Adapted from Plangenhoef, Patterns of Human Motion. The CoR can be measured directly by velocity measurements but often it is handier to measure the height of rise of the ball after it bounces relative to the height that it fell. For example a regulation tennis ball is tested at low speed where a ball is dropped from about 1 meter. The selection of balls for official games includes the Cor test in tennis or baseball or any other game. Effects of Air Resistance.
Air resistance is zero at zero velocity.
However, it increases with speed and is the limiting factor in high speed travel in bikes or cars. The high speeds encountered in baseball and tennis also have a large effect on the flights of these balls. The subject of fluid effects in the general case are difficult to calculate exactly but we can approach this subject more narrowly for limited conditions. The first is to consider the speed of the ball compared to it's terminal velocity. If it is a small percentage of the terminal velocity , we can safely ignore the air effects.