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Relative Velocities

  1. Jan 18, 2015 #1
    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. jcsd
  3. Jan 18, 2015 #2

    Doc Al

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    Staff: Mentor

    What results did you get? Why do they seem absurd?
  4. Jan 18, 2015 #3
    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
  5. Jan 18, 2015 #4

    Doc Al

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    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.
  6. Jan 18, 2015 #5
    C is speed to O
  7. Jan 18, 2015 #6


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    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).
  8. Jan 18, 2015 #7
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