As a child, I wondered which fundamental force a pressure cooker used. My guess right now is electromagnetism as the others seem to be very unlikely. Which fundamental force does it use and how? For example, friction depends on the EM force.
Since the strong and weak force are restricted (mostly) to act within a nucleus and gravity is much too weak in a regular sized pressure cooker, the only fundamental force that is left is electromagnetism.
It is basically the atoms or molecules in the cooker bouncing off each other, where the repulsion comes from the EM force, because the shell electrons repell each other.