I dont think I spelled it right, but you get the idea. Unless the Flat Earth rotates, the pendelum proves it wrong.
For those that dont know what I am talking about, if you but a ball on a string, hung it on a sort of beam, started swinging it so it goes in one direction, then left a domino a little bit to the side of it, at some point the earths rotation will move its swinging path and it will knock over the domino.