> It takes energy to lift these filings. Where does that energy come from? (It never seems to be exhausted.) That's potential energy. When you made the magnet,

> It takes energy to lift these filings. Where does that energy come from? (It never seems to be exhausted.) That's potential energy. When you made the magnet, you created a potential between everything else and the magnet. When you unmake the magnet, you change the potential again in the other direction. Changing said potential consumes energy. The potential can be exhausted as only so much mass/magnetic-potential can fit within the magnets field. To use the field with more stuff, you have to pull some stuff out of the field, which takes energy.