THE INCLINED PLANE 



297 



FlG l6l . The nutcracker is a lever. 



of the wheelbarrow kind ; the nearer the nut is to the fulcrum, 



the easier the cracking. 



Hammers (Fig. 162) tack lifters, scissors, forceps, are impor- 



tant levers, and if you will notice how many different levers 



(Fig. 163) are used by all 



classes of men, you will un- 



derstand how valuable a ma- 



chine this simple device is. 

 The inclined plane. A 



man wishes to load the 1600- 



pound bowlder on a wagon, 



and proceeds to do it by means 



of a plank, as in Figure 153. Such an arrangement is called an 



inclined plane. 



The advantage of an inclined plane can be seen by the fol- 



lowing experiment. Select a 'smooth board 4 feet long and 



prop it so that the end A (Fig. 164) is I foot above the level 



of the table ; the length of the in- 

 cline is then 4 times as great as 

 its height. Fasten a metal roller 

 to a spring balance 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 j g raiged a j 

 . 



the incline, the balance 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 A along the incline ; but the smaller force must 

 be applied throughout the entire length of the incline. In 



7* 



FIG. 162. The hand exerts a small 

 force over a long distance and draws 

 out a nail. 



