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

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Discussion Overview

The discussion revolves around the concept of electric field strength and force vectors in different inertial frames, specifically the lab frame and the center of mass (COM) frame. Participants explore the implications of switching frames when calculating torque due to electric dipoles in an electric field, touching on the broader topic of how physical quantities transform between frames.

Discussion Character

  • Conceptual clarification
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether the electric field strength vector and force vector need to be re-defined when switching from the lab frame to the COM frame.
  • Another participant asserts that in non-relativistic scenarios, fields and forces at specific points remain the same across all inertial frames.
  • A participant expresses confusion regarding the term "non-relativistic" and its implications for understanding inertial frames.
  • Further clarification is provided that non-relativistic means not considering special relativity, and that fields and forces are consistent between the lab and COM frames.
  • Participants discuss additional quantities that remain unchanged between the lab and COM frames, including masses, relative velocities, and distances, while noting that position, velocity, kinetic energy, and momentum may vary.

Areas of Agreement / Disagreement

There appears to be a general agreement on the concept that fields and forces do not change between the lab and COM frames in non-relativistic contexts. However, some participants express uncertainty about the terminology and implications, indicating that the discussion remains partially unresolved.

Contextual Notes

Participants have varying levels of familiarity with the concepts discussed, particularly regarding inertial frames and non-relativistic physics, which may affect their understanding and contributions.

elemis
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So let's say I'm computing the torque as a result of the interaction between two electric dipoles in the lab frame. Let's 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 ?
 
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Non-relativistic? Fields and forces (at specific points) are the same in all inertial frames.
 
mfb said:
Non-relativistic? Fields and forces (at specific points) are the same in all inertial frames.

I'll be honest, I don't 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.
 
I'll be honest, I don't completely follow what you mean by non-relativistic.
Non-relativistic = you don't care about special relativity. Okay, it's fine.

I'm a first year Chemistry student so the idea of inertial frames is a very new concept.
It is just a more general way to say "fields and forces are the same for the lab and the center of mass frame".
 
mfb said:
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".

Oh, okay, I see what you mean now. Thanks !

Beside fields and forces what else does not change between the lab and COM frame ?
 
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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