fcOTES 



If ABC, fig. 40, is the hemisphere of disturbance 

 which left a at a given previous instant, and if DEF is 

 that which left a a second later, the distance between 

 the two hemispheres in direction is 



V - v cos 



The momentum between the surfaces per unit area of 

 one of them is 



This was emitted from a in one second. Resolving 

 along the normal and integrating for the hemisphere 



P = / ^ M(V v cos 0)27^2 sin cos OdO 



= _L* + J *? to the first power of 

 3V 2 V' 2 V 



(2) Tangential stress on an area moving in its own 

 plane. 



Let A (fig. 41) be a point towards which a is moving 

 with velocity v. 



G 



