Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Does moving mass produce a field?

  1. Oct 9, 2011 #1
    I just watched an experiment where current was ran through two parallel wires in the same direction and the wires attracted. This was explained by the magnetic field produced by the moving charges.

    So I wondered if mass were to move through a wire would it produce a similar field to the one demonstrated above(Call it the Y field.) This would cause the mass to attract greater than the expected results from the standard G field.

    Has this experiment ever been done??
    Last edited: Oct 9, 2011
  2. jcsd
  3. Oct 9, 2011 #2


    User Avatar
    Gold Member

    You have to be careful with analogies. Gyroscopes utilize torque. It's not an emanating field though, it's intrinsic to a rotating mass.
  4. Oct 9, 2011 #3


    User Avatar
    Gold Member

    The magnetic field caused by the current through the wires is the force which force the wires together. This has in general nothing to do with mass and the movement of the mass itself. Since the wire is the "carrier" of the magnetic field, the wire must follow the field.

    If you had ran different polarity through the wires they would be forced to separate.

    Only when a magnetic field is moving through the same wire, the wire will transform the energy in the moving magnetic field into an electric current.


  5. Oct 9, 2011 #4
    Not really what I was wondering.

    My idea was that if you ignored charge completely, would moving mass have similar properties to a moving charge...

    I don't think I am right anymore but I thought I was onto something.
  6. Oct 9, 2011 #5


    User Avatar
    Gold Member

    The only similarities is that both moving masses and moving charges is that they carry a given amount of energy. There is no "fileld" around a moving mass except it might be possible to translate the moving mass into a moving kinetic field. However, I have never heard of a moving kinetic field, so I don't think science use this term at all.


  7. Oct 9, 2011 #6


    User Avatar
    Gold Member

    “Qualitatively, frame-dragging can be viewed as the gravitational analog of electromagnetic induction.”

    Rotational frame-dragging (the Lense–Thirring effect) appears in the general principle of relativity and similar theories in the vicinity of rotating massive objects. Under the Lense–Thirring effect, the frame of reference in which a clock ticks the fastest is one which is revolving around the object as viewed by a distant observer. This also means that light traveling in the direction of rotation of the object will move past the massive object faster than light moving against the rotation, as seen by a distant observer. It is now the best-known effect, partly thanks to the Gravity Probe B experiment. Qualitatively, frame-dragging can be viewed as the gravitational analog of electromagnetic induction.

    Linear frame dragging is the similarly inevitable result of the general principle of relativity, applied to linear momentum. Although it arguably has equal theoretical legitimacy to the "rotational" effect, the difficulty of obtaining an experimental verification of the effect means that it receives much less discussion and is often omitted from articles on frame-dragging (but see Einstein, 1921).

    Static mass increase is a third effect noted by Einstein in the same paper.[5] The effect is an increase in inertia of a body when other masses are placed nearby. While not strictly a frame dragging effect (the term frame dragging is not used by Einstein), it is demonstrated by Einstein that it derives from the same equation of general relativity. It is also a tiny effect that is difficult to confirm experimentally.

  8. Oct 9, 2011 #7

    This is what I was thinking of right here. I'm not quite up to that math level yet but Einstien predicts that the field I was describing does exist.

    Only it is so weak that it hasn't been experimentally verified.

    Which makes sense since the Electric field is so much stronger than the Gravitational field it makes sense that their own "magnetic" fields produced while in motion will have the same ratio of strength.

    One would need to measure two objects the size of earth moving parallel to each other at high speed to verify the prediction....
  9. Oct 10, 2011 #8
    Well moving objects with mass give off gravitational waves I think, but they need to be the mass of a neutron star, so doing experiments is a bit tricky.
  10. Aug 21, 2012 #9
    Postulate: EVERY field has its magnetic equivalent.

    Very nicely, I should say that MotoPayton is offering a very elegant discussion that makes an intellectual thought experiment, easy and predictable.

    I have thought of the same thing, much more simply, for years, but never expanded on it much until now. Rather than wires, think of only two charged particles, rather than a wire.

    Two electrons, fired off in parallel at near-relativistic speed, seem to repel each other slower than should be expected from their mutual repulsion in the electrical field. Two separate approaches thoroughly explain this phenomenon. One can choose either for satisfaction.

    1) General relativity allows for the electrons' mutual repulsive affects to appear less robust, due to time dilatation. The point is that relativity can thoroughly explain the observation.​

    2) On the other hand, Maxwell's equations can also thoroughly explain the phenomenon, as the moving electrons each comprise a current, generating a magnetic field, which acts upon the other so as to show a contrary attractive force that lessens the electrical repulsive forces.​

    Of course, an observer moving along with the electrons sees no velocity, and only sees the simple electromagnetic repulsion.

    Since each explanation is true and sound, the thought experiment simply shows the interchangeability of "electrical" and "magnetic" effects in relativistic physics. They are well known to appear different only in certain circumstances due to the frame of reference. However, the usual frame of reference in which we do experimental physics in the laboratories of Earth, favor an apparent difference. Neither explanation is the true one, and the other somehow lesser.

    However, it becomes quickly obvious that for ANY particle that moves in any sort of field capable of producing a force, F=∇U, will show similarly apparent modulations of the force between the two particles. This decrease in action is also thoroughly explained by general relativity. ALL fields capable of producing force, whether known or unknown, recognized or unrecognized, will produce the relativistic effect.

    It is only an accident of history that Maxwell's equations antedated Lorentz and Einstein, that we came up with the pure theory of magnetism, which can be considered not a fundamental thing in its own right, but rather a manifestation of electricity in motion.

    The strong force will have a "strong-magnetism" and gravity will have "gravito-magnetism," simply because the time-dilatation and mass effects of general relativity can be expressed in the field curl terms of Maxwell's equations.

    Yes, MotoPayton, you are right, and I offer you the gold medal for Armchair Physics for the summer. :)
    Last edited: Aug 21, 2012
  11. Aug 23, 2012 #10
    Actually, there is a small mystery to this matter. Two electrons dashing off into the distance not only APPEAR to be separating more slowly, they also APPEAR to have more mass due to their "speed."

    The separation might or not be proportionate to their "speed," it's thru the Lorentz transformation.

    However, the ONE field that would be more perplexing to observe would be the gravitational field. In such an instance, there would be a second-order effect to the particles dashing off and having more mass - that is, the apparent greater mutual attraction that would offset the "gravitomagnetic" effect.

    Or would it?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook