Another use for rare earth magnets

I think so, but I'm not sure.

I made them fall slower simply by putting 4 together (4 was all I had) and dropping them through the pipe. Can't say I really understand why they fall slower when together. The combined magnetic field would be larger but so would the combined weight so I don't know why the two effects don't just cancel each other out and end up with the magnets falling at the same rate. Maybe the field from one magnet tends to make the field from the others stronger so the combined field is more than the sum of the parts???

I think if you were to replace the copper pipe with a wire coil and then connect the ends of the coil together it might make it fall slower. That is, the magnets would be inside the wire coil. Or maybe just use many small copper wire rings???

Yeah, but your answer I think is the easiest way to make someone grasp what is happening even if the truth is more complex. I'll be using that answer the next time I have to explain it to someone... :)

That is the case. Less air space is better. The pipe and the magnet will be in closer proximity to the magnetic fields. The field weakens through space. Making the walls of the pipe thicker, or using a material that is a better conductor will also make the magnet fall slower.

That is not really true. Consider a permanent magnet generator. The magnet is spinning within what? A coil of copper wire. Magnets affect more than just ferrous materials.

I'll try.

A. First, you drop the magnet in close proximity to a conductor. From playing with generators, we've all learned that when we move a magnetic field in proximity to a conductor, we induce electrical current.

B. Now we have current flowing through the pipe.

C. We've learned that when we run electrical current through a conductor, we induce a magnetic field. The current running through the pipe is inducing a magnetic field.

D. The magnetic field is repelling the magnet and opposing the force of gravity.

Now go google or wiki on Lenz' Law.

Rob

Not much, untill it fits so closely it starts acting like a pneumatic damper. Retarding force is proportional to flux density thru the pipe and pipe wall conductivity. Flux density varies inversly with path length. Making a tighter fit will have a fairly small effect because the gap from magnet to pipe ID is a small percentage of the pathlength from pole to pole of the magnet.

Increasing pipe wall thickness will increase conductivity and thus induced current, thus making it fall slower.

The magnet, in this case, is affecting electrons within the metal. Anything conductive will respond to magnet movement. The key is movement: the field has to be cutting through a conductor to generate electron flow, and whether it's the field that's moving through the conductor (as in an alternator) or the conductor moving through the field (as in a generator) the result is the same. No movement equals no electron flow generated. The magnet hovering over a superconductor assumes that a current was stimulated within the superconductor in the first place. The hovering magnet cannot do that, since there is no field movement. Nothing is free.

Dan

I always thought the act of bringing the magnet into place over the superconducter was what created the current in the superconducter.

Dave

It can be done by placing the magnet on the superconductor before chilling it. No (apparent) motion is required.

Actually, even the tiniest vibrations are enough to set up currents that disturb the stability of the setup enough to wiggle it a bit more, causing more current, wiggling it more... ad nauseum, until the thing levitates, and becomes quasi-stable.

LLoyd

:-) Use a "superconductor" peice of pipe and it wont fall at all. :-)

...lew...

They have the super-strong Neodymium (or other rare-earth) magnets? I thought that they only had the ferrite ones -- but they may have improved over time. A ferrite one does not have the strength to demonstrate the effect anywhere near as obviously.

Enjoy, DoN.