Foucault pendulum how does it work

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. But if you were on a planet with a very fast rotation rate, your friend would have moved much more in the time it takes the ball to travel.

The ball could entirely miss your friend, going straight past her left arm. Because of that, the plane of oscillation is co-rotating with the Earth. Away from the equator the co-rotating with the Earth is diminished. Between the poles and the equator the plane of oscillation is rotating both with respect to the stars and with respect to the Earth. Many people found the sine factor difficult to understand, which prompted Foucault to conceive the gyroscope in The gyroscope's spinning rotor tracks the stars directly.

Its axis of rotation turns once per day whatever the latitude, unaffected by any sine factor. Now let's take the same setup and place it in Paris - as Foucault did. Here you would see that the pendulum's plane rotates a full degrees, give or take, in 24 hours.

What about at the equator? At the equator, all things being equal, and the pendulum's swinging plane will not rotate at all. This phenomenon i. It is this that is responsible for much of the Earth's weather patterns and ocean currents. Pendulum experiments of this nature require careful precautions to ensure it is not acted upon by external forces other than the gravity of course. When starting one, for example, the pendulum is held at an angle by a string.

This string is then burnt to release it. Any other action, like cutting by hand or released from the hand could impart undesired momentum in a particular direction. Long pendula, like Foucault's, with heavy bobs suspended on a rigid wire, have enough momentum to keep swinging for long periods of time.

However, the ever-present resistance created by air will eventually rob the pendulum of energy and will come to a halt eventually. To counteract this, most displays have installed an electromagnetic drive to keep the pendula in motion. This solution is ideal as it provides the extra energy needed without impacting the pendulum's direction of motion.

This system usually comprises of two iron collars that are attached to the pendulum's wire near the top. This is fed through a doughnut-shaped electromagnet built into the ceiling. Other solutions place the electromagnetic drive on the floor. As the cable swings back and forth so to do the iron collars inside the hole of the doughnut. As the cable reaches a particular point in its arc it is detected by an electronic device that activates the electromagnet.

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. As the path of the pendulum shifts due to Earth's rotation, the bob will gradually knock over all of the vertical rods around the circle's circumference. Wikimedia Commons Looking down, visitors would see a symmetrical hollow brass bob weighing about pounds and shaped like an inverted teardrop.

The Smithsonian pendulum was ultimately decommissioned on the grounds that it didn't have much to do with American history, the new focus of the former Museum of History and Technology.