. The elements of railroad engineering . pulley merely changes the direction in which Pacts, so that a weight of 1 j^ound hung on the free end of thecord will balance 2 pounds hung from the movable pulley. 938. A combination of pulleys, as shown in , is somelinics used. In this case thereare three movable and three fixed pulleys,and the amount of movement of If, owing toa certain movement of /*, is readily found. It will l)e noticed that there are six partsof the rope, not counting the free end; hence,if the movable block be lifted 1 foot, /re-maining in the same position, there wouldbe
. The elements of railroad engineering . pulley merely changes the direction in which Pacts, so that a weight of 1 j^ound hung on the free end of thecord will balance 2 pounds hung from the movable pulley. 938. A combination of pulleys, as shown in , is somelinics used. In this case thereare three movable and three fixed pulleys,and the amount of movement of If, owing toa certain movement of /*, is readily found. It will l)e noticed that there are six partsof the rope, not counting the free end; hence,if the movable block be lifted 1 foot, /re-maining in the same position, there wouldbe 1 foot of slack in each of the six parts ofthe rope, or six feet in all. Therefore, Pwould have to move G feet in order to takeup this slack, or/moves six times as far as , 1 pound at /will support G poundsat \\\ since \.\\ uiultiplied by the dis-tanee through which it moves equals the weightmultiplied by the distance through which itjuoxcs. It will also be noticed that there arethree movable pulleys, and that 3 X !^ = Fig. J-lo, ELEMENTARY MECHANICS. 343 Rule VIII.—/// any combination of pulleys where one con-tinuous rope is used a load on the free end ivill balance axveight on the movable block as many times as great as theload on the free end as there are parts of the rope supportingthe load—not counting the free end. The above law is good, whether the pulleys are side by-side, as in the ordinary block and tackle., or whether they arearranged as in the figure. Example.—In a block and tackle having five movable pulleys, how-great a force must be applied to the free end of the rope to raise 1,250pounds ? Solution.—Since there are 5 movable pulleys, there are 10 parts ofthe rope supporting them, and 1 pound on the free end will balance 10pounds on the movable block; therefore, the ratio of P to \Vrs,\\ 10,1,250 and / = 10 = 125 pounds. Ans. 939. In Fig. 149 is shown an arrangement called a dif-ferential pulley. It will be seen that if a force be appli
Size: 942px × 2654px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, booksubjectrailroadengineering
