Cool Effect: Dropping a neodymium magnet down a copper pipe [Video]

Check out what happens when you drop a neodymium magnet down a copper pipe.

The movement of the magnet induces an electric current in the copper and with electric current comes a magnetic field, which makes the magnet attracted to it. The magnet doesn’t stick to the wall as it falls because the induced current, and its corresponding magnetic field, are perfectly distributed so that the magnet feels magnetic force equally from all sides.

The magnetic field slows the magnet, but can’t stop its fall because if the magnet stopped moving, the induced electric field would go away and the magnet would start falling again.

[Via]

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15 Responses to Cool Effect: Dropping a neodymium magnet down a copper pipe [Video]

  1. This is cool. It could be used as an auxiliary backup for elevators, which would slow their descent, even if external electricity is lost…

    • If it'll work at that high of speeds / weight proportions. I suspect the reason it seems to float so slowly is because it's a relatively small, extremely high powered magnet to an equally small tube. I don't think there'd be a way to effectively scale up the magnetic power involved without the inclusion of electricity to make it an electromagnet, which would undermine the whole point of using it as an auxiliary system and might not function the same. I don't know for sure, this is all a massive guess.

      • I don't think it would be impossible, just impractical. The ammount of copper and rare-earth magnets needed would make elevator safety systems ridiculously expensive, with no clear-cut advantage over the braking systems currently in use.
        The ones currently in use are very safe in fact that's what the elevator was invented for, as a way to safely lift loads without worry of them falling, even if the lift cable breaks – how many "elevator cable snapping" accidents do you hear about?

        • the whole copper/rare earth part isnt absolutely necessary. the copper could be aluminum and the magnet just needs to be strong relative to the attached mass. not justifying it, just playing devil's advocate.

        • Except Aluminum is just about as expensive as copper (possibly more? Prices fluctuate a lot these days), and only Rare Earth magnets would be strong enough relative to their mass (and the mass of the elevator) to have a significant impact on the speed of elevator without significantly increasing it's mass (thus increasing it's momentum and further increasing the amount of speed that would need to be expelled for the elevator to hit the bottom safely).

          Part of Engineering is being economic in your solutions, and while the Copper and Magnets solution can almost certainly be made to work, it would be significantly more expensive than traditional friction and centrifugal brakes – which would still be needed in some form to actually stop the elevator. You end up drastically increasing the price (go ahead, compare the price of Copper and Aluminum to metals like iron and steel), without creating an increase in performance that can justify the price difference.
          It would be a poor braking technique, however, I can see it being used to recapture some of the energy used to raise the elevator – which is very much in vogue right now in engineering.

      • The faster the elevator falls, the more current is created and the greater the stopping power would be. Every mass:magnet:distance ratio will have it's own terminal velocity.

      • Also not useful as emergency-braking-system for elevators since it cant be turned off and would work upwards just the same. The Elevator would have to be pulled upwards against the braking force (which gets stronger, the faster the elevator goes) and would have a maximum descend-rate limited by the magnets and couldn’t go faster down even when perfectly save and operational…

  2. I feel like that pipe, if it was insulated from the ground (i.e. not being held by a human or metal stand) could eventually build up a substantial charge in it. But that's just an educated guess on my part.

    • a charge built up between what? the falling magnetic field creates a difference in potential inside the metal. remember, voltage isnt an absolute quantity – you need something to reference.

      • I know I'm more familiar with mechanics than I am electrical, but wouldn't you have a difference between the inside of the pipe and outside of the pipe? Electricity doesn't like to flow through, just across the surface of, objects (where there are empty electron orbitals – since the interior atoms are more likely to have filled their orbitals by borrowing or stealing electrons from their neighbors). Nor does it like to flow around right angles (the ends of the pipe).
        Similar to how a static charge can be built up with friction, you end up with differences between the interior and exterior, as well as the ambient environment around it.
        All generators are are moving permanent magnets (traditionally spinning, but not necessary – just needs to be changing polarity) inside copper coils (tightly packed to increase the exposure to the magnetic field).

        I still wonder if it might be made to generate electricity. As I mentioned above, you might be able to recapture some of the energy used to raise the elevator in the first place. Obviously, the specifics would need to be worked out in greater detail.