Dane McPherson, of Balclutha Primary School, asks :-
How does a magnet pick things up?
Richard Blakie, an electrical engineer at the University of Canterbury, responded.
Magnets stick to very few materials, only those we call magnetic materials.
Magnets are attracted to certain materials, and if the attraction is strong enough they can hold on even when upside down. If you've played with magnets you might have seen that two magnets either repel each other (North pole to North pole or South pole to South pole) or attract each other (North pole to South pole).
So why does a magnet always stick to a magnetic material such as a fridge door made of painted steel , no matter which way around it is? If the fridge door was a magnet then sometimes a magnet would be attracted and stick, and some times it would be repelled and fall off. Well, when a magnet comes close to the door it makes some of the metal into a magnet - if the North pole of the magnet is closest to the door then the surface of the door becomes a South pole and if the South pole of the magnet is closest to the door then the surface of the door becomes a North pole. This means that a magnet will always be attracted to the door.
Not all metals are the same, and not all attract magnets in this way. Metals with iron in them - like the steel under the paint of the fridge door - are magnetic but not always. Some stainless steels aren't very magnetic. Most other metals such as aluminium are not magnetic materials. Try sticking a magnet to an aluminium drink can and see what happens. What about a can of baked beans?