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Do I have to re-define electric field strength in Centre of Mass frame

  1. Apr 3, 2013 #1
    So lets say I'm computing the torque as a result of the interaction between two electric dipoles in the lab frame. Lets imagine they are in some electric field.

    I then do : τ = r×F

    If I now switch to the centre of mass frame I have to find their position vectors from the COM.

    Why do I not have to re-define the electric field strength vector and ultimately the force vector on each dipole with respect to the centre of mass frame ?
     
  2. jcsd
  3. Apr 3, 2013 #2

    mfb

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    Non-relativistic? Fields and forces (at specific points) are the same in all inertial frames.
     
  4. Apr 3, 2013 #3
    I'll be honest, I dont completely follow what you mean by non-relativistic.

    I'm a first year Chemistry student so the idea of inertial frames is a very new concept.
     
  5. Apr 3, 2013 #4

    mfb

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    Non-relativistic = you don't care about special relativity. Okay, it's fine.

    It is just a more general way to say "fields and forces are the same for the lab and the center of mass frame".
     
  6. Apr 3, 2013 #5
    Oh, okay, I see what you mean now. Thanks !

    Beside fields and forces what else does not change between the lab and COM frame ?
     
  7. Apr 3, 2013 #6

    mfb

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    Masses, relative velocities, distances, all internal paramters of objects, ...
    Position, velocity, kinetic energy and momentum (and maybe angular momentum, depending on its definition) are the only changing things, unless I forgot something.
     
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