CLASSES OF LEVERS 



177 



FIG. 171. 



Well Sweep: a Lever Used in Raising 

 Water from a Well. Courtesy of 

 the Ansco Co. 



power, and the resistance are 

 placed with regard to one an- 

 other. In the crowbar and 

 balance the fulcrum is between 

 the other two. Such a lever is 

 of the first class. 



In the nut-cracker (Fig. 172) 

 the resistance (the nut) is be- 

 tween the other two : the fulcrum 

 is at one end. This is a lever of 

 the second class (Fig. 173). 



A wheelbarrow is also of the 

 second class. The fulcrum is the 

 axle of the 

 wheel, the 



power is applied to the handles, and 

 the weight is between them. The 

 rule of machines applies here, just as 

 in levers of the first class. In making 

 the calculation we will not count the weight of the wheel- 

 barrow. If you place a piece of. ice, 

 weighing 100 pounds, 1 foot from 

 the axle of the wheel, and grasp the 

 handles 5 feet from the axle, you 

 need exert a force of only 20 pounds 

 to lift the ice. 



Levers of the 



third class have the fulcrum at one 

 end, just as those of the second class 

 have, but the power is applied be- 

 twecn the resistance and the fulcrum 



FIG. 173. 



Lever of Second Class. The 

 resistance is between the 

 fulcrum and the power. 



Lever of tfe Third class 



' 1 at P 



