Since aluminum is non magnetic why will it slow down when quickly passed by a magnet.?

Question

Since aluminum is non magnetic why will it slow down when quickly passed by a magnet.?

Answer 1

Explanation 1.

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When a magnet moves past aluminium, there is a change of magnetic flux in the Aluminium.

According to Faraday's Law, there is therefore an induced e.m.f. (voltage) in the Aluminium

Because aluminium is a conductor, the induced e.m.f. causes a current to flow in the Aluminium. This is  an induced current. ( or an eddy current here)

According to Lenz's law, the induced e.m.f acts in such a direction as to oppose the change causing it.

The change causing it was the movement of the magnet, - this change was opposed, causing the magnet to slow down, or its motion resisted.

You could also say that the induced current in the Aluminium creates its own magnetic field, which opposes that of the magnet.

Explanation 2.

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There is also another way to look at it.  Since an induced current flows in the Aluminium, heat is generated in it.

Where did this heat energy come from??   Not from the magnet as it did not become weaker.

The energy came from whatever was pushing the magnet, e.g. the hand.

If nothing was pushing the magnet at the time, the energy must come from the Kinetic Energy of the magnet, which therefore slows down.

Extra.

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This idea is used, e.g. in electronic balances to produce "damping". i.e to bring the balance to a stop fairly quickly and to stop it oscillating backwards and forwards for too long.

Inside the case a powerful magnet moves past a copper or aluminium vane.

Answer 2

Aluminum is a conductor, so the electrons are free to move on the surface.

The moving electrons feel a force from the magnetic field and tend to move in a manner that sets up "eddy currents".

These "eddy currents" will generate a field that opposes the flux induced by the motion and thus exerts a force on the aluminum.

So much fun to play with in an MRI scanner ...

=)

Answer 3

Aluminium may be non-magnetic but it is not non-conduting to electric current

So Faraday's Law applies

Answer 4

.They are called "Eddy Currents."  Any conductor will have a current generated within them if a magnetic field moves past the conductor.  Those electric currents have a polarity opposite the magnetic field that generated them. Soon as the aluminum starts to move, the eddy current stops it.  Soon as it stops the eddy current goes away and it starts to move again.  Result: Slow movement through the field