# Homopolar motor and Lorentz force

My second grader thought making a homopolar motor for her science experiment would be fun. And, it was. Now I am trying to explain how it works and the Lorentz force. Please help me by giving me a very simple explanation to what is turning out to a very complex theory (or law).

• Welcome to StackExchange! In general, questions should be somewhat specific, so reference requests for basic introductions are generally not paid much attention, but you may find the Hyperphysics explanation at hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magfor.html to be a helpful starting point. – DumpsterDoofus Jan 11 '14 at 23:02
• There is current inside the wire - electrons moving from the minus pole to the plus pole of the battery. There are magnetic field lines emanating out from the magnet. On the wikipedia page of the motor, you can see a very nice picture of this. The battery puts the electrons in motion, so the magnetic field from the magnet can push them around, making the wire rotate. – Mathusalem Jan 11 '14 at 23:27
• + I'd never seen that before. What a nifty demonstration! If you have a wire cutting through magnetic field lines a current is induced. Then the reverse has to be true also, and that's what you're seeing. – Mike Dunlavey Jan 11 '14 at 23:40
• Is the magnetic field emanating from the neodymium magnet or is the magnetic field from the battery charging the copper wire? – user37213 Jan 12 '14 at 1:45
• The magnetic field comes from the magnet. The battery provides the moving electrons. Electrons moving in a magnetic field sense a force unless they are completely parallel to the field. – Mathusalem Jan 12 '14 at 10:22