. Practical physics. Fig. 133. The vise THE PRINCIPLE OF WORK 119 Let the student show from tlie principle of work, namely Es — Rs, that the mechanical advantage, that is, —, of such a device is circum. of a no. coos in d no. cogs in / X 5 X ^—__i£.. circum. of e no. cogs in c no. cogs m a (8) 140. The worm wheel. Another device of high mechanical advantageis the worm wheel (Fig. ). Show tliat if / is the length of the crankarm C, n the number ofteeth in the cogwheelW, and r the radius ofthe axle, the mechanicaladvantage is given by 2Trln HZT- = :- (»). Fig. 134. Train of gearAvheels Fk: 1
. Practical physics. Fig. 133. The vise THE PRINCIPLE OF WORK 119 Let the student show from tlie principle of work, namely Es — Rs, that the mechanical advantage, that is, —, of such a device is circum. of a no. coos in d no. cogs in / X 5 X ^—__i£.. circum. of e no. cogs in c no. cogs m a (8) 140. The worm wheel. Another device of high mechanical advantageis the worm wheel (Fig. ). Show tliat if / is the length of the crankarm C, n the number ofteeth in the cogwheelW, and r the radius ofthe axle, the mechanicaladvantage is given by 2Trln HZT- = :- (»). Fig. 134. Train of gearAvheels Fk: 135. The wormo-ear This device is usedmost frequently whenthe primary object is todecrease speed rather than to multiply force. It will be seen that thecrank handle must make n turns while the cogwheel is making one. Theworm-gear drive is generally used in the rear axles of auto trucks. 141. The differential pulley. In the differential pulley (Fig. 136) anendless chain passes first over the fixed pulley A, then down andaround the movable pulley C,then up again over the fixed pul-ley B, which is rigidly attachedto A, but differs slightly from itin diameter. On the circumfer-ence of all the pulleys are projec-tions which fit between the links,and thus keep the chains from slip-ping. When the chain is j^i^Heddown at E, as in Fig. 13 G, (2),until the upi^er rigid system ofpulleys has made one completerevolution, the chain between theupper and lower pulleys has beenshortened by the difference be-tween the circumferences of the
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectphysics, bookyear1922
