160 MAN^S WAY OF HELPING HIMSELF 



lower his end of the lever 3 feet in order to raise the bowlder 

 6 inches out of the ground. He does not at any time exert a 

 large force, but he accomplishes his purpose by exerting a 

 small force continuously through a correspondingly greater 

 distance. He finds it easier to exert a force of 100 pounds con- 

 tinuously until his end has moved 3 feet rather than to exert 

 a force of 600 pounds on the bowlder and move it 6 inches. 



By the time the stone has been raised the man has done as 

 much work as though the stone had been raised directly, but 

 his inability to put forth sufficient muscular force to raise 

 the bowlder directly would have rendered impossible a result 

 which was easily accomplished when through the medium 

 of the lever he could extend his small force through greater 

 distance. 



154. The Wheelbarrow as a Lever. The principle of the 

 lever is always the same ; but the relative position of the im- 

 portant points may vary. 

 For example, the fulcrum 

 is sometimes at one end, 

 the force at the opposite 

 end, and the weight to be 

 lifted between them. 



Suspend a stick with a 

 hole at its center as in 

 Figure 98, and hang a 



1 1 Ibs. 



FIG. 98. - A slightly different form of lever. 4'POUnd Weight at a dlS- 



tance of I foot from the 



fulcrum, supporting the load by means of a spring balance 2 

 feet from the fulcrum. The pointer on the spring balance 

 shows that the force required to balance the 4-pound load is 

 but 2 pounds. 



The force is 2 feet from the fulcrum, and the weight (4) 

 is I foot from the fulcrum, so that 



