It's the Earth which is rotating underneath the pendulum, which makes it appear that the pendulum is in fact changing direction. At the North Pole, the pendulum would appear to rotate through a whole degrees once a day, because the Earth rotates all the way round underneath it.
Here in the UK, because we are at a lower latitude, the rate of rotation is lower, at around degrees per day. At the equator, a Foucault pendulum wouldn't rotate at all. Jean Bernard Leon Foucault not to be confused with Michel Foucault, the 20th century philosopher first demonstrated his pendulum during the very first World Fair, held in London in He went on to invent the gyroscope the following year. A superb image of the sun's corona, captured during the total eclipse.
Copyright by Fred Espenak. The rate of rotation of Foucault's pendulum is pretty constant at any particular location, but in , during an experiment with one, a physicist named Maurice Allais got a surprise. You probably nodded and watched the weight swing for a while.
This famous experiment, now found in museums around the world , was first demonstrated in French physicist Leon Foucault suspended a pound weight from a foot-long wire at the Pantheon in Paris and set it swinging.
He needed the bob to be so heavy and the wire so long to ensure that the pendulum would be able to swing for a long time, at least an hour. A pin on the bottom of the weight drew a line in a circle of wet sand set underneath the experiment. After an hour, the line the pin drew in the sand intersected with the first line at an angle of roughly The demonstration was an international sensation and was quickly repeated to crowds across Europe and North America.
By this point, everyone knew that the Earth rotated but this was the first experiment to measure the speed at which it did so. Foucault got eternal fame by having a pendulum named after him, which later became the title of a mind-bending book by Umberto Eco you probably tried to read in college before turning to the much easier candy of Dan Brown novels.
So how does this all work? You stand on one side of the pole and toss the ball directly over the pole to your friend, who is standing opposite you. It will travel in a straight line toward the point that you threw it. But in the time it takes the ball to travel, the Earth has rotated just a tiny bit.
Your friend has moved ever so slightly to the right. Using his sine law, Foucault predicted that the path of his pendulum in Paris would shift And it did.
His sine law allows anyone with a decent grounding in trigonometry to use a pendulum to determine their latitude. But mostly, at museums around the world, the pendulum has become an object that elicits wonder. Children and adults alike would stare at the pendulum, meditating on its motion and meaning. One morning in , before the museum had opened, the cable snapped, sending the massive bob hurtling towards the floor, narrowly missing a staffer.
Its director at the time decided the device did not have much to do with either America or history, says Liebhold. The decision divided staffers. Pro-pendulum employees said it was cool and fun to watch. When not chasing down a story from our nation's capital, she takes in the food, music and culture of southwest Louisiana from the peaceful perch of her part-time New Orleans home. Ask Smithsonian A Smithsonian magazine special report.
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