Any motion that is repeated is called periodic motion. Examples of periodic motion are the moon's orbit of the earth, a beating heart, the whirring tail of a frightened rattlesnake, the wings of a hummingbird, and the movement of the valve on a revolving bicycle tire. A vibrating body in contact with the atmosphere will produce sound waves. One simple example is a vibrating piston.
Basic Features of Periodic Motion
There are thus three parameters which characterise the basic features of any periodic motion.
1. The period, T is the time required for one complete cycle.
2. The frequency, f is the number of cycles occurring in a given time period.
3. The Amplitude, A. The "extent" of the motion.
Thus the frequency is the inverse of the period (and vice versa), i.e.:
Frequency used to be expressed in cycles per second (cps). The unit Hertz (abbreviated Hz) is now used. 1 cycle/second = 1 cycle sec.-1 = 1 Hz.
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