Question about magnets?

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Alan in Little Washington

Alan Schaffter
Corporate Member
It may seem O.T. but actually it is exactly in the right place.

Anyone up on magnetism, magnetic lines of force, etc. theory and all that physics stuff?

I am building something that will have three small, cylindrical rare earth magnets. The magnets are 1/8" dia. X 1/16" thick and will be mounted in pockets spaced about 1/4" apart in a 1/8" thick piece of (non-magnetic) aluminum. I want to make sure the poles are lined up properly so the magnets hold the piece of aluminum to ferrous metal with max force.

If there were just two magnets I think I would know how to do it- it would be like a horseshoe magnet, but three magnets confuses me. The diagram below shows how I think they should go, but I am not sure. I don't show the piece of aluminum since it has no part in the problem, it just supports the magnets. The red represents a ferrous surface that the aluminum/magnets will be attached to. I guess I can put two magnets on a piece of iron and see what happens when I try to add the third one, either between the two or at the end. If the third magnet is attacted to the iron then that is how it should be mounted. But what if the third magnet can be attached either way? Or should I just try to go with two magnets?


LMM_magnets-1.jpg
 

mlzettl

Matt
Corporate Member
Alan,

Theory is great, and it is certainly admirable to know why things work the way that they do, but sometimes it is just better to be pragmatic. I would make up two trial pieces of aluminum, and then just measure the force required to pull the aluminum/magnet assemblies off of the ferrous metal. One could use a simple small spring scale, like a fish scale, to do this. Knowing how meticulous, thorough, and intelligent that you are, I am sure that you have already thought of this, but are just seeking the scientific explanation. Sometimes though, you just need to get on with it. ;)

That being said, I will be interested to hear the scientific explanation and the physics behind it if anyone here knows it.

Matt
 

jerrye

New User
Jerry
I always thought that pole position only mattered when mounted magnet to magnet. Is there a difference in pole position otherwise? I would be interested in this answer too.
 

Jim M.

Woody
Corporate Member
Allan, it looks good to me; if I recall correctly when you place the north pole of one magnet near the south pole of another magnet, they are attracted to one another. When you place like poles of two magnets near each other (north to north or south to south), they will repel each other. So if you place the poles alternately north/south in a chain they should produce the desired effect you're looking for. Jim
 

tarheelz

Dave
Corporate Member
Assuming the magnets are physically affixed to the aluminum (e.g. glue, epoxy, screws, etc.), then, as Jerry notes, in theory it will not matter how the three are arranged. N and S are each equally happy to bind themselves to iron and thus the aluminum will be stuck to the iron as well.
 

aplpickr

New User
Bill
Heart pendant.jpgMy grandson made a heart pendant/locket for his girlfriend. It was held together with 8 rare earth magnets. It was turned and carved from olive wood. It has been worn daily for 4 years with no problems. The magnets were all oriented the same way.
 

batk30msu

New User
brent
I cannot imagine much of a measurable difference but you could always use a compass to make sure the poles are alternating (as your drawing shows) and compare it to the strength of the same set up with the poles all lined up in the same direction.
 

Gotcha6

Dennis
Staff member
Corporate Member
I would think that the distance between the magnets would dictate the necessity of proper polarity orientation. Magnetic attraction drops exponentially with distance, so at some point, the effect of improper polarity would be negligible in an application. Perhaps you could make up your prototype and sprinkle some iron filings around it when it's attached to a steel or iron top to see what the fields are doing. I always wanted to do this with a magnet in a jar of water.........
 

Jeremy Scuteri

Moderator
Jeremy
The big difference between a horseshoe magnet and what you have is the fact that the "horseshoe" is a ferrous material which allows the magnetic flux to travel inside the horseshoe instead of in the air. You may be able to improve the holding power by using a ferrous metal instead of aluminum to hold the magnets. I am interested to see what you come up with.
 
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