Just to clarify, I wasn’t proposing it was the force of one coin falling against the other.
I do know we did some strange things with coins as kids, with just a couple of things springing to mind, such as opening modelling paint tins, making cross-pistol mechanisms from old penny pieces and, maybe relevant to this situation, we used to squeeze chunky washers edge-to-edge in a vice until they’d finally fly off like a game of buckaroo!