CHARLES D. WINTERS / SCIENCE PHOTO LIBRARY CHARLES D. WINTERS / SCIENCE PHOTO LIBRARY
Magnetism. Horseshoe magnet pulling iron strips out from a mixed pile of copper and iron strips. Magnetism is a manifestation of one of the funda- mental forces of physics: electromagnetism. Iron filings display very strong magnetic effects known as ferromagnetism. The magnetic effects are due to moving subatomic particles called electrons. They have an angular momentum (spin) which gives them a magnetic moment so that each filing acts like a tiny bar magnet. In iron the electrons' magnetic moments point in the same direction when a magnetic field is applied. The moments add up to make the iron strips act like bar magnets and so be attracted towards the original magnet.
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