My 3⅓ year old nephew was playing with a magnetic construction kit (rods with magnets on both ends, steel balls; you’ve probably seen them); I was helping. We were testing which materials were magnetic and which were not. His naïve understanding seemed to be that metal things would stick to the magnet and other things (skin, plastic, cardboard) would not; except for the toy cat, which has fridge magnets in its feet so obviously would stick. I tried to surprise him by showing him some coins and asking him whether he thought they would stick to the magnet. “Oh yes” he said. I was the one that was surprised when a 2p coin stuck to his “magnet crane”.
It turns out that “copper” coins from 1993 stick to magnets; those produced up to 1990 do not. And evidently I’ve stopped playing with magnets or I would’ve known this simple fact.
Bet that’s not on the AQA Physics exam.
code monk 
2007-06-28 at 10:03:21
Coolest thing about geomag is how the ball-bearings acquire magnetic polarity depending on how many of each polarity magnet are attached to them. Took me a bit of practice to get the hang of this, and it makes a world of difference to the strength of the resulting structures.
(For instance, you *can* attach (say) 4 N poles to one ball, but it’s a whole lot stronger with 2 N and 2 S).
We had a *lot* of geomag; unfortunately it all went to the children’s other home, so I don’t get to play with it any more.
2007-06-28 at 14:34:46
The Royal Mint’s specifications say that 2p and 1p coins have been copper-plated steel since 1992.
2007-06-28 at 17:00:45
I knew that sort of document would be around somewhere, thanks.
My mother’s partner suggests that some coin operated machines use a magnet as a cheap way of rejecting fake coins. Sounds plausible, because it also explains why coin operated machines no longer take 1p and 2p coins.
2007-07-04 at 10:28:41
did you know if you swallow two magnets separately they can stick together across your intestines?
2007-07-04 at 13:07:33
Is that a rhetorical question?