ArcanaNoir said:
Oh come on, I know a thing or two, just try me. I'd really like to know.
'Like OmCheeto said.
Putting it another way, aluminum is a paramagnetic material with a relative permeability (
μr) of only 1.000022. Empty space has a
μr of 1.0000000. Which means aluminum is not very magnetic at all. (For comparison, steel has a
μr of around 100.)
But aluminum is a fairly good conductor. And any time you wave a magnet around a conductor you get
emf (a.k.a. voltage), and in a closed circuit that means currents, even if the currents are circulating within the aluminum sheet itself. Any time you get current, you get magnetic fields (whether the conductor is magnetic or not).
This induced current always opposes the *
change* in magnetic field. So when the magnet falls on the aluminum sheet, the magnetic field is changing because the magnet is moving. The induced current in the aluminum opposes this
changing magnetic field, producing its own magnetic field which in turn slows the magnet.
This phenomenon shown in the video is more common than you might think. It is the principle behind the
induction motor. This is what household fans use, as well as laundry dryers (among may other things). Using a number of stationary coils connected to a 3-phase AC source (actually, any number of phases is possible, it doesn't need to be 3-phase), a rotating magnetic field is created. Then what is essentially an aluminum hamster wheel naturally spins around inside trying to keep up with the spinning magnetic field (no brushes or any external electrical connections whatsoever are needed on the hamster wheel). This is similar to how the aluminum plate moved with the magnet when the magnet was moved back and forth.
