A continuous **change in the position** of the object with respect to time is called motion.

**Rectilinear motion:** If an object moving in a straight line changes its position with respect to time.

**Circular motion:** When an object moves at a constant distance from a fixed point, its motion is called circular motion.

**Periodic motion:** A motion which repeats itself after certain fixed interval of time is called periodic motion.

**Oscillatory motion:** A motion which is repeated about its mean position periodically is called oscillatory motion. For example, motion of simple pendulum.

**Distance:** The length of the path fallowed by a body is called distance.

**Displacement:** The shortest distance between initial and final position of the object is called displacement. It is vector quantity.

The SI unit of distance and displacement is metre (m).

**Speed:** Distance traveled by a body in unit time is called speed.

Speed = Distance / Time

**Average speed:** Total distance traveled / Total time taken

**Velocity:** Displacement of a body in unit time is called velocity.

Velocity = Displacement / Time taken

The unit of velocity in SI system is m/s. Other commonly used unit is km/h. It is a vector quantity.

**Acceleration:** The rate of change of velocity is called acceleration.

Acceleration = (Final velocity – initial velocity) / Time

a = (v - u)/t

The unit of acceleration in SI unit is ms^{-2}. It is a vector quantity.

**Equations for uniformly accelerated motion:**

- v = u + at
- s = ut + ½at
_{2} - v
^{2}= u^{2}+ 2as

where u = initial velocity, v = final velocity, a = acceleration, s = distance, t = time