Movement of a magnet due to repulsion (help)

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Discussion Overview

The discussion revolves around the behavior of a magnet placed inside a sealed tube with magnets at both ends, specifically whether the magnet will find a resting place or continue to move due to magnetic repulsion and gravity. The scope includes theoretical considerations of magnetic levitation and oscillation, as well as practical implications for a potential project.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant suggests that the magnet will find a resting place where gravitational force is balanced by magnetic repulsion, but it may oscillate initially due to damping effects from air resistance and induced currents.
  • Another participant proposes using a pendulum instead of the tube setup, citing potential issues with the magnet flipping and causing friction against the tube's sides.
  • A different participant raises a concern regarding Earnshaw's theorem, which suggests that stable magnetic levitation may not be achievable, depending on the assumptions about frictional forces and stability.
  • There is a mention that sufficient friction could lead to multiple 'stable' resting places, while less friction might result in less stability.

Areas of Agreement / Disagreement

Participants express differing views on the stability of the magnet's position and the implications of Earnshaw's theorem. The discussion remains unresolved regarding the feasibility of achieving stable levitation without external power.

Contextual Notes

Limitations include assumptions about friction, the application scope of Earnshaw's theorem, and the specific conditions under which the magnet operates within the tube.

Kieranlavelle
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Basically I was wondering if I was to place a magnet inside a tube sealed at both ends via two magnets (as the diagram shows) would the magnet keep on moving up and down or would it find a resting place. I think it would find a resting place but then I also thought there will also be gravity acting on it when it was falling down and I wondered if that would make a difference. Also If it would find a resting place is there anyway I could stop it from doing so without an external power source.http://img535.imageshack.us/img535/7071/diagramv.png
 
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It will find a 'resting place' where the effect of gravity is balanced by the magnetic repulsion but it will oscillate for a while until the oscillation is damped by a) air resistance and b) magnetic fields set up by opposing induced currents in the magnets – look up Lenz's law in a search engine
 
Ok thanks for your help I appreciate it.
 
If this is a real project you might want to use a pendulum instead.

The tube has at least one problem. The magnet will try to turn over and doing so will cause friction against the sides of the tube or whatever guide you use. A pendulum will try to twist in a similar way, but should be easier to control with less of a friction problem.

DC
 
I thought Earnshaw's theorem argues against a stable magnetic levitation...but I don't know the application scope of the theorem nor your assumptions about 'stabilizing' frictional forces.

http://en.wikipedia.org/wiki/Magnetic_levitation

Also If it would find a resting place is there anyway I could stop it from doing so without an external power

You can get some insights at the same link, above. Usually, absent friction, the issue is not stability but instability...

In your diagram, my guess is that sufficient friction will likely cause a multiplicity of 'stable' resting places... but the less friction, the less stability.
 

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