WORK 



175 



motion. It is only by the performance of experiments with 

 pulleys that these questions can be satisfactorily answered. 



We might arrange a set of small pul- 

 leys and cord similar to the arrange- 

 ment for moving the boat, but employ 

 them for lifting a weight. It will be 

 noted that in this arrangement, as 

 shown in the figure, the hanging, or 

 movable, pulley is supported by 6 

 strands of cord (fig. 89). If one experi- 

 ments with this apparatus, it is imme- 

 diately discovered, first, that the force 

 exerted by the apparatus in lifting the 

 weight is much greater than the force 

 applied to the free end of the cord, and 

 second, that the weight moves a much 

 shorter distance than does the hand 

 which is pulling at the end of the cord. 



If the distances are measured, it 

 will be found that the hand travels 

 6 times as far as the weight in the 

 case of the pulley system so arranged 

 that 6 strands of cord are sup- 

 porting the weight. A measurement 

 of the force applied at the end of 

 the cord will show that it is a little 

 more than one sixth of the amount 

 which must be applied to the weight 

 in order to lift it. There is, of 

 course, some friction in the appara- 

 tus, and if care is taken to reduce 

 this as much as possible, it will be 

 found that the force applied is very 

 little greater than one sixth of the 

 weight lifted. We may conclude that 



FIG. 89. Pulleys and cords 



The pull on the cord is meas- 

 ured by the spring balance. 

 The weight of the load is 

 divided between strands of 

 cord by which it is suspended. 

 Disregarding friction, the pull 

 on the spring balance will be 

 one sixth as great as the pull 

 exerted by the load 



