Abstract
Using a high-speed video camera, we have recorded the trajectory and the rotation of a hard baseball and a sphere thrown by real pitchers and pitching machines. We measured the drag and lift coefficients by analyzing the video images. We altered pitching machines on the market in order to throw a ‘gyro-ball’, whose rotational axis lies almost i n the translational direction. The drag coefficient of a gyro-ball decreases with the Reynolds number (Re) and attains its minimum at Re = 1.8 × 105, while the drag coefficient of a straight ball is independent of Re in the range 1 × 105 < Re < 2 × 105. The drag coefficient of a sphere is larger than that of a hard baseball for straight- and gyro-pitches, indicating that seams on the ball surface have substantial influence on the flow field.
