- To demonstate how a simple homopolar motor works.
One side of a small neodymium disc magnet is stuck to the level head of a ferromagnetic screw. The screw, in turn, becomes magnetised owing to the strength of the of the neodymium magnet.
The pointy end of the screw can now be stuck to the bottom terminal of a D-cell battery where it hangs freely under gravity since the battery's casing is ferromagnetic and provides a very low fricion connection between the hanging magnet and the battery.
If one end of a copper wire is pressed against the top terminal of the battery using your finger. brushing the other end of the wire aqgainst the rim of the disc magnet completes the circuit and not only causes current to flow but leads to a spinning in the disc.