The Foucault Pendulum is named for the French physicist Jean Foucault (pronounced “Foo-koh), who first used it in 1851 to demonstrate the rotation of the earth. It was well established and accepted that earth rotates about its axis and revolves around the Sun. But this activity is not physically experienced by people on earth. The Foucault Pendulum is a deceptively simple device used to illustrate the earth’s rotation. At the time Foucault set up the first public display of the pendulum, the earth’s rotation was a well-established fact. It was the first satisfactory demonstration of the earth’s rotation using laboratory apparatus rather than astronomical observations. First Foucault Pendulum device in India is said to be installed at the Inter-University Centre for Astronomy and Astrophysics (IUCAA), Pune, in the year 1991. Long back, I had the opportunity to visit PRL Ahmedabad where I saw this unique device and it was a source of my articles published in different magazines at that time.
Foucault’s Pendulum
The Foucault’s pendulum is a spherical pendulum and is used to demonstrate the rotation of the Earth. The Foucault’s pendulum provides visual evidence of the rotation of the Earth — which rotates at a speed of 1,670 kmph — that we cannot feel. As it is made today, the device has a long and heavy pendulum suspended from a high roof above a circular area and mounted so that its perpendicular plane of swing is not confined to a particular direction and, in fact, rotates in relation to the Earth’s surface. Wherever we put it, Foucault’s Pendulum swings from a motionless point while the earth rotates beneath it. Every point of the universe is a fixed point: all we have to do is hang the Pendulum from it. When Leon Foucault first conducted his experiment with his pendulum, it was the first satisfactory laboratory demonstration of the Earth spinning on its axis. The original device, assembled in Paris, is a 28-kg metal sphere suspended on a 67-m steel wire from the dome of the Pantheon and recreates the physicist’s experiment. The most important aspect of a Foucault’s pendulum to work to its full ability is to ensure that its motion is primarily influenced by gravity. A heavy pendulum on a long, rigid wire can continue oscillating for long periods of time, but eventually air resistance will cause the motion to lessen and stop. Museums will often use an electromagnetic drive to keep their pendulum moving, because such a setup provides additional energy to the pendulum without affecting its direction of motion.
Foucault Pendulum in Indian Parliament Building
The new Parliament building, inaugurated by Prime Minister Narendra Modi on May 28, houses a Foucault’s pendulum. Suspended from the ceiling of the Central Foyer of India’s new Parliament building, inaugurated on Sunday (May 29, 2023), is a Foucault pendulum that all but touches the floor as it rotates on its axis. The pendulum hangs from a skylight at the top of the Constitution Hall, and signifies the “integration of the idea of India with the idea of the cosmos”. In a structure that showcases India’s democratic traditions from the Vedic period to the present day, the pendulum gives a modern touch as it hangs from a large skylight of the triangular roof of the Constitution Hall. Created by the National Council of Science Museum (NCSM) in Kolkata, the pendulum is being dubbed as the largest such piece in India, 22 metre in height, and weighing a staggering 36 kg. One will find a circular installation on the ground. The purpose of the installation is to allow the movement of the pendulum. The circular installation also comes with a grill around it. The grill permits visitors to stand around and view the pendulum. At the height of the Parliament, the pendulum requires a timeframe of 49 hours, 59 minutes, and 18 seconds to finish one complete rotation, according to the details mentioned at the installation. The pendulum was created in a matter of 10 to 12 months and is completely made in India by Project In-charge Tapas Moharana. The suspension system is mounted on the ceiling, and there is a continuous power supply to eliminate any hindrances to the pendulum’s motion. It is made with gunmetal and equipped with an electromagnetic coil to ensure smooth movement. Popular in science museums and universities across the world, the Foucault’s pendulum in the new Parliament building has become a major source of attraction. It is being claimed that this is the largest such pendulum in India.
How does it work?
To understand how this device works, it is also necessary to understand how a simple pendulum works. The Britannica Encyclopedia describes a pendulum as a “body suspended from a fixed point so that it can swing back and forth under the influence of gravity”. These devices are used to regulate the movement of clocks as the interval of time for each complete oscillation, called the period, is constant. It was Italian scientist Galileo, who first noted how the pendulum represents a period. According to Britannica, a simple pendulum has a bob suspended by a thread, which is “so light as to be considered massless”. There are different kinds of pendulums in existence. A spherical pendulum, like the Foucault’s pendulum, is one that is “suspended from a pivot mounting that enables it to swing in any of an infinite number of vertical planes through the point of suspension”, states Britannica. Hence, the plane of the pendulum’s oscillation rotates freely. Just like any other pendulum, according to a simple understanding of any such device, we are accustomed to knowing that the ball on the end of the thread will swing back when moved in one direction. But if you start a Foucault’s pendulum swinging in one direction, you will notice after a few hours that it is swinging in quite a different direction.
The simple answer to this would be that the pendulum swings on a fixed plane and the Earth rotates beneath it. But, according to a description of the workings of this device published by Brown University, this explanation is misleading. If you are observing such a pendulum, you will feel as though the plane of the pendulum’s swing is changing but, in reality, the Earth is rotating and the pendulum remains in a fixed plane of swing as the Earth moves beneath it. Since we as observers are also rotating with the earth, we cannot feel the Earth moving but can notice the change in the pendulum’s orientation. For example, at the north or south pole, the pendulum is moving on a fixed plane, so the plane of the pendulum seems to rotate through 360 degrees as the Earth makes one full rotation in 24 hours. At any other point on Earth, however, the point at which the pendulum is attached cannot be considered a ‘fixed point’ because that point also moves as the Earth rotates. The plane in which the pendulum swings is similarly in motion, states an article published by Brown University.
