Reducing the effect of the ball on bat performance measurements

Abstract

A simple physical model is presented that relates the ball–bat coefficient of restitution e to the ball coefficient of restitution e ₀ and dynamic stiffness k ₀. The model is used to develop a technique to normalize e to values of e ₀ and k ₀ for a “standard ball.” The efficacy of this normalization technique is demonstrated by comparison with experimental data. It is shown to be vastly superior to a widely used technique that is based on the physically unjustified assumption that the ratio e/e ₀, commonly referred to as the Bat Performance Factor or BPF, is independent of both e ₀ and k ₀. A residual, but much reduced, dependence of the normalized e on k ₀ is observed and is shown through finite element simulations to be due to a dependence of the bat stiffness on the ball stiffness.

Keywords:

• baseball
• softball
• performance
• coefficient of restitution