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How does a compass work?

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Hello and welcome to CoreFacts, where we're always short on time and big on science. I'm Steve Sobieszczyk. So...

How does a compass work?

The needle of a compass is a small magnet, one that is allowed to pivot freely. When the needle experiences a magnetic field either from a nearby magnet or the Earth's magnetic field it moves. The reaction to this movement is the needle's preferred alignment this magnetic field. The ‘north' end of the compass needle is simply the north end of the magnet, and it is the end of the compass needle that points in the general direction of the geographic north pole; naturally, the ‘south' end of the compass needle is the south end of the magnet and it points in the opposite direction, towards the general direction of the geographic southern pole. Having said this, the preferred directionality of a compass can be affected by local interference in the magnetic field, like those set up by (say) a near-by electrical system; a compass can also be affected by local magnetization of the Earth's crust, particularly near large igneous or volcanic rock deposits.

And now you know. Join us every weekday for a new CoreFact. If you have a question you think we should answer on the air, email it to us at corefacts@usgs.gov or leave us a voicemail at 703-648-5600; long distance fees do apply.

The USGS CoreFacts is a product of the U.S. Geological Survey, Department of the Interior.

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Title: How does a compass work?

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Date Recorded: 4/21/2008


Usage: This audio file is public domain/of free use unless otherwise stated. Please refer to the USGS Copyright section for how to credit this audio.

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USGS CoreFacts


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