MECHANICS 



the points D' and D" two additional weights X and Y, 

 bearing the same ratio to each other as the weights 

 of AD and DB had previously borne. Then the balance 

 will still remain undisturbed in spite of the greater 

 weight suspended on one side of C compared to that 

 on the other side of it. 



A lever is a rod we will suppose to be perfectly rigid 



FIG. 8. 



W 



A 



W 



u 



fi 





F 



W 



HI 



(and we will here assume it to be also straight), 

 which turns on a fixed point called the fulcrum. A 

 force is applied at some point in the lever, while at some 

 other point there is a resistance acting, which resistance 

 the force has to overcome. The portions of the lever 

 which may be on either side of the fulcrum are called 

 the arms of the lever. 



Levers may be of three orders: a lever of the first 



