野球のバッティングにおけるバットのローリング発生メカニズム

抄録

The purpose of this study was to describe how the rotation of the bat about the long-axis, named “rolling”, was generated in baseball batting. Sixteen baseball players performed four trials of free-batting aiming at hitting the ball toward the center field. An electromagnetic tracking device (240Hz) was used to record three-dimensional orientation data of the bat during the performance. Rolling angular velocity was determined from the recorded orientation data. The rolling may be generated by two mechanisms: The first is attributable to an angular impulse exerted by the batter on the bat about the long-axis (1^st mechanism). The second mechanism is attributable to the change in the orientation of the long-axis of the bat relative to the angular momentum vector (2^nd mechanism). This change in the bat orientation results in an increase in the rolling component of the angular momentum even if the angular momentum vector stays constant. The results showed that the rolling angular velocity was-738±149 °/s at ball impact, which was resulted from 1044±310 °/s due to the 1^st mechanism and-1714±243 °/s due to the 2^nd mechanism. These results indicate clearly that changing orientation of the long-axis of the bat is the primary mechanism of generating the rolling during baseball batting.