I'm not sure who I saw do this first. It might have been David Keenahan? But whoever it was, I was reminded of it this week, while working through the periodic table with a Junior Cycle group and trying to convince them that everything they can see around them (stones, soil, wood, their desks, their pens, themselves...and whatever else they can think of) are all manufactured from the same 92 naturally occurring elements. And while also working through magnetism with a 6th year group.
It's a great demo that covers so much....
it lets us see that there's iron (or at least something that responds to a magnet) in a cheerio.
helps students understand that the food they eat is made from the same elements as the rest of the world.
it demonstrates the presence of magnetic fields.
it's sort of fun.
its easy to do and (unlike so many physics demos) it actually works reliably!
Apparently each individual cheerio contains about 15 micro-grams of iron. Which isn't much, and that's why you need to use very strong magnets to see this effect. And it wouldn't create a strong enough force to move the cheerio on a table top - the frictional forces are far too strong. But on water, with its very small limiting friction, the effect is easily strong enough to move the cheerio around.
I think I got the magnets from here, but there are plenty of suppliers in the eurozone too.
Several sources say you can remove visible quantities of iron from breakfast cereal by grinding them down and moving a magnet above the remaining powder. We've tried it here, but haven/t got it to work (yet). I'd love to hear from anybody who has - particularly if they have pictures....