Why outlets spark when unplugging - EMF & Inductors

Sorry, but your summary is a little off.  An inductor produces higher voltage than what was put into it, when the circuit is opened due to the energy stored in its magnetic field collapsing.  The current produced by this effect flows in the opposite direction to the flow of current when the circuit is closed (when powered by DC).  It’s a misnomer to think of it as the momentum of current, or relate it to water hammer.  Also, circuits generally have flyback diodes to allow prevent the excess voltage from damaging components, so you shouldn’t get a spark when unplugging a well designed inductive circuit.