The dynamic impact characteristics of tennis balls with tennis rackets.
The dynamic properties of six types of tennis balls were measured using a force platform and high-speed digital video images of ball impacts on rigidly clamped tennis rackets. It was found that the coefficient of restitution reduced with velocity for impacts on a rigid surface or with a rigidly clamped tennis racket. Pressurized balls had the highest coefficient of restitution, which decreased by 20% when punctured. Pressureless balls had a coefficient of restitution approaching that of a punctured ball at high speeds. The dynamic stiffness of the ball or the ball-racket system increased with velocity and pressurized balls had the highest stiffness, which decreased by 35% when punctured. The characteristics of pressureless balls were shown to be similar to those of punctured balls at high velocity and it was found that lowering the string tension produced a smaller range of stiffness or coefficient of restitution. It was hypothesized that players might consider high ball stiffness to imply a high coefficient of restitution. Plots of coefficient of restitution versus stiffness confirmed the relationship and it was found that, generally, pressurized balls had a higher coefficient of restitution and stiffness than pressureless balls. The players might perceive these parameters through a combination of sound, vibration and perception of ball speed off the racket.
Haake
S J
SJ
Department of Mechanical Engineering, The University of Sheffield, Mappin Street, Sheffield S1 3JD, UK. s.j.haake@shef.ac.uk
Carré
M J
MJ
Goodwill
S R
SR
D000054:Acceleration; D008962:Models, Theoretical; D009038:Motion; D055585:Physical Phenomena; D010825:Physics; D019876:Sports Equipment; D013715:Tennis