Tennis ball degradation

Despite anecdotal evidence of changes to tennis ball characteristics and play properties, little research has been directed towards understanding the causes and effects of tennis ball degradation. Improved racket technology and player fitness have contributed to an increase in the speed of the game, yet balls have seen few advancements over the same period. There are several obvious factors contributing to tennis ball degradation: natural pressure loss in pressurised balls, changes to the cloth covering due to court and racket impacts, and precipitation and environmental factors. As recent tennis research has focused on the properties of new balls, there is a need to investigate other ball conditions present in the game of tennis. This thesis provides a structured investigation into the causes and effects of ball degradation, an objective assessment of the effects of degradation on ball performance, and incorporates subjective perceptions of ball aesthetics and play properties noted by players. Particular attention is given to ball fuzziness. Excessive fuzziness can occur from manufacturing variability, court and racket interactions, and environmental conditions - though there is currently no standardised method to assess ball surface condition. An objective measure of ball fuzziness has been developed and used in the analysis of nearly 4000 individual ball images. The effects of court and racket impacts, precipitation, natural pressure loss, and repeated impacts have been analysed for their effects on ball degradation. An assessment of ball performance utilised ball impact and aerodynamic data to determine significant differences between balls and develop an improved ball trajectory model. Several player perception investigations were conducted using professional, elite, and standard club players. Two internet based investigations incorporated aspects of sensory evaluation studies to produce new techniques in evaluating products for the sports industry. An investigation into ball aesthetics was used to determine the relative importance of ball attributes on ball playability and important areas of perceived ball feel and performance were assessed during testing with elite players. Significant differences in perception were then combined with objective data to establish perceptible thresholds of wear and degradation in tennis balls and significant areas in player perception. This thesis presents a large body of work on tennis ball degradation. Results provide a mechanism to structure future investigations, new analysis techniques, and objective and subjective analyses of ball degradation. The developed digital fuzziness metric shows good agreement with player perception and aerodynamic data and provides a method to objectively compare ball conditions. Naturally aged and fuzzy balls produced the most noticeable differences in ball impact properties, though the aerodynamic data used in the development of an improved trajectory model suggests that ball spin could play a more significant role in ball flight than drag force differences. Subjective assessments of ball appearance suggest ball fuzziness is nearly twice as important as the condition of the ball's logo in determining ball playability. Player testing indicated inconsistent responses and limited differentiation in the perceived feel and performance properties of naturally aged balls. The visible differences in the fuzzy balls improved player responses, indicating the importance of aesthetics in perceived ball properties. Flight speed, hardness, liveliness, bounce speed, and bounce height are areas of perceived ball feel and performance that show good agreement with measured ball properties and usefulness in future work. Directions for future work include developing a ball performance model, expanding the digital fuzziness metric to produce an overall measure of ball degradation, and further laboratory and perception testing.