The Kid Should See This website has posted this neat electromagnetic train
that is easily built. Neodymium magnets are attached to each end of an AA batter, and fed into a coil of bare copper wire. The magnets are conductive and cause current to flow in the copper wire which creates a magnetic field around the magnet battery assembly. A force develops between the fixed magnets and the field produced in the copper wire by the battery, and propels the battery magnet assembly through the coil of copper wire.