SIMPLE MACHINES 



195 



of the wheel and axle. The mechanical advantage of 

 the windlass is equal to the result obtained by dividing 

 the radius of the circle described 

 by the crank by the radius of the 

 axle. 



Cogwheels are also modifications 

 of the wheel and axle, but the wheels 

 which turn each other are fastened 

 on different axles. The number of 

 cogs on the large wheel divided by 

 the number of cogs on the small 

 wheel, will give the mechanical ad- 

 vantage; or the radius of the large 

 wheel divided by the radius of the COMPOUND WINDLASS OF A 

 small wheel will also give the me- 

 chanical advantage. The sizes of the wheels can be made 

 to have such a relation to each other that a very heavy 

 weight can be lifted by a small force. 



Cogwheels are also used to control the speed of ma- 

 chinery. Where high- 

 speed engines are used, 

 as in the automobile, the 

 cogwheel attached to 

 the engine shaft is a 

 small one which turns in 

 a larger one, thus reduc- 

 ing the speed of the 

 wheels of the automo- 

 bile. High speed of ma- 

 chinery can be obtained 



GEARING OF AN AUTOMOBILE 



by applying the force to a large cogwheel which turns a 

 small one, or even a series of smaller ones, as is done on 

 the cream separator. 



