At the Paris Observatory in 1851, Jean Foucault used a
long pendulum to prove that Earth is rotating. As it
swings, the pendulum appears to change its path.
However, it is not the pendulum that changes path, but
the room rotating underneath it. At the North Pole,
Earth revolves 360° underneath the pendulum for over
24 hours. The path of a pendulum at the equator does
not revolve at all, instead, the pendulum travels in a huge
circle while Earth spins. At points between the two, the
pendulum cannot show how far it travels, but it can show
how much planet Earth is revolving underneath it.
