MAN">S WAY OF HELPING HIMSELF 



165. Application. Windlass, Cogwheels. In the old-fash- 

 ioned windlass used in farming districts, the large wheel is 

 replaced by a handle which, when turned, describes a circle. 

 Such an arrangement is equivalent to wheel and axle (Fig. 

 112); 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 hence rotation of 



A causes rotation of B. Several 

 revolutions of the smaller wheel, 

 however, 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 revo- 

 lutions of A will correspond to one 

 of B\ if the radius of A is one third 

 that of B, three revolutions of A 

 will correspond to one of B. 



Experiment demonstrates that a 

 weight W attached to a cogwheel of 

 radius 3 can be raised by a force P, 



equal to one third of PFapplied to a cogwheel of radius I. There 

 is thus a gr^eat increase in force. But the speed with which Wis 

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

 tates, 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 attached 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'f aised, will be less than W, the force exerted, but if 

 speed is our aim, this machine serves our purpose admirably. 



FIG. 113. Cogwheels. 



