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...
