THE CillVIXG OF A BASEBALL 



203 



)::D/ a: 



r;:o Oiwc 



::o 



Fig. 8. 



Fig. 9 



in end view of Fig. 9). This is equivalent to the bail going through the 

 air with a rotary motion and the difference in pressure on the two sides 

 curves it as shown by the heavy arrow. 



If the rotation of the ball is reversed, the lower-pressure region 

 (higher velocity region) is on the other side of the ball. This is equiv- 

 alent to the ball going through tlie air with a rotary motion as shown in 

 Fig. 10 and the difference in pressure on the two sides of it causes it to 

 curve as shown by the heavy arrow. 



