The invisible force around a magnet spreads out in curved lines. You can see those lines in three dimensions by filling a plastic bottle of baby oil with tiny steel fibers cut from extra-fine steel wool. Hold a magnet against the outside and shake gently. The fibers swing into alignment and trace the curved field lines through the oil. Move the magnet around the bottle and the pattern shifts in real time.

Magnetism pulls iron objects toward a magnet. Tiny steel fibers made from extra-fine steel wool respond the same way. You mix the fibers into baby oil inside a plastic bottle and hold a magnet near one side. The fibers align themselves, making the invisible pulling force visible.