Simple magnet mystery

[Ginarley]

Hi all

I have this cool magnetic toy which I accidentally dropped a paper clip on the other day and discovered something cool:

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The set up: There are two red bar magnets attached horizontally, a collection of loose nuts making the person, and a paper clip. No glue, etc. The paper clip hangs there roughly parallel with the ground.

The paper clip seems to be in an equilibrium point because if I push or lift it, it bounces back to the same horizontal position in the picture. It works either side of the head or attached to the arms.

If I rearrange it so it is higher, the paper clip hangs lower and vice versa, so it is obviously related to the proximity to the red magnets, but if I push the paper clip too close to the red magnet it snaps to it. The easy answer seems to be that the paperclip and red magnet are the same polarity and repelling each other until the upwards force equals gravity, but I can't quite reconcile that with the magnets themselves - why doesn't the magnet repel the nuts then?

I am assuming the answer is fairly obvious to anyone with a smattering of physics so any help understanding it would be appreciated. Regardless of explanation it is pretty cool and understanding it will make it even cooler

Cheers

 

[Skeptic Ginger]

While the paper clip was not necessarily magnetized ahead of time, the magnetic field, nonetheless travels through it making it magnetic while attached. The clip becomes polarized and that results in it being in the position it is in. If you were to move it somewhere else along the nuts you could make it line up with the polarized fields of the bolts and it would lay flat against them.

Very cool.

 

[epepke]

The equilibrium is probably caused in this case by small irregularities in the nuts and paperclip, according to which all the positions around the position involve the paperclip being slightly farther away.

A much subtler problem is this: When you position a small magnet over a superconductor, it just stays there. You can push it a bit, and it will stay there. It doesn't just slide off. Why is this? It's a fascinating answer, which I shall leave as an exercise for the reader.

 

[Ginarley]

Thanks for the answers

While the paper clip was not necessarily magnetized ahead of time, the magnetic field, nonetheless travels through it making it magnetic while attached. The clip becomes polarized and that results in it being in the position it is in. If you were to move it somewhere else along the nuts you could make it line up with the polarized fields of the bolts and it would lay flat against them.

Very cool.

I get the first bit - that it becomes magnetic. Does polarization mean something different? And how does the polarization holds it horizontal?

The equilibrium is probably caused in this case by small irregularities in the nuts and paperclip, according to which all the positions around the position involve the paperclip being slightly farther away.

You definitely lost me

A much subtler problem is this: When you position a small magnet over a superconductor, it just stays there. You can push it a bit, and it will stay there. It doesn't just slide off. Why is this? It's a fascinating answer, which I shall leave as an exercise for the reader.

I've seen videos of those - and since I can't figure out the obvious example in the OP this one is definitely way over my head!

 

[BNRT]

A much subtler problem is this: When you position a small magnet over a superconductor, it just stays there. You can push it a bit, and it will stay there. It doesn't just slide off. Why is this? It's a fascinating answer, which I shall leave as an exercise for the reader.

I think I might know part of the answer:

Does it have something to do with the fact that the magnetic is channeled through certain areas in the superconductor? So that the magnet floating above it is at a stable equilibrium only in one spot?

I seem to remember something like this from my short stint in physics. Mainly a high school project involving superconductors and high magnetic fields.

 

[DrDave]

Hi all

I have this cool magnetic toy which I accidentally dropped a paper clip on the other day and discovered something cool:

__

<snip>


*********** magnets, how do they work?

ftfy

 

[Careyp74]

ftfy

Dang, beat me by 12 minutes!

 

[Ginarley]

ftfy

Yeah probably should have started with that

 

[Olowkow]

Feynman's explanation of how magnets work, one of the best examples of scientific thinking I have heard. It is amazing to watch as his mind attempts to find a way to satisfy the questioner.

 

[Skeptic Ginger]

I get the first bit - that it becomes magnetic. Does polarization mean something different? And how does the polarization holds it horizontal? ..

It's following the magnetic field lines.

Paper clips lined up in an analogous magnetic field

Kind of a long explanation of stuff you probably know: Charged Particles and Magnetic Fields

Exploring Magnetic Fields: Activity 2

7. Now ask your teacher for another magnet of a different shape. This magnet might be shaped like a doughnut or a horseshoe. Try to see what the magnetic field looks like around this magnet. Draw a picture of it on your data sheet. Do all magnetic fields look alike? Do they change shape with the shape of the magnet?

The point is, the paper clip is revealing the magnetic field lines of your configuration.

 

[epepke]

I think I might know part of the answer:

Does it have something to do with the fact that the magnetic is channeled through certain areas in the superconductor? So that the magnet floating above it is at a stable equilibrium only in one spot?

I seem to remember something like this from my short stint in physics. Mainly a high school project involving superconductors and high magnetic fields.

Nice try, but no cigar. It's one of those answers that makes your slap your forehead when you hear it.

There are many stable equalibria in many spots.

 

[Brian-M]

Are you familiar with flux lines? Put a piece of paper on top of a magnet and sprinkle it with iron filings. The filings that don't end up on top of the magnet will form a distinct series of curved lines between the two poles bulging outward from the magnet showing where the flux lines are.

I think the paperclip is becoming magnetized and aligning itself with the flux lines from the magnetized nuts.

Check out the Wikipedia entry, it's got a picture of the iron filing thing in it...

http://en.wikipedia.org/wiki/Magnetic_field#Magnetic_field_lines

But I that picture doesn't seem as clear as when I tried it. (Assuming my memory of trying it many years ago is accurate.) It may depend on the size and strength of the magnet.

ETA:

Ah, Skeptic Ginger beat me to the mention of magnetic field lines. I posted this directly after watching the Feynman video, so I missed her post.