Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: sw20 on 22/05/2020 20:09:14

Title: Sudden polarity reversal in opposing permanent magnets?
Post by: sw20 on 22/05/2020 20:09:14
Hi all,

I'm working with a pair of multi-pole neodymium ring magnets (rated ~119lbF, McMaster-Carr part number 2494N17) and finding that if the opposing poles are forced together, with the magnets in alignment, that at very close range (may be a millimeter or two apart?) the two magnets will suddenly snap together as if one has reversed polarity. There is NO electric current involved, but the only resources I am finding about this phenomenom are related to electromagnets and induced magnetism.

Can anyone point me to a source explaining what's happening?

Thank you!
Title: Re: Sudden polarity reversal in opposing permanent magnets?
Post by: evan_au on 22/05/2020 23:12:30
As they are multi-pole magnets (6 North+6 South on the same side), there will be a rotational force to bring the North pole of one magnet into line with the South pole of the other magnet.
- Since this configuration causes strong attraction, the two magnets will move together (away from your fingers), and you may not feel them rotating by 30 to align.

I suggest that you place a mark on both magnets when they are together (attractive): There are several points, 60 apart where they will be aligned...
- Then separate them
- Press them together when they are misaligned (repulsive)
- When they snap together, see if they are now aligned.

 
Title: Re: Sudden polarity reversal in opposing permanent magnets?
Post by: sw20 on 22/05/2020 23:27:35
I have tried that previously, and just did it again many times for the sake of confirming - they will snap together at any rotational alignment. I notice that it is more difficult (requires more force) in some alignments, but the apparent polarity change happens regardless. It's weird!
Title: Re: Sudden polarity reversal in opposing permanent magnets?
Post by: Petrochemicals on 24/05/2020 16:39:51
Is magnetic force alteratable or does it have to be diffused ?

Edit:

"Polarity of magnetic force" for clarity
Title: Re: Sudden polarity reversal in opposing permanent magnets?
Post by: sw20 on 24/05/2020 21:29:18
Petrochemicals, I'm not following your question. I'm working with two permanent magnets, so not alterable in any way.
Title: Re: Sudden polarity reversal in opposing permanent magnets?
Post by: Petrochemicals on 24/05/2020 22:15:37

Petrochemicals, I'm not following your question. I'm working with two permanent magnets, so not alterable in any way.
if the opposing poles are forced together, with the magnets in alignment, that at very close range (may be a millimeter or two apart?) the two magnets will suddenly snap together as if one has reversed polarity.

It seems to be what you are asking , either the magnets (or at least one) is reversing polarity, or somehow dissipating its force?
Title: Re: Sudden polarity reversal in opposing permanent magnets?
Post by: evan_au on 24/05/2020 23:02:09
Quote from: OP
Sudden polarity reversal in opposing permanent magnets?
As they are two identical magnets from the factory, I do not think that one is suddenly reversing polarity.

Especially since, after you separate them, they still have a strong repulsion at certain angles. It's not like one suddenly got demagnetised.
Title: Re: Sudden polarity reversal in opposing permanent magnets?
Post by: sw20 on 25/05/2020 00:30:05
With you now. Yes it's clear there is no permanent polarity reversal or full demagnetisation.

Situation appears like a temporary one, but I agree that does not make sense since they are identical factory-produced magnets. Thus the original post.
Title: Re: Sudden polarity reversal in opposing permanent magnets?
Post by: hamdani yusuf on 27/05/2020 14:11:47
Can you show a diagram for this experiment?