Science Buddies: "Ask an Expert"

Hi! I'm building a "train" using a "tunnel" of curled copper wire, a AAA battery and a pair of neodymium magnets. the magnets are stuck on either side of the battery and the battery runs through the tunnel; it becomes a "train". I am struggling to find an explanation for why this happens. So far I have 2 possible explanations which i do not really understand:
1) The coil touches each magnet (so the + and - sides of the battery) and forms a circuit which turns the section of wire into a solenoid that turns the battery into an induced magnet which is shot out and the process continues as the battery moves to a new section of wire. can a battery be magnetised by the solenoid it powers? i would have thought that the magnets are pushed out of the solenoid and take the battery for a ride?
2) The inverse of a homopolar motor is created: i understand a homopolar motor to be a battery connected to a magnet with a coil of wire attached to each end of the battery. the right-hand rule shows that the force perpendicular to the magnetic field and the movement of charge is in a direction that makes the wire spin. in the train the section of wire cannot spin so in this case the "charge" remains still and the force pushes the magnets out of the tunnel with the battery. the wire has been curled and goes round the battery so I can kind of see how the force would go forward rather than inducing torque. however I have tried to apply the right hand rule from many points of reference and always end up with a force going into the battery from the side rather than pushing it forward. I am probably doing it wrong.
i would be so grateful for some help please

Hi Valarie,

Good job trying to think this through! Your explanation in #1 is almost there, you just have one thing confused. "The coil touches each magnet (so the + and - sides of the battery) and forms a circuit which turns the section of wire into a solenoid" - that part is right. When current flows through the solenoid it generates a magnetic field. That magnetic field pushes on the *magnets* that are attached to either end of the battery, which makes it move. So "can a battery be magnetised by the solenoid it powers? i would have thought that the magnets are pushed out of the solenoid and take the battery for a ride?" - you're right, it's the magnets that are getting pushed out of the solenoid, and the battery itself is just along for the ride (MAYBE the metal in the battery itself is also magnetized, I'm actually not sure - but my guess is that the vast majority of the "push" comes from the neodymium magnets and not the metal in the battery).

Some of these concepts are covered in our electricity and magnetism tutorial if you haven't seen that:

https://www.sciencebuddies.org/science- ... omagnetism

I did a quick google search and it looks like someone made this page in response to a popular YouTube video showing the magnetic "train":

http://skullsinthestars.com/2014/12/12/ ... tic-train/

Hope that helps!

-Ben

Thanks so much Ben!