24 MECHANIC POWERgS. 



no friction or inertia. When this equilibrium is 

 established, it will be then necessary to add so 

 much more power as will be sufficient to overcome 

 the friction of the machine, and to give the requi- 

 site velocity. 



THE LEVER. 



The lever is the simplest of all machines, and 

 is only a straight bar of iron, wood, or other ma- 

 terial, supported on, and moveable round, a prop 

 called the fulcrum. 



In the lever, there are three circumstances to be 

 principally attended to : 1. The Julcrum, or prop, 

 by which it is supported, or on which it turns as an 

 axis, or centre of motion : c 2. The power to raise 

 and support the weight: 3. The resistance or 

 weight to be raised or sustained. 



The points of suspension are those points where 

 the weights really are, or from which they hang 

 freely. 



The power and the weight are always supposed 

 to act at right angles to the lever, except it be 

 Otherwise expressed. 



The lever is distinguished into three sorts, ac- 

 cording to the different situations of the fulcrum 

 aBd the power, with respect to each other. 



1. When the fulcrum is placed between the 

 power and the weight. 



2. When the fulcrum is at one end of the lever, the 

 power at the other, and the weight between them. 



3. When the fulcrum is at one end, the weight 

 at the other, and the power applied between them. 



A poker, in stirring the fire, is a lever of the first 

 sort ; the bar of the grate upon which it rests is the 

 fulcrum ; the fire, the weight to be overcome; and 

 the hand is the power. The lever of the first 

 kind is principally used for loosening large stones; 



