Steel is ferromagnetic. That means it contains microscopic regions called magnetic domains. Each domain is like a tiny bar magnet with its own magnetic moment. In an unmagnetized piece of steel, these domains are randomly oriented, so their magnetic fields cancel out. Earth itself generates a magnetic field (on the order of ~25–65 microtesla depending on location). That field is weak compared to a neodymium magnet — but it’s not zero. If you align a steel rod along the direction of Earth’s magnetic field (roughly north–south and slightly inclined downward depending on latitude), and then mechanically disturb it — by tapping, striking, or vibrating it — you provide energy that allows domain walls to move. This mechanical energy helps domains that are already slightly aligned with Earth’s field grow at the expense of misaligned domains. Over repeated impacts, more domains rotate or expand into alignment with the external field. Result: the steel develops a net magnetic moment in the ...