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Foucault’s Pendulum

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Foucault’s Pendulum

Why in news:

  • India’s newly inaugurated Parliament building, unveiled on Sunday by Prime Minister Narendra Modi, boasts several new features and installations compared to the old structure.

  • One notable addition is the historical ‘Sengol’, a sceptre positioned next to the chair of the Lok Sabha Speaker in the chamber.
  • Another intriguing installation is ‘Foucault’s Pendulum’ and can be found in the gallery section of the Constitutional Hall, adding to the new Parliament’s unique elements.

About Pendulum:

  • 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”.
  • 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.
  • On the ground, a circular installation has been created to allow the pendulum’s movement, with a short grill around it, allowing the visitors to stand around.
  • At the latitude of the Parliament, it takes 49 hours, 59 minutes, and 18 seconds for the pendulum to complete one rotation.

What is a Foucault’s pendulum?

  • The original Foucault’s pendulum, named after 19th century French scientist Leon Foucault, is a simple experiment to demonstrate the earth’s rotation.
  • When Foucault carried out this experiment for the public in 1851, it was the first direct visual evidence of the fact that the earth rotates on its axis.
  • The experimental set-up involves a heavy object hung from a height with a string, free to swing in any direction.
  • Once set in to-and-fro motion, the pendulum is seen to change its orientation slowly over time.
  • For example, if the initial motion imparted to it was in the north-south direction, after a few hours it could be seen moving in the east-west direction.
  • Actually, it is not the pendulum that changes its plane of motion, but the ground beneath it.
  • Observers standing on the ground do not notice the earth’s rotation, because they too are rotating with the earth, but can notice the change in orientation of the pendulum.
  • At the north and south poles, when the pendulum is aligned with the axis of rotation of the earth, the pendulum’s back-and-forth motion comes back to its original plane in exactly 24 hours.
  • That is, if it starts swinging in the north-south direction, it then slowly turns in the northeast-southwest direction, then in the east-west direction.
  • It keeps on changing its orientation, till it is back in its original orientation after 24 hours.
  • At other latitudes, it takes longer for the pendulum to return to its original orientation of swinging.
  • That is because the pendulum is not aligned with the axis of rotation of the earth.
  • At the equator, the pendulum is perpendicular to the axis of rotation, and hence it never changes its orientation of the swing.
  • Meaning, a Foucault’s pendulum at the equator would not show any deviation from its original course.
  • At other latitudes it will, and would return to the original course after fixed time periods.

Syllabus: Prelims

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