A YEAE IN SCIENCE 



129 



mass moved. Power is the force used to move the 

 mass. Weight arm (W. A.) is the distance from the 

 fulcrum to the point of application of the weight. 



Fig. 33. 



Power arm (P. A.) is the distance from the fulcrum 

 to the point of application of the power. 



Levers are divided into three classes based upon 

 the relative positions of the three points : fulcrum, 

 power, and weight. 



In the first class lever, the fulcrum is in the middle, 

 the weight at one end, and the power at the other. 



The second class lever has the fulcrum at one end, 

 the power at the other end, and the weight in the 

 middle. 



The third class lever has the fulcrum at one end, the 

 weight at the other end, and the power in the middle. 



Fasten one end of the yard stick to the ring stand. 

 From the second ring stand suspend the spring bal- 

 ance. Wire the free end of the yard stick to the hook 

 of the spring balance. Take the reading of the 

 indicator on the scale. Suspend the 500 gm. weight 

 from the zero point on the yard stick. 



