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.

Foucault Pendulum

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

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

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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an asteroid with a pendulum. The pendulum's latitude can be changed, as well as the asteroid's rate of rotation.
The Coriolis Effect
download Foucault pendulum on the app store
The pendulum with more pegs knocked down.
the pendulum begins to swing

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

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

several pegs are knocked down
a lit candle

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map of the world showing locations of pendulums

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