Foucault pendulum


  • One of the features of the new Parliament building in New Delhi, inaugurated on May 28, is a Foucault pendulum suspended from its ‘Constitutional Gallery’ area.

    • It has been designed and installed by the National Council of Science Museums (NCSM), Kolkata.

About Foucault pendulum

  • The Foucault pendulum is named for Léon Foucault (1819-1868), the French physicist who first devised the apparatus in the mid-19th century. The new Parliament building in New Delhi inaugurated by Prime Minister Narendra Modi on May 28, 2023.

    Foucault pendulum
    Photo Credit: PTI
  • It 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.
    • His achievement, instead, was to provide a proof that didn’t involve intricate astronomical observations and calculations.
  • The pendulum consists of a heavy bob suspended at the end of a long, strong wire from a fixed point in the ceiling.
  • As the pendulum swings, the imaginary surface across which the wire and the bob swipe is called the plane of the swing.
  • If the pendulum is installed at the North Pole, the pendulum will basically be swinging as the earth rotates ‘below’. But someone standing on the earth’s surface doesn’t notice the planet’s rotation (without e.g. looking up at the sky from time to time); instead, to them, the plane of the swing will seem to rotate by a full circle as the earth completes one rotation.
  • If the pendulum is installed over the equator, the plane won’t appear to shift at all because it will be rotating along with the earth.
  • On any other latitude, the plane will shift through 360º in “one sidereal day divided by the sine of the latitude of its location”, per a Brown University note.
  • A Foucault pendulum is not a simple matter of setting up a pendulum with large parts.
  • It must be designed, installed, and set swinging in such a way that the bob’s motion is influenced to the extent possible only by gravity.
  • In 1991, the then-new Inter-University Centre for Astronomy and Astrophysics, Pune, commissioned the country’s first Foucault pendulum for public display from NCSM. After several studies and failed tests, NCSM installed the setup in 1993.

Source: TH

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