Final answer:
Current can flow through an uncharged metal wire due to the free electrons responding to an applied electric field from a voltage source, drifting from the negative to the positive terminal.
Step-by-step explanation:
Even though a metal wire is uncharged, it is possible for a current to flow through it due to the presence of free electrons in the metal. These electrons are not tightly bound to any individual atom and can move through the metal when an electric field is applied.
The electric field, created by a difference in electric potential from a voltage source, exerts a force on the electrons, causing them to drift from the negative terminal to the positive terminal of the voltage source. Despite numerous collisions with atoms within the wire, this drift of electrons constitutes an electric current.