air pressure for a pressurised tennis ball reduced the coefficient of restitution by approximately 20% at typical ball racket velocities. The duration of impact was also found to decrease with impact velocity and the removal of internal air pressure caused the contact time to lengthen by 15%. An objective method of measuring the 'feel' of tennis balls was suggested as a combined plot of the 'dynamic' stiffness versus the coefficient of restitution. In comparison to a standard pressured ball, 'better feel' was defined as a ball with a higher dynamic stiffness and with a higher coefficient of restitution. It was found that a punctured ball had much worse 'feel' and only one ball had a better 'feel' than the pressurised ball. It was concluded that this method gave intuitively correct results which need verifying through player testing.