balls. It is difficult to give a quantitative description of the results of these experiments because the drag and the lift depend on at least three variables, the speed of the ball through the air, the rate of the spin of the ball, and the surface texture of the ball (smooth and with various dimple patterns). We may make some very general statements. The drag on a ball increases with its speed through the air and with its spin rate. It may become about as large as the weight of the ball. The lift on a dimpled ball increases with the rate of spin at a given air speed and increases with air speed at a given rate of spin. It may become nearly as large as the weight of the ball. Every golfer knows that a ball hit into the wind will not go as far as one hit with the wind; this is a practical indication of the increase of drag with air speed at the ball. Every golfer knows that a ball hit into the wind will move on a higher trajectory than one hit with the wind; this is a practical indication of increase of lift with air speed. COMPETING EFFECTS OF LIFT AND DRAGFrom what we know about lift and drag on a spinning dimpled ball, it appears there are, due to spin, two competing effects on the flight of a ball. A larger spin produces a larger drag which makes the ball slow down more rapidly and thus keeps the ball from going so far, but a larger spin produces a larger lift which keeps the ball in the air for a longer time and thus allows the ball to fly farther. Experience tells us that the latter effect is predominant. ATTEMPTS AT CALCULATIONSVarious attempts have been made to calculate the trajectories for a ball hit at various velocities and spins and those obtained look very much like those seen on the golf course. Such calculations are of little practical use to the individual golfer. The golfer had best approach this aspect of the game experimentally. He should bear in mind the effect of spin on lift and drag and should realize that the ra...
