Length-contraction-magnetic-force between arbitrary currents

Discussion in 'Physics & Math' started by PengKuan, May 12, 2017.

  1. PengKuan Registered Senior Member

    Yes, there are details needing to be considered. But these details do not overthrow longitudinal force. For invalidating longitudinal force one has to prove that it is zero. Without doing so, these details are only equally possible details needing to be considered, but not the correct and only cause that kills others.
    By ad hoc I mean for specific situation. Arcing works for multi-arc generator but not for Nasi owski's wire fragmentation. Arcing is specially for this situation or ad hoc for this situation. And all details you mentioned are of this sort. If particular complexities pleases you better, yes they are.

    Since you formally forbid to consider Lorentz forces from part circuit, Grassmann's expression is compatible with SR only in this particular situation, that is, a closed circuit acting on one current element. Ampere’s and my expressions are equally compatible with SR since they give the same result than Grassmann's expression for the case of closed circuit acting on one current element.

    Rejecting longitudinal force appears to you straightforward, but it is only your personal judgment. Yes, most people reject longitudinal force. So, this is not your personal judgment but the judgment of all physicists, so what? A judgment is from human mind, not physical reality. 100% people were against Copernicus, but their judgment was wrong and the theory of Copernicus was right. Occam's razor is far more powerful than human mind to shave off non necessary details needing to be considered from physical reality.
    My formulation is different from theirs.

    Again, Grassmann's expression is compatible with SR only for closed circuit and not compatible with SR otherwise. When considering Lorentz force between one current element and another, will it still be compatible with SR? That is, you can derive Lorentz forces using SR from the B field of a closed circuit computed using Biot-Savart’s law. But can you derive Lorentz forces using SR from the B field from a part circuit equally computed using Biot-Savart’s law? Obviously not. Then, how can you be so sure that Grassmann's expression is the unique and only law compatible with SR?
    I know that length contraction of electron flow is questionable for some. Someone else has made the same remark and said that if this were true, then one should see electric field from a coil. I have tried to do experiment in this direction but still not succeeded.

    It seems to me that length contraction was used to explain the distance between electrons in cathode ray. Was this accepted in physics?

    Here, http://www.iflscience.com/physics/4-examples-relativity-everyday-life/ they explain that engineers had to account for length contraction when designing the magnets that directed the electrons to form an image on the screen. Without accounting for these effects, the electron beam's aim would be off and create unintelligible images.

    In the same page, they also explained that if this charged object moves alongside the wire, then it starts to feel the effects of length contraction in the moving electrons. This means that the density of stationary protons becomes larger than the flowing electrons and the metal exhibits a positive charge, causing the object to be attracted or repelled.

    So, length contraction of electron flow is accepted by at least some physicists and cathode TV set.
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  3. Q-reeus Valued Senior Member

    You have evidently misunderstood. Longitudinal forces will occur, but not owing to the 'fundamental' longitudinal force expression you derived. They are the result of particular processes - and I now think hydrostatic pressure transfer at local melt or even plasma regions under pinch pressure is the main one relevant for those experiments listed in Johansson's article.

    Beyond that, geometry alone dictates longitudinal stresses in the case of say a circular loop current. Transverse i.e. radial acting Lorentz forces must be balanced by a circumferential i.e. longitudinal hoop stress tension in the loop. The tension itself is purely the result of mechanical equilibrium being satisfied. It would be entirely wrong to conclude there that longitudinal EM forces were acting. That's where I think Johansson gets it wrong - he evidently believes the longitudinal component of magnetic Maxwell stresses has to be locally countered by mechanical stresses. It only works out that way in certain cases like for instance that circular current loop. And even there the detail is not satisfied since the hoop stress will be essentially uniform across the wire section, whereas for a thin wire of radius r << R (R the loop mean radius) the Maxwell stress plunges approximately from a maximum at the surface, to near zero at the wire center. It so happens the radial component of Maxwell stress is mechanically countered in detail - something identically found by applying Lorentz force expression to the wire current. Lorentz forces are always the best approach. No extraneous assumptions are required.
    Wrong. Point to where you think I did so.
    You haven't specified whether that one current element is within the same circuit or part of a different one. Scarcely matters though. There can never be justification for somehow excluding a particular interaction as part of a whole. Unless of course the context establishes it to be superfluous for the matter at hand.
    Yes, because it is precisely the SR derived Lorentz force expression applied to two arbitrarily oriented interacting current elements. See e.g. '1.3 Background and historical review' in:
    Which is Johansson's article in pdf form. Near the top of p3 the Grassmann formula shown is explicitly the cross-product one owing to magnetic Lorentz forces acting.
    And you never will. For the reasons I gave back in #34 point 1. There is no way around that. Face up to the fact your idea would allow generating excess charge at will - violating conservation of charge and/or charge invariance. Doesn't happen. Can't happen. Has never been experimentally observed.
    Of course and as explained before, there is no conflict with what I wrote above since the constraints are different between a closed conducting loop and a cathode ray.
    See above.
    See above. No contradiction exists. Differing system constraints lead to different net results.

