176 



SIMPLE MACHINES 



lifted, by the distance through which the resisting object, 

 or weight, moves. 

 Power X power distance = weight X weight distance. 



198. The Lever. The claw hammer, pitchfork, and 

 crowbar are common forms of the lever. The fixed 

 support on which the lever rests is 

 called the fulcrum. If, in Fig. 168, 

 the distance from the fulcrum (F) to 

 the point at which the weight (R) is 

 attached is 1 foot, and the distance 

 from F to the point (P), where the 

 power is applied, is 2 feet, then the weight that can be 

 lifted at 72 is twice the power applied: 40 pounds at P 

 can support 80 pounds at R. If the distance from F to R 

 is 3 inches, and that from F to P is 51 

 inches, then 40 pounds at P can sup- 

 port 680 pounds at R. 



FIG. 168. 

 A Lever of the First Class- 

 The fulcrum is between 

 the force exerted and the 

 resistance to be overcome. 



FIG. 169. 



Fish Scales: a Lever of 

 the First Class. 



The balances (Fig. 9) are a lever. If the 

 two arms are of equal length, equal weights in 

 the two pans will just support each other. 



In fish scales (Fig. 169) the arm holding the pan is the shorter, 



hence a heavy object on 

 this pan can be supported 

 "weighed " by a small 

 weight on the longer arm. 

 The weighted gate (Fig. 170) 



and the Well Sweep (Fig. 171) 



**e other examples of the lever. 



FIG 17Q 



Weighted Gate. The stone nearly balances the 



uft te the gat h e at very Uttte effort " ***** ' 



199. Classes of Levers^ We divide levers into three 

 classes according to the way in which the fulcrum, the 



