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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

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2011 ASEE Annual Conference & Exposition


Vancouver, BC

Publication Date

June 26, 2011

Start Date

June 26, 2011

End Date

June 29, 2011



Conference Session

Teaching Dynamics

Tagged Division


Page Count


Page Numbers

22.218.1 - 22.218.13

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Paper Authors


Josue Njock-Libii Indiana University Purdue University, Fort Wayne

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Josué Njock Libii is Associate Professor of Mechanical Engineering at Indiana University-Purdue University Fort Wayne, Fort Wayne, Indiana, USA. He earned a B.S.E in Civil Engineering, an M.S.E. in Applied Mechanics, and a Ph.D. in Applied Mechanics (Fluid Mechanics) from the University of Michigan, Ann Arbor, Michigan. He has worked as an engineering consultant for the Food and Agriculture Organization (FAO) of the United Nations and been awarded a UNESCO Fellowship. He has taught mechanics and related subjects at many institutions of higher learning: The University of Michigan, Eastern Michigan University, Western Wyoming College, Ecole Nationale Supérieure Polytechnique, Yaoundé, Cameroon, and Rochester Institute of Technology (RIT). He has been investigating the strategies that engineering students use to learn engineering subjects for many years.

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Applying Dynamics to the engineering of the perfect bounce: Experimental investigation of whythe NBA requires a specific inflation pressure for basketballs used in professional games.AbstractThe National Basketball Association (NBA) has definite specifications for the ball that must beused in its game. The ball must be orange in color, have a circumference of 29.5 inches, andweigh 22 ounces (size 7); it must also have an internal pressure between 7.5 and 8.5 psi. TheWNBA has similar requirements. Why is it necessary to specify the internal pressure?This paper discusses experiments done as a class assignment in a Dynamics course in order toanswer this question. After analysis had been presented in lecture on the relation between workand energy and on the connection between linear impulse and linear momentum, this basketballproject was assigned as a hands-on application of the results of analysis.First, the relationship between the mechanical energy dissipated by a ball bouncing off a rigidsurface and the duration of the impact was investigated. Three different kinds of balls were usedto collect data: basketballs, tennis balls, and ping pong balls. Data were collected using digitalcameras and processed using software freely available on the web.For each of the tested balls, experimental data showed that when the duration of impactsincreased, so did the amount of energy that was dissipated. Similarly, when the duration ofimpact decreased, so did the amount of energy that was dissipated.Secondly, it was hypothesized that inflation pressure affected the duration of the impact betweena basketball and the floor. In order to understand the effect of the inflation pressure on energydissipation during an impact, we tested the same basketball multiple times; before each test, theball had been inflated to a different level of internal pressure. It was found that increasing theinflation pressure of a basketball reduced the duration of its impact with the floor, reduced theenergy dissipated during the impact, and increased the height to which the ball rebounded.Internal pressures between 7.5 and 8.5 psi yielded excellent results in that the durations ofimpacts were low and the rebound heights very large.

Njock-Libii, J. (2011, June), 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 Paper presented at 2011 ASEE Annual Conference & Exposition, Vancouver, BC.

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