Question

How does a Foucault's Pendulum work?

Answer 1

The best description is visual so try this site first, the effect is partly an illusion.

http://www.animations.physics.unsw.edu.au/jw/foucault_pendulum.html

then for more information,

https://en.wikipedia.org/wiki/Foucault_pendulum
and
http://www.abc.net.au/surf/pendulum/pendulum.htm

The pendulum is used to show/measure various cosmological and earthly matters, particularly the earth's rotation..

Answer 2

@cryptic: thanks for the link.