This is a Foucault Pendulum. Awesome to watch, most big science museums have one somewhere.
It’s conclusive proof the Earth is rotating with the pesky need for all the awesome space travel.
Imagine you’re at the North Pole. I’m cold.
You start the pendulum swinging and then hide from polar bear. The pendulum swings up, then the Earth turns, but there’s so little friction that the pendulum doesn’t, so when it comes down it crosses a different line of Earth. You can watch it go, knocking over the pins here. It’s a gorgeous, simple experiment.