Originally published at: https://boingboing.net/2018/01/30/watch-some-strange-ways-strong.html
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Thank you for the direct links to the videos, the embedds don’t normally work for me.
Also, you know, great science!
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The effect is really kind of spooky in person; I’d recommend trying it if you have the chance (being a scrounging nerd I’d say that “magnet from old/dead HDD plus conveniently chunky and flat-based aluminum or copper heatsink”; but I suspect that this isn’t always the easiest option, if anyone has a preferred internet purveyor do tell).
Moving the magnet when it is on top of the metal plate feels sort of like moving it through some sort of peculiar non-newtonian fluid: at very low speeds it feels almost the same as moving it again an ordinary surface; but the apparent ‘viscosity’ rises extremely sharply as you speed up; decreasing almost instantly when you slow down again. Very peculiar feeling.
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The resistance should be linear with velocity (neglecting a dozen confounding factors).
I have a toy that’s simliar to this. I have a copper tube just big enough to pass a steel ball. I also have a rare earth magnet the same size as the steel ball. I let people take turns putting the two balls through the tube. The steel ball just drops through. The magnet takes several seconds. People usually think there’s some trick to it, so I hand them the parts and let them play with it. It’s not magic, it’s science.
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Magnet: “You’ll never take me alive, copper!”
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Or, if the hard drive’s motor is not integrated into the frame and can be detached, take the motor out and reassemble the platters onto the spindle (assuming they’re aluminum rather than glass). When you spin the platters, putting the magnet near them will quickly slow them down.
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This is how it was shown to me at school, although with an aluminium tube rather than copper.
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Oooh, I loved the glimpse of Faraday’s lab. I just visited a Sunday School class last week and talked about Faraday to the kids (and we disassembled old SCSI drives).
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Lately I’ve also seen circulating this thing about the diamagnetic properties of silver.
We should also probably have this here:
And the ol’ pendulum-with-slits:
https://youtu.be/38XPT9sWIso
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This is exactly how eddy current brakes (now common on many roller coasters) work. They’re great because there are no brake pads to wear out. But since the effect goes away when speed approaches zero, mechanical caliper brakes are still needed to hold the train stationary.
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It’s all done with birds.
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