466 TRANSFERRING AND TRANSFORMING ENERGY 



wheel (A) while the weight travels through the distance 

 of the circumference of the other wheel, or axle (C). If 

 the circumference of the power wheel is three times the 

 circumference of the weight wheel, a force of 5 pounds 



exerted on the power wheel 

 will lift a weight of 15 

 pounds on the weight wheel. 



The Pulley. Experiment 

 146. (a) After well oiling 

 some small pulleys arrange one 

 of them as in Figure 141, hav- 

 ing a weight of about 500 g. 

 ^ ^*r on one end of the cord and a 



i~i . r~i r"S spring balance on the other. 



Hfrl |g r I iff" Slowly pull down on the spring 



FIGURE 141 ' FIGURE 142 FIGURE 143 balance and note the reading 



on the scale. Allow the balance 



to rise and note the reading. Friction accounts for the difference 

 between the first and the second reading of the scale. Average 

 the two readings and see how nearly the average equals the weight 

 on the other end of the cord. May we say that the force exerted 

 by the hand is equal to the weight? Does the hand 

 move through the same distance as the weight ? 



(6) Arrange the pulleys as in Figure 142. Allow the 

 balance to descend, noting the force recorded on the 

 scale. Pull up on the balance, noting again the reading 

 on the scale. Find the average between the two forces, 

 which may be called the true force. Is the force now 

 ^exerted by the hand equal to the weight? If not, 

 what are the relations of these two forces? 



Note the distance moved by the hand and also the distance 

 moved by the weight. How do they compare? 



(c) Arrange the pulleys as in Figure 143. Make determinations 

 similar to those in (a) and (6) . How does the force exerted by the 

 hand now compare with the weight ? How does the distance moved 

 by the hand compare with that moved by the weight ? 



FIGURE 144 



