# Foucault pendulum and a round globe

Imagine we are all cavemen without satellite technology and just discovered the Foucault pendulum! As we know the angle of presession depends on the latitude. This can be used to prove that the earth is rotating, right? Now by putting several Foucault pendula around the Earth, at equidistant longitude and latitude, can we prove that the Earth is a sphere as well?

A.T.
Now by putting several Foucault pendula around the Earth, at equidistant longitude and latitude, can we prove that the Earth is a sphere as well?
You could exclude a lot of potential shapes, and by assuming certain smoothness between your sample positions narrow it down to a sphere.

cool. then all pendula must be installed at the same altitude to guarantee smoothness.

A.T.
cool. then all pendula must be installed at the same altitude to guarantee smoothness.
It's not about the altitude, but how densely they are spaced.

Also, since pendulums are based on gravity, you have to assume some model of gravity, which by itself might already imply an equipotential surface, without even the need for swinging pendulums.

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anorlunda
Staff Emeritus
Imagine we are all cavemen without satellite technology and just discovered the Foucault pendulum! As we know the angle of presession depends on the latitude. This can be used to prove that the earth is rotating, right? Now by putting several Foucault pendula around the Earth, at equidistant longitude and latitude, can we prove that the Earth is a sphere as well?

Wouldn't it be much easier for them to just glance at the sky and notice how the position of the North Star varies with latitude?
(Flaw: The North Star moves, it was not north in all periods of history.)

sophiecentaur