Foucault's Pendulum in New Parliament: A Unique Device Showing Earth's Rotation | Details

The new Parliament building, inaugurated by Prime Minister Narendra Modi on May 28, houses a Foucault’s pendulum. 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.

Signifying the idea of India with that of the universe, the Foucault’s pendulum in the new Parliament building was installed by the National Council of Science Museums (NCSM). In simple terms, this unique scientific device demonstrates the rotation of the earth.

An experimental device in all its simplicity, the Foucault’s pendulum was introduced in 1851 and named after French physicist Leon Foucault. It was the first device of its kind to provide direct evidence of the Earth’s rotation.

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, standing 22 m tall.

What is a Foucault’s Pendulum?

The Foucault’s pendulum is a spherical pendulum and is used to demonstrate the rotation of the Earth. When Leon Foucault first conducted an experiment with it, the idea that the Earth revolves was nothing new or even radical but it gave a simple demonstration of proof that did not require minute observations of astronomical objects.

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.

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.

So, 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. How does this happen?

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.

According to the Smithsonian, which had a Foucault’s pendulum displayed for many years before it was removed in late 1998, if you are standing and watching the pendulum, you will naturally feel like the floor is stable and the device is moving. “This is because we assume that the base on which we are standing is stable unless our eyes or sense of balance tells us otherwise. If our base moves slowly or accelerates smoothly, we are easily fooled into thinking that another object we see is moving,” states the article published by the Smithsonian.

This is a common experience when we are in a train station. If we are inside a train that begins to move very slowly and smoothly, we think that a train or any other stationary object seems to move. It also happens when a train next to ours starts to move very slowly, we feel like the one we are in is also moving with it.

“At the north pole the apparent rotation would be a full circle of 360 degrees each 24-hour day, or about 15 degrees per hour. This case is fairly simple, because here the Earth and the pendulum are not exerting much influence on each other,” states the Smithsonian article. But if you move away from this point towards the south, the Earth not only rotates under the pendulum but carries the place you are in and the pendulum in a great circle about its axis. The further south you go, the slower the rotation is and, at the equator, there is no rotation at all. Below the equator the apparent rotation begins again, but in the opposite direction.

What are the features of the Foucault’s pendulum in Parliament?

The recently installed pendulum stands at a height of 22 m and weighs 36 kg. It takes the pendulum a total of 49 hours, 59 minutes and 18 seconds to complete one full rotation. All parts of the pendulum were manufactured in India and it took 10 to 12 months to construct the device. It is made with gunmetal and equipped with an electromagnetic coil to ensure smooth movement.

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. The Brown University article states that for the experiment to be accurate, precautions must be taken so that the pendulum is not influenced by any outside force other than gravity. “For example, to start the pendulum moving, it is usually held at an angle by a string, which the experimenter then burns to release the pendulum. Letting the pendulum go from one’s hands, or even cutting the string, could give the pendulum undesired momentum in a particular direction. 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,” states the article.

The Foucault’s pendulum in Parliament was created by Tapas Moharana, the person in charge of the project. He told The Indian Express that he started working on it after receiving a call from the Central Public Works Department (CPWD) last year.

The NCSM has also installed other such devices. The first public installation was commissioned by Pune’s Inter-University Centre for Astronomy and Astrophysics in 1991. The council then installed another pendulum at the Queensland Science Museum in Brisbane.