The sweet spot of a baseball bat Physics of （棒球棒物理的甜点）.pdf

The sweet spot of a baseball bat Rod Cross Physics Department, University of Sydney, Sydney 2006, Australia Received 10 November 1997; accepted 22 January 1998 The sweet spot of a baseball bat, like that of a tennis racket, can be defined either in terms of a vibration node or a centre of percussion. In order to determine how each of the sweet spots influences the ‘‘feel’’ of the bat, measurements were made of the impact forces transmitted to the hands. Measurements of the bat velocity, and results for a freely suspended bat, were also obtained in order to assist in the interpretation of the force waveforms. The results show that both sweet spots contribute to the formation of a sweet spot zone where the impact forces on the hands are minimised. The free bat results are also of interest since they provided particularly elegant examples of wave excitation and propagation, suitable for a student demonstration or experiment. © 1998 American Association of Physics Teachers. I. INTRODUCTION amplitudes that increase as the distance from the respective nodes increases. Consequently, the vibrations felt by the Given the popularity of baseball,1 and the natural curiosity hand are minimised for impacts between about 13 and 17 cm of physicists to understand collision phenomena, it is surpris- from the end of the barrel, as indicated by the ‘‘sweet vibra- ing that very few measurements have ever been made on the tions’’ zone in Fig. 1. The vibration modes of a hand-held behaviour of a baseball bat when it impacts with a ball. In bat are similar to t