THE LEVER. 83 



cord = l m is wrapped round the axle, and the force 

 required, multiplied into the space of 7 m *5, must also 

 be 50 kilogrammetres ; hence the force required is 



j>0 = 6 kgr '66. 

 7-5 



The above law on the equality of work holds for all 

 simple machines; namely, the lever, the pulley, the 

 inclined plane, the wedge, and the screw. 



A lever is a rigid rod moveable about a fixed point, 



FIG. 57 (y^ real size). FIG. 58 (an. proj., real size). 



icted on by two or more forces, which tend to move it 

 in opposite directions. The fixed point is called the 

 rum. 



'ig. 57 represents a form of the lever, applicable to 

 tperiments on the relations of these forces. It con- 

 ists of a rectangular wooden rod, 50 cm long, 2 cm broad, 

 nd l cm thick. 25 horizontal holes are bored through 

 t at distances of 2 cm from each other, the middle hole 

 equally distant from both extremities of the rod. 



