Magnet Question

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HeroicFail
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Magnet Question

Postby HeroicFail » Wed Jan 07, 2009 2:01 am UTC

I was working on my PJAS project in my chemistry teacher's room after school today. My project is basically this, but on a slightly larger scale. The magnets I'm using are 12mm cubed neodymium permanent magnets. When my friend chipped a magnet by letting a nickel ball hit it, the fragments wouldn't "fit" back into their spot. See picture for what my memory provides. I must have some erroneous connotations about magnets.

Does anyone know how or why the fragments reversed polarity on top?

EDIT: I don't know why I typed reversed polarity.

Thank you to both of you.
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Seraph
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Re: Magnet Question

Postby Seraph » Wed Jan 07, 2009 2:08 am UTC

I can't figure out what your drawing is supposed to show, but what makes you think the magnets reversed polarity?

The chip is going to want to align so it's North is near the big magnets South. So if the chip was not perpendicular to the North-South direction you'd expect that chip would try to go in backwords, and therefor wouldn't fit. Does that differ from what you experienced?

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danpilon54
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Re: Magnet Question

Postby danpilon54 » Wed Jan 07, 2009 2:19 am UTC

basically, the magnet wasnt held together by its own magnetism at first. It was held together because it was a solid. There was probably an internal stress due to the non-aligned magnetic regions before it broke. Ur gunna need glue now or something.
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GrimReaper
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Re: Magnet Question

Postby GrimReaper » Wed Jan 07, 2009 2:40 am UTC

The reason the chunk is repelled from the main magnet is because it always was.
You know how if you hold two magnets close to each other with their North poles facing they repel?
Well this is the same thing, say the fragment broke off the North pole of the magnet, since both the fragment and its home is North, they repel.
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HeroicFail
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Re: Magnet Question

Postby HeroicFail » Wed Jan 07, 2009 2:49 am UTC

It's not that the chunks didn't want to go into the spaces, they just kept moving to the top. Moving them into position wasn't a problem, but after letting go they would naturally go to the top face.

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GrimReaper
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Re: Magnet Question

Postby GrimReaper » Wed Jan 07, 2009 3:12 am UTC

They now have a more southern pole and a more northern pole, so their poles will seek their natural opposites. Like any normal magnet.
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Senefen
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Re: Magnet Question

Postby Senefen » Wed Jan 07, 2009 4:06 am UTC

Visualisation!
You have
Big Magnet
>>>>>>>>>>>>>
S>>>>>>>>>>>>>N
>>>>>>>>>>>>>

chip it you have
the chip
S>>>N
and
big magnet
___>>>>>>>>>>
S>>>>>>>>>>>>>N
>>>>>>>>>>>>>

Now you're trying to fit
S N
>>>>>>>>>>>>>
S>>>>>>>>>>>>>N
>>>>>>>>>>>>>

The chip has become a little magnet in it's own right, with it's own field and you're trying to pull two like poles together, so it's going to automatically move away. Once you break it it becomes a new magnet, not 'part of a magent'
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Interactive Civilian
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Re: Magnet Question

Postby Interactive Civilian » Wed Jan 07, 2009 5:28 am UTC

I have nothing to add to the above explanations, but just a thought/question.

Based on the explanations, if one took a hammer and smashed one of the magnets how would the fragments orient themselves? I guess for simplicity's sake, imagine the fragments are of equal size and shape. I'm imagining a few possible visualizations but have no idea which is right because magnets have always been a bit mysterious to me (I need to educate myself more about them).
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Re: Magnet Question

Postby Carnildo » Wed Jan 07, 2009 6:52 am UTC

The fragments would arrange themselves in a formation that is a local minima for potential energy. Even for uniform fragments, there's no good way of working this out. For non-uniform fragments, the term "chaotic" comes to mind.

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danpilon54
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Re: Magnet Question

Postby danpilon54 » Wed Jan 07, 2009 3:36 pm UTC

Interactive Civilian wrote:I have nothing to add to the above explanations, but just a thought/question.

Based on the explanations, if one took a hammer and smashed one of the magnets how would the fragments orient themselves? I guess for simplicity's sake, imagine the fragments are of equal size and shape. I'm imagining a few possible visualizations but have no idea which is right because magnets have always been a bit mysterious to me (I need to educate myself more about them).


Tell me the exact orientation of each magnetic region and then give me a super computer...
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Shadowfish
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Re: Magnet Question

Postby Shadowfish » Wed Jan 07, 2009 11:16 pm UTC

I have nothing to add to the above explanations, but just a thought/question.

Based on the explanations, if one took a hammer and smashed one of the magnets how would the fragments orient themselves? I guess for simplicity's sake, imagine the fragments are of equal size and shape. I'm imagining a few possible visualizations but have no idea which is right because magnets have always been a bit mysterious to me (I need to educate myself more about them).


If the fragments were small enough, you would end up with a non-magnetic pile of magnetic material. If you put two bar magnets next to each other, they will line up so that the north pole of one will be next two the south pole of the other. Their magnetic fields cancel, so that the net field is weaker. In general, a lower energy configuration will have a smaller magnetic field.

Think of a piece of non-magnetized steel. It has a large number of small regions that are magnetized in a given direction(domains). The directions of these are random, so their magnetic fields cancel each other out. This is the lowest energy configuration.
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GrimReaper
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Re: Magnet Question

Postby GrimReaper » Thu Jan 08, 2009 6:47 am UTC

Even if the chunks were large, if you hit it hard enough it would lose its magnetism because the particles would lose their nice and fancy alignment.
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IIAOPSW
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Re: Magnet Question

Postby IIAOPSW » Fri Jan 09, 2009 6:10 pm UTC

i had the same issue with neodynium. i think that as a whole the magnet has a net allginment in one direction but when you chip off a piece that piece has a field equivalent to its net direction. and so once it chips it doesnt stick back. also, where did you get your magnets and what grade are they (i need some myself)
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HeroicFail
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Re: Magnet Question

Postby HeroicFail » Fri Jan 09, 2009 11:05 pm UTC

I got them https://www.scitoyscatalog.com/Merchant ... ory_Code=M

I'm not sure what grade they are. Thanks for the replies.

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GrimReaper
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Re: Magnet Question

Postby GrimReaper » Sat Jan 10, 2009 1:04 am UTC

Here is an excellent place to buy magnets: http://www.unitednuclear.com/magnets.htm
They are all N45 and above.
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Rentsy
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Re: Magnet Question

Postby Rentsy » Tue Jan 13, 2009 4:50 am UTC

Here's a thing to do, test its strength to that of a virgin neodymium magnet of the same size.

I bet it will be less. Why? Neodymium magnets have lots of domains lined up. Domains hate this. In Neodymium, there are so many domains, that give them a chance and they'll shatter to unaligne their domains. This is why Neodymium magnets break so easily, they literally want to tear themselves apart. Yours did.


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