. A text book of elementary mechanics, for the use of colleges and schools. oyed in practice; for example, in moving the tube ofa microscope up or down. 215. Toothed wheels are extensively used in theworks of a clock. The point practically considered ishere the relative velocity to be given to the successiveaxes; the relation of P to TTis not taken into account. 216. Use of Belts. In machines the motion of oneaxis is communicated to another by the use of belts, aswell as by toothed wheels; there may or may not be achange of velocity. The use of the belt or strap dependson the friction of the s
. A text book of elementary mechanics, for the use of colleges and schools. oyed in practice; for example, in moving the tube ofa microscope up or down. 215. Toothed wheels are extensively used in theworks of a clock. The point practically considered ishere the relative velocity to be given to the successiveaxes; the relation of P to TTis not taken into account. 216. Use of Belts. In machines the motion of oneaxis is communicated to another by the use of belts, aswell as by toothed wheels; there may or may not be achange of velocity. The use of the belt or strap dependson the friction of the surfaces in contact (85). The velocities of the two axes, assuming that the strapdoes not slip at all, are in the inverse ratio of the radiiof the wheels, and the mechanical advantage is in thedirect ratio, as was true of the toothed wheels. Thus, in the case of the cone-pulley (E, Fig. 156) on 226 STATICS. [217. the shaft communicating the power in the shop, andthat (F) of the lathe below, the velocity of the axis ofthe lathe will be greatest, and the power of overcoming. Fig. 156. resistance the least, when the belt passes over the largestwheel of the latter, and conversely. In general, according as the straps are or are notcrossed, the motion of the second wheel is in the sameor opposite direction to that of the first. iy. Pulley. 217. The Pulley consists of a circular wheel turningabout an axis which is attached to a surrounding frame,called the block. About the circumference of the wheel,which is grooved, passes a rope, and at one end of thisthe power acts. Sometimes two wheels are placed sideby side, as in Fig. 157. The necessity of making the wheel turn on its axisarises from the friction, which is very much diminishedin this way; except for this, fixed pegs would answer aswell 219.] PULLEY. 227 The efficiency of the pulley is based upon the prin-ciple (122) that the tension of a given string is the sameat every point. 218. Single Fixed Pulley. In the single fixed pulley
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectmechanics, bookyear18
