The CPR numbers give a hint as to whether a ball will bounce higher or lower on a specific surface, and how much friction there is to either slow the ball or allow it to skid on.

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When a spinning ball hits a low friction surface such as grass, it will continue to spin.

BBC: SPORT | Tennis | Rules and Equipment | On the rebound

But on a high friction surface like clay, the ball will grip more and change the trajectory of the ball quite significantly.

BBC: SPORT | Tennis | Rules and Equipment | On the rebound

He then tested how much friction there was when a ceramic ball and a polyethylene socket were immersed in a liquid with the same properties as synovial fluid.

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But if the friction created by those connections was greater than the friction between the tabletop and the roller ball, the mouse would skip.

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Friction also affects the amount of spin on the ball.

BBC: SPORT | Tennis | Rules and Equipment | On the rebound

The friction of the court affects the horizontal bounce of the ball.

BBC: SPORT | Tennis | Rules and Equipment | On the rebound