Transactions of the Wisconsin Academy of Sciences, Arts and Letters
volume IV (1876-1877)
McMurphy, J. G.
Rotation as a factor of motion, pp. -240 PDF (1.5 MB)
Rotation as a Factor of Mfotion. resistance finally throws the ball to the right If the ball had balloted on the left side last, in leaving the muzzle, it would have been deflected to the right by touch and afterwards to the left by resistance and reaction of the compressed air. Thus it is possible with a smooth-bored gan to " shoot round " a nearer object in direct line and hit a more remote object behind it. I wish to give but one more instance of the effect of rotation on direct motion. It is vulgarly called " curved ball." It may be witnessed in any good base-ball match. The pitcher desires to elude the strokes of the batter; after delivering a few balls in simple parabolic curves or with axial rotations, he will deliver the ball from the hand in-such a way that when the ball leaves the hand the fingers touch it from below, causing the underside to be retarded while the upperside moves forward. Then the ball ro- tates upon a horizontal transverse axis, relative to its motion of translation. The greatest resistance from compressed air is in front and above the moving ball. The ball seeks a path of less resistance, preserving its plane of rotation and drops enough to form a depressed curve. By a skillful adjustment of rotation and translation, the pitcher is able to produce about such a curve. as he wishes. To the batter the ball seems coming toward a point it is destined to fall short of. Again, by delivering the ball from the hand with the fingers touching above. a backward rotation is produced on the top of the ball and a forward motion to the under side. Such a ball continues its course until accumulated resist- ance of air from ahead and below throws it upward. So the batter sees the ball coming toward a point it is destined to pass clearly above. By skillful manipulation the right side of the de- liverer the ball may be retarded, and the ball will curve to the right, and by retarding the left side it will curve to the left. The amount of curvature is variously estimated by different persons. % With the rotation or twist of the best pitcher, it is no uncommon thing to make a ball curve a yard from its direct path, while many cannot effect any curve. This purports to be only the outline of a subject worthy of much greater investigation, in its relation to great scientific prob- lems. 239
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