| MadSci Network: Earth Sciences |
This one had me stumped for a while. Aside from happening to find magnetite ore (the old fashioned "lodestone" that mariners used), I wasn't sure how you could do this. If you happen to be backpacking near an old magnetite mine, you'd be all set, but magnetite ore isn't exactly common (magnetite is, but there is usually not enough of it in a rock to give significant magnetism). I did some poking around and I found one curious reference from Moby Dick in which tapping an iron shaft causes it to become magnetized and then it can be used to fashion a compass. See: http://www.melville.org/diCurcio/124.htm Impacts can damage magnets and diminish their strength, but I have never heard of it being used to induce magnetism. As I said, curious. You really need a magnetic field of some sort to magnetize your needle. One way to generate a magnetic field is with an electric current. A straight current-carrying wire has a circular field induced around it. If you coil the wire, you produce a linear field along the axis of the coil (this device is known as a solenoid). An iron or steel core in the solenoid produces a classic electromagnet. So, if you had an bit of insulated wire and bolt or one of the pins that sometimes hold packs to frames (as long as it isn't aluminum) and a battery, you should be able to fashion an electromagnet and use that to magnetize your needle. I have to say that I have never tried to do this, but the American Academy on Physics Teaching publishes a book of activities (Teaching About Magnetism, by Robert Reiland) which includes using a solenoid to magnetize a needle and then map out the magnetic field: http://oliver.aapt.org/aapt_forms/catalog/description.cfm?ID=WSP%2D07 This should have details on how to do it. David Smith Department of Geology, Environmental Science, and Physics La Salle University, Philadelphia, PA
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