In 1851, Jean-Benard-Leon Foucault proved that the Earth turns using a pendulum like this one. At 9:30 am The Franklin Institute starts the pendulum swinging in a North-South direction. Every 20-25 minutes during the day the pendulum knocks down one peg from a ring of pegs in the center, making the pendulum appear to change direction. By 5:00 pm, half of the pegs have been knocked down. The fact that the Earth is spinning and the pendulum is swinging creates this interesting effect. If the Earth was not spinning, then the pendulum would continuously maintain a North-South swing.

04.16.25