4 ms·

It looks convincing to my naive eyes, but how would you differentiate between this and diamagnetic levitation of something like pyrolitic graphite?

cthalupa 3y ago
https://twitter.com/Andercot/status/1687748594563268608 https://twitter.com/Andercot/status/1687748594563268608 seems to indicate that simply diamagnetic levitation cannot create the level of stability shown in this video.
- Enginerrrd 3y ago
  I don't think that's right. Diamagnetic levitation is one of the ways you can get around Earshaw's theorem. Funny enough this is a quote taken directly from the wikipedia article that Andercot linked, in the "loopholes" section: >Earnshaw's theorem has no exceptions for non-moving permanent ferromagnets. However, Earnshaw's theorem does not necessarily apply to moving ferromagnets,[4] certain electromagnetic systems, pseudo-levitation and diamagnetic materials. These can thus seem to be exceptions, though in fact they exploit the constraints of the theorem. ... >Diamagnetic materials are excepted because they exhibit only repulsion against the magnetic field, whereas the theorem requires materials that have both repulsion and attraction. An example of this is the famous levitating frog (see Diamagnetism).
  - cthalupa 3y ago
    Sure enough. Which, well, makes sense, since superconductors are "perfect" diamagnets, so them being able to do it seems to necessitate that the greater class of diamagnets on the whole can too. The only examples I can find of stable non-superconductor diamagnets involved 4+ magnet arrays, though, or multipole magnets, e.g. https://phys.org/news/2014-08-diamagnetic-levitation-pyrolitic-graphite-magnet.html https://phys.org/news/2014-08-diamagnetic-levitation-pyrolit... and not dipole configurations like this video seems to show.
  - sudosysgen 3y ago
    How can a diamagnet be stable on top of a single dipole? Earnshaw's criterion being invalid just means that there is at least one static arrangement of magnetic dipoles that lead to stability. However, if you have a point-like diamagnet resting on top of a single dipole it can't possibly be stable because there is no point at which it will have zero net force and stable higher-order derivatives. You need something like a bowl-shaped magnetic field arrangement for it to stay in a single point, or have the diamagnet itself be shaped something like a bowl over the field.
    - Enginerrrd 3y ago
      Yeah you bring up a good point... I don't think it can. But you CAN do it with concentric rings of magnets. Such magnets seem common for this exact demonstration actually. It doesn't look like one of those in the video though.
deleted 3y ago
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cthalupa 3y ago

https://twitter.com/Andercot/status/1687748594563268608 https://twitter.com/Andercot/status/1687748594563268608 seems to indicate that simply diamagnetic levitation cannot create the level of stability shown in this video.

Enginerrrd 3y ago
I don't think that's right. Diamagnetic levitation is one of the ways you can get around Earshaw's theorem. Funny enough this is a quote taken directly from the wikipedia article that Andercot linked, in the "loopholes" section: >Earnshaw's theorem has no exceptions for non-moving permanent ferromagnets. However, Earnshaw's theorem does not necessarily apply to moving ferromagnets,[4] certain electromagnetic systems, pseudo-levitation and diamagnetic materials. These can thus seem to be exceptions, though in fact they exploit the constraints of the theorem. ... >Diamagnetic materials are excepted because they exhibit only repulsion against the magnetic field, whereas the theorem requires materials that have both repulsion and attraction. An example of this is the famous levitating frog (see Diamagnetism).
- cthalupa 3y ago
  Sure enough. Which, well, makes sense, since superconductors are "perfect" diamagnets, so them being able to do it seems to necessitate that the greater class of diamagnets on the whole can too. The only examples I can find of stable non-superconductor diamagnets involved 4+ magnet arrays, though, or multipole magnets, e.g. https://phys.org/news/2014-08-diamagnetic-levitation-pyrolitic-graphite-magnet.html https://phys.org/news/2014-08-diamagnetic-levitation-pyrolit... and not dipole configurations like this video seems to show.
- sudosysgen 3y ago
  How can a diamagnet be stable on top of a single dipole? Earnshaw's criterion being invalid just means that there is at least one static arrangement of magnetic dipoles that lead to stability. However, if you have a point-like diamagnet resting on top of a single dipole it can't possibly be stable because there is no point at which it will have zero net force and stable higher-order derivatives. You need something like a bowl-shaped magnetic field arrangement for it to stay in a single point, or have the diamagnet itself be shaped something like a bowl over the field.
  - Enginerrrd 3y ago
    Yeah you bring up a good point... I don't think it can. But you CAN do it with concentric rings of magnets. Such magnets seem common for this exact demonstration actually. It doesn't look like one of those in the video though.

deleted 3y ago

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