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Length of a rod(GR)

  1. Feb 16, 2009 #1
    1. The problem statement, all variables and given/known data
    A long rod lies radially in the field of a spherical object of mass M. If the r-coordinates of its ends are r1 and r2 (r1>r2) what is it's length? also show that your result gives th right newtonian approximation, when applicable.


    2. Relevant equations
    dl2=(1-2GM/rc2)c2dt2-1/(1-2GM/rc2)dr2-r2(dθ2+sin2θdφ2)

    dt=0 and φ and θ are also 0 cause we're only interested in the r-coordinates

    dl= [tex]\sqrt{\frac{1}{1-\frac{2GM}{rc^2}}}[/tex] dr


    3. The attempt at a solution
    Now to my problem, the newtonian approximation.. The newtonian relativistic equation I know is l=l0γ but the rod have no speed, v, so l=l0 which is not correct
     
  2. jcsd
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