MadSci Network: Physics |
Turns out, you have company. There are aspects of magnetism that present some deep problems. From one point of view, "fields", whether electric, magnetic, gravitational, or whatever, are just abstractions. Over a long period of time, physicists have observed how various objects interact. Two particles with charges on them can exhibit a rather complicated behavior. The electric and (for moving particles with charges) magnetic "fields" were invented purely to simplify the description of how the objects move. But, funny thing, as we learned more about these things, particularly after the invention of relativity theory, it came to seem more and more like these "fields" described something real. But even to this day, the story of "fields" is not complete: one of the most active parts of physics research is Field Theory. Now that point of view may be a bit much for your science project, but I wanted you to know that you are smart to feel a bit puzzled -- they really are mysterious! When I think of magnetic fields, I think of a mess of invisible rubber bands running next to each other. Magnetic fields (at least those we can make) always run in circles -- they have no ends. And they can be streched like rubber bands too, if you have something, like a conducting fluid, that can "get a grip" on them. When you sprinkle iron filings near a magnet, the little pieces of iron act like little bar magnets and try to line up with the field lines (rubber bands), so you can sort of imagine how the lines run even though you can't actually see them. If you do this with some paper over a big bar magnet, you can sort of see how the lines run out one end, loop around to the other, then continue back through the magnet to make closed loops.