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Why dont magnets around earth fly towards the earths magnetic poles?

  1. May 28, 2010 #1
    Why don't magnets fly to earths magnetic poles? I understand that earths magnetic pull must be strong enough to pull a magnet to the pole, but what is the force required for a magnet to get pulled the over their? How does one calculate whether a magnetic field is strong enough in order for two magnets to pull into each other?
  2. jcsd
  3. May 28, 2010 #2
    At the surface of the earth the magnetic field is very weak, in the region of microteslas. A strong lab magnet is about 10 teslas for comparison. We can walk past most labs without having metal object snatched from our hands afterall! The magnetic field at the earths core is substantial, but remember that we are about 6400km away from it!
  4. May 28, 2010 #3
    On a compass there is a force pulling on its magnetic poles. What is the force of the earth magnetic force acting on a small compass? How strong does the earth's poles need to be in order to pull on a magnet?
  5. May 28, 2010 #4
    Same force, order of microteslas, compass needles are very light so are easily moved.

    The earth and the magnet pull on eachother. The earths magnetic field pulls on all magnets.

    I suppose its a bit like asking why a westerly wind doesnt blow all the cars into the ocean, since it does for feathers.

    Are you simply asking what is the force between two magnets of of known strength?
  6. May 28, 2010 #5
    Well I was looking for the strength of the earths magnetic field acting on an object.
  7. May 28, 2010 #6
    The strength of the earth's magnetic field isn't something that depends on the thing you're testing it with. The forces and accelerations due to the earth's magnetic field change though [pedantic language point].

    I really don't understand magnetism, despite knowing enough mathematics to model quite a lot of phenomena caused by it.

    Where does the magnetic force come from? Or how do we predict it?

    F=qvXB I know, but what are the q's and v's in a paper clip that gets stuck to a magnet?
    (Free electrons?)

    For the electrostatic charge, we can say "Right, this thing is + and that thing is -, so they should both experience a coulomb force towards each other". Norths attract souths is the analogue, but both also attract paper clips.
    What's that about?

    Where does "norths attract souths" appear in the equations anyway? What is a north pole?
    (I seem to remember, once had a problem on a sheet that asked to prove that a magnetic dipole is like a tiny circuit loop...but I never did it and don't remember the answer x.x)
  8. May 28, 2010 #7
    I could be wrong here but about the paper clip thing.

    There are free electrons in the paper clip, when put at a positive pole, the electrons are attracted towards it holding onto it.

    When put at a negative pole the electrons are pushed to the far side of the paperclip, giving the side closest to the pole a 'positive' value, therefore attracting again.
  9. May 28, 2010 #8
    I thought all metals had free electrons though, not just magnetic ones (of which there are fairly few I think? Fe, Ni, Co? God, school feels so long ago)
  10. May 28, 2010 #9
    If you drop a magnet a couple times will it land one way or the other over and over?
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