MECHANICAL ADVANTAGE 



335 



Three classes of levers. There are three classes of 

 levers which depend on the position of the fulcrum, the 

 weight, and the force. The relative positions of these 

 are as follows : In levers of the first class, the fulcrum 

 comes between the weight and the force ; in levers of the 

 second class, the weight comes between the fulcrum and 

 the force ; in levers of the third class, the force comes 



Levers of the Tinst Class 



/uJc'runv. 

 y ; 



/orce 



CD. 



weight 



levers y the Second Clcrss 



/ulcru 



>reigrKt /orce 



r w 



r w 



levers of the Third Class 



Common examples of the three classes of levers. 



between the weight and the fulcrum. The shears belong 

 to the first class of levers, the wheelbarrow to the second 

 class, and the sugar tongs to the third class. 



Mechanical advantage. We use ordinarily a machine 

 to overcome a force greater than that which we apply. If 

 by means of a machine we can lift 200 pounds by applying 

 a force of 25 pounds, then the mechanical advantage of 

 the machine is 8 ; it is equivalent to the force moved di- 

 vided by the force applied. With levers of the third class 



