162 



MAWS WAY OF HELPING HIMSELF 



FIG. 101. The nutcracker is a lever. 



The nutcracker (Fig. .101) is an illustration of a double 

 lever of the wheelbarrow kind ; the nearer the nut is to the 



fulcrum, the easier the 

 cracking. 



Hammers (Fig. 102), tack- 

 lifters, scissors, forceps, are 

 important levers, and if you 

 will notice how many differ- 

 ent levers (fig. 103) are used 

 by all classes of men, you will 

 understand how valuable a machine this simple device is. 



155. The Inclined Plane. A man wishes to load the 600- 

 pound bowlder on a wagon, and proceeds to do it by means 

 of a plank, as in Figure 93. Such an arrangement is called 

 an inclined plane. 



The advantage of an inclined plane can be seen by the 

 following experiment. Select a smooth board 4 feet long 

 and prop it so that the end A (Fig. 104) is I foot above the 

 level of the table ; the length of the incline is then 4 times 

 as great as its height. Fasten . 

 a metal roller to a spring bal- 

 ance and observe its weight. 

 Then pull the roller uniformly 

 upward along the plank and 

 notice what the pull is on the 

 balance, being careful always to 

 hold the balance parallel to the 

 incline. 



When the roller is raised FlG ' ioa _ The hand exerts a small 



along the incline, the balance force over a long distance and draws 

 . , ni r .1.1 out a nail. 



registers a pull only one fourth 



as great as the actual weight of the roller. That is, when the 



roller weighs 12, a force of 3 suffices to raise it to the height 



