eli5: how Foucault pendulum works
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It’s a pendulum with the added feature of a frictionless ball bearing where the rope attaches to the ceiling.
What this means is that the ceiling can spin in circles and not transmit that spinning to the rope of the pendulum, so the pendulum swings back and forth in a straight line forever.
Since the Earth is spinning on it’s axis, and the building is attached to the Earth, and the ceiling is attached to the building, the ceiling is spinning. But the ceiling cannot transfer that spinning to the pendulum because of the special connection.
So the typical experiment is array 24 cylinders around the room in a circle at the ends of where the pendulum swings. As the Earth spins, the room spins, and the pendulum stays in the same place. So eventually a cylinder will move into the path of the pendulum and get knocked down.
It’s a way of showing that the Earth spins on an axis and is not stationary with the universe spinning around it.
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