I’ve never fully understood how compasses work, and how the magnetic North Pole can affect them. Like how aren’t other things affected by it? And apparently the magnetic North Pole also moves? Please help me make it make sense!
In: Physics
Have you noticed that the closer to a magnet you get something the stronger that magnet works on it? And that for a bigger magnet, it works from further away but it still needs to be close in order to be really strong?
Inside the earth is basically a big magnet. This magnet is HUGE and strong, which means that the effects of it can travel *very* far (from where it is in the earth to most of the way past the earth’s atmosphere). But because it is still a magnet, the strength of its effects falls off exponentially. This means that every single thing on the earth is feeling this magnet, but because we are most of the earth’s radius away from it we don’t feel it very strongly (and in fact have grown used to it enough to just not notice it most of the time).
So because everything on the earth’s surface is being affected by the magnet, if we have tools sensitive enough to them we can measure the magnet. And one of the important parts about a compass is that they are *very* easy to spin, so that even the small amount of magnet that they can feel will still push the needle around. And what that needle does is have one side that is attracted to the ‘north’ pole of the earth.
As for the poles moving? Much of our understanding of the magnet’s details comes from paying attention to that. We now know that this magnet is about at the center of the earth, we know that it’s spinning, and we know that it’s moving. We know that its ‘north’ pole pointing ‘actual north’ is a happy coincidence, and that throughout geological history this hasn’t always been true (though for the last thousands of years of civilization it’s always been at least northish). It’s the explanation that makes the most sense for how we’ve seen the poles move, and it is also what has allowed us to predict where the poles will move in the future (and have done that accurately so far).
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