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How can a rotating wheel stop using magnetic power? For example, consider a rotating iron wheel: can it be made to stop suddenly with using magnetic power? If so, how?

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    $\begingroup$ In a practical magnetic brake, you would make the "wheel" from some material such as copper or aluminum that is (a) not ferromagnetic, and (b) a better conductor than iron. Being a better conductor makes it work more efficiently. Not being ferromagnetic avoids mechanical issues by eliminating any attractive force between the disk and the poles of the magnet. $\endgroup$ Apr 25, 2019 at 15:35

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By placing the two poles of a strong magnet normal to the plane of rotation, eddy currents develop [if the moving object is a solid plate] and cause the motion to cease. Thank you.

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By Lenz's law the direction of the current induced in a conductor (your iron wheel) by a changing magnetic field (the rotating iron wheel between magnet's poles feels a changing magnetic field relative to it) is such that the magnetic field created by the induced current opposes the initial changing magnetic field.

Or, more vaguely, the induced current opposes the change which induced it.

So the result is that the wheel will eventually stop (= no more change in a magnetic field).

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