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Mass in SR

  1. Aug 18, 2009 #1
    is the mass invariant in special relativity or what ?
    i'm so confused , is the mass of a body change with the change of the body's speed ?
     
  2. jcsd
  3. Aug 18, 2009 #2

    Fredrik

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    Two different conventions are being used. The one favored by most people today is this one:

    Mass is invariant. It's denoted by [itex]m[/itex]. The quantity

    [tex]\frac{mc^2}{\sqrt{1-\frac{v^2}{c^2}}}[/tex]

    is called "energy". If we have to use a name for the quantity

    [tex]\frac{m}{\sqrt{1-\frac{v^2}{c^2}}}[/tex]

    we call it "relativistic mass", but we prefer not to use it at all.

    The other convention is to use the notation [itex]m_0[/itex] and the term "rest mass" for what I would call "mass", and the notation [itex]m[/itex] for what I would call "relativistic mass". This convention makes "mass" a function of speed:

    [tex]m=\frac{m_0}{\sqrt{1-\frac{v^2}{c^2}}}[/tex]
     
  4. Aug 18, 2009 #3

    ZapperZ

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    Please read an entry in our FAQ in the General Physics forum.

    Zz.
     
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