THE LEVER 



293 



perform the impossible ? Simply, by the use of some of the 

 machine types mentioned above, illustrations of which are 

 known in a general way to 

 every schoolboy. The very 

 knife with which a stick is 

 whittled is a machine. 



The lever. Balance a 

 foot rule, containing a hole 

 at its middle point F, as 

 shown in Figure 157. If 

 now a weight of I pound is 

 suspended from the bar at 

 some point, say 12, the bal- 

 ance is disturbed, and the 

 bar swings about the point 

 F as a center. The balance 

 can be regained by suspend- 

 ing an equivalent weight at the opposite end of the bar, or by 

 applying a 2-pound weight at a point 3 inches to the left of F. 

 In the latter case a force of i pound actually balances a force 

 of 2 pounds, but the i-pound weight is twice as far from the 

 point of suspension as is the 2-pound weight. The small weight 

 makes up in distance what it lacks in magnitude. 



Such an arrangement 

 of a rod or bar is called 

 a lever. In any form 

 of lever there are three 

 things to be considered : 

 the point where the 

 weight rests, the point 

 where the force acts, 



and the point, called the fulcrum, about which the rod rotates. 

 The distance from the force to the fulcrum is called the force 



FIG. 156. Separating rice grains by flailing^ 



L 2 Ibs. 



FIG. 157. The principle of the lever. 



