RBJUUCB ON THE E3UMPUB. 



force P, it equivalent to the algebraical ram of Ute ilfiiiili 

 components A", and V, ; and the perpendicular on tke 

 former from the origin is y l sin , and on the latter , n . 



The conditions for equilibrium are, at before, 



r-o, S()X 



ng Examples may be solved by means of the 

 inlcs given in the price ! . 'When different 



bodies occur in a question, the equations : 



:h rvsprrt t> r i,7,. in ..r.!. r that there may be 



equilibrium. In cases where only Iftrst forces act on a body, 



t'tt-n convenient to use the proposition of Art. &8. Since 



7 the moments of the forces with respect to amy 



must vanish, we may, if we please, take different engine 



>rm the corresponding equation for each. Bee Art. 



orae of the Examples we anticipate the results of the 



subsequent Chapters so &r as to assume that the weight of 



vxly acts through a definite and known point, which is 



of gravity of the body. When two bodies are in 



- is assumed that whatever force one exerts on the 



H an equal and opposite force on the 



bodies are smooth this force acts in the direction 



: mal to the surface* at the point of contact. 



ourselves to the supposition of smooth bodies 



until ( 'h;ijti I 



In attnnj-t:!!.: to solve the problems the student will find 



it advisable when the system involves more than one bodv 



i to one at a time of those bodies which 



apable of in.ti..:i. and :> be careful to take into eon- 



O-H which act on that body. When 



bodies are in contact some letter should be used to denote 



mtual force between them, and the magnitude of this 



must bo found from the 



body or bodies which are capable of motion. And when 

 two of the bodies are connected by a string a letter should 

 be used to denote the tension 



wion must be found from the conditions of etjtnV 



