Question

What is a Foucault pendulum and what does it show? Why is the length of the pendulum usually large?

Answer 1

Foucault pendulum is an easy experiment to demonstrating earth's rotation. The French physicist Leon Foucaultperformed this experiment in 1851 at Paris. It consist of a large mass suspended to a string mounted in such way that perpendicular plane of swing is not confined to a particular direction and rotate's with respect to earth surface. The first Foucault pendulum consisted of a 28-kg iron ball suspended from inside the dome of the Panthéon by a steel wire 67 metres (220 feet) long and set in motion by drawing the ball to one side and carefully releasing it to start it swinging in a plane. The rotation of the plane of swing of Foucault’s pendulums was the first laboratory demonstration of the Earth’s spin on its axis. It swings back and forth in a plane, rotation of earth beneath it, both motion are relative. The plane of pendulum observed from above found to rotate in a clockwise direction once a day. It always rotates clockwise in the Northern Hemisphere, oscillation's becomes slower as it approaches the Equator. Foucault’s original pendulums at Paris rotated clockwise at a rate of more than 11° per hour, or with a period of about 32 hours per complete rotation. The oscillations are completely depends on latitude. It does not rotate at the equator as the latitude 0° . The oscillations are counterclockwise in southern hemisphere. The rate of rotation of a Foucault pendulum can be same as rate of rotation of earth. The earth rotates 360° in a day or 24 hrs, its rate of rotation 15° per hour, which is same as rate of rotation of a Foucault pendulum at the North or South Pole.

The length of pendulum is large so that it continue oscillating for longer period of time.