ROPE 6 i 



pounds. It is thus seen that the pull exerted by the fall- 

 block on its support is greater than the pull or lifting 

 force exerted by the other block on the load, by an amount 

 which is equal to the pull on the fall-rope. 



By application of the same method of reasoning to Figure 

 85 a weight may be lifted which is nearly equal to four 

 times the pull on the fall-rope, for there are four plies lead- 

 ing from the block which would be attached to the load. 

 The fall-block will pull down on its support with a force 

 which is nearly five times the pull on the fall-rope. 



In a similar way by use of a set of blocks like those shown 

 in Figure 86 a weight may be lifted which is approximately 

 five times the pull on the fall-rope. The pull down by the 

 fall-block on its support will be nearly six times the pull on 

 the fall-rope. 



Moving heavy objects. In the previous discussions regard- 

 ing the lifting force of blocks it has been shown that the 

 fall-block pulls down'on its support with a force which is 

 greater than that exerted by the other block on the object 

 to be lifted. It is then advisable, if possible, when heavy 

 objects such as buildings are to be moved, that the fall- 

 block be fastened to the object to be moved. The pull on 

 the fall-rope should also be directly toward the fixed block. 

 In this way all of the pull exerted on the fall-block will be 

 in the same direction and it will have a greater effect on the 

 object to be moved. When the fall-block is not fastened 

 to the object to be moved, the pull on the fall-rope may be 

 in any direction, without changing the direction or amount 

 of the pull exerted on the object to be moved. 



BIBLIOGRAPHY 



Blue Book of Rope Transmission. American Manufacturing Co., New 

 York. 



Encyclopedia Britannica. 



Frear, J. B. "Rope and Its Use on the Farm," Bulletin 136, Uni- 

 versity of Minnesota Agricultural Experiment Station. 



