Apologies if I've shared this before.
In my teens, (goodness that's 50 yrs ago), I helped a friend look after a showman's engine which was housed, with the rest of his collection, in an old foundry. We steamed the showmans engine most days, with a long extension chimney running out through the roof and the dynamo running the lights. One day I overheard a dad explaining to his two young boys how it worked. "That big motor at the front (the dynamo) turns the belt which makes the big wheel (the flywheel) turn and that makes all the levers (the notion) move".