Magnetization properties: Help!

[Phlosphr]

OK I have a quick question. I was sitting at dinner with my wife and the most peculiar thing happened, I noticed one of our forks (one that we have had for over ten years) was now magnetized? What the heck could have happened to it? The only thing I can think of is that it was dropped somehow, the right way and it suddenly became magnetized??? I am really not sure however. Does anyone know how this could happen? I know there are some physics brains out there who can tell me what happened…Need to know. thanks folks…

[Mangetout]

I think it is possible, but I’m not sure how it works; when I was at school, some of my fellow pupils would deliberately magnetise the metalworking files (by banging them together or something), making them harder to use (filings of ferrous metals would stick to them)

[cynic]

Some alloys can become temporarily magnetized when they are exposed to a magnetic field. There are two possible sources for magnetic fields in your house that I know of: 1) prolonged contact with a permanent magnet, such as a refrigerator magnet, and 2) exposure to a magnetic field induced by an electric current, such as the wiring in your kitchen.

I am a little surprised that your fork became magnetic, because I thought most silverware was made from austenitic (300 series) stainless steel, such as 18/8. You must have ferritic (400 series) stainless steel silverware.

[Mangetout]

I found this:

It is also possible to magnetise metal with a hammer and the earth’s magnetic field (FIG. 3): Place the nail/needle against the ground aligned with magnetic North/magnetic South, the raised end pointing South in the Northern hemisphere, North in the Southern hemisphere. The angle that the earth’s magnetic field enters the ground (angle A) - the angle to which you elevate the rod - unfortunately varies from place to place; it is 68 degrees in England, but between 62 and 80 degrees around Europe.
This angle of elevation should be as accurate as possible, though good results can be achieved with up to 10 degrees error either way. Hit the positioned metal with hammer, and with trial and error,and time, you should be able to produce a magnetised compass needle this way.

[El_Zagna]

Wow! How does this work, though? What’s the physics behind it?

[cynic]

It works by using the earth’s magnetic field to align the pin’s microscopic magnetic domains, which should become “loose” when the ferromagnetic object is struck by a hammer. Basically the same process involved as when you leave a nail on a magnet overnight, only this is much faster.

[femtosecond]

Anyone remember the MacGyver episode where he has to get an antidote vial out of a gully drain? He magnetized a metal pole by banging it against a hydrant(?) and it worked great. No stinkin’ aligning. Or maybe they cut the scene where he computed the inclination and declination.

[Phlosphr]

Maybe Phlosphr’s wife dropped said fork and it magnetized itself. And the inclination was a perfect match to the earths gravitational merridians(sp?)??? I am really not sure. But one thing I would like to know the physics behind this type of magnetization… It is quite fastinating…

[Chronos]

The thing with iron (and other ferromagnets) is that the magnetic domains try to line up with any external magnetic field. Neighboring domains then have an even stronger field present (original plus the field from the magnetized domains), so it’s even easier for them to align. It’s this chain reaction that makes spontaneous magnetization possible, even if the original field is very small (like the Earth’s). So why doesn’t it happen more often? Because the domains are, to some degree, stuck in place, and you need to put in some energy to get them to move. Heating and hitting it are two possible ways to do this.

[Phlosphr]

Thanks Chronos, You spurred an idea…I bet this happened in the Dish washer. It must have, heat and shock would both be present. It is pretty extraordinary I think… Thanks all!