Describe the motion of electrons in an AC current. Well, picture a tube of tennis balls. Direct current is when you take a ball and push it in one end causing one at the other end to pop out. Alternating current on the other hand is when you push a ball in one end and it pops out the other, then push one from the other end and this pops out from the former. Over time, for a constant frequency AC, the total change in distance for any ball inside the tube is zero.