810 



The Dynamics of a Golf Ball. 



[March 18^ 



moving horizontally forward from right to left, the effect of the 

 impact will be the same as if the club were at rest and the ball were 

 shot against it horizontally from left to right. Evidently, however, in 

 this case the ball would tend to roll up the face, and would thus get 

 spin about a horizontal axis in the direction shown in the figure ; this 

 is underspin, and produces the upward force which tends to increase 

 the carry of the ball. 



Suppose, now, the face of the club is not square to its direction of 

 motion, but that looking down on the club its hue of motion when 

 it strikes the ball is along P Q (Fig. 28), such a motion as would be 



Fig. 30. 



Fig. 31. 



produced if the arms were pulled in at the end of the stroke, the effect 

 of the impact now will be the same as if the club were at rest and the 

 ball projected along R S, the ball will endeavour to roll along the face 

 away from the striker ; it will spin in the direction shown in the figure 

 about a vertical axis. This, as we have seen, is the spin which produces 

 a slice. The same spin would be produced if the motion of the club 

 was along L M and the face turned so as to be in the position shown 

 in Fig. 29, i.e., with the heel in front of the toe. 



If the motion and position of the club were as in Figs. 30 and 

 31, instead of as in Figs. 28 and 21), the same consideration would 

 show that the spin would be that possessed by a pulled ball. 



[J. J. T.] 



