I know what is circulation by a mathematical point of view, but in the reality (in the physical world), what is circulation? I'm thinking that the electrical current through of a circuit, that the water current through of an pipe or of an river, that the water vortex formed over a drain or that the wind around of a twister are example of circulation. I'm right? Detail: the term "circulation" presuppose that the trajectory of the flux/current is a closed loop, but I don't think so, if the water current through of a pipe or of a river follows an open loop, so the circulation can be computed simply how the flux/current through of path and not necessarily of a circle (a closed loop), correct!?