# Velocity: Definition, Formula and Units

The rate of change in position of an object (displacement) with respect to time and frame of reference. Further, the key elements of the velocity are distance and displacement. If there is no displacement in the object and it does not cover any distance, there will be no velocity. Velocity is a vector quantity because it has a vector function of displacement.

## Velocity formula

Velocity is directly proportional to displacement and inversely proportional to time. Velocity formula is given below:

Velocity = Displacement / Time

Where  displacement is the change in an object’s position. (Final position – Initial position)

And

time is taken to cover the distance

If X1 is the initial position while X2 is the final position of the object and time taken to cover this distance is t then velocity will be:

Velocity = (Final position – Initial position) / Time

v = (X2 – X1)/ t

v = △x/△t

Other formulas of velocity are:

Angular velocity, ω = θ/t

Average velocity, v = △x/△t

Linear velocity, v = s/t

Escape velocity, v= √2GM/r, where G is gravitational constant equal to 6.674 ×10-11Nm2/kg2

SI units of velocity are meter per second ( ms-1 ) and its dimensions are [ LT-1]

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## Example

A bullet train has covered a distance of about 1Km in 1 hour. Calculate its velocity

Data:

Distance covered = 1Km = 100 meters

Time = 1hr = 3600s

To calculate:

Velocity (v) = ?

Solution:

v = s/t

= 1000/3600

= 0.28 ms-1

So the velocity of a bullet train is about 0.28 meters per second.

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