I lence if we remove the last 



wesli.ili sccordingly 



.liriuin. Ilir. 



ince thev act in the Mime direction, 

 parallel forces P cannot be balanced bj a tingle 

 therefore do not admit of a tingle resultant. 



il. A couple consists of two equal forces acting in parallel 



The arm of a couple is the perpendicular distance between 

 the directions of its forces. 



moment of a couple is the product of either of its forces 

 he perpendicular distance ~ 



' of a couple is a straight line perpendicular to the 

 plane of the couple and proportional in length to the moeMPL 



me roar differ with respect to 

 middle point of the arm of a 

 to be fixed, and the a ve in the 1. 



res of the couule tend to urge it ; there are 

 two t: n the arm may rotate. Sup* 



pose a perpendicular drawn to the plane of the couple through 



> that \\licn an observer is 



1 along t with hi- t'.---t against the plane. 



the rotation which tin- forces give to the arm appears to take 



'licular so drawn we shall 

 take : 



now give three propositions shewing that the 

 ;.!.- is not altered when certain changes are nude 



of a couple 



> be supnoacd in all these 

 body i* in equilibrium und r 

 roes, including an assigned couple; ami it 

 i ti.at t!..-n tin- r.}iiilii>rmm will not be disturbed bjr the 

 specified changes with respect to the couple. 



42. The eff*A of a couple a not a/fera/ 1/ to arm 



>jh any angle about OM erlrwiiVjf i* tk* pUu* of 0* 

 ample* 



