[in Japanese]

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[in Japanese]

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Using a high-speed video camera, we measured the trajectory and the rotation of a hard baseball thrown by a pitchingmachine which can launch Gyro-balls (rifle spinning balls). We determined the drag coefficient by analyzing the videoimages.The measurements were performed in the range of 0.6×10⁵<Re<2.5 × 10⁵, and for three values of thespin parameter (SP: dimensionless spin rate) ≈0.12, 0.23 and 0.35. Two seam patterns relative to the translationaldirection were investigated, i. e. 2-seamand 4-seam. The drag coefficients of 4-seam gyro-balls (for any SP), decreasegradually with Re. However, the drag coefficients of 2-seam gyro-balls with SP≈0.12 and 0.23 decrease in two steps, their minima are attained at Re≈2.2×10⁵ and 1.8×10⁵, respectively. The drag coefficient of 2-seam gyro-ballwith SP0.35 is nearly constant in the range of Re>1.3×10⁵, it decreases with Re in the range Re>1.3 ×10⁵, and attains its minimum at Re≈1.6×10⁵. These findings confirm the occurrence of the drag crisis for Gyro-balls. Thedifferent Re-dependencies are due to the different seam patterns.

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