# Hidden momentum

I'm trying to learn about hidden momentum. After reading what I could find with a google search, I understand that it is equal to the momentum carried by radiation, calculated with the Poynting vector. I can't really understand how the momentum conservation laws apply to the situations in which there is a magnet(current through the loop) and in which this magnet is turned off. How should i write these laws?
I think I somehow understand the origin of hidden momentum, but I don't see how everything sums up in both situations. Could you please help me understand?

The momentum can be stored in static fields ($D\times B$); the mechanical momentum ($mv$) + electromagnetic momentum ($D\times B$) $= constant$.