Let the ball swing at the Ångström Laboratory


The Ångström Laboratory is getting a new attraction. Students, teachers, researchers and others will soon be able to marvel at a special device in one of the new buildings currently under construction at the Ångström Laboratory. This is where the “Foucault pendulum” will be installed. It consists of a heavy ball that swings on a long cable suspended from the ceiling. The pendulum’s movement demonstrates that the Earth rotates around its own axis.

Foucault pendulum
Illustration of what the Foucault pendulum will look like in the atrium of Building 10 at the Ångström Laboratory.
Photograph: PE Teknik & Arkitektur
Foucault pendulum at the Panthéon
The Foucault pendulum at the Panthéon in Paris.
Photo: Wikimedia.

French physicist Jean-Bernard-Léon Foucault was the first to use an experiment to prove that the Earth rotates around its own axis. Scientists already suspected this in the 17th century, but now the phenomenon could be proved. Foucault’s first major demonstration took place in 1851 at the Panthéon in Paris, where he suspended a 28-kilo iron ball on a 67-metre-long iron wire. The ball’s pendulum movements showed the surprised audience that the Earth actually revolves. The experiment became legendary and spread rapidly throughout Europe. The first experiments in Sweden were conducted a few years later at Uppsala Castle – a suitable place with high ceilings.

But now Uppsala University will soon have its own permanent Foucault pendulum. This has been made possible by a private donation from Johan Tysk, Vice-Rector of the Disciplinary Domain of Science and Technology.

The initiative for a pendulum in the Ångström Laboratory came from Mattias Klintenberg, a professor of physics.

“The idea of installing a Foucault pendulum in one of the new buildings was an exciting idea, and he helped move the process forward,” says Johan Tysk.

Johan Tysk
Johan Tysk. Photo: David Naylor

“And I have always been fascinated by Foucault’s pendulum. It raises questions about how on earth everything can work together, and illustrates the interaction between science and technology. It is a magical gadget that gives us the feeling of being part of something big,” says