CORDELIA MOLLOY / SCIENCE PHOTO LIBRARY CORDELIA MOLLOY / SCIENCE PHOTO LIBRARY
Magnetic attraction. Iron filings in a magnetic field generated by bar magnets. The iron filings have a high permeability (the degree of magnetism in a material), which makes them strongly attracted to the magnetic field. The field itself is continuous, however interactions between the filings cause them to accumulate in thin arching lines.
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