Q.What is meant by periodic and non-periodic motion? Give any two examples, for each motion.

Motion in physics splits into periodic motion (any motion repeating itself after a fixed, regular time interval -- the swing of a pendulum-clock hand, the Earth's yearly orbit round the Sun, the Moon's monthly waxing and waning) and non-periodic motion (motion with no such fixed repetition interval, such as an earthquake or a volcanic eruption). Oscillatory (or vibratory) motion is a more specific idea: motion in which a body moves repeatedly back and forth about some reference or mean position -- a heartbeat, an insect's beating wings, or a pendulum clock's swinging bob. Every oscillatory motion is automatically periodic, since moving back and forth about a fixed point necessarily brings the system back to the same state after a fixed time. But the reverse fails: the Earth orbiting the Sun is periodic (repeats every year) yet is not oscillatory, because it travels around a closed loop rather than genuinely reversing direction about a mean position. So all oscillatory motions are periodic, but not all periodic motions are oscillatory -- oscillatory motion is the narrower, more specific category, and it is this narrower category that Simple Harmonic Motion, the subject of the rest of the unit, belongs to.