

the strui //(,' from B towards i\ and to on. 



AH the forces maj be replaced by a resultant 



loivc at an ail-itr.iry ..ri^'in " .v,l | . . .} ! . \ .. \ -.-.. . - 



>aed of ail the forces All, BC t ...... moved each parallel 



0\ the rcriulunt consequent!/ vanishes bjr 



Jl. 



resultant couple u the mil of tha 



omponent conplet, and in therefore repre- 



c the \n*nx\Q AOB+ twice the triangle BOO 



< tX* ana of At /to/wo*. Ilence the 



forces reduce to a resultant couple measured bjr twice the area 



observe that the algebraical sum of the 



form a couple U the 

 int it be taken; it is in (act equal to the 



sum of the moments of the forces P. 

 be required about a point whose co-ordinates arc A, I- instead 



we must in the expression for ' 

 /i, J", - i . respcctivclj, and 



J/.-*. y,-^-.. fory^y,,... respectiyelj. 

 toe result by G } , we have 



O^ -I -A"(y-*)) 



-^ 



ice the value of G l depends in general on the situation 

 of the point about \\ hi.-ii we take momenta. If, however, 



*JT- AS r- a constant, 



lie point (A,*) more along any straight line 

 parn c direction of the resultant force JZ, then 0, 



remains unchanged. 



