North vs. South

Wendy

Joined Mar 24, 2008
23,053
No this is not a political thread. I have a bunch of powerful rare earth magnets, but I have no idea which the north and south poles are. It occurred to me, glue one to something that floats and put it in a bowl of water. Will the North pole point north or the south? A practical solution to a real world problem. My gut tells me the south pole will point North, but a little voice dissents. Once I have a standard I can use it to identify the poles of the other magnets.

BR-549

Joined Sep 22, 2013
4,928
Have you got a compass?

SamR

Joined Mar 19, 2019
4,407
North pole points to the North Pole where Santa lives and it is actually the south magnetic pole. Same as a compass needle.

Wendy

Joined Mar 24, 2008
23,053
So, North pole of unknown magnet points North? I am not really mobile, I have only one working arm and one working leg.I had trouble gluing a large rare earth to my phone case today. I can't get to the garage to get to either nail, screws, nor wire. Keep it simple guys, I know the direction North is in my house. So does the north pole of the magnet point north? Since I can't get to any tools, or hardware. I am asking what I hope is a simple physics question I don't know the answer. I can't even run the experiment to find the answer.

The one definitive answer I have is the north pole is actually the earths southern magnetic pole. which means the north pole of a magnet points north. Any one care to confirm this?

No I do not have a compass.

BTW, @SamR , thank you for a clear concise answer.

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MrChips

Joined Oct 2, 2009
27,129
Confirmed correct.

The end of the compass needle that points towards geographic north is a north pole.
Hence the earth's magnetic south pole is at the geographic north (but moving fast, about 30 miles per year).

Wendy

Joined Mar 24, 2008
23,053
Never mind, Googled it SamR called it.

@MrChips , Thank you. Learned something new.

BR-549

Joined Sep 22, 2013
4,928
Have you a long, thin piece of magnetizable metal and a string? You can induce a M field in that thin piece with super magnet. By stroking.

Hang mid section of thin piece from string.

Edit: Even a RR spike should work, but probability need a cradle of some sort, to balance it from one string.

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KeepItSimpleStupid

Joined Mar 4, 2014
5,088

joeyd999

Joined Jun 6, 2011
4,602
Got a smart phone?

You got a compass.

Wendy

Joined Mar 24, 2008
23,053
Shoot, I can barely see my phone nowadays. Have to wear reading glasses to see it. As I said I know where North from here is, and I stated the original problem quite clearly. So that last comment was of no help what so ever. Put your pokey stick away @joeyd999 .

joeyd999

Joined Jun 6, 2011
4,602
So that last comment was of no help what so ever.
You wanted to know how to detect north on your miscellaneous magnets.

You said you do not have a compass.

I said yes you do if you have a smart phone.

I was helping -- ever so concisely.

No pokey stick. But, next time, you've earned it.

BobaMosfet

Joined Jul 1, 2009
2,028
No this is not a political thread. I have a bunch of powerful rare earth magnets, but I have no idea which the north and south poles are. It occurred to me, glue one to something that floats and put it in a bowl of water. Will the North pole point north or the south? A practical solution to a real world problem. My gut tells me the south pole will point North, but a little voice dissents. Once I have a standard I can use it to identify the poles of the other magnets.
Very light, small needle.
Bowl of water.
Run needle over magnet (rubbing it) in same direction over and over for a minute. This will magnetize and polarize the needle.
Float the needle in the water (viscocity), or float it on a small leaf in the water.
See that the needle orients to the magnetic poles (you have a compass). Mark your dish for north and south. paint the North end of your needle with red mail polish.
Now put one of your magnet near the dish and see which end of the needle is attracted

BobaMosfet

Joined Jul 1, 2009
2,028
So, North pole of unknown magnet points North? I am not really mobile, I have only one working arm and one working leg.I had trouble gluing a large rare earth to my phone case today. I can't get to the garage to get to either nail, screws, nor wire. Keep it simple guys, I know the direction North is in my house. So does the north pole of the magnet point north? Since I can't get to any tools, or hardware. I am asking what I hope is a simple physics question I don't know the answer. I can't even run the experiment to find the answer.

The one definitive answer I have is the north pole is actually the earths southern magnetic pole. which means the north pole of a magnet points north. Any one care to confirm this?

No I do not have a compass.

BTW, @SamR , thank you for a clear concise answer.
Or you could get fancy and make a hall-effect sensor circuit and it will tell you which end of your magnet is north or south by which way the sine goes.... just saying .

MrChips

Joined Oct 2, 2009
27,129

I made my own very sensitive galvanometer in a similar fashion when I was a kid.
Instead of hanging the needle by the thread, I pierced the needle through a rubber elastic band and suspended the needle by both ends of the rubber band. By using the Right-Hand-Rule you can determine either the direction of the current or the magnetic polarity of the needle.

SamR

Joined Mar 19, 2019
4,407
Float the needle in the water (viscocity)
Spot on! Except its the surface tension of the water that allows you to gently place and float the needle. Any soap residue will lower the surface tension and prevent the needle from floating. Since you already know where north is, that is where the North Pole of the magnetized needle will point. Then introduce your magnets to determine which end repels or attracts.

BobaMosfet

Joined Jul 1, 2009
2,028
Spot on! Except its the surface tension of the water that allows you to gently place and float the needle. Any soap residue will lower the surface tension and prevent the needle from floating. Since you already know where north is, that is where the North Pole of the magnetized needle will point. Then introduce your magnets to determine which end repels or attracts.
Yes, I know. Surface tension is defined by viscocity. I meant 'on' the water, not 'in' it. sorry.

Wendy

Joined Mar 24, 2008
23,053
You wanted to know how to detect north on your miscellaneous magnets.

You said you do not have a compass.

I said yes you do if you have a smart phone.

I was helping -- ever so concisely.

No pokey stick. But, next time, you've earned it.
Given that a smart phone does not use magnetic fields to sense direction. How is a compass going to help again?

crutschow

Joined Mar 14, 2008
30,801
By definition, the north pole of a magnet points north (hence the name ).

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