88 THE LEVER. 



equal to the work of the load, the power expended in the 

 machine itself being disregarded. The following laws are, 

 therefore, applicable to machines of every kind. They are 

 called the general or great laws of machines : 



(I.) What is gained in intensity of power is lost 

 in time, velocity, or distance; and what is 

 gained in time, velocity, or distance is lost in inten- 

 sity of power. 



(2.) Tlie power multiplied by the distance through 

 which it moves, equals the iveight multiplied 

 by the distance through which it moves. 



(3.) The power multiplied by its velocity, equals the 

 weight multiplied by its velocity. 



168. What is a Lever? A lever is an inflex- 

 ible bar capable of being freely moved about a 

 fixed point or line, called the fulcrum. 



In every lever, three points are to be considered, viz.-, 

 the fulcrum and the points of application for the power 

 and the weight. Every lever is said to have two arms. 

 The power-arm is the perpendicular distance from the ful- 

 crum to the line in which the power acts ; the weight-arm 

 is the perpendicular distance from the fulcrum to the line 

 in which the weight acts. If the arms are not in the same 

 straight line, the lever is called a bent lever. 



169. Classes of Levers* There are three classes 



of levers, depending upon the 

 relative positions of the power, 

 weight, and fulcrum. 



FIG. 37. (1.) If the fulcrum is be- 



