# Page:Popular Science Monthly Volume 90.djvu/202

The "Why" of a Golf Ball's Flight

The corrugations on a golf ball are not meant to beautify the ball; they determine its maximum carrying distance

The secret of a golf ball's motion is to be found in the churning of the air by the corrugations on the surface. A blanket of air packs against it and diverts it

At right: A pitcher is able to "curve" the ball by making the ball churn the air. In a vacuum a body might be imagined to continue in a perfectly straight line

WE are told in school that when a ball is thrown into the air it generally travels in only one kind of vertical path, the so-called parabolic, while its path as seen from above never diverts from a straight line. But that this is not exactly true during baseball games and during golf contests, may be confirmed by any "fan." And when a long "brassie" drive is made, the golf ball may even rise upward during some part of its flight; so that its path can hardly be called para- bolic. The schools would be exactly right in their statements if the effects of the air upon the spinning ball were not considered. But the fact is that if it were not for the influence of the air, a baseball could never be made to bewilder a batter nor a golf ball be made to "take" an obstructing "hazard."

When a pitcher desires the path of a base- ball to curve in a certain direction, he gives the ball as it leaves his hand a rapid spin in this same horizontal direction. The effects of the air upon the whirling ball are exactly those that would occur on a more pro- nounced scale if the ball were thrown through a long strip of watei. The lacing

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��on the ball churns the air in which it spins and carries the air around with it. But the side which is turning in the same direction about the ball's center as the direction the ball itself is to turn, will be "packing" the air against its side, just as it would be doing with the water. Thus the air will be slightly compressed on that side, and as the ball skims along on the blanket of air so formed, it naturally will be pushed away from it and be made to curve in its path. The corrugated marking on a golf ball causes exactly the same phenomenon to take place. Here, however, the ball is rotated around a horizontal axis instead of a vertical axis as in the previous case. The golf stick hits the ball on its under side so that this side rotates upward in front of the ball as it spins through the air. In this way the air packs the blanket this time under- neath the ball, and so tends to divert the ball upward. As a consequence, the ball, instead of continuously being forced down- ward is also slightly pushed in an upward direction by the blanket of air underneath. The golf ball is thus able to stay up in the air longer and the length of its flight is pro- portionally increased.

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��A golf ball need not even travel in a parabola. By hitting it properly it can be made to rise up at a higher angle than that which it was initially given, and so lengthen its flight. The Stick should hit the ball on its imder side so that side will rotate upward in front of the ball

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