Periodic Motion is motion repeated in equal intervals of time. In Periodic Motion, the interval of time for a repetition, or cycle, of the motion is a period, while the number of periods per unit time is the frequency. Circular Motion is the movement of an object along the circumference of a circle or rotation along a circular path. Circular Motion can be uniform, with constant angular rate of rotation and constant speed, or non-uniform with a changing rate of rotation.