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) = VB – VA
The relative velocity of B with respect to A (VAB) = VA– VB
*VA is the velocity of body A
*VB is the velocity of body B
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
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.