A visit to an asteroid with a pendulum helps explain. We spin with the asteroid, watching the stars go by, and discover that the pendulum seems to be rotating with the universe.

Gradually it rotates enough to knock down another peg. Why?

It starts to swing, knocking down a peg on the perimeter and then the peg opposite.

The pendulum is started in the traditional way, with flame.

Foucault Pendulum

The Coriolis page shows why the pendulum is moving the way it does: the pendulum's precession is due to the Coriolis Effect.

download Foucault pendulum on the app store
several pegs are knocked down

Back at the home page we find that the pendulum has continued its rotation, dependent on our latitude, in synchrony with the universe.

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map of the world showing locations of pendulums
a lit candle
an asteroid with a pendulum. The pendulum's latitude can be changed, as well as the asteroid's rate of rotation.
The Coriolis Effect
The pendulum with more pegs knocked down.
the pendulum begins to swing

Look up the locations of the Earth's Foucault pendulums to find one nearby.