Does the coefficient of restitution change?
1 Answer
It depends on what you mean by "change”.
The coefficient of restitution is based on the surface properties of the ball and surface it collides with. So for a given ball the coefficient will be different for different surfaces it collides with, in this sense it changes. A good example of this is a tennis racquet. The face of a racquet can be divided into different sectors, each has its own coefficient of restitution. The central sector a little above the handle has the highest coefficient. This is what players term the "sweet spot".
Another way that the coefficient can change for a given ball is that over time its internal structure may degrade. This is more the case with balls that are made out of rubber / plastic. Hence worn out balls are replaced during games where appropriate.
