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Abstract
In this study, we aimed to determine the direction of the spin axis and the spin rate of pitched baseballs and to estimate the associated aerodynamic forces. In addition, the effects of the spin axis direction and spin rate on the trajectory of a pitched baseball were evaluated. The trajectories of baseballs pitched by both a pitcher and a pitching machine were recorded using four synchronized video cameras (60 Hz) and were analyzed using direct linear transform (DLT) procedures. A polynomial function using the least squares method was used to derive the time‐displacement relationship of the ball coordinates during flight for each pitch. The baseball was filmed immediately after ball release using a high‐speed video camera (250 Hz), and the direction of the spin axis and the spin rate (ω) were calculated based on the positional changes of the marks on the ball. The lift coefficient was correlated closely with ωsina (r = 0.860), where a is the angle between the spin axis and the pitching direction. The term ωsinα represents the vertical component of the velocity vector. The lift force, which is a result of the Magnus effect occurring because of the rotation of the ball, acts perpendicularly to the axis of rotation. The Magnus effect was found to be greatest when the angular and translational velocity vectors were perpendicular to each other, and the break of the pitched baseball became smaller as the angle between these vectors approached 0°. Balls delivered from a pitching machine broke more than actual pitcher's balls. It is necessary to consider the differences when we use pitching machines in batting practice.
