Why does a spherical magnet fall so slowly through an aluminum tube?

This trick is easily demonstrated with a magnet salvaged from a dead hard drive and a shee of aluminium (cookie sheet).

Hold the cookie sheet at about 45 degrees and let go of magnet at the top. It will slowly slither down the tray.

This is also how recycling centers sort out the aluminium cans - Eddy currents


The right hand rule does not hint at a handedness of the universe. There are circulatory currents in your magnet or magnetic coil. Remember that you are applying the right-hand rule twice. Once to get the B-field from a current and then again to get a force from field and charge velocity. A left hand rule would lead to the same force but use a different convention for B.
Or expressed without any chirality: The electrons are attracted towards comoving charges in a magnetic coil or magnet.
For real asymmetries you might want to have a look here: CPT symmetry


Every electric generator - power plants, regenerative brakes in hybrid cars, etc. rely on induction.

Also, rail guns.

Correct (though the weak force does).
Actually, electromagnetism is a relativistic effect.
Special relativity’s 2 postulates (laws of physics are the same in every inertial reference frame, speed of light is the same for all observers) give us length contraction.
The electric field of a point charge is spherically symmetric.
Make that charge move, and its field is length contracted - field lines closer together in the plane perpendicular to the direction of motion.
So for a circular current, a charge passing through the loop see an increasing force acting on it parallel to its motion the faster it moves relative to the current.

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Crack sensors. The cracks break up the eddy currents, so you can make a really sensitive crack sensor using this effect.

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My favorite linear brake is http://en.wikipedia.org/wiki/Top_Thrill_Dragster . The coaster is launched up the hill, over the top and then back down where it hits a brake and comes to a near stop. They also pop up a metal slats right behind the train after the train passes the launcher. These slats work as a brake in case the coaster doesn’t make it over the top of the hill and comes flying back towards the launcher (not infrequent).

They don’t mention the brakes but the guy talking about the reliability is leaning on them at one point.

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This is basically what regenerative brakes in hybrids are based on.

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You don’t need aluminum (copper pipe works even better). You don’t need a spherical magnet. Any shape will do.

Cow magnets*, as it happens, work exceptionally well for vertical falls.

*For the uncountry, cows are dumb as a bag of hammers. They will happily eat little bits of wire left over from those used to bale their hay, staples, barbed wire, etc. This leads to a condition called hardware disease. Cow magnets are fed to them at birth. They trap all the metal fragments for life in the cow’s rumen, preventing them from passing on through the system and causing problems. They used to be the cheapest easily obtained really strong magnet.

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Was it about mind control and targeted amnesia?


So what if I dropped a cow down an empty grain silo?


is anyone there to see it?


Pro tip: do not go on this rollercoaster if you cannot handle being extremely hungover from a bachelor party the night before. I have it on good authority from some friends who did not enjoy the experience (I thoroughly did… Though I wish we got to do a “double” where it doesn’t make it all the way up the first time. :))

I don’t know, exactly, how to parse what you wrote but the right hand rule for electromagnetism does tell us that the universe is orientable. i.e. it does not contain 3D Moebius tubes. If we had one of those in the universe, you couldn’t define a consistent right OR left hand rule.

Then you’d be drunk and disorderly.

Which I think makes you prom King.

We used to do the inverse - stick a quite massive aluminium plate under an electromagnet and watch it tumble like a leaf in the wind. Or try tossing it upwards while giving it a spin.
Of course it helps if your magnet is of the 20 Tesla variety.

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This is described by Lenz’s law http://en.wikipedia.org/wiki/Lenz’s_law. It effectively states that as the magnet passes down the tube, it induces currents in the field which push back against the magnetic field of the sphere and slows it down.

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Not real rail guns.


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