A Study of Softball Player

A field study was conducted to measure the effect of a bat’s weight and mass moment of inertia (MOI) on the swing speed. The study involved 16 amateur slow-pitch softball players of two skill levels and two groups of bats. One bat group had a constant MOI, but varying weight, while the other group had constant weight, but varying MOI. Players were assigned to either the constant MOI or constant weight group of bats and asked to swing at pitched softballs, using each of the five bats in that group ten times. Bat motion was recorded using high speed video for each swing. The results from the batters were combined by normalizing each swing speed to the respective batter’s average. The swing speed of the constant MOI bats was observed to be nearly independent of the bat weight, while the swing speed of the constant weight bats showed a strong dependence on MOI. The dependence of swing speed on bat weight and MOI was similar for the two player skill levels considered. The bat’s center of rotation during the instant of impact with the ball was found to roughly correspond to the location of the center of the batter’s wrists. The results of this study will be used to develop test methods to correlate bat performance.