THE DYNAMICS OF A GOLF BALL 185 



Thus if, as in Fig. 1, C the center of the ball is moving horizontally 

 to the right, A will be the nose of the ball; if it is moving horizon- 

 tally to the left, B will be the nose. If it is moving in an inclined 

 direction CP, as in Fig. 2, then A will be the nose. 



Now let the ball have a spin on it about a horizontal axis, and 

 suppose the ball is travelling horizontally, as in Fig. 3, and that the 



Fig. 1. 



direction of the spin is as in the figure, then the nose A of the ball is 

 moving upwards, and since by our rule the ball tries to follow its nose, 

 the ball will rise and the path of the ball will be curved as in the 

 dotted line. If the spin on the ball, still about a horizontal axis, 

 were in the opposite direction, as in Fig. 4, then the nose A, of the 

 ball, would be moving downwards, and as the ball tries to follow its 



Fig. 2. Fio. 3. 



nose it will duck downwards, and its path will be like the dotted line 

 in Fig. 4. 



Let us now suppose that the ball is spinning about a vertical axis, 

 then if the spin is as in Fig. 5, as we look along the direction of the 

 flight of the ball the nose is moving to the right; hence by our rule 

 the ball will move off to the right, and its path will resemble the dotted 



Pig. 4. Fig. 5. 



\ 

 \ 



line in Fig. 5, in fact, the ball will behave like a sliced ball. Such 



a ball, as a matter of fact, has spin of this kind about a veriiical axis. 



If the ball spins about a veri;ical axis in the opposite direction as 



in Fig. 6, then, looking along the line of flight, the nose is moving to 



VOL. LXXVIII. — 13 



