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Author Topic: Why won't my magnets repel each other?  (Read 8038 times)

Offline Fozzie

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Why won't my magnets repel each other?
« on: 07/12/2010 11:54:39 »
I have two bar magnets. They attract each other in whatever position I put them in. Also, when I rotate them in the presence of a compass, the needle does not turn to face the opposite direction as I would expect. I cannot get them to repel each other however hard I try. What's going on?
« Last Edit: 08/12/2010 20:01:26 by chris »


 

Offline Foolosophy

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Re: Why won't my magnets repel each other?
« Reply #1 on: 07/12/2010 12:19:53 »
what is the shape or geometry of the magnets?

have you identified where the poles are? the field lines?
 

Offline Fozzie

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Re: Why won't my magnets repel each other?
« Reply #2 on: 07/12/2010 13:43:09 »
They are rectangular. About an inch long. I don't have any iron filings to check the force field. Do you have any suggestions how I can check this?
 

Offline techmind

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Re: Why won't my magnets repel each other?
« Reply #3 on: 07/12/2010 21:56:36 »
Where did you get the magnets from?

Are they really bar magnets made of solid metal or are they perhaps something else?

They make stupid toy "magnets" typically big red plastic shapes with tiny little real magnets stuck onto the ends of the plastic "cartoon" magnet. Pah!


Another thing you frequently see, particularly on "fridge magnets" and other magnetic advertising things, is a dark brown rubbery plastic - typically just 1-2mm thick - which has magnetic metal particles embedded in it, usually in thin lines a couple of millimeters apart. If you "stick" two of these together on their flat faces, you'll find that in one direction instead of sliding over each other, they'll jump in jumps of a few millimeters - which is the spacing (or twice the spacing) between the rows of magnetic particles.
You can buy this magnetic rubber sheet in any shape, but it is particularly often found in a "tape" about 1cm or half an inch wide.
 

Offline Foolosophy

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Re: Why won't my magnets repel each other?
« Reply #4 on: 08/12/2010 02:20:05 »
They are rectangular. About an inch long. I don't have any iron filings to check the force field. Do you have any suggestions how I can check this?

The magnetic field is simple for a rectangular shaped magnet - you should be able to get the magents to repel and attract eachother depending on which poles you push together

(easy to check magnetic field lines - some iron filings on thin paper, placing the magnetic driectly underneath should produce the field lines roughly can also use a sensitive compass needle and move it around the magetic ntoing down the driection of the field)

 

Offline Geezer

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Re: Why won't my magnets repel each other?
« Reply #5 on: 08/12/2010 02:56:18 »
They are rectangular. About an inch long. I don't have any iron filings to check the force field. Do you have any suggestions how I can check this?

The magnetic field is simple for a rectangular shaped magnet - you should be able to get the magents to repel and attract eachother depending on which poles you push together

(easy to check magnetic field lines - some iron filings on thin paper, placing the magnetic driectly underneath should produce the field lines roughly can also use a sensitive compass needle and move it around the magetic ntoing down the driection of the field)



Which part of

I don't have any iron filings to check the force field.

did you not understand?
 

Offline Fozzie

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Re: Why won't my magnets repel each other?
« Reply #6 on: 08/12/2010 08:54:05 »
Also:

Quote
The magnetic field is simple for a rectangular shaped magnet - you should be able to get the magents to repel and attract eachother depending on which poles you push together

If you read my original post you will see that I said I cannot get them to repel each other.

They are solid metal, not rubber or toy compounds and only attract. I found them in a geocache so I have no idea of their provenance. When a compass is moved along them, the needle doesn't rotate as it would if the magnets had north and south poles, but simply points in the same direction. They appear to be "pole-less".
 

Offline BenV

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Re: Why won't my magnets repel each other?
« Reply #7 on: 08/12/2010 09:05:00 »
There is another way to plot field lines, but ideally you need a very small compass. Lay the magnet in the middle of a sheet of paper, place the compass by one end and draw a dot at north & south. Then move the compass so the south point is on the north dot and mark the new north. Repeat this a few times, then join the dots. Then start back at the magnet again in a different place. It's time consuming, but it should work.

The other option would be to place it near the screen of a CRT tv or monitor, but this is a bit harder to interpret.
 

Offline imatfaal

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Re: Why won't my magnets repel each other?
« Reply #8 on: 08/12/2010 10:58:18 »
Fozzie could you take a photo and paste it?  Cos frankly this is all a bit weird.  What do they look like, are they a single material, heavy as lead/light as aluminum? 

