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

In summary, the conversation discusses the concept of inertial frames and how they relate to the calculation of torque between two electric dipoles. The speaker explains that in the non-relativistic case, fields and forces are the same in all inertial frames, including the lab and center of mass frames. The other things that do not change between these frames are masses, relative velocities, distances, and internal parameters of objects. The only changing factors are position, velocity, kinetic energy, and momentum, with angular momentum possibly being affected depending on its definition.
  • #1
elemis
163
1
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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  • #2
Non-relativistic? Fields and forces (at specific points) are the same in all inertial frames.
 
  • #3
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.
 
  • #4
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".
 
  • #5
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 ?
 
  • #6
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.
 

1. What is the definition of electric field strength in the Centre of Mass frame?

The electric field strength in the Centre of Mass frame is defined as the amount of force per unit charge experienced by a charged particle at rest in the frame. It takes into account the combined effects of both the electric and magnetic fields in the frame.

2. Why is it necessary to re-define electric field strength in the Centre of Mass frame?

In classical mechanics, the electric field strength is defined as the force per unit charge experienced by a charged particle in a fixed frame of reference. However, in the Centre of Mass frame, the electric field is not constant and changes as the particles move. Therefore, it is necessary to re-define the electric field strength in order to accurately describe the behavior of charged particles in this frame.

3. How does the electric field strength change in the Centre of Mass frame?

In the Centre of Mass frame, the electric field strength is affected by the relative velocities of the charged particles. As the particles move, the electric field strength changes in both magnitude and direction. This is due to the transformation of the electric field in the frame.

4. Is the re-definition of electric field strength only applicable in the Centre of Mass frame?

No, the re-definition of electric field strength is applicable in any frame of reference where the relative velocities of charged particles are significant. This includes frames of reference moving at constant velocities, as well as accelerating frames.

5. How does the re-definition of electric field strength impact our understanding of electromagnetism?

The re-definition of electric field strength in the Centre of Mass frame allows for a more accurate description of the behavior of charged particles. It also helps to reconcile classical mechanics with the principles of relativity. This understanding is crucial in fields such as particle physics and astrophysics, where particles may be moving at high velocities.

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