What is the relative velocity equation?

1 Answer
Jul 26, 2015

If an object A moves with velocity vA and object B with vB, Then velocity of A with respect to B (As observed by observer B) is,

vAB = vAvB.

Explanation:

As an example, let us consider linear motion for simplicity and assume that our observations in one dimension holds for two and three dimensions. (By using vector notation, this happily turns out to be the case.)

Two cars A and B moving with velocities vA and vB.

Velocity of A as observed by a person sitting in car B is then naturally,

vAB=vAvB

if vA is greater than vB.

The observer sees the car A going away (ahead) from it with speed vAB.

If the opposite is the case, vAB is negative.

The car B goes ahead of A with the speed vAB.

Extending what we observed here to three dimensions is trivial.
We just have to use vector notations for that. Other details remain unchanged.