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May 12, 2014

Relative Velocity


  • Introduction

Relative Velocity is the velocity of a particular object with respect to the other object which might be stationary, moving slowly, moving with the same velocity, moving with higher velocity either in the same or opposite direction.

The relative velocity of A with respect to B (VBA) = V– VA

      The relative velocity of B with respect to A (VAB) = VA– VB

*Vis the velocity of body A

*Vis the velocity of body B

Suitable Example:

Let there is car A traveling at a velocity of 100km/hr and another car B is traveling at a velocity of 70 km/hr.

If the cars are moving in opposite direction

Car A and Car B are moving in the opposite direction, so the velocity of both cars is added up to calculate the relative velocity as a whole.

100km/hr + 70km/hr = 170km/hr

If the cars are moving in the same direction

Car A and Car B are moving in the same direction, so the velocity of both cars is subtracted to calculate the relative velocity as a whole.

For Car A: 100km/hr – 70 km/hr = 30km/hr

For Car B: 70km/hr – 100km/hr = -30km/hr

If the cars are moving with same velocity

Car A and Car B are moving with the same velocity of 100km/hr, the relative velocity is calculated through the difference of velocities of both cars. Though the cars are moving yet they appear stationary.

100km/hr – 100km/hr = 0km/hr

  • Applications of Relative Velocity
  1. The relative velocity is used commonly by used scientist to calculate the distance between two objects in space. The velocity of the moon and stars are compared with the earth’s velocity to calculate the distance between them.
  2. It is also used to explain the concept of illusions. The person in a train sees everything in the train stationary but a person outside the train sees everything moving because of the relative velocity. 
  • Importance of Relative Velocity

Relative velocity carries much importance in real life. It is meant for the purpose of a reference frame, used as a tool for referring one object to the other. Like referring moon and stars with the earth’s velocity.

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