Applying Dynamics to the Engineering of the Perfect Bounce: Experimental Investigation of Why the NBA Requires a Specific Inflation Pressure for Basketballs used in Professional Games

This paper discusses the bouncing of a basketball as an application of what is learned in dynamics. The National Basketball Association (NBA) has definite specifications for balls that are used in its games. The ball must be orange in color, have a circumference of 29.5 inches, and weigh 22 ounces (size 7); it must also have an internal pressure between 7.5 and 8.5 psi. The WNBA has similar requirements. Why is it necessary to specify the test height and the internal pressure? Three sets of experiments are presented; they were done as a class assignment in a Dynamics course in order to answer this question. These experiments show that the results from the central impact of two particles can be used to explain and demonstrate why these two requirements are necessary. It is shown that increasing the height from which a basketball is dropped decreases its rebound height relative to the original drop height but that increasing the internal pressure of a basketball increases its rebound height and, hence, compensates for the effects of increasing the drop height. Therefore, it is possible to achieve the same rebound height with a given ball by using various combinations of the internal pressure and the drop height. Accordingly, specifying the height from which a basketball is dropped during a ball-drop test and its internal pressure during the subsequent fall is essential in order to interpret the quality of the bounces of different basketballs accurately and without ambiguity.