MACHINES IN EVERYDAY LIFE 



159 



FULCRUM 



RESISTANCE 



FIG. 256. LEVERS OF THE FIRST CLASS 



In some levers the fulcrum is found at one end 

 of the bar, the weight or resistance on the other end, 

 and the effort between them. A common example of 

 this class of lever is the sugar tong. Figure 258 shows 



A 



FULCRUM 



t) 



/IOOH)\ 



RESISTANCE 



T 

 FORCE 



FIG. 257. LEVERS OF THE SECOND CLASS 



the arrangement of the forces and also suggests other 

 examples. The arrangement of the forces acting does 

 not affect the application of the discovery of Archi- 

 medes. The effort force multiplied by its distance from 

 the fulcrum always equals the weight multiplied by its 



FULCRUM 



i ' ) 



/"\ 

 FORCE RESISTANCE 



FIG. 258. LEVERS OF THE THIRD CLASS 



distance from the fulcrum if the lever is in balance. 



Sometimes the lever is bent ; that is, the effort 

 force, fulcrum, and weight are not in a straight line. In 

 this case the shortest distance from the fulcrum to the 



FIG. 259 



point at which the forces are act- 

 ing is taken. A good example of a 

 bent lever is a hammer when used 

 for pulling a nail. Figure 259 will 

 illustrate this. 



The windlass is a lever. The 

 windlass, or wheel and axle, as it 

 is sometimes called, is made up of 

 a crank which turns a smaller axle attached to it. A 

 common example of this special lever was formerly 

 much used to raise buckets 

 of water from wells. In 

 modern life we find many 

 uses for the wheel and 

 axle. Can you suggest 

 any? Figure 260 shows 

 that the wheel and axle is 



\ 



FIG. 260. WHEEL AND AXLE 



a lever. The fulcrum is at 

 the common center of the 

 wheel and axle. It is 

 marked F in the diagram. 

 The weight hangs at the 

 rim of the axle, and the 

 distance from the fulcrum is always the radius of the 

 axle, marked r in the diagram. The effort is applied 

 at the rim of the wheel, and this distance from the ful- 

 crum is always the radius of the wheel, marked R in 

 the diagram. When the machine is in balance as 

 shown, the effort X the wheel radius = resistance X 

 the axle radius. 



Can you explain why this is true? One can tell how 

 heavy a weight can be lifted with a certain effort force 

 by dividing the wheel radius by the axle radius. 



The pulley is also a lever. Pulleys are of two kinds : 

 those which are fixed or attached to something solid, 

 and those which are movable. In order to gain an ad- 

 vantage of force over a resistance, some form of mov- 

 able pulley must be used. A study of the fixed and 

 movable pulleys in Figure 261 will teach you how the 

 pulley is a special kind of lever. 



The fixed pulley is a lever like the see-saw lever 

 when two people of equal weight are balanced. The 

 fulcrum is at the center of the pulley marked F in the 

 diagram. The effort is applied on one side of the pulley 

 and the weight is raised on the other side. In each 

 case the distance from the fulcrum is the same and is 

 always the radius of the pulley. In using a pulley of 

 this type one must apply an effort which is a little 

 greater than the weight to be lifted. The only gain is 

 a change of direction in applying a force. Thus horses 

 are driven along a roadway and are hitched to a hay 

 fork which rises into the barn. The change of direction 

 is made possible by the use of fixed pulleys. 



The single movable pulley is a lever of the second 

 class. Here the weight is attached to the center of the 



