Iron filings attracted to a bar magnet. Iron filings are sprinkled over a bar magnet. The magnetic field induces magnetism in each of the filings, which then line up in the field. Although the field is actually continuous, interactions between the filings cause them to accumulate in thin arcing lines. The magnetic field is strongest at the poles, and the iron filings can be levitated to follow the three-dimensional field. As the field weakens away from the poles, the field is no longer strong enough to levitate the filings against their own weight.