I always have trouble understanding potential energy. Here's a realistic question which bothers me a lot. Let's say I have a horse shoe electromagnet on a table. And I also have a permanent horse shoe magnet. I turn on the circuit(the electromagnet is functioning) And I bring the electromagnet and the permanent magnet closer to each other( I'm doing work because like poles are facing each other and repelling). Now the system seems to have some kind of energy because if I let go they will move apart with some velocity. But what if I turn off the electromagnetic? Will that energy disappear?