Observe the motion of the hand of a clock. The hand of second rotates round its centre once in a minute. The hand is rotating continuously in one direction and its motion is repeated. This kind of motion is a periodic motion. Remember the four round race of your school’s annual athletic competition. Suppose you remain standing at one corner of the field. One sprinter of four round race will cross you four times from the same direction (after certain definite intervals of time). It is also periodic motion. The motions of clock hands, round race, electric fan, etc, are examples of periodic motion. Some examples of periodic motion include a bouncing basketball, a swinging tire swing, a metronome or a planet in its orbit
Hence, if an object travels a certain distance of its path from the same direction after certain definite intervals of time repeatedly, the motion is called a periodic motion. Whatever the motion may be, the period of time it takes to get back to where it started is called the time period of the motion.