I've been reading through my son's physics textbook (junior high) and got puzzled by the chapter on magnetism. I do understand that this is addressing young teens but still, I find the logic presented somewhat confusing. It goes like this:
- Considering rod-shaped magnets, they have a North pole and a South pole. If you put two such magnets together, opposite poles attract and when they snap together, they basically form a longer rod-shaped magnet.
- Thus we might consider doing the opposite: cutting or breaking a rod-shaped magnet in half, which gives us two smaller rod-shaped magnets that, again, have a North and a South pole.
- If we imagine that we keep on doing that (cutting a magnet in two over and over again), eventually we'll end up with some smallest building blocks which we call "elementary magnets".
- Even an iron nail consists of such "elementary magnets" on the inside but the difference between such a nail and a magnet is that the elementary magnets are all oriented identically inside the magnet while they are randomly oriented in the nail.
- If you rub a magnet over a nail, your aligning some of the latter's elementary magnets so that it also (temporarily) behaves like a magnet.
I find this model leaves to be desired.
For one, this whole idea of point 3. seems questionable to a lay person like me: what exactly is meant by "smallest building blocks"? Atoms? Or is this purely an abstract thought?
But more importantly, point 5 seems to suggest that these "elementary magnets" can either move or rotate - so how come they don't auto-align themselves all the time, given that they and their surroundings (i.e., other elementary magnets) are magnetic? As in, if there was one elementary magnet located next to another one but oriented in the opposite direction, shouldn't their poles make it so that they want to rotate away from each other in order to face the same direction?
Even if they just happened to be in some kind of attraction/repulsion equilibrium that's different from all elementary magnets being oriented the same way, why would a temporarily magnetized nail ever lose its magnetic property again?