What is the formula for calculating relative velocities in Special Relativity?

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Discussion Overview

The discussion revolves around the calculation of relative velocities in the context of Special Relativity, specifically focusing on three objects O, A, and B, and the challenges participants face in applying the correct formulas for their relative motions.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant presents a scenario with three objects O, A, and B, with A moving at 0.3c relative to O and B moving at 0.5c relative to O, seeking a formula for their relative velocities.
  • Another participant questions the results obtained by the first participant, asking for clarification on why they seem absurd.
  • A participant attempts to apply a formula for relative velocity, VC_B = V_OB - V_OC, but acknowledges that this approach is incorrect in the context of Special Relativity.
  • There is a suggestion that velocities must be added using the principles of Special Relativity rather than Galilean methods.
  • Clarification is sought regarding the definition of terms, particularly the variable "C," which is later identified as the speed of O.
  • A participant provides the correct formula for relative velocity in Special Relativity, v_{AB} = (v_{OB} - v_{OA}) / (1 - (v_{OB} v_{OA} / c^2)), noting that this applies when all velocities are parallel.

Areas of Agreement / Disagreement

Participants express differing views on the application of relative velocity formulas, with some acknowledging the need for Special Relativity corrections while others struggle with the initial assumptions and results. The discussion remains unresolved regarding the specific calculations and interpretations of the velocities.

Contextual Notes

There are limitations in the definitions and assumptions made by participants, particularly regarding the use of terms and the application of different relativistic formulas. The discussion does not fully resolve the mathematical steps involved in calculating the relative velocities.

Quarlep
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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
 
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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 ?
 
Last edited:
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[tex] v_{AB} = v_{OB} - v_{OA}.[/tex]Then in special relativity it is[tex] v_{AB} = \frac{ v_{OB} - v_{OA} } { 1 - \frac{ v_{OB} v_{OA} } {c^2} },[/tex](provided all velocities are parallel).
 
Thanks
 

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