Sports Engineering

, Volume 12, Issue 4, pp 163–169 | Cite as

A determination of the dynamic response of softballs

  • Lloyd V. Smith
  • Alan M. Nathan
  • Joseph G. Duris
Original Article


An apparatus is described for measuring the stiffness and coefficient of restitution (COR) of balls with application to softballs. While standardized test methods currently exist to measure these properties, they do not represent the displacement rate and magnitude that occur in play. The apparatus described herein involves impacting a fixed, solid cylindrical surface (matched to the diameter of the bat) with a ball and measuring the impact force during impact and speed of the ball before and after impact. The ratio of the ball speeds determines the COR, while the impact force is used to derive a ball stiffness. For an example of the contribution of the new ball test, the performance of hollow bats, which is sensitive to ball stiffness, was compared. Bat performance showed a much stronger dependence on the proposed ball stiffness than the traditional measure. Finally, it was shown that to achieve similar conditions between impacts with fixed and recoiling objects, the impact speed should be chosen so that the centre of mass energy was the same in the two cases. The method has application to associations wishing an improved method to regulate ball and bat performance.


Coefficient of restitution Ball compression Ball stiffness Ball performance 


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Copyright information

© International Sports Engineering Association 2010

Authors and Affiliations

  • Lloyd V. Smith
    • 1
  • Alan M. Nathan
    • 2
  • Joseph G. Duris
    • 1
  1. 1.School of Mechanical and Materials EngineeringWashington State UniversityPullmanUSA
  2. 2.Department of PhysicsUniversity of IllinoisUrbanaUSA

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