Foucault’s pendulum, the 19th-century experiment that exemplified the Earth’s rotation without complex calculations, has found a new home in the recently inaugurated Indian Parliament building. The pendulum is located in the area of ​​the Constitutional Gallery of the Parliament. It was designed and installed by the National Council of Science Museums (NCSM), Kolkata.

Invented by 19th-century French physicist Jean Bernard Lon Foucault, the pendulum provided simple physical evidence that the earth rotated on its axis.

However, as E. Islam, a member of the NCSM team that built Foucault pendulum models in India and abroad, pointed out in a research paper, the invention was actually an accident. According to Mr. Islam, Foucault was setting up a long thin metal rod in a lathe when he accidentally stripped it off, causing the end of the metal rod to vibrate in the same plane. Its other end rotated as it was clamped onto the lathe’s headstock.

The accident paved the way for the current version of the Foucault pendulum. To test the theory, Foucault suspended a short pendulum from the spindle of a drill press and set it in swing. He then started the drill press and noticed that the pendulum was swinging in its original plane, whether or not its mounted end was rotating. Foucault knew he understood something. He installed an 11m long wire in the Paris Observatory for analysis and found that it too rotated clockwise.

The physicist organized the public display of the pendulum for the first time at the Pantheon in Paris in 1851. It consisted of a hollow brass sphere filled with lead to reach a mass of 28 kg. It measured 17 cm in diameter and was suspended from a pendulum 67 meters long.

According to his findings, it is much easier to understand the phenomenon of the Earth’s rotation using the pendulum at the Poles than at lower latitudes. At the Poles, the plane of the pendulum rotates once every 24 hours (which is the approximate period of one rotation of the Earth), while at the Equator it does not rotate at all. This is because the earth rotates faster at the equator than at the poles because it is wider in the center and therefore must cover more area in the same amount of time than at the north or south pole.

The pendulum swings on a plane, which is the surface swiped by the motion of the sphere, also called a pendulum. As the earth rotates, the plane of the pendulum’s swing appears to rotate slowly. However, it is not the pendulum, but the earth itself that is rotating.

Coriolis effect

This relative motion explains the Coriolis effect. The Coriolis force is a phenomenon that appears to act on moving objects in a rotating frame of reference, such as the earth. In the northern hemisphere, the Coriolis force causes moving objects to deflect to the right, while its effect is opposite in the southern hemisphere. This deviation is called the Coriolis effect. The direction in which the Foucault pendulum swings is in line with the Coriolis effect. With each swing, the weight of Foucault’s pendulum swings slightly to the right in the northern hemisphere and vice versa in the southern. This is why the plane of the wobble is observed to have rotated clockwise in the northern hemisphere over a period of time.

The Royal Astronomical Society of London states that certain conditions must be met for the accuracy of the Foucault pendulum. The pendulum must be able to swing freely, independently of any torque, in any plane. The bobsleigh must be heavy and the rope must be long to reduce the effect of air resistance. The pendulum must be released from its rest position gently to avoid any instinctive movement and to ensure that it swings in one plane.

For people standing on the surface of the earth, spinning is not an obvious part of daily life. This is why if the pendulum is set up at the North Pole, it will swing as the earth rotates beneath it, and the plane of the swing will appear to rotate one complete revolution in 24 hours, like the rotation of the earth. However, a pendulum at the equator appears to stay in the same plane because it rotates with the earth.

India’s first Foucault pendulum was commissioned in 1991 by the Inter-University Center for Astronomy and Astrophysics in Pune. It was installed by the NCSM in 1993.

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