Uses of the Pendulum
المؤلف:
GEORGE A. HOADLEY
المصدر:
ESSENTIALS OF PHYSICS
الجزء والصفحة:
p-94
2025-11-05
44
The most common use of the pendulum is as a timekeeper. Since the vibrations are performed in equal intervals of time (i.e., are isochronous), all that is needed is to make the to-and-fro motion of the pendulum regulate the rotary motion of the hands. This is done by the use of an escapement by means of which each complete vibration lets one tooth of a cogwheel escape, so that if the wheel has 30 teeth, it will rotate once while the pendulum vibrates back and forth 30 times. This wheel is one of a train of cogwheels that move the hands. The by the motion of the pendulum is kept up by a push from each cog as it escapes, and the motion of the train is kept up by the pressure of a spring or pull of a weight. In order that the times of vibration may be equal, the length must always be the same, and corrections must be made for the changes in length due to changes of temperature. In most pendulums this is done by moving the bob up or down by means of a nut running upon the wire support. It is done automatically in various forms of compensation pendulums. In some of these two different sets of metal rods are used so that the expansions shall oppose each other. In the mercurial pendulum (Fig. 1), glass tubes filled with mercury are used for the bob, and are so arranged that the expansions and contractions of the mercury just counteract the effect of the contraction and expansion of the suspending rod.
Fig. 1
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