Transportation on Land 



257 



utensils such as a can opener, a spade, a doubletree of a wagon, 

 a spoon, knife and fork, and so on, to see whether they make 

 use of the principle of the lever, and if so, how. 



Exercise. At first sight a 

 crank, such as that of an auto- 

 mobile, a windlass, a pedal 

 crank of a bicycle, or a driving 

 wheel of a locomotive, may not 

 be associated with the principle 

 of the lever as it appears in the 

 crowbar. But imagine a crow- 

 bar bent into the form of a 

 crank, and the resemblance is 

 unmistakable. Note that the 

 crank has its fulcrum, its re- 

 sistance arm and force arm, 

 just as the simple lever has. 

 Identify each of these in a 

 windlass, a bicycle pedal crank, 

 a Dover egg-beater, or any 

 other machine of this character. 

 What is the effect of increasing the length of the force arm ? Of shorten- 

 ing it? Such tools, moreover, as scissors, pliers, forceps, and the like, 

 are obviously based on the principle of the lever, for they simply com- 

 bine two levers on a common fulcrum or axis of movement (Fig. 76). 



futcrum 



FIG. 75. The lever. A, its use as a 

 lift ; B, its use as a pry. In what other way 

 may the lever be used ? Give illustrations. 





FIG. 76. Identify in each of the tools or machines the fulcrum and arms of 

 the lever ; show how the lever is used in each case. 



