A determination of the dynamic response of softballs |
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| Authors: | Lloyd V Smith Alan M Nathan Joseph G Duris |
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| Institution: | (1) School of Mechanical and Materials Engineering, Washington State University, Pullman, WA 99164, USA;(2) Department of Physics, University of Illinois, Urbana, IL 61801, USA |
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| Abstract: | 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. |
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