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Suppose, we have two magnets, MA, MB, and we have a third magnet MC in between the two magnets.

Each magnets' north pole faces the other magnets south pole, and the magnets are placed horizontally side by side. We spin the magnet MC at a speed between super fast and slow. What will happen then?
I mean, once MC's north pole faces MA's south pole and MC's south pole faces MB's north pole, then the next moment MC's south pole faces MA's south pole and MC's north pole faces MB's north pole. So what will happen then?the image

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  • $\begingroup$ Are any of the magnets fixed? Are any of the axes of rotation fixed? Are we in space, or is there friction? $\endgroup$ – user121330 Sep 2 '14 at 17:12
  • $\begingroup$ there is friction, and what do you mean by fixed? $\endgroup$ – Ruhan Habib Sep 2 '14 at 17:18
  • $\begingroup$ Fixed means constrained - if you glued a magnet to the table, it'd be fixed. If you put a magnet on an axle, it'd be rotationally fixed. $\endgroup$ – user121330 Sep 2 '14 at 17:27
  • $\begingroup$ No. None of the magnets would be fixed, except the middle one MC, which can and will rotate / spin. $\endgroup$ – Ruhan Habib Sep 2 '14 at 17:31
  • $\begingroup$ Perhaps update the question with a diagram to avoid confusion? $\endgroup$ – user121330 Sep 2 '14 at 17:32
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The middle magnet is spinning, so it attracts and repulses the other two magnets once per rotation.

It is spinning "super fast" - that is so fast that the attraction and repulsion phases are super short. The other magnets are just too heavy to even start moving visibly in one or the other direction, before the direction of the force changes again.

We could say "nothing happens" - except the outer magnets oscilate slightly with each rotation.


If the middle magnet would spin "super slow", the others would just jump to the middle one, stick to it, and rotate with it as if it's all one magnet.


What happens if the middle magnet would spin with a frequency in betwen?
That's difficult, because much depends on how the rotation starts, and we only know it has started...

If the rotation starts slowly and gets faster then, up the middle speed, different things can happen during the first rotation. The magnets could stick to the rotating one, or move away a little bit; That whould have a big influence on what happens later.

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  • $\begingroup$ If it is spinnig a little slower? $\endgroup$ – Ruhan Habib Sep 2 '14 at 17:36
  • $\begingroup$ How the rotation starts? What do you mean by that? $\endgroup$ – Ruhan Habib Sep 2 '14 at 18:01
  • $\begingroup$ If the rotation starts slowly and gets faster then, up the middle speed, different things can happen during the first rotation. The magnets could stick to the rotating one, or move away a little bit; That whould have a big influence on what happens later. $\endgroup$ – Volker Siegel Sep 2 '14 at 18:04

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