Consider a variable frequency oscillator (or phase modulation). Sometimes a frequency isn't either. In your example (and mine) the "signal" is not characterized by a "frequency" (either cyclical or periodic, which I assert are the same). It is best described, as the phase being some (unusual) function of time, and a non-constant derivative. Some "signals" exist both electrically and on shafts.
--- On Wed, 3/25/09, [email protected] <[email protected]> wrote: From: [email protected] <[email protected]> Subject: [USMA:44112] Periodic Motion To: "U.S. Metric Association" <[email protected]> Date: Wednesday, March 25, 2009, 11:37 AM John, Consider the rotation of the wheels of a domestic vacuum cleaner in irregular forward then backward motion. Is the rotation of the wheels periodic motion? There is no fixed point or fixed time interval. Rotation is *sometimes* periodic motion, but not always. "John M. Steele" <[email protected]> wrote: >... > *Rotation is certainly periodic motion. > Periodically, the same point on a shaft passes a > fixed point of observation...
