424 RICE ART. K 



since 47?f is the area of this face. Across the face containing U 

 there will be a pull in the opposite direction XO of amount 



The difference of these, viz., 



dXx 



dx 



Hvt 



is the resultant of these two in the direction OX. To proceed, 

 we also have a shearing force on the parallelopiped in the 

 direction OX of amount 



/ dXy \ 



across the face containing R, and one of amount 



/ dXy \ 



across the face containing V in the direction XO. These two 

 forces yield a resultant 



dXr 



dy 



8^^r 



in the direction OX. The remaining pair of faces contribute a 

 resultant force in the direction of OX of amount 



dXz 



dz 



Thus the stress actions exerted by the surrounding medium on 

 the parallelopiped are equivalent to a force whose x-component 

 is 



(■ 



dXx dXy dXz\ ^ 



dx dy dz 



The resultant body force arising from external influences on the 



