5 ms·

So in a nutshell what seems to be happening is that the moving magnetic field is causing the electrons in the copper to move, this electrons then give rise to a

So in a nutshell what seems to be happening is that the moving magnetic field is causing the electrons in the copper to move, this electrons then give rise to a magnetic field which repulses the original magnetic field which is why the magnet slows down.

jacquesm 15y ago
What about the part of the tube where the magnet has just past half-way (the magnet length, not the tube), wouldn't you get an opposite effect right past that point where the magnet is slowed down due to an attraction from above? After all, a magnet has two poles, the leading end I'd imagine would be repelled while the trailing part would be attracted. If that were not the case not then the forces would cancel out and the magnet would fall at its normal speed. (I'm assuming the magnet has 'top' and 'bottom' as the poles).
- deleted 15y ago
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- mpyne 15y ago
  No, it's still be going slow. The very short story is "Lenz's Law" (IIRC), but basically this of it like this: top | |N |S | As the south pole falls down, it induces currents in the part of the pipe below it which tend to form a south pole to inhibit the movement (a north pole is also formed, above the south pole which also adds to the effect) As the north pole falls down, it also induces currents, in the part of the pipe above, which tends to form a south pole above it and a north pole below it, and both of those effects act to retard the acceleration of the magnet. Perhaps easiest to visualize as: s s N n | n n | n S s s where the lowercase letters are the poles in the piping formed from the eddy currents as the magnet falls.
  - jacquesm 15y ago
    > As the north pole falls down, it also induces currents, in the part of the pipe above, which tends to form a south pole above it and a north pole below it, and both of those effects act to retard the acceleration of the magnet. Yes, that was exactly my point. So it is not just a 'repelling' force, there is attraction involved as well. The 'root' comment just mentioned 'repels' as if that was the whole story, but it clearly isn't.

jacquesm 15y ago

What about the part of the tube where the magnet has just past half-way (the magnet length, not the tube), wouldn't you get an opposite effect right past that point where the magnet is slowed down due to an attraction from above? After all, a magnet has two poles, the leading end I'd imagine would be repelled while the trailing part would be attracted. If that were not the case not then the forces would cancel out and the magnet would fall at its normal speed. (I'm assuming the magnet has 'top' and 'bottom' as the poles).

deleted 15y ago
[deleted]
mpyne 15y ago
No, it's still be going slow. The very short story is "Lenz's Law" (IIRC), but basically this of it like this: top | |N |S | As the south pole falls down, it induces currents in the part of the pipe below it which tend to form a south pole to inhibit the movement (a north pole is also formed, above the south pole which also adds to the effect) As the north pole falls down, it also induces currents, in the part of the pipe above, which tends to form a south pole above it and a north pole below it, and both of those effects act to retard the acceleration of the magnet. Perhaps easiest to visualize as: s s N n | n n | n S s s where the lowercase letters are the poles in the piping formed from the eddy currents as the magnet falls.
- jacquesm 15y ago
  > As the north pole falls down, it also induces currents, in the part of the pipe above, which tends to form a south pole above it and a north pole below it, and both of those effects act to retard the acceleration of the magnet. Yes, that was exactly my point. So it is not just a 'repelling' force, there is attraction involved as well. The 'root' comment just mentioned 'repels' as if that was the whole story, but it clearly isn't.