I like those types of videos! In the pipe versus magnet example, the falling magnet causes a current to be induced within the copper pipe. The magnitude of the current is proportional to the velocity of the moving magnet and is inversely proportional to the resistance of the pipe material.
I suppose you can think of this simple system as a type of motor where the generated force is directed against the motion of the magnet and proportional to its velocity. In that case the downward velocity would reach a value where the motor force is balanced against the force of gravity. The current induced within the metal is going to depend upon how rapidly the magnet falls hence a better conductor would maintain a greater current at the same velocity. So, I would expect to see the falling velocity of the magnet to become less and less as the conductor used for the pipe become less resistive. But, the geometry is also going to enter into the equation. This is because a very wide opening for the pipe would not allow the material to capture a significant amount of the magnetic field and therefore offer only a small force as the magnet passes through. This scenario would be interesting to model. If we assume that the pipe diameter is sufficiently small then it would make sense to assume that the magnet would be suspended at zero velocity if placed within a super conducting pipe. I believe you are thinking of the inverse case for the effect of resistance which would apply to an insulator. Dave -----Original Message----- From: Eric Walker <eric.wal...@gmail.com> To: vortex-l <vortex-l@eskimo.com> Sent: Sat, Nov 14, 2015 1:24 pm Subject: Re: [Vo]: How many atoms to make condensed matter? On Sat, Nov 14, 2015 at 12:25 AM, David Roberson <dlrober...@aol.com> wrote: The loss in the current carrying magnet is due to series resistance and if that resistance is eliminated it would not require any additional power once the current is set up. Consider this video: https://www.youtube.com/watch?v=uh0bbW6S3BY Here the falling of a permanent magnet is slowed down as it falls through a copper pipe. As it falls, it is inducing a current in the pipe. My uninformed impression is that the only thing that is keeping it from falling faster is the resistance in the pipe to the flow of the current. If we replace the copper pipe with a superconductor, the magnet could then fall through as fast as gravity will accelerate it, will it not? If there is a current already set up in the superconductor, it would counteract the falling of the magnet, but this would be a matter of degree and not a permanent situation, or am I mistaken? Eric
