5 ms·

The Varda Team just posted a really high-resolution video of the diamagnetism: https://twitter.com/andrewmccalip/status/1687405505604734978 https://twitter.com

The Varda Team just posted a really high-resolution video of the diamagnetism: https://twitter.com/andrewmccalip/status/1687405505604734978 https://twitter.com/andrewmccalip/status/1687405505604734978

thomasmg 3y ago
Nice! For show, I would try to levitate. Probably using a stronger magnet, inside a small (tiny?) glass tube, so it slides up a bit. I wouldn't do "rock surgery" just yet, to remove dead weight. Levitation with 4 magnets in a checkboard fashion, as usually done for pyrolytic carbon sheets, maybe doesn't work as the sample is not flat. Also, turning the magnet upside down seems useful. And then, heating up to show that it drops at a certain temperature. I wonder what would be needed in this case; I guess less than 100° C. In any case, the "show" part is important. Good video quality is important.
panki27 3y ago
Finally a video with quality that doesn't look like it was filmed with a camcorder from the early 2000s.
tetris11 3y ago
Nitter link: https://nitter.net/andrewmccalip/status/1687405505604734978#m https://nitter.net/andrewmccalip/status/1687405505604734978#...
stronglikedan 3y ago
It's cool that they left the dialog in there.
pmontra 3y ago
Noob question: if whatever is happening is strong enough to raise one of the ends of the sample, why doesn't raise both? After all gravitation is many order of magnitudes weaker than electromagnetism. Did they calibrate the setup to closely match the gravitational force on the sample? Why not push a little more and make it fly up the the cap of the container?
- Sharlin 3y ago
  Magnetic force scales as 1/r^3, not 1/r^2 like gravity. That's why your standard issue fridge magnet measurably attracts stuff only from a very close distance, but when it does, it easily counters the gravitational attraction of the entire planet¹. This 1/r^3 relationship can be derived easily enough by integrating, but essentially it's because magnets are dipoles and the farther away you are, the smaller the apparent distance between the poles and the "more neutral" the magnet looks like. Anyway, that's why there's an equilibrium distance where the forces balance. But superconductors also exhibit a very strange phenomenon called flux pinning [1] where a levitating object is held in place by magnetic field lines and you can even turn the whole thing upside down and it still levitates even though the forces don't cancel each other out anymore! [1] https://en.wikipedia.org/wiki/Flux_pinning https://en.wikipedia.org/wiki/Flux_pinning --- ¹ To be fair, "the entire planet" is also around 6000 km away, calculation-wise, but still!
  - pmontra 3y ago
    Thank you.
  - dotancohen 3y ago
    > Magnetic force scales as 1/r^3, not 1/r^2 like gravity The magnetic force and gravity are two of the four fundamental forces, no? The others being the strong and weak nuclear force? At what rate do those two scale at?
    - salty_biscuits 3y ago
      If you are really close to one pole of a magnet and far away from the other then the force scales like 1/r^2, it is in the far field under the influence of both poles of the magnet that it scales like 1/r^3. Electrostatics scales like 1/r^2 (because you fet isolated charges). The other two are a complicated story.
      - dotancohen 3y ago
        If you have time, I would love to hear that complicated story. I remember once hearing that the rate of those forces' decay indicates (but does not prove) that they decay in more than three dimensions. This was an accomplished chemist talking, so I'm sure that she was being concise but factual.

thomasmg 3y ago

Nice! For show, I would try to levitate. Probably using a stronger magnet, inside a small (tiny?) glass tube, so it slides up a bit. I wouldn't do "rock surgery" just yet, to remove dead weight. Levitation with 4 magnets in a checkboard fashion, as usually done for pyrolytic carbon sheets, maybe doesn't work as the sample is not flat. Also, turning the magnet upside down seems useful. And then, heating up to show that it drops at a certain temperature. I wonder what would be needed in this case; I guess less than 100° C. In any case, the "show" part is important. Good video quality is important.

panki27 3y ago

Finally a video with quality that doesn't look like it was filmed with a camcorder from the early 2000s.

tetris11 3y ago

Nitter link: https://nitter.net/andrewmccalip/status/1687405505604734978#m https://nitter.net/andrewmccalip/status/1687405505604734978#...

stronglikedan 3y ago

It's cool that they left the dialog in there.

pmontra 3y ago

Noob question: if whatever is happening is strong enough to raise one of the ends of the sample, why doesn't raise both? After all gravitation is many order of magnitudes weaker than electromagnetism. Did they calibrate the setup to closely match the gravitational force on the sample? Why not push a little more and make it fly up the the cap of the container?

Sharlin 3y ago
Magnetic force scales as 1/r^3, not 1/r^2 like gravity. That's why your standard issue fridge magnet measurably attracts stuff only from a very close distance, but when it does, it easily counters the gravitational attraction of the entire planet¹. This 1/r^3 relationship can be derived easily enough by integrating, but essentially it's because magnets are dipoles and the farther away you are, the smaller the apparent distance between the poles and the "more neutral" the magnet looks like. Anyway, that's why there's an equilibrium distance where the forces balance. But superconductors also exhibit a very strange phenomenon called flux pinning [1] where a levitating object is held in place by magnetic field lines and you can even turn the whole thing upside down and it still levitates even though the forces don't cancel each other out anymore! [1] https://en.wikipedia.org/wiki/Flux_pinning https://en.wikipedia.org/wiki/Flux_pinning --- ¹ To be fair, "the entire planet" is also around 6000 km away, calculation-wise, but still!
- pmontra 3y ago
  Thank you.
- dotancohen 3y ago
  > Magnetic force scales as 1/r^3, not 1/r^2 like gravity The magnetic force and gravity are two of the four fundamental forces, no? The others being the strong and weak nuclear force? At what rate do those two scale at?
  - salty_biscuits 3y ago
    If you are really close to one pole of a magnet and far away from the other then the force scales like 1/r^2, it is in the far field under the influence of both poles of the magnet that it scales like 1/r^3. Electrostatics scales like 1/r^2 (because you fet isolated charges). The other two are a complicated story.
    - dotancohen 3y ago
      If you have time, I would love to hear that complicated story. I remember once hearing that the rate of those forces' decay indicates (but does not prove) that they decay in more than three dimensions. This was an accomplished chemist talking, so I'm sure that she was being concise but factual.