OK, we’re going to get scientific for this bit so make yourself a cuppa and bring your concentration face! A homopolar motor creates rotational movement because of what is known as the Lorentz force.
What’s happening is that electrical current is flowing from the positive terminal of the battery to the negative and into the magnet. This current then flows from the centre of the magnet to the edge where the wire connects, it travels up the wire back to the positive terminal of the battery and the circuit is complete.
Simple. But how does this generate movement you may well ask? Well, the key is the direction of the current and the magnetic field produced by the permanent magnet. We’ve put together the below diagram to support the explanation. The direction of the magnetic field is demonstrated by the red arrows and the direction of current is shown by the blue arrows. As the current travels perpendicular to the magnetic field, a Lorentz Force is exerted on the on the conductor (the wire) which again is perpendicular to both the direction of the magnetic field and the current, generating the spinning motion.