When you put two loose magnets close to each other, odds are that they will close the space between each other, usually quite quickly. But why? Because they attract? But don’t they also repel?
It is possible to align two loose magnets such that they have similar poles on their nearest sides. In this arrangement, you can carefully push one magnet and see that it repels the other one, pushing it in the same direction. But if you push too hard, or turn the magnet, they will stop repelling and start attracting, and snap together.
Based on this observation, it seems to me that magnetic attraction is effectively more powerful than magnetic repulsion. But my understanding is that the two behavior are equal components of the same force-thingy. If that makes any sense.
My co-worker has a theory that attraction is a function of surface area, while repulsion is a function of the magnetic field. I kind of think that’s hooey. If this were true, then you would see magnetic iron filings fly apart more frequently than fridge magnets. In my extensive electromagnetism laboratory background (i.e. 1 day in high school science class) I didn’t see this happen.
My argument is that repulsion is purely a function of the magnetic field, but attraction works both on the field and on the physical materials of the magnet - in much the same way that you can magnetically attract but cannot magnetically repel an otherwise ordinary piece of iron. My co-worker thinks that this combined with my profound dislike of country music is a sign of dementia, and has threatened to call the authorities.
So…my sanity is apparently on the line. Someone help me out here!
I’d say it’s simpler than that. When two magnets are repelling each other, the repulsive force decreases as the distance between them increases - so repulsion effectively limits itself. But when they’re attracting each other, the attractive force increases as the distance beween them decreases - so attraction is a positive-feedback effect.
If you offer up the South pole of a bar magnet to the South pole of another, the “slave” magnet can either move straight away or skew around. There isn’t a self-correction mechanism going on to bring it back into line. But if you offer up South to North, everything stays lined up.
You can’t magnetically repel an ordinary piece of iron, simply because the presence of a magnet induces temporary magnetic poles which are always opposite to the magnet you’re holding up to it. (But a few substances do spontaneously exhibit same poles - look up “diamagnetism” for this uncommon and weak phenomenon. In other words, you can hold up a powerful magnet to a diamagnetic material and it will be spontaneously repelled.)
It’s not a matter of attraction being stronger than repulsion (the strength of the field–of a symmetrical magnet, anyway–is the same regardless of which orientation it is in) but rather one of stability. Try this out for style; take a quarter, and with just your fingernail, push it across your desktop. Notice how difficult it is to make the coin go in a straight line. Now, pressing down lightly on the rim of the coin, pull the quarter toward you, while observing how it naturally tends to go straight. Ditto for magnets; because the center of gravity of the magnet is close to (or if geometrically symmetrical, as most magenets are) coincident with the locus of the magnet field, it is horribly unstable when pushed, but very stable when attracted.
One comment you made bothers me:
This will never happen with a permanent magnet, although it is certainly possible with a weak non-permanent ferromagnet, like an iron rod weakly magnetized and then forced into a strong magnetic field. The reason you always attract nonpermanent, diamagnetic, or paramagnetic substances with a magnet is because they induce a sympathetic magnetic field in that substance. So neither you nor your coworker are strictly correct in your assertions. Go shake hands and buy each other a beer.
See the Wikipedia entry on magnetism for more detail. (Not the best source–the article is a little messy–but the quickest thing I can come up with while running late for work.)
Stranger
Both poles of both magnets are interacting with each other; unless you happen to present the magnets to each other so that all poles are aligned along a single axis, then the repulsion won’t just push the magnets away from each other, it will push them slightly to one side as well - thus rotating them slightly and bringing the attracting pole closer, and the closer it gets, the more attracted it is (and this relationship is not linear).