    A thought! Going back to that example of hoop stresses in a circular loop current. Lorentz forces are always normal to the circumferential direction. Whereas your idea has additionally circumferential forces acting 'internally'. That should manifest as an additional hoop stress hence hoop strain.
    I'll leave it to you to figure out what the fractional increase is owing to supposed longitudinal forces acting. Once that's determined, consider doing experiments to unequivocally determine which theory gives the actual strain. No issue here with contact effects that plague those other experiments.
    However there is a complication that needs accounting for. Thermal expansion owing to Joule heating.

    You could try approaching some university physics department and propose such an experiment. Might have trouble overcoming skepticism.
    Here's an article going into gory detail as it relates to magnetically induced stresses in coils: https://arxiv.org/pdf/1501.02932
    Maybe you could correspond with the author and ask if longitudinal forces as you propose have been ruled out via actual tests done.

    Really though, the killer is your initial conceptual error predicting violation of charge conservation and/or charge invariance. Post 34, item 1. READ CAREFULLY.
    Last edited: Apr 17, 2018
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  5. PengKuan Registered Senior Member

    Why misunderstood? And evidently. I do never talk longitudinal force other than the 'fundamental' one. By saying “For invalidating longitudinal force one has to prove that it is zero” I mean one has to prove that the 'fundamental' longitudinal force is zero. You take this for given, because it is contrary to Lorentz force. But the 'fundamental' longitudinal force has not been proven to be zero neither in theory, nor in experiment. That we have not seen it until now in experiment does not mean it will never be. It has not been proven to be zero in theory because the present theory does not take it into account. This does not mean that other theories will not do in the future.
    In #34 you said “But this is not overall violating Newtonian mechanics - a counter-torque will be experienced in the exterior feed portions of the circuit. In any overall analysis the entire circuit must be evaluated.”

    By saying this, you deny my analysis of my experiment of rotating coil. Your denial means that I have not the right to consider the force on the central lead and the coil alone because there are others things in the circuit. So, your “In any overall analysis the entire circuit must be evaluated” is a prohibition to see the force on the central lead and the coil because they are a part of a whole circuit.

    Also in #34 you said,
    This is also a denial of seeing the force on one side of a triangular coil which is a part of a loop. And your deduction using filamentary loops is based on the whole loop. By saying that mine is wrong and yours is correct, you do not allow analyzing force on a part of the loop.
    One of my triangular coil analysis is here http://pengkuanem.blogspot.fr/2012/03/lorentz-forces-internal-to-equilateral.html

    And you insist again in #37 : “The entire circuit will experience zero net torque and linear force.” That is, only entire circuit is good, part circuit is bad.
    We will see. Never knows.
    Conservation of mass is sacrosanct. It was.
    No one accepts to do crackpot like experiment. Too ridiculous for them.
    In conclusion, your position is:
    The 'fundamental' longitudinal force cannot exist.
    My magnetic force law is wrong for violating conservation of charge.

    You will not change your opinion because no contradiction exists between Lorentz force law and all the experiments and also, my theory is in conflict with SR and conservation of charge.

    My position is:
    The 'fundamental' longitudinal force exists because I see it in my experiments and those of others. Also because I have derived it in my theory.
    My magnetic force law is correct and does not violate conservation of charge. Simply it needs to address this aspect in other terms.
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  7. Q-reeus Valued Senior Member

    Which quotes I stand by as obviously true - and entirely relevant to the contexts applying.
    Another typo? Presumably you meant conservation of charge.
    Sorry but it would for sure violate conservation of charge if true. It aint. You will never detect any excess charge owing to a steady current flowing in a coil of whatever configuration. Given your entrenched contrary outlook, our discussion should end now.
  8. PengKuan Registered Senior Member

    Showing tangential magnetic force by experiment
    Theoretical explanation of tangential magnetic force and the experiment of rotating coil. Tangential magnetic force is tangent to the current on which it acts. For the classical theory this force does not exist. However, my experiment « Continuous rotation of a circular coil experiment » showed that a force tangent to the current must be there. If tangential magnetic force exists, why was it not detected in almost 200 years?
    Please read the article at
    Showing tangential magnetic force by experiment
    PDF http://pengkuanem.blogspot.com/2018/05/showing-tangential-magnetic-force-by.html
    Word https://www.academia.edu/36652163/Showing_tangential_magnetic_force_by_experiment
  9. PengKuan Registered Senior Member

  10. PengKuan Registered Senior Member

    Abstract for the above post
    Theoretical explanation of longitudinal magnetic force and its practical application in high field magnet. Although longitudinal force is not explained in classical theory, its action has been demonstrated by several experiments long time ago. For example Nasilowski effect. But why is it not recognized in theory? The reason is that it shows no significant effect on practical devices, so no physicist is interested in exploring these experiments. But I have found a huge effect of longitudinal force in high field resistive magnets which could improve their performance.
  11. PengKuan Registered Senior Member

  12. origin In a democracy you deserve the leaders you elect. Valued Senior Member

    Reported. This is a discussion forum, not a place to advertise your blog.
  13. James R Just this guy, you know? Staff Member


    Off-topic links to your blog are unacceptable. Also, excessive linking to your blog will be considered advertising, for which you may be banned from sciforums. Please post links only where they are directly relevant. Better still, summarise the material you're linking to so that you can have the discussion here rather than on your blog.

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