19th-Century French Physicist's Pendulum Unveils Earth's Rotational Motion.
Image Courtesy: The Hindu
Foucault's pendulum, an experiment from the 19th century that demonstrated the Earth's rotation without complex calculations, has found a new home in India's recently inaugurated Parliament building. The National Council of Science Museums (NCSM), based in Kolkata, designed and installed the pendulum in Parliament's Constitutional Gallery area. Originally invented by French physicist Jean Bernard Léon Foucault, the pendulum provided tangible evidence of Earth's axial rotation. Interestingly, the pendulum's creation was accidental, as recounted by E. Islam, a member of the NCSM team. Foucault's initial experiment involved a vibrating metal rod that ended up rotating due to the lathe it was fixed to. This serendipitous incident laid the foundation for the Foucault pendulum we know today.
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To test his theory, Foucault suspended a short pendulum from a vertical drill press and observed that it swung consistently in its original plane, despite the rotation of its mounting end. This discovery prompted further analysis using an 11-meter-long wire at the Paris Observatory, which also exhibited clockwise rotation. In 1851, Foucault publicly displayed the pendulum at the Pantheon in Paris. The pendulum consisted of a brass sphere filled with lead, weighing 28 kg and measuring 17 cm in diameter. It was suspended from a 67-meter-long pendulum. Foucault's findings revealed that understanding the Earth's rotation using the pendulum was easier at the Poles than at lower latitudes. At the Poles, the pendulum's plane completed one rotation every 24 hours, aligning with the approximate period of Earth's rotation. In contrast, at the Equator, the pendulum exhibited no rotation because the Earth rotated faster due to its wider circumference in that region.
The pendulum's swinging plane, which corresponds to the path swept by its bob, appears to slowly rotate as the Earth itself rotates. This phenomenon can be explained by the Coriolis effect, a result of the Earth's rotation. In the Northern Hemisphere, the Coriolis force causes objects in motion to deflect to the right, while the opposite occurs in the Southern Hemisphere. Foucault's pendulum swing direction aligns with the Coriolis effect, resulting in a gradual clockwise rotation of the swing plane in the Northern Hemisphere over time. The Royal Astronomical Society in London outlines specific conditions for accuracy when using the Foucault pendulum: it must swing freely without torque, have a heavy bob, and employ a long string to minimize air resistance. The pendulum should be smoothly released from rest to avoid abrupt motions and ensure a single plane of swing. While rotation may not be noticeable in daily life, the pendulum's installation at different locations, such as the North Pole or the Equator, illustrates the relative motion between the pendulum and the Earth.
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