The modelling of spin generation with particular emphasis on racket ball games

The use of spin in racket sports is vital in a player's shot portfolio to aid control and accuracy coupled with increased difficulty for any opponent. Experts agree that the use of spin is of considerable importance to the way in which the game is played, yet no complete understanding or knowledge of the science has been developed. A number of basic models exist, but these do not accurately predict the behaviour of a high deformation oblique impact under dynamic conditions such as in the tennis ball and racket string-bed situation. This thesis provides a detailed explanation of the creation of spin for tennis, which should be generically applicable to other racket sports. A mathematical model has been developed which incorporates the significant deformation of the ball during impact and also racket and ball parameters. As measurement of the dynamic racket / ball impact phenomena during play is difficult, an experimental programme was established simulating realistic impact conditions using a stationary racket and balls fired from a pneumatic cannon. High-speed digital camera technology was employed to obtain new information regarding ball string interactions, and in particular, detailed information of oblique impacts of tennis balls on racket string-beds. High performance rackets utilising different string tensions, types and string patterns were set at a range of impact angles to study the phenomena and over 2000 impacts yielded some 73,000 individual frames of information. Analysis of the visual data enabled the contact time, footprint size and shape, and the random movement of the strings as the ball passed over them to be determined. Post impact flight images of the ball were also recorded, to complete the data required for accurate analysis of the ball/string-bed interaction and validation of the analytical model. The results presented will enable manufacturers to develop equipment with spin enhancement in mind and raise further research questions for investigation.