60.—Chinese Capstan.details

A pulley is often used in conjunction with a capstan, the rope passing round a pulley attached to the weight, and the mechanical advantage of the capstan is thereby doubled. Moreover, the free end of the rope, instead of being rigidly fixed, may be coiled round another smaller axle with the same centre F, so that its tension shall help the force P (fig. 60). By this means the mechanical advantage can be increased to any desired extent, for the weight is now would up only becuase the cord wraps itself on to one, the larger, axle faster than it unwraps itself from the other smaller axle; and the two axles may be as nearly the same size as one pleases. The mechanical advantage is the radius of the wheel (or the length of P’s arm) divided by the difference of the radii of the two axles, the whole being multiplied by two because of the pulley. (p. 138)