MACHINES 



EXPERIMENT 55. THE LEVER 



BALANCE a foot rule with a hole at its middle point as 

 shown in Figure 51. 



Suspend from the bar at the point 12 a weight of 

 i pound. The balance is disturbed. Then from the point 

 3 suspend such a 

 weight as will re- 

 store equilibrium 

 to the bar. 



How does the 

 weight P sus- 

 pended at the point 



'- 



FIG. 51. A balanced ruler. 



3 compare with the weight W suspended at the point 



12? 



Such an arrangement of a bar is called a lever. The 

 point about which the bar rotates is called the fulcrum. 



The distance from the fulcrum 

 to the force P is called the 

 power arm, while the distance 

 from the fulcrum to the weight 

 W is called the weight arm. 



In this case what is the nu- 

 merical value of the force arm, 

 and of the power arm ? Under 

 what circumstances will a small 

 weight suffice to balance a 



FIG. 52. A curved lever. large 



CL. LAB. 5 65 



