Rotational energy from linear fields

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Discussion Overview

The discussion revolves around the relationship between linear acceleration of charged objects and the potential increase in their rotational energy or angular momentum. Participants explore various scenarios involving linear fields, electric and magnetic forces, and the implications for both classical and quantum physics.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant questions how a charged object, accelerated by a linear field, could increase its rotational energy, suggesting that any object would accelerate in a straight line through its center of mass or charge distribution.
  • Another participant clarifies that while linear and angular momentum are related, a uniform magnetic field can cause circular motion, potentially linking to the original question about rotational energy.
  • A participant notes that central forces do not change angular momentum, but combinations of electric and magnetic fields can affect it, implying that electromagnetic forces can transfer angular momentum to particles.
  • There is a mention of an electron in a cathode ray tube being accelerated by a linear electric field, which raises questions about its frequency and energy, but some participants argue that this does not involve rotation.
  • One participant suggests that the increase in frequency could relate to relativistic effects and spin angular momentum, introducing a quantum perspective to the discussion.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between linear acceleration and rotational energy, with some questioning the relevance of rotation in the context of linear fields. The discussion remains unresolved, with multiple competing perspectives on the topic.

Contextual Notes

Some participants reference classical physics and quantum mechanics, indicating a potential overlap in concepts that may not be fully reconciled. The discussion includes assumptions about the nature of forces and their effects on angular momentum that are not universally agreed upon.

Chris FW
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I am trying to understand how a charged object or an object with mass which is being accelerated by a linear field and therefore should accelerate in a purely linear fashion could possibly increase its rotational energy?
I am not looking for trivial answers perhaps a certain distribution of mass/ charge that is the shape of an object? But I would consider that any object independent of shape would accelerate in a straight line through the centre of mass/charge distribution.
Any suggestions would be gratefully appreciated.
Chris FW
 
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Hmm, "rotational energy"? Do you mean you want to know how to increase it's angular momentum about some axis? When an object is moving in a straight line, it already has angular momentum about every axis except an axis passing directly through the line of its path (someone correct me if I'm wrong). Linear and angular momentum are the same thing from two different points of view.

That being said, uniform magnetic fields tend to accelerate things (moving charges) in a circular way. Is this what you're looking for?
 
Chris FW said:
I am trying to understand how a charged object or an object with mass which is being accelerated by a linear field and therefore should accelerate in a purely linear fashion could possibly increase its rotational energy?
I am not looking for trivial answers perhaps a certain distribution of mass/ charge that is the shape of an object? But I would consider that any object independent of shape would accelerate in a straight line through the centre of mass/charge distribution.
Any suggestions would be gratefully appreciated.
Chris FW

What do you mean with a linear field? As you know central forces cannot change angular momentum as the force is parallel to the position vector. There are however combinations of electric and magnetic fields that can change the angular momentum of a particle, notice that in this case the electromgnetic force has angular momentum of itself transferred to the particle! E.g. an electrically charged particle in a magnetic field is surrounded by both electric and magnetic fields that carries angular momentum.
 
Last edited:
Chris FW said:
I am trying to understand how a charged object or an object with mass which is being accelerated by a linear field and therefore should accelerate in a purely linear fashion could possibly increase its rotational energy?
I am not looking for trivial answers perhaps a certain distribution of mass/ charge that is the shape of an object? But I would consider that any object independent of shape would accelerate in a straight line through the centre of mass/charge distribution.
Any suggestions would be gratefully appreciated.
Chris FW

For Example an electron accelerated by a uniform linear electric field in say a cathode ray tube will receive energy from the field and accelerate but its frequency will also increase (wavelength decrease) nothing to do with magnetic fields (F= q(VxB) but E=hf
 
Chris FW said:
For Example an electron accelerated by a uniform linear electric field in say a cathode ray tube will receive energy from the field and accelerate

True. That's classical physics, and no rotation involved.

but its frequency will also increase (wavelength decrease) nothing to do with magnetic fields (F= q(VxB) but E=hf

What do you mean by "its frequency"? Do you mean the frequency of the quantum mechanical wave function of the electron? If so, this is a correct statement, but then it's a quantum physics question. And yet, I still don't understand what that has to do with rotation or angular momentum. There is still no rotation involved.
 
Xezlec said:
What do you mean by "its frequency"? Do you mean the frequency of the quantum mechanical wave function of the electron? If so, this is a correct statement, but then it's a quantum physics question. And yet, I still don't understand what that has to do with rotation or angular momentum. There is still no rotation involved.


I think he means the 'relativstic' increase in energy (frequency) ...and thus what happens to the spin angular momentum in such a relativistic case.
 

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