APPLICATION 



305 



w 



FIG. 175. Cogwheels. 



to wheel and axle. The capstan used on shipboard for raising 

 the anchor has the same principle. The kitchen coffee grinder 

 and the meat chopper are other familiar illustrations. 



Cogwheels are modifications of the wheel and axle. Teeth 

 cut in A fit into similar teeth 'cut 

 in B, and rotation of A causes rota- 

 tion of B. But several revolutions 

 of the smaller wheel are necessary 

 in order to turn the larger wheel 

 through one complete revolution. 

 If the radius of A is one half that of 

 B, two revolutions of A will be re- 

 quired to turn B through one revo- 

 lution. 



Experiment shows that a weight 

 W (Fig. 175), attached to a cogwheel 

 of radius 3, can be raised by a force 



P, one third as large, applied to a cogwheel of radius I. There 

 is thus a great increase in force. But the speed with which W 

 is raised is only one third the speed with which the small wheel 

 rotates, or increase in power has been at the decrease of speed. 

 This is a very common method for raising heavy weights by 



small force. 



Cogwheels can be made to 

 give speed at the decrease of 

 force. A heavy weight W, at- 

 tached to B, will in its slow fall 

 cause rapid rotation of A, and 

 hence rapid rise of P. It is 

 true that P, the load raised, 

 will be less than W, the force exerted, but if speed is our aim, 

 this machine serves our purpose admirably. 

 An extremely important form of wheel and axle is that in 



FIG. 176. By means of a belt, motion 

 can be transferred from place to place. 



