Abstract des Autors

When a tennis ball is incident at an oblique angle on a tennis racket, the ball slides or rolls along the strings before it rebounds. The dynamics of this interaction in a direction perpendicular to the string plane are determined by the coefficient of restitution (C0R). In a direction parallel to the string plane, the dynamics depend on the coefficients of sliding (micro-s) and rolling (micro-r) friction, and also depend on the COR. For example, if, micro-s = 0, and if the ball impacts in the middle of the strings, then the ball will rebound with no change in its spin or parallel speed. Spaghetti strings, with a high value of micro-s, are banned from competitive tennis since they can be used to impart excessive spin to the ball. It is shown that the most useful strings are those with micro-s > 0.3 and that the performance of the strings deteriorates sharply if micro-s drops below about 0.3. Verf.-Referat