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Hi! Thanks for your help with previous questions. I have a question for you guys involving a compass and the earth's magnetic field. I REALLY want to be SURE about this answer. Would a compass spin around in circles if it were directly on the magnetic North Pole? If not, Why? If so, would there be a way I could reproduce that spinning in some sort of experiment? Maybe like putting the compass (or some sort of charged needle or pole) in a circular magnet... what do you think? Thanks for your help!
Question Date: 2009-09-30
Answer 1:

A magnet at a location on earth such that the magnetic force lines are orthogonal to the surface would exert a force to orient a bar magnetic parallel the forces lines, hence vertical... there would be no net magnetic horizontal force. So if a compass needle was set spinning AND there was no mechanical friction it would continue to rotate. In reality however the magnetic force is neither exactly up down nor stationary so its a moot point

Answer 2:

No, the compass needle would not spin. At the magnetic pole, the magnetic field lines of the Earth are coming vertically out of the ground, which is perpendicular to the orientation of the compass. This means that the magnetic field is exerting torque on the compass needle, but perpendicular to the plane in which the needle can rotate (determined by the pivot point of the needle). As a consequence, the pivot point itself will exert opposing torque so that the needle won't bend out of its plane of rotation.

Now, if your compass were not held horizontally, then that would be a different story. Now, the magnetic field will rotate the compass needle to point downward (if on the magnetic north), or upward (magnetic south).

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