MECHANICS. 69 



I. In treating of the lever, it is usual to distinguish 

 the forces by the names of the Power and the 

 Weight, or the Power and the Resistance, terms 

 that have a reference to the intention with which 

 the machine is used, not to any real difference in the 

 action of the forces. 



We shall begin with abstracting entirely from the 

 weight of the lever itself. 



124. If two forces be applied to a lever having 

 equal and opposite momenta, that is, tending to pro- 

 duce motion in opposite directions, and being in- 

 versely as the perpendiculars drawn to their direc- 

 tion from the fulcrum, they will be in equilibrium 

 with one another. 



When the forces are parallel, this proposition coincides 

 with the property of the centre of gravity, 105. 

 When they are oblique, the case is reduced to the 

 preceding by the resolution of forces. 



125. If any number of forces be applied to a le- 

 ver, there will be an equilibrium if the sums of the 

 opposite momenta be equal to one another. 



This proposition also coincides with a property of the 

 centre of gravity, ( 108 and 109.) 



126. When any number of forces are perpendi- 

 cularly applied to a lever, the fulcrum is loaded 



with 



