10 



VflOtf OF FOI 



Conversely if three forces act on a particle, and each t 

 it as the sine of the angle between the dim; otfcer 



two, it may be shewn that one of the forces is equal in 

 niltulc to the resultant of the other twu, and acts either in the 

 tome direction T in the owite direction: in the latter case 

 the three forces are in 



It should be noticed that if the sides of a triangle l>< drawn 

 parali HI of the forces, the length of any side 



will be proportional to the sine of the an-'le betweeq tin- : 

 which correspond to the other two .-ides. 



20. Any force acting on a particle may he replaced hy 

 two others, if the sides of a triangle. drawn parallel t< the 

 directions of the forces have the same relative pr.].nrtin 

 that the forces have. For by the parallelogram <f I 



the resultant of the latter two forces is equal to the 

 force. 



This is called the resolution of a force. 



21. Since the resultant of two forces acting on a par- 

 is represented in magnitude and direction l>y the dia 



of the parallelogram constructed ujmn the straight lines which 

 represent these forces in magnitude and direction, it f..ll.ws 



in order to obtain the resultant of the forces P v P r 

 which act on a particle -4, and are represented l>y t: 

 lines AP lt AP t , AP t ,...wc may proceed as follows. 



d the resultant of P and JP 



with 



P t , this 



t t , compound this resultant 



new resultant with P 4y and so on. It fulluws 



