About Foucault pendulums:
I understood that the plane of oscillation remains fixed relative to the ground. But isn't it that the point of attachment and the observer are both fixed with respect to the ground? Then why is the plane of oscillation changing for an observer fixed to the ground?

Question

About Foucault pendulums:
I understood that the plane of oscillation remains fixed relative to the ground. But isn't it that the point of attachment and the observer are both fixed with respect to the ground? Then why is the plane of oscillation changing for an observer fixed to the ground?

fretje · Answer

we rotate with the earth because we are pushed sideways from the earth, the pendulum's swing plane of oscillation stays the same in space because the pendulum it is not pushed from the earth, but the earth under it rotates, so the plane changes relative to the ground.

fretje · Answer

that is the principle of how gyroscopes are working to indicate direction changes.
Foucault pendulum does not work on the equator, and works best on the poles of the earth

anonymous · Answer

I didn't get you when you say 'we are pushed sideways by the earth'. Can you please expand on that?

fretje · Answer

a body that is attached has freedoms depending on the way it is attached.  The pendulum's swing plane exists because the body of the pendulum has the freedom to move like it does.  If you would make a disc instead with a rigid axis connected to the earth, it would not seem to rotate:
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