It’s always nice to be reminded that we’re on a giant ellipsoid floating through space that is spinning at 465 m/s and what better way to do this with a bit of classical physics involving a pendulum. At the base level a Foucault’s Pendulum is no different from an ordinary pendulum but serves more of an illustrative purpose. The bob at the end of course has it’s own momentum which causes it to oscillate back and forth. The thing is that if left for long enough with no decay in amplitude (done by using a very massive pendulum) we notice something peculiar. As the day goes on it appears that the angle of the pendulum’s swing changes (as can be seen in this animation). In reality the momentum of the pendulum keeps it oscillating back and forth relative to the universe, the change in angle is actually due to the Earth rotating while the pendulum remains swinging in more or less the same plane. As it does this it traces out what is known as a Rose Curve (the type of shape you get using spirographs) when viewed from above.