THE INCLINED PLANE 61 



a. Support a pulley as in Fig. 175, 201, of the text, and 

 fasten a weight, such as a book, to one string. 



How much force must you exert, pulling downward, to 

 lift the book? Prove this by fastening a second book, of 

 the same weight as the first, to the free end of the string. Do 

 the books balance each other? What is the use of such a 

 pulley? 



b. Now try two pulleys, as in Fig. 176 of the text. Do you 

 need to exert more, or less, force than the - 



weight of the book? Note carefully how far 

 down you must pull the free cord, and how 

 far the weight rises. How do the distances 

 compare? 



Put two books for the weight, and one on 

 the free end of the string. Can the one be 

 made to balance the two? Why? 



c. Finally, support two pulleys as shown in 

 Fig. 25, this manual. Can one book be made 



FIG. 25. 



to balance two? 



d. If you can get no pulleys for this exercise, use casters, 

 such as are put under bureaus and tables. In this case use tape 

 for your pulley cord, as this will not slip off so easily as string. 



EXERCISE 59 

 THE INCLINED PLANE 



Apparatus and Materials. A board about 3 ft. long (a drawing 

 board, moulding board, or ironing board will do for 6), spool, nail to 

 fit it, two-pointed tacks, cord or tape, round dowels or spools or a 

 cart, books for weights. 



a. Make an inclined plane out of a board about 3 ft. long 

 (Fig. 26). To make the friction small at the edge of the board 



