• Quick note - the problem with Youtube videos not embedding on the forum appears to have been fixed, thanks to ZiprHead. If you do still see problems let me know.

Magnets repelling metal

Here's a stab.....

A magnet has a negative and a positive pole.
Metal consists of molecules which have negative and positive poles
If you present the positive pole of the magnet to the metal object, it attracts the negative poles of these molecules - because opposites attract.
So now you have the magnet's positive pole attracting a multitude of negative molecular poles in the metal.

The opposite occurs if you present the negative pole of a magnet to the metal object - it attracts the positive poles of these molecules - again, because opposites attract.
And now you have the magnet's negative pole attracting a multitude of positive molecular poles in the metal.

The difference between the magnet and the metal object is that the molecules in the magnet are all lined up with their positive poles pointing in one direction and their negative poles pointing in the opposite direction whereas, in the metal object, the orientation of these molecular dipoles is random - until exposed to the magnet of course.

BJ
 
A piece of metal can be thought of as a bunch of tiny magnets. Ordinarily, they are all aligned randomly, so no net magnetic field is present. When in the presence of a strong magnetic field, the little magnets all align with the field, just as a bar magnet will align with a strong magnetic field, by spinning. Once aligned, the magnetized piece of metal is going to have its North/South axis aligned the same way as the permanent magnet, and will thus be attracted to it.

You can see the same effect if you put two bar magnets on a nearly frictionless surface, at random orientations to each other. They will spin around, until they are both aligned the same way, and then move together. This is exactly what the tiny magnets in the piece of metal are doing.

Dr. Stupid
 
I suppose then that the reason some metals (i.e., paperclips) continue to be magnetic for a short period after being removed from the influence of the permanent magnet is that it takes a while for all the little magnets (as it were) in the metal to become misaligned again?
 
not quite true

I just checked around a bit, and it turns out that there are some metals that will be repelled by a magnet.

There are three basic categories for the behaviour of materials in a magnetic field: ferromagnetic (things like iron, nickel, cobalt, etc.) in which neighbouring atoms tend to line up their magnetic moments - these materials can be made into permanent magnets; paramagnetic (aluminum and platinum, among others), in which an external magnetic field will cause the magnetic moments to line up in the same direction as the applied field (as in Stimpy's example); and diamagnetic, in which the magnetic moments line up in the opposite direction to an external field.

It turns out that mercury, silver, lead, and copper are diamagnetic, and will be repelled, albeit very weakly (diamagnetism is by far the weakest of the three effects), by a magnet.

You can read more about magnetism here: Hyperphysics.
 
Hmmm...just noticed some errors in my post above.

First, Diamagnetism is not due to magnetic moments lining up, rather it's due to induced magnetic moments (which are induced in the direction opposing the magnetic field). If the atoms in a material have any inherent net magnetic moment, the material will be either paramagnetic or ferromagnetic.

Second, I wasn't really justified in saying that diamagnetism is "by far" the weakest: from what I can tell, it's generally weaker than any paramagnetism that might be present, and that ferromagnetism is generally far stronger than either one.

There may be more errors, but sadly I cannot offer prizes for finding them.

:(
 
Just to make things more complicated...

There are also antiferromagnets, where the magnetic moments for staggered patterns anti-aligned with each other like a checkerboard. Most people don't care about these because they don't have any net magnetic moment (they tend to be weakly paramagnetic in an applied field), but there is some pretty interesting stuff associated with some antiferromagnets (including high temperature superconductivity). There's also ferrimagnetism ("i" instead of "o"), which is like antiferromagnetism, but where the two sublattices of opposite moments don't have the same strength so that you do get a net magnetic moment. And there's even more complicated magnetic arrangements, but there aren't really specific terms for those (which are fairly rare).

One other note, most forms of magnetism are due to the alignment of electrons' spin. Diamagnetism, however, is not due to the electron's spin, but due to its orbit around an atom.
 
The photo is rather misleading as the superconductor is composed of a mixed ceramic that is not magnetic in the traditional sense, no?
 
Joshua Korosi said:
I suppose then that the reason some metals (i.e., paperclips) continue to be magnetic for a short period after being removed from the influence of the permanent magnet is that it takes a while for all the little magnets (as it were) in the metal to become misaligned again?
Click to expand...

I recall from a blacksmithing book that you can take a non-polar iron rod, give it a good whack on one end, and instantly turn it into a magnet. The reason is the whack makes the molecules line up somewhat.

H.
 
You're overlooking one obvious example of a magnet repelling something metal: the same-pole end of another magnet.

COCT
 
a_unique_person said:
Why is it that magnets only attract metal, not repel metal. My 10 year old son wants to know.
Click to expand...
If you hold the magnet backwards, it should repel the metal.
 
Re: Re: Magnets repelling metal

The Central Scrutinizer said:


Because that's the way god created it.
Click to expand...
Interesting Hypothesis... take that to the JREF Institute and try to snatch up that US$1,000,000. Try a more scientific approach. If every question was answered with "Thats the way God made it" then I would should myself in the head with a very big gun... because very big gun make very big holes... because thats the way god made the holes.
 
You must log in or register to reply here.

Back
Top Bottom