The characterization of the performance of baseball bats is presented from a physics point of view. The goal is to define a set of laboratory measurements that can be used to predict performance in the field. The concept of a model-independent collision efficiency, which relates the post-collision ball speed to the initial ball and bat speeds, is introduced and its properties are investigated. It is shown to provide a convenient link between laboratory and field measurements. Other performance metrics are presented, related to the collision efficiency, and evaluated according to their predictive power. Using a computational model, it is shown that bat performance depends on the interplay of the elasticity of the ball–bat collision, the inertial properties of the ball and bat, and the bat swing speed. It is argued that any method of determining performance needs to take all of these factors into account. A new method is proposed and compared with commonly used existing methods.

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Actually, the laboratory measurement of the bat recoil speed is used along with the bat recoil factor r to derive the BPF, which is then recombined with r to calculate vf under standard conditions. This is completely equivalent to our description albeit unnecessarily complicated, because the laboratory measurement can be used to extract eA and then predict vf without ever using or even knowing r.
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