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Sliding Magnet

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abbarue

New Member
When I slide a Neo. Magnet down an Aluminum bar I see an interesting phenomenon.

When the South pole is facing down the magnet slides down the bar very slowly.
This is a commonly mentioned phenomenon.

But when I try doing the same thing with the North pole facing down, the magnet
starts to tumble.
If I get the angle of the bar just right I can see the magnet start to lift off
the Aluminum bar as it slides down.

With the South pole facing the bar the bottom side of the magnet lifts off the bar,
and keeps on going down the bar in slow motion

With the North pole facing the bar the top side of the magnet lifts off the bar and starts tumbling
down the bar.

Does anyone know why there is this difference in effects?
Try it yourself and you will see what I'm talking about.

I think this phenomenon could be useful for something if utilized properly.
 
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Sceadwian

Banned
Are you sure your magnets are polarized exactly north and south in the orientation you think they are? There shouldn't be any difference that I know of, the 'hovering' effect is from induced currents in the aluminum from the moving magnetic field, I've seen spinning aluminum discs used to hover magnets, in your case the magnet is moving causing the effect.
 

Mike_2545

Super Moderator
Does the surface of the magnet have a 'grain' to it? Try taping a piece of paper to the bottom of the magnet and running your experiment again.
 
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Sceadwian

Banned
abbarue do a search on youtube for aluminum plate, or aluminum levitation. There are dozens of videos, believe me you're not the first person that's noticed it =) There's a particularly impressive one with a spherical magnet which comes to a dead stop where as a steel bearing flys right across the top and rings a gong. The tumbling and turning affect you're seeing is some inconsistancy of the magnets or something in the plate itself, I'm guessing the magnetic poles of the magets you're using are slightly off center.
 

abbarue

New Member
I personally used 2 different types of magnets.
One is a 1/2 inch magnet with a 3/8 inch hole through the center, I bought 50 of these magnets online.

The second type is a simple 5/8 inch dia. magnet 1/8 inch thick, I bought those at my local Princess Auto.

Both types of magnets display the same phenomenon with the same pole facing down.

Be realistic, all the magnets in the world can't have uneven fields always on the same side.
This is definitely a solid characteristic of magnets.
Anyone can prove this to themselves, just use an aluminum step ladder and a flat neo. magnet.
I don't believe anyone will have trouble getting it to work.
When I say north pole I mean the compass needle that points to the earths north pole points to the north pole of my magnet.
I believe this is the standard used by the scientific community.

So every time I place the north pole of a magnet towards the aluminum bar I get the flipping effect.
 
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Sceadwian

Banned
It's obviously some kind of lead/lag effect in the induced current and hence the magnetic field in the plate, Aluminum alloys contain somewhere between .1% and .7% iron, perhaps it's related to the alloy you're using. Most of the other tests I've seen using eddy current interactions use pure aluminum from what little I can guess. Where did you get the plate from?
 

tcmtech

Banned
Most Helpful Member
weird.
I had a coworker discover something like that years ago when we were working one day moving aluminum plates. Our little pocket magnets would do similar stuff.
We just figured they were F'ed up and not polarized right.

So in conclusion. Hmm. :confused: :p
 

Sceadwian

Banned
My mind kind of goes numb when I try to think about the induced current creating a magnetic field never could wrap my mind around magnetics very well.
 

duffy

Well-Known Member
I just tried it, got the same effect. It gets real sensitive as to how you release the magnet, but there does seem to be a difference.

My guess is that it's due to a manufacturing constraint that causes the field on one pole to diverge more than the other. A simple air gap on one side when the magnetizing field is applied would be probably be enough to do it. I seriously doubt there's new physics being demonstrated.
 

tcmtech

Banned
Most Helpful Member
I would still like someone to come forward and actually explain how exactly manufactured magnets are polarized at the factory. Especially the high powered rare earth and neodymium type magnets.

I recall playing with iron dust on a sheet of paper and a magnet as a kid and seeing small force line abnormalities on some magnets. (my parents were teachers so got to have extra after class time with the science lab stuff)

I think duffy may have a point.
 

Sceadwian

Banned
tcmtech, I thought I already explained this in a post aways back? The material is put in a large oven, it's heated to it's currie point, the magnetic field is applied via a large electric magnet and it's cooled to solidify the field orientation in the solid material. Depending on exactly where in the magnetic chamber a particular magnet is it's not going to have a N/S magnetic pole that is 100% perfectly aligned with the shape of the material. I'm guessing that is primarily what's causing the 'turn' depending on the side, because of Lenz law the produced magnetic field directly opposes the causing field, it only has to be off by a tiny fraction of a degree to cause it to gradually curve as it slides. You wouldn't be able to see this slight distortion in the orientation unless you went to some extreme degrees to measure the level of the magnetic and used photo software to determine exactyl where absolut true north was relative to iron powder or something of the like.
 
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Pommie

Well-Known Member
Most Helpful Member
If the effect was caused by the magnetic field being slightly angled then surely both faces would react the same. I'd like to see the effect with something (eg thin plastic) glued to both sides of the magnet.

Mike.
 

Sceadwian

Banned
Pommie I think the magnets are rotating as they slide down and the 'curve' you're seeing is nothing more than the uneven magnetic field causing one side to lift slightly and the whole magnet to tend to roll on one edge in a specific direction, friction from the magnetic forces is going to cause a resonant spinning effect that will tend always to go in one direction though I can't quiet work out why N/S would be different. I'd like to see tests as well with a solid dark black line from the center of the magnet to the edge with N and S sides clearly marked. I'd try them myself but I have no way of getting hold of a large piece of aluminum, well at least I don't want to go stealing street signs =)
 
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tcmtech

Banned
Most Helpful Member
Oops. I just got done planting 400+ pencil sized trees in two days. My memory is a bit off. :eek:

When a person reads tens of pages of random information daily the when, where, and what tends to get a bit fuzzy some days.
I have great reading comprehension and retention skills but not so great time and place recollection skills.

You right it was explained a while back. Got any video references to go with it? I would like to see how its done! :)

If the magnetic field is even slightly weaker in one point on one side of the magnet the induced counter magnetic forces in the aluminum will act as a weak friction reducer on one part VS another part of that side.
That would tend to cause a slightly uneven friction coefficient and thusly cause the magnet to favor one direction.

Now if we can get some one from the south side of the planet to try this and see if the effect is reversed there then it would be more plausible as to being a natural phenomenon with possibly earth based geomagnetic influences.
 
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j.friend

New Member
if the flaw in the magnetic field of the magnet is the case, would it be possible to recitfy this by 'making' the magnet in the middle of a high pwered solenoid. I'mm sure the lines of force would be adequately parralell to allow perpendicular polarisation
 

duffy

Well-Known Member
You could use a Helmholtz Coil, that has straight magnetic field lines in the middle. The issue is probably economic - probably just easier to have the magnetizing coil under the thing, and if the field lines diverge out of the top a little more most people don't even notice.
 

j.friend

New Member
the other thing that had me wondering about this is that if it is due to differences of the magneric field from the magnet, why would it always behave as it does, with it always being the north pole down sliding and south down tumbling (or whichever way it is).

Surely if it were due to the differences in magnetic field there would be magnets where the north would tumble, and on others the south side would tumble.

I would hazard a guess that mass produced magnets aren't limited to being only in the top half of a solenoids magnetic field, meaning that for the intents of this experiment the south side up always tumbles.

am i making any sense?
 
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