A SYSTKM 01 



by (a), w 



2(Zr)-0, and2(y)-0 ..... (7). 



from (2) and (5), 



1 -0, an -f )-0 ....... (8). 



, (7), and (8) ore true, (3), (4), and (5) are true 



appears from the prece iin.; investigation that when 

 net I'M one plane on a rigid body a. 

 Atarj and sufficient add it 

 .-. i'|uilibriuiu may subsist after tin- lx*Jy has been 



; an nxi- icular to tlic plane wbi 



inixva remain | un lei to tbeii original directionSy ii 



106. A system of forces acts on a rijnd bocl :nine 



aust bold in order that when the 

 any straight line these resolved parts 



juilibrium. 



Take a straight line whose i, *. 



e resolved parts of the forces parall 



may be in equilibrium we must 



I 



as these are to be true for all ratios of /, m, n we 



r-o, sz-o, 



.--0, SZr-0, 22>-0, 

 -IZr. 



<e are the necessary and sufficient conditions, 



7 a 



