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What are these formulas representing?

  1. Dec 7, 2014 #1
    u = (v + u') / (1 + v u' / c2)

    f´ = f √ [ ( 1 + v / c) / ( 1 – v / c) ]

    What are the difference between these two formulas? My formula sheet doesn't specify the two. I believe one of them has to do with doppler effect.
  2. jcsd
  3. Dec 7, 2014 #2


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    First is colinear relatavistic velocity addition. Second is frequency change due to Doppler for a source emitting at f approaching a detector at v; f' is the frequency that will be be measured by the detector.
  4. Dec 7, 2014 #3
    Thank you so much PAllen
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