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Comment by sillysaurus2 | Hacker News Reader

Could this be used as a kind of elevator tech? I'd love to ride one of these down a gigantic copper tube.

It'd be completely impractical, of course, but a whole lot of fun.

The inverse square law of force strength falloff would make it very hard to scale this linearly, that combined with the fact that weight increases with the cube of size means that the magnets involved would have to be incredibly strong.

Not impossibly strong mind you, if magnets can hold a hundred ton train car off the ground I am sure they could slow the fall of an elevator.

I'd not want to be inside that elevator with anything magnetic in my pocket, though.

> The inverse square law of force strength falloff ...

Because there aren't any magnetic monopoles, I believe in ordinary circumstances the relationship is inverse cube of distance. Reference: http://www.newton.dep.anl.gov/askasci/phy05/phy05629.htm

Yup, magnetic field falls off as 1/(distance3). That's why being 5 feet from an NMR magnet is bad news bears, while being 8 feet away is fine (numbers made up, do not test). I remember seeing signs all over the place at our labs at the uni, saying to not enter if you wear a pacemaker or if you are wearing a wrist watch.

Every elevator you've been in has been held up by a magnet. They're just not obvious inside the motor housing.

To be pedantic, they're usually held up by a counterweight or by hydraulics. They generally move by magnets, though.

You could probably use eddy-current brakes as a safety system for elevators. Many roller coasters use eddy-current brakes.

It would take a hell of a lot of magnets to strap to a person to allow them to jump down a copper pipe though.

Yea my hs physics teacher demoed this and talked to us about possible applications for a while. i don't remember any but thank you wikipedia: http://en.wikipedia.org/wiki/Eddy_current#Applications

Another fun example of braking are the electrodynamic tethers [1], in which you (a satellite) are the copper tube and the entire earth is the magnet!

[1] http://en.wikipedia.org/wiki/Electrodynamic_tether

But it's possible to the same experiment with a battery and an electro-magnet, isn't it? (Not sure how the power-density of lithium-ion batteries would relate to floating 80 kgs down a tube... but seeing as people have demonstrated hover-boards, it should be doable) ? Assuming the purpose is a) float down tube, and b) SCIENCE! -- and not c) with rare earth magnets...

> It'd be completely impractical, of course, but a whole lot of fun.

And at the end of the ride, you want to take a selfie and email it to all your friends but you can't because your phone is fried.

actually not true, modern phones use SSD, and don't really get affected by magnets in the way you might expect.

True, they would only get fried if they used electronic components.

If the elevator carries the magnets, the magnetic field relative to the phone is constant, thus no induced current and no fried components.

Even hard disks are not affected by external magnetic field in the way most people expect. Strong magnetic fields interfere with the operation of drive (seeking voice coil) but accidental erasure of data on platters by external magnetic field is relatively improbable.

Generally most of the damage caused by strong external magnetic fields to any electronics are caused by second order effects, i.e. something gets confused and causes data-destroying failure.

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