2 9 6 



HOW MACHINES LIGHTEN LABOR 



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 



or 



Force x distance = weight x distance, 

 2 x 2 = 4 x I. 



Move the 4-pound weight so that it is very near the ful- 

 crum, say but 6 inches from it ; then the spring balance regis- 

 ters a force only one 

 fourth as great as the 

 weight which it sus- 

 pends. In other words, 

 a force of I at a dis- 

 tance of 24 inches (2 

 feet) is equivalent to a 

 force of 4 at a distance 

 of 6 inches. 



One of the most use- 

 ful levers of this type is 

 the wheelbarrow (Fig. 

 159). The fulcrum is 

 at the wheel, the force 



FIG. 1 60. A modified wheelbarrow. . i u Ji i_ 



is at the handles, the 



weight is on the wheelbarrow. If the load is halfway from 

 the fulcrum to the man's hands, the man has to lift with a 

 force equal to one half the load. If the load is one fourth as 

 far from the fulcrum as the man's hands, he needs to lift with 

 a force only one fourth as great as that of the load. 



This shows that in loading a wheelbarrow, it is important to 

 arrange the load as near to the wheel as possible. 



The nutcracker (Fig. 161) is an illustration of a double lever 



