304 



HOW MACHINES LIGHTEN LABOR 



at the window and at a distant support. By means of pulleys, 

 awnings are raised and lowered. The use of pulleys by furni- 

 ture movers is familiar to every 

 wide-awake observer on the 

 streets. 



Wheel and axle. The wheel 

 and axle consists of a large wheel 

 and a small axle so fastened that 

 they rotate together (Fig. 173). 



When the large wheel makes 

 one revolution, P falls a distance 

 equal to the circumference of the 

 wheel. While P moves down- 

 ward, W likewise moves, but its 







0* 



FIG. 173. The wheel and axle. 



motion is upward, and the distance it moves is small, being 

 equal only to the circumference of the small axle. But a small 

 force at P will sustain a larger force at W. If the circumference 

 of the large wheel is 40 inches, and __, 

 that of the small wheel 10 inches, 

 a load of 100 at W can be sustained 

 by a force of 25 at P. The ad- 

 vantage of the wheel and axle de- 

 pends upon the relative size of the 

 two parts, that is, upon the circum- 

 ference of the wheel as compared 

 with the circumference of the axle. 

 Figure 174 illustrates a wheel and 

 axle used in the home. 



Application. Windlass, cog- 

 wheels. In the old-fashioned 

 windlass used in farming districts, 

 the large wheel (Fig. 173) is replaced by a handle which, when 

 turned, describes a circle. Such an arrangement is equivalent 



FIG. 174. Bread mixer. 