I know you have already said they won't repel, but could we be more exact?I am presuming that the magnets are simple rectangular solids.  If you place them on a flat surface, with their two largest sides downwards flat, you should be also able to identify four 'sides' and a top; whilst stopping the magnets jumping up:
- do all four sides of magnet A feel an attraction to all four sides of magnet B? 
- flip one of the magnets over by 180deg - do all four sides still have same attractions
- how much "upwards" force is there when you bring them together - ie does one try and jump on top of the other  :o
- if you believe that all the sides attract all the other sides ( and similarly after flipping one magnet) does the top of magnet A attract bottom and/or top of magnet B

For all the above might be worth thinking of in terms of repel / attract / neither rather than simple binary
 

Offline Foolosophy

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Re: Why won't my magnets repel each other?
« Reply #9 on: 08/12/2010 11:29:54 »
Fozzie,

I am not aware of how a permanent magnetic can be pole-less???

check and see if they are compostie magnets that are been held together by force

A bar magnet has the following magnetic field lines




and if you carried out a simple iron filling test you will be able to reproduce that field shape
« Last Edit: 08/12/2010 11:34:23 by Foolosophy »
 

Offline Fozzie

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Re: Why won't my magnets repel each other?
« Reply #10 on: 08/12/2010 11:55:53 »
Quote
Fozzie could you take a photo and paste it?  Cos frankly this is all a bit weird.  What do they look like, are they a single material, heavy as lead/light as aluminum?

I'll try a do some photos this evening. They weigh about what I expect iron or steel would weigh but I'll give you some more precise data tonight. And here was I thinking this one would be answered in one post!
 

Offline imatfaal

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Re: Why won't my magnets repel each other?
« Reply #11 on: 08/12/2010 12:11:48 »
Fozzie - no this is a tricky one. As Foolosophy states and shows above; magnets have poles and the "field lines" are loops, not lines that disappear off into the distance (which is what a magnet with only one pole would do). 
 

Offline Foolosophy

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Re: Why won't my magnets repel each other?
« Reply #12 on: 08/12/2010 13:48:05 »
If you force 2 magnets together (ie like poles) and then tape them up, you get a single magnet that has identical poles on either end.

try it.

I am not sure what happens over a long time though - maybe this state reverses or even magnetism diminishes to zero 
 

Offline imatfaal

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Re: Why won't my magnets repel each other?
« Reply #13 on: 08/12/2010 15:29:30 »
I will try it - but I think that you either have two magnets very close to each other, or you have one larger and much weaker magnet with a north and south pole (I would guess the NS alignment would follow the stronger of the two).  there are no magnetic monopoles - find one, get a nobel nod.
 

Offline Foolosophy

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Re: Why won't my magnets repel each other?
« Reply #14 on: 08/12/2010 16:03:23 »
I will try it - but I think that you either have two magnets very close to each other, or you have one larger and much weaker magnet with a north and south pole (I would guess the NS alignment would follow the stronger of the two).  there are no magnetic monopoles - find one, get a nobel nod.
identical magnets that are physically in contact with one another at like poles - taped together

try it - see if you get the same effect as me

not sure what actually happening - whether field leakage is occuring or its a transient thing
« Last Edit: 08/12/2010 16:06:56 by Foolosophy »
 

Offline Fozzie

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Re: Why won't my magnets repel each other?
« Reply #15 on: 08/12/2010 17:12:35 »
OK, I have had another play with these things and found that this time they were repelling when I picked them up! Further examination revealed that they do indeed have poles, but not in the way I expected. You have to TURN THEM OVER to reverse them. SO I still don't quite understand what's going on.

You can see a short video I made of this at www.fuchsiamagic.com/misc/magnets.avi 

Sorry for the TV sounds in the background!  [:I]
 

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Offline Foolosophy

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Why won't my magnets repel each other?
« Reply #16 on: 09/12/2010 02:42:11 »
Shrunk
So you only tried 2 faces of the magnet?

in a retangular bar magnet there are 6 sides - like a dice

You didnt try all the combinations before assuming you had discovered the world's FIRST mono-pole permanent magnet whose very existence violates the laws Physics?

........interesting
 

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Offline Foolosophy

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Why won't my magnets repel each other?
« Reply #17 on: 09/12/2010 06:30:00 »
Shrunk
OK, I have had another play with these things and found that this time they were repelling when I picked them up! Further examination revealed that they do indeed have poles, but not in the way I expected. You have to TURN THEM OVER to reverse them. SO I still don't quite understand what's going on.

You can see a short video I made of this at www.fuchsiamagic.com/misc/magnets.avi 

Sorry for the TV sounds in the background!  [:I]

Did you not understand?
 

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Offline Fozzie

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Why won't my magnets repel each other?
« Reply #18 on: 09/12/2010 10:37:37 »
Shrunk
No, that's why I asked the original question. The confusing thing about these magnets to me is that their poles must lie on their opposite sides rather than at the ends. Not what I would expect from a bar magnet! Thanks for all the replies anyway. Next time, I'll do some more exchaustive checks before posting!
 

Offline CliffordK

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Why won't my magnets repel each other?
« Reply #19 on: 09/12/2010 10:48:34 »
You can get the magnets polarized through any face or direction. 
I believe a lot of "motor magnets" are polarized through their flat faces.

They are probably a lot stickier through the flat faces too..  perhaps good for a refrigerator magnet, or a number of other odd applications.
 

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Why won't my magnets repel each other?
« Reply #19 on: 09/12/2010 10:48:34 »

 

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