c motion, in physics, motion repeated in equal intervals of time. Periodic motion is performed, for example, by a rocking chair, a bouncing ball, a vibrating tuning FORK, a SWING in motion, the Earth in its orbit around the Sun, and a waterwave. In each case the interval of time for a repetition, or cycle, of the motion is called a period, while the number of periods per unit time is called the frequency. THUS, the period of the Earth’s orbit is one year, and its frequency is one orbit per year. A tuning fork might have a frequency of 1,000 cycles per second and a period of 1 millisecond (1 thousandth of a second).Examples of periodic motion include a rocking chair, swing, tuning fork, and a pendulum. A satellite orbiting our planet and a mass bouncing on a SPRING are also examples of periodic motionRandom motion ...--Unpredictable kind of motion where an object moves in any DIRECTION and the direction keeps changing continuously.Examples: kite flying in the air, fish swimming underwater, helium balloon in the sky