We develop a simple model to investigate the orientation-dependence of the drag force acting on a magnet falling inside a vertical conducting pipe. We approximate the magnet by a point magnet and the pipe by a two-dimensional cylindrical surface. Independent of the magnet's orientation, the drag force is proportional to its velocity: F d = k v . We show that the coefficient k of the horizontally oriented magnet is about 2/3 of the coefficient k for the vertically oriented magnet. If the magnetic moment makes an angle θ with the vertical direction, the drag coefficient k can be expressed as k = k cos 2 θ + k sin 2 θ. When the magnet falls with a non-vertical orientation, a local charge distribution is induced in the pipe, which plays a role as important as that of the time-varying magnetic field due to the falling magnet in generating the eddy currents. The model's predictions are compared with experimental results.

1.
There are many on-line demonstration videos available on YouTube. For example, see “
Lenz's Law
” in TSG@MIT PHYSICS <https://www.youtube.com/watch?v=N7tIi71-AjA>.
2.
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and
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,
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R.
Wolfson
,
Essential University Physics
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,
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,
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), Prob. 27-10.
3.
Many demonstration kits are commercially available; for example, Arbor Scientific Co., “Lenz's law apparatus,” Item # P8-8400, and Leybold GmbH, “Lenz's law demonstrator” Item #560 361.
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7.
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11.
An extensive list of recent pedagogical papers on the interaction of magnetic fields and conducting materials can be found here: https://aapt.scitation.org/doi/suppl/10.1119/10.0003508.
12.
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14.
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16.
Because of the tilting and precession, the magnet touches the pipe and one may hear the sound of the magnet sliding on the pipe surface. In that case, friction is no longer negligible, and Eq. (28) does not hold.
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