# Motion

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:

1. v = u + at
2. s = ut + ½at2
3. v2 = u2 + 2as

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