158 MAWS WAY OF HELPING HIMSELF 



he help himself and perform the impossible ? Simply, by 

 the use of some of the machine types mentioned above, illus- 

 trations of which are 

 known in a general way to 

 every schoolboy. The very 

 knife with which a stick is 

 whittled is a machine. 



152. The Lever. Balance 

 a foot rule, containing a 

 hole at its middle point F, 

 as shown in Figure 97. If 

 now a weight of I pound 

 is suspended from the bar 

 at some point, say 12, the 

 balance is disturbed, and 



FIG. 96,-Separating rice grains by flailing. the bar Swin S S ab Ut the 



point -F as a center. The 



balance can be regained by suspending 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 dis- 

 tance what it lacks in 

 magnitude. {-+-*- 3 4 5 F 7 8 9 10 u 12 



Such an arrange- 

 ment of a rod or bar is 

 called a lever. In any 

 form of lever there are A zlbs - 



only three things to be FlG ^ _ The prindple of the ]ever 



considered : the point 



where the weight rests, the point where the force acts, and 

 the point called the fulcrum about which the rod rotates. 



