(KSTKK OK K..Ur|:.H. 



A'hcn a syst. m/W forces acting on a rigid 



body has a sin.c that resultant always passes 



body whatever may 1 



posit to body. \\ hen any system of forces acts on 



Uv we might investigate the consequences of turn- 

 ing the body from one poaiti.m into anoth. the forces 

 riginal d <, or of the forces in 

 a manner as to leave their relative directions unchanged 

 body remains fixed. We shall here give some 

 the general theorems that have been demon- 

 tratea on this subject The forces are supposed to act at 



fixed point, in the Uly. 



\M PA and QA Iw the directions of two forces 



r at the 

 I Q re*|> 



i of their resultant. 



Suppose the forces in PA, QA to 



ic points Pand Q 



rapt i^h the Mime an- 



vards the same dire 

 since PA and QA will in 

 angle as before, ti. 



will move on a 



passing through P and Q. And 

 as the magnitudes of the forces are i 

 magnitude of the resultant and 

 with the components ren 

 ction of the result 



turned ;:.r ;uh the angle a round the point 



same conclusion holds if instead of supposing the body 

 to be fixed and the forces to revolve, we suppose each force 

 main parallel to itself and the body to be turned through 

 any ang a perpendicular to the plane of the forces, 



point T through which the resultant always passes 



're of the forces which act at P and Q. 



.at if a third force pass 



through a fixed point S and meet the straight line 7-1, we 



th 



Meed unchanged. 



igles which it makes 

 e if T be the 



;ind the circle originally, it will 

 PT and QT are proportional to 

 the resultant will therefore have 



