THE LEVER, 



91 



Under such circumstances, the lever will be in equilibrium, 

 when the sum of the moments of the forces tending to 

 turn the lever in one direction is equal to the sum of the 

 moments of the forces tending to turn the lever in the 

 other direction. Eepresenting the moments of the several 

 forces acting upon the lever represented in the figure by 

 their respective letters and numerical values, * 



b + c + d = a + e + f 30 + 30 + 40 = 30 + 25 + 45. 

 or, c + d a = e + fl 30 + 4030 = 25 + 4530. 



173. Bent Levers. When the lever is not a 

 straight bar, or ivhen, for any reason, the power and 

 weight do not act parallel to each 

 other, it becomes necessary to distinguish 

 between the real and apparent arms of the 

 lever. This will be easily done, if you are 

 familiar with the definition of the arms 

 of a lever, given in 168. In Fig. 41, we 

 have represented a very simple kind of 

 bent lever, which is sufficiently explained 

 by the engraving. In Fig. 42, we have a 

 representation of a curved rod lever, W'P', at the ends of 



which two forces, 

 /\ not parallel, are 



"W" '' v * v 



/\ / \^ acting. Our def- 



Xlr// inition of the 



arms of the lever, 

 already learned, 

 removes every dif 

 ficulty arising from the form of the lever, or the direction 

 in which the forces act. The arms are not FP' and FW', 

 but FP and FW. 



FIG. 41. 



FIG. 42. 



