SIMPLE MACHINES 183 



From the lever described on the opposite page, 



25 g io cm . 



= 2.5 = mechanical advantage. 

 10 g 4 cm 



F. distance is the distance the force moved, and W. 

 distance is the distance the weight moved. The force 

 multiplied by the force distance (the work spent on the 

 lever) is equal to the weight multiplied by the weight 

 distance (the work accomplished by use of the lever). 

 It is evident from this that the lever is not a machine to 

 save work, but it is a device by which a large weight can 

 be moved by a small force, but the force must move a 

 much greater distance than that through which the weight 

 lifted moves. For example, we can lift a 4oo-pound 

 stone by a force of 100 pounds if we place one end of a 

 lever under the stone and then place a block of wood or 

 a small stone under the lever for a fulcrum, and then 

 apply to the lever a force of 100 pounds at a point on 

 the lever four times as far from the fulcrum as the fulcrum 

 is from the weight. If the force arm is eight feet and 

 the weight arm is two feet, the force will move four times 

 as fast as the weight, and the force will move' four feet 

 while the stone moves one foot. The work done on the 

 stone will be 400 pounds X i foot, or 400 foot pounds. 



LEVERS or THE FIRST CLASS 



123. Classes of Levers. Since there are three im- 

 portant positions on the lever, namely, the fulcrum, the 

 position of the force, and the position of the weight, 

 levers are divided into three classes according to the 



