68 



(b) Fasten one end of a string to a nail and the opposite 

 end to a spring balance as shown in Figure 56. 



Place a movable pulley in the string and from it hang 

 the 2O-pound weight. What pull is now registered in the 

 spring balance ? Can you suggest any reason why the 

 pull in case () is different from that in case (a) ? 



Raise the spring balance (Fig. 56) through a vertical 

 height of about 12 inches; the load ^likewise moves; 

 determine the vertical distance through which it is raised 

 by the change in the position of the spring balance. 



What is the advantage of such a pulley ? 



What is the disadvantage of such a pulley ? 



Is it, on the whole, advantageous or not ? Illustrate. 



EXPERIMENT 58. THE POWER OF STEAM 



For this experiment the pupil 

 should provide herself with a 

 toy pin wheel made at home 

 (Fig. 57). 



(a) Heat a pint or a quart of 

 water in an open vessel, and 



FIG. 57. Toy pin wheel. 



FlG. 58. Steam as a source of 

 power. 



