Foucault's Pendulum

posted Nov 29, 2010, 1:30 AM by Professor Katz   [ updated Dec 12, 2011, 2:06 PM ]
How could you prove that the earth rotates on its own axis, before the first astronaut saw it from outer space?

In 1851, Jean-Bernard-Leon Foucault (1819-1868) suspended a 67-metre, 28 kilogram pendulum from the dome of the Pantheon in Paris.  The plane of its motion, with respect to the earth, rotated slowly clockwise.  This motion is most easily explained if the earth turns below the pendulum.

There are lots of Foucault's Pendulums around: there's one in the Weizmann Institute, and another at the observatory in Givatayim, I think.

Have a look at a Foucault's Pendulum in action:

If you still don't get it, listen as a Dartmouth professor explains how it works: