104 



THE PULLEY. 



say, eacli section of the cord carrying the weight must be 

 shortened one foot. Thus the hand, by lifting 50 pounds 

 two feet, is able to raise 100 pounds one foot. It is to be 

 noticed that we have here no creation or increase of 

 energy, working power, but that we do 

 secure an important transformation of 

 velocity into intensity. 



195. A Combination of Pul- 

 leys. By the use of several fixed and 

 movable pulleys in blocks, the number 

 of parts of the cord supporting the mov- 

 able block may be increased at pleasure. 

 In all such cases, the tension of the cord 

 will be uniform, and the part of the cord 

 to which the power is applied, will carry 

 only a part of the load. The value 

 of this part of the load depends upon 

 the number of sections into which the 

 movable pulley divides the cord. 



196. Law of the Pulley.- 



With a pulley having a contin- 

 uous cord, a given power ivill support a 

 weight as many times as great as itself as 

 there are parts of the cord supporting the 

 movable Hock. 



197. Concerning the Number of 

 Parts of the Cord. By observing the sev- 

 eral figures of pulleys in this section, it will be 

 seen that when the fixed end of the cord is at- 

 ^ tached to the fixed block, the number of parts of 

 FIG. 54. the cord supporting the weight is twice the num- 



FIG. 53. 



