Today we think about how the earth rotates as it revolves around the sun, giving us day & night. We know this to be a scientific fact thanks to Jean Bernard Léon Foucault, French physicist and astronomer.
In 1851 physicist Léon Faucault demonstrated that the earth rotates by suspending a 62 lb brass-coated iron ball by a 220 ft steel wire from the dome of the Panthéon in Paris, France.
Gravity on the pendulum proved right before everyone’s eyes that the earth rotates.
Brown University tells us, “When Léon Foucault first performed the experiment in 1851, the concept that the Earth revolves was nothing new or radical; the pendulum’s accomplishment was to provide a proof that did not require minute observations of the stars or other objects far removed from Earth. Foucault’s pendulum is a highly localized, easily prepared experiment whose result is clear, powerful, and accessible even to the non-scientist. In short, the pendulum provides everything a science teacher could ask for in an instructional experiment.”
Foucault set the pendulum in motion by pulling the ball to one side and releasing it to start it swinging in a plane.
The rotation of the plane of swing demonstrates the Earth’s spin on its axis.
So how does it work? Brown’s University further explains: “The elegant answer is that the pendulum swings in a fixed plane and the Earth rotates beneath it. [Only] at the north or south pole the pendulum is moving in a fixed plane (if we disregard the fact that the Earth is also revolving through space), so the plane of the pendulum seems to rotate through 360° as the Earth makes one full rotation.”
“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. Because of this, the amount of time that it takes for the pendulum to make one full rotation (with respect to its surroundings) is equal to one sidereal day (23.93 hours) divided by the sine of the latitude of its location.
Since sin(0)=0, the plane of a pendulum located at the equator will not appear to move at all.”
The period of Foucault’s original pendulum was seconds. Because the latitude of its location was = 48°52′ N, the plane of the pendulum’s swing made a full circle in approximately = 31.8 hours (31 hours 50 minutes), rotating clockwise approximately 11.3° per hour.
Did you know that Earth is spinning faster than it has in 50 years?
The Daily Mail reports that time is passing faster now than at any point in the past 50 years. July 19, 2020, was the shortest day since scientists began keeping records in the 1960s by 1.4602 milliseconds. This is interesting, especially when for decades it has usually taken longer than the 24 hours for the earth’s rotation.
They tell us, “The world’s timekeepers are now debating whether to delete a second from time to account for the change, and bring the precise passing of time back into line with the the rotation of the Earth. While the addition of a so-called ‘negative leap second’ has never been done before, a total of 27 ‘leap seconds’ have been added since the 1970s, in order to keep atomic time in line with solar time.”
However, the International Earth Rotation and Reference Systems Service (IERS) stated that no “leap second” would be added to the world’s official timekeeping in December 2020. (The last time they added a leap second was December 2016.)
How to Celebrate Earth’s Rotation Day
1. Visit your local Foucault Pendulum.
Universities, museums and science centers all over the world have their own working example of a Foucault pendulum.
Find one near you and share a selfie using hashtag #earthsrotationday.
Visitors at Griffith Park, Los Angeles, CA watching the pendulum.
2. Create art with a pendulum.
Paint with a pendulum.
Create sandart with a pendulum.
Play a Pendulum Game
Pendulum strategy board game by Stonemaier Games for 1-5 players.
Pendulonium STEM Challenge Game for kids
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