The rocks comic is funny, although its not a great example. If the rock is in the glare of the hot middle eastern sun it should be heating up despite being hotter than the surrounding air. The unimpressed people have probably seen rocks out in the sun before. “Sometimes rocks get hot, for example if they are exposed to sun light”. Show me a rock that gets hot in the shade.
You could be right and it is levitation, but I had a thing called a “magnetic sculpture” as a child, and to me this video just doesn’t look any different from how the metal rectangles in that toy stood on the magnet, usually at some preferred angle. Google “Magnetic sculpture” to get a lot of pictures of things like this:
On the other had, I have also seen the demonstration where an actual superconductor is lifted out of a bath of liquid nitrogen with some tool, then put floating (maybe also spinning) above the magnet. I thought that looked quite different, although all the liquid nitrogen “smokyness” could have just been adding so much cool that I was more easily impressed.
I am not seeing the relevance of Earnshaw. I thought that a superconductor floating in a magnetic field was distinct from one magnet pushing on an induced magnet. My vague understanding is that the magnetic field lines got “locked” inside the superconductor and that this was indeed stable (flux pinning is the term I think). I mean, I have seen countless demonstrations with cold superconductors and it seemed pretty stable, you could poke it to make it spin, and the poke wouldn’t make it immediately collapse or fly away.
“Sometimes, rocks just get hot.”
This looks like legit levitation to me, with the stability forbidden by Earnshaw.
The rocks comic is funny, although its not a great example. If the rock is in the glare of the hot middle eastern sun it should be heating up despite being hotter than the surrounding air. The unimpressed people have probably seen rocks out in the sun before. “Sometimes rocks get hot, for example if they are exposed to sun light”. Show me a rock that gets hot in the shade.
Yes, that is the video I found on twitter.
You could be right and it is levitation, but I had a thing called a “magnetic sculpture” as a child, and to me this video just doesn’t look any different from how the metal rectangles in that toy stood on the magnet, usually at some preferred angle. Google “Magnetic sculpture” to get a lot of pictures of things like this:
On the other had, I have also seen the demonstration where an actual superconductor is lifted out of a bath of liquid nitrogen with some tool, then put floating (maybe also spinning) above the magnet. I thought that looked quite different, although all the liquid nitrogen “smokyness” could have just been adding so much cool that I was more easily impressed.
I am not seeing the relevance of Earnshaw. I thought that a superconductor floating in a magnetic field was distinct from one magnet pushing on an induced magnet. My vague understanding is that the magnetic field lines got “locked” inside the superconductor and that this was indeed stable (flux pinning is the term I think). I mean, I have seen countless demonstrations with cold superconductors and it seemed pretty stable, you could poke it to make it spin, and the poke wouldn’t make it immediately collapse or fly away.