Q: "How can a compass work on a Flat Earth?"
A: The magnetic field is generated in the same fashion as with the RE (Diagram). Thus, the magnetic south pole is near the geographic north pole, just like on the RE. The magnetic north pole is on the underside of the Earth. The Ice Wall is not the south pole, but acts as it, as it is the furthest from the center of the earth that you can follow the magnetic field. The field is vertical in this area, accounting for the aurora australis.
This is wrong, and I'm going to show you why.
Let's say we have a magnet. Most of you will be familiar with similar diagrams such as this:
What I'm showing here are the lines of magnetic flux decreasing in strength with greater distance, but this doesn't mean much if we don't know its polarity, so let's give it poles.
You'll notice now that the lines of magnetic flux move from the north pole to the south one while outside the object (and from south to north while inside it). What does this have to do with the shape of the Earth? Well, let's bring another magnet closer to this field and see how it acts.
The magnet I've put next to it is a compass, with its red side designating north and its blue side designating south. We can move this compass anywhere around the magnet and watch it trace out exactly where the lines of magnetic flux are located. Any dipole can do this. Notice how it acts when we approach the poles; north opposes north but attracts south. South opposes south, but attracts north. Opposites attract and likes repel. Now, let's see what happens when we change the shape of the magnet. Let's have a spherical one (like a planet), as well as the disk-shaped one the FAQ says to use.
Let's check out the spherical one first. Notice how (following the lines of magnetic flux) it is in most places horizontal (parallel to the ground), only acting strangely when we approach the poles. This is completely consistent with what we observe in the real world. The disk model, however, presents a problem. Let's take a closer look.
The compass isn't horizontal--it is vertical, perpendicular to the ground. Not only that, but it doesn't move much no matter where on the disk you are, regardless of which side of the disk you're on! Since we know compasses don't act in this way, the disk model has a major flaw. Compasses act only in the manner we would predict on a spherical planet. The only way to stick to the disk model is to fix the magnetism problem. I'll play devil's advocate and see exactly what kind of lines of magnetic flux we would need on a disk to have compasses act in the manner we know they do...
Now let's add the poles.
Well this is strange. A magnet that is north in the middle, but south around the edge. Not only does this never occur naturally, it is actually an impossible configuration for a permanent magnet! Okay, let's not make it permanent. I'll play devil's advocate one step beyond too far and say there are two gigantic copper coils with some serious current flowing through them to induce this magnetic field manually.
Hrmm, notice how the northern poles in the middle oppose each other? That's why this doesn't occur naturally--it would fly apart.
So there you have it. A simple compass hints at the shape of our planet--not telling us exactly what it is, of course, but certainly telling us exactly what it
isn't. Not only have I shown how magnets act in relation to each other, I bent over backwards to fit the disk model. Using the model the FAQ states does not properly explain the direction of compasses (in the disk model, compasses point vertically instead of horizontally). Trying to keep with the disk shape, I was forced to break from the failed model and bent over backwards to create a magnetic form that would explain compass directions. There are no natural magnets of such a configuration, and artificially made ones would force themselves apart. The planet can not be a disk, and magnets do not act in the manner proposed by the FAQ; therefor, I move that this section of the FAQ be altered or removed, as it does not fit the data. If you have a problem with any steps in this process, please tell me exactly where it is.