Why outlets spark when unplugging - EMF & Inductors

FYI . . .

Flux and Change . . . synonymous  . . . the same word

I tend to think of it as dropping a bowling ball from the top of World Trade Center . . .
and having a sheet of glass at each floor to stop the ball if possible . . . 
(the glass represents the gap you create when you open the switch)
if the first pane does not slow it down sufficiently it will continue to pick up speed on the way down . . .

likewise the arc is picking up momentum in its state of flux (change)