# Relative Velocities

• Quarlep
In summary, the conversation discusses the setup of three objects in the universe and their relative velocities, with the speaker attempting to use a formula for special relativity. They express frustration and confusion over the results and ask for help in finding all possible velocities for the three objects. The responder asks for clarification on terms and explains the need for using special relativity instead of Newtonian theory.

#### 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

Quarlep said:
In Special Relativity we have relative velocities formula I want to formule it but result seems absurd
What results did you get? Why do they seem absurd?

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 isn't it ?

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Quarlep said:
VCB=VOB-VOC
You'll need to define your terms. (What is C, for example?)

Quarlep said:
I thought like this But this is not true in special relativity.In special Relativity it like the relative formule for special relativity isn't it ?
You'll certainly need to add the velocities using special relativity, not Galilean relativity.

C is speed to O

Quarlep said:
VCB=VOB-VOC
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).

Thanks