# Relative Velocities

1. Jan 18, 2015

### Quarlep

Lets suppose three objects O,A and B are set up in universe and nothing else.Then O seems A is moving 0.3c And B is moving 0.5c .In Special Relativity we have relative velocities formula I want to formule it but result seems absurd can you find me all possible velocities I mean A, O and B observer
Thank you

2. Jan 18, 2015

### Staff: Mentor

What results did you get? Why do they seem absurd?

3. Jan 18, 2015

### Quarlep

VCB=VOB-VOC I thought like this But this is not true in special relativity.In special Relativity it like the relative formule for special relativity isnt it ?

Last edited: Jan 18, 2015
4. Jan 18, 2015

### Staff: Mentor

You'll need to define your terms. (What is C, for example?)

You'll certainly need to add the velocities using special relativity, not Galilean relativity.

5. Jan 18, 2015

### Quarlep

C is speed to O

6. Jan 18, 2015

### DrGreg

But you said there were only 3 objects O, A and B, so there is no object C? I'm going to assume by "C" you mean "A", so, in Newtonian theory it would be$$v_{AB} = v_{OB} - v_{OA}.$$Then in special relativity it is$$v_{AB} = \frac{ v_{OB} - v_{OA} } { 1 - \frac{ v_{OB} v_{OA} } {c^2} },$$(provided all velocities are parallel).

7. Jan 18, 2015

Thanks