Comments by "ricomajestic" (@ricomajestic) on "How Special Relativity Makes Magnets Work" video.

  1. Steven Wang No. That's wrong. In the stationary cat's frame of reference the protons are not moving!
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  2. Steven, it depends on the frame of reference. From a stationary cat frame of reference (i.e.- a cat that is not moving relative to the wire), the protons are not moving but the electrons are moving to the right. However, from the electron's frame of reference the protons (and cat) are moving to the left.
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  3. sidewaysfcs0718 Yes. The space  between th electrons is length contracted in the stationary cat frame. The wire is neutral AFTER taking length contraction into effect!
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  4. Volbla The electrons are already contracted in the frame where the  cat is stationary! They are contracted in such a way that the charge density due to the protons and the charge density to the electrons is the same. That is why the wire is neutral and there is no electrostatic force between the charged cat and the neutral wire. In the moving cat frame, the electrons are at rest and that is why their separation increases. In this frame, the protons are the ones that are moving and so their seperation decreases hence the positive charge density in the wire is greater than the negative charge density in the moving cat frame.
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  5. ***** The electrons are already contracted in the frame where the  cat is stationary! They are contracted in such a way that the charge density due to the protons and the charge density due to the electrons is the same. That is why the wire is neutral and there is no electrostatic force between the charged cat and the neutral wire. In the moving cat frame, the electrons are at rest and that is why their separation increases. In this frame, the protons are the ones that are moving and so their separation decreases hence the positive charge density in the wire is greater than the negative charge density in the moving cat frame.
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  6. ***** There is a always a force on the cat and it always points in the same direction.From the frame of reference where the cat is stationary (i.e- relative to the cat and electrons), the force is an electric force due to length contraction between protons. From the frame of reference in which the cat is moving (i.e-relative to the protons), it is a magnetic force. In both frames of reference, the force on the cat is away from the wire-a repelling force. "Assume no current flow and stationary cat" -That would be a completely different problem not the one given here. You can only change the frame of reference. In this problem, if we were to some how stop the flow of charge there would a higher electron density in the wire and the positively charged cat would be attracted to it!
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  7. My bad. You are right the animation is not clear in the video. I believe your question had already been answered in some of the other comments from other people.
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  8. ***** Volbla is right! He explained it well too!
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  9. LuizBHMG 
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  10. Brandon Spicer "Or are we just assuming the wire is neutral after taking length contraction into effect, meaning the wire would be positively charged with no current"- YES!
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