Magnetism - stability of a ring with a sphere inside it?

[gazorpazorp]

Hey, is it possible to have a cylindrical ring (made of permanent magnet) and a magnetic sphere sitting inside it and staying in one place without touching the inner sides of the ring and not falling through?

The object doesn't necessarily have to be a sphere. If it would work with any other shaped object it would also be fine. The main problem is, would be able to stay inside.

The illustration:
http://imgur.com/a/woyvi

 

[Drakkith]

I don't think so. Magnetic levitation via static fields is not stable and the object would most likely either fall through or touch the side.

 

[mfb]

Magnetic levitation will need one of those elements:
- active electromagnets controlling the position
- some point of contact of the levitated object (so it is not completely free)
- rotation of something, typically the levitated object
- superconductors
- strong permanent magnets and very exotic lightweight diamagnetic materials that can't carry any additional load
- strong electromagnets and diamagnetic materials

 

[feli_x]

Hello gazorpazorp,

mfb is right. There exists a theorem named after Earnshaw, which states that

static, stable, free levitation of matter is impossible, if the exerted forces show a 1/r^2 law

[S. Earnshaw: 1842 On the Nature of the Molecular Forces which regulate the Constitution of the Luminiferous Ether; Transactions of the Cambridge Philosophical Society 7, p. 97–112].

This theorem has been extended by Braunbeck to various kinds of electromagnetic levitation [Werner Braunbeck: 1939 Freischwebende K ̈orper I am elektrischen und magnetischen Feld; Zeit- schrift fu ̈r Physik 112 , p. 753]. He ends up with the conclusion:

Static, stable and free levitation of a system 1 in an electric, magnetic and gravitational field of a system 2 is impossible, unless diamagnetic matter is present at least in one of both systems.