Sympathetic Vibrations
المؤلف:
GEORGE A. HOADLEY
المصدر:
ESSENTIALS OF PHYSICS
الجزء والصفحة:
p-206
2025-11-16
34
Whenever a sounding body is near another that has the same time of vibration, it is found that the pulses of air sent out by the first will put the second in motion.
Demonstration. -Select two tuning forks that are mounted upon resonance boxes, and that give the same number of vibrations per second. Place them parallel to each other at opposite ends of a table, and put one of them in vibration with a heavy bow. Stop its vibrations with the fingers, after a few seconds, and the second fork will be heard. Its vibration may also be shown by suspending a light ball by a thread so that it will just touch one side of the fork.
The minute and rapid blows of the condensed waves of air striking upon the fork have enough energy to set it in motion, provided that the rate of the blows is the same as that of the vibrations. That this is also the case with a heavy swinging body may be shown as follows:
Demonstration. - Suspend from a hook in the ceiling a 20-pound weight, and find the time in which it will vibrate as a pendulum. Strike the weight light blows with a cork hammer, when it is at rest, timing the blows to the same rate as that in which it vibrated. If the blows are given at the right times, the result will be to set the pendulum swinging.
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