Foucault Pendulum was used in 1851 to simply demonstrate the rotation of the Earth. It is easiest to understand the mechanism if it is swinging at the North Pole. The pendulum's plane of swing is fixed relative to the stars while the Earth gently rotates underneath it in 24 hours. 1 key gives a side perspective Space key hides/shows the Earth. This demo employs a 3D interface. Up/Down Right/Left arrows and a/z keys rotate the object along the x,y,z axis.
You can read about this fascinating mechanism and its history: https://en.wikipedia.org/wiki/Foucault_pendulum The 3D interface is a based on a projection algorithm I developed some years ago to make Geometer's Sketchpad display 3D curves. I learned a tremendous amount from @Mr_Pyro_ 3D Wireframe Engine project about optimizing rendering and keyboard effects. Much much thanks.
