47^ PARTICULAR CASES. 



we get for the first integration, in which the distance s is taken 

 constant, 



or 



/ 



The second integration relative to ds is easily effected, for we 

 have in general 



l>(-u + ^WT^ 2 )du = ul\-u + ^W^ 2 



we get then 



p *-*W(^g+g 



Jo -*+^ 2 +^ 2 



Changing the sign of this expression and replacing /$ by the 

 distance # of the sides AB and CD', we get in like manner the term 

 relating to this last side. If the rectangle is a square, h' = ,Ja 2 + h 2 , 

 and the two terms of the energy corresponding to the side AB 

 give 



The total energy is then 



_ + , 



W J I n-f , o TTi 7 



When the distance of the frame is altered by dh, the variation 

 of the energy ^W, is equal to the work -Mfc of the force F, 



