The takeaway lesson here is that a loop of current will behave pretty much the same as an ordinary permanent magnet; that is, North and South poles will attract, while North-North and South-South combinations will repel.
This immediately gives us a simple explanation of how the “magneto-electric train” works! When we place our battery, capped with magnets, inside the coil, we complete a circuit and a current flows through the coil. The coil is, in essence, multiple loops of current stacked on top of one another, and the result is that the region of coil between the permanent magnets is a magnet itself!
We illustrate the situation below. What happens: the “virtual bar magnet” created by the current flowing through the coil pushes the magnet in front and pulls the magnet behind. Of course the battery between them gets taken along for the ride!
trainexplanationThis highlights an important point that wasn’t covered in the original video above — at least according to my experiments, it is necessary to make sure that the two magnets on either end of the battery have their North poles pointing in opposite directions! Otherwise, they are either both pushing or both pulling, and the “train” doesn’t move.
Here’s my own short demonstration of the “magneto-electric train.” It is surprisingly easy and cheap to put together. I used a AAA battery as the power source, and a pair of strong neodymium magnets I had on hand; to give the train more “oomph,” additional magnets could be used on either side of the battery. I used 18 gauge copper wire for the coil, and wrapped it around a 1/2” ring stand to coil it. It is important that the wire be uncoated — otherwise current will not flow and nothing will happen! The 18 gauge wire seemed like the right balance of being easy to bend but rigid enough to hold a shape. Also, it was all I could find at short notice.