Let us discuss the meaning or definition of periodic motion, oscillatory motion, simple harmonic motion and difference among them:

**Periodic Motion:**

The motion which repeats itself over and over again after equal intervals of time is known as periodic motion.

**Example of periodic motion:** Motion of planets around sun motion of earth above its own axis.

**Period of Motion:**

The fixed interval of time after which a periodic motion is repeated is called as the period of that periodic motion.

**Example period motion:** Period of earth around its own axis is 24n. Around the sum is 365 h.

**Oscillatory Motion:**

When a body moves in to and fro motion over and over again about a fixed point, then its motion is called oscillatory motion. (In case of a spring, we call it as a vibratory motion).

The fixed points is called as the equilibrium position or the mean position of that body and such a motion is combined between the extreme limits and it is present on the either side of the mean position.

**For Example:**

1. The mean of the pendulum of a clock.

2. Motion of a spring strings of the musical.

3. Motion of a loaded spring.

**Note:**

- An oscillatory motion is a special type of periodic motion in which the body vibrates to and fro about the mean position.
- Every oscillatory motion is periodic but every periodic motion is not oscillatory.

**Harmonic Oscillations:**

The oscillations which can be expressed in terms of a single harmonic function i.e. the sine function or the cosine function are known as the harmonic oscillation.

**Simple Harmonic Oscillations:**

The harmonic oscillations of constant amplitude and a single frequency is known as Simple Harmonic Oscillations.

**Simple Harmonic Motion:**

A body is said to be executing a simple harmonic motion if its acceleration is directly proportional to the displacement from the mean position at any instant and it is always directed towards the mean position.

These are the differences among periodic motion, oscillatory motion and simple harmonic motion.

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