194 



GENERAL SCIENCE 



ONE FORM or WHEEL AND AXLE 



128. Wheel and Axle. --The wheel and axle consists 

 of a large wheel fastened to an axle which extends out 

 from the wheel far enough so that a rope can be wound 

 on it. Its mechanical advantage is explained by the 



principle of the lever. The 

 radius of the axle is the 

 weight arm, the radius of 

 the wheel is the force arm, 

 and the center of the axle 

 is the fulcrum about which 

 the two arms turn. So the 

 mechanical advantage of 

 the wheel and axle is equal 

 to the radius of the wheel 



divided by the radius of the axle. Sometimes the rope is 



wound on both axle and wheel but in opposite directions. 



If the radius of the wheel is 2 feet and the radius of the 



axle is 6 inches, the mechanical advantage is 24 in. -f- 6 in. 



or 4. With such a system 



a force of 100 pounds will 



balance a weight of 400 



pounds attached to the 



rope wound on the axle. 

 The Capstan is a form 



of the wheel and axle: the 



lever corresponds to the 



radius of the wheel, and 



the radius of the barrel corresponds to the radius of the 



axle. 



129. Windlass and Cogwheels. -- The windlass, which 

 is extensively used for drawing water from wells, is a 

 form of wheel and axle. When it is turned, the crank 

 handle describes a circle which corresponds to the wheel 



CAPSTAN or A VESSEL 



