Hello, I have seen several videos online where a small AA battery with neodymium magnets attached to its poles manages to move inside a coil of copper. I think I understand how the battery moves. would a large coil be better than a small coil to make the battery move faster since the area of the coil increases the magnetic moment of the coil? What if instead of a copper coil we had a tube of copper? I don't think the battery would move inside the hollow tube the same it moves inside the coil. Why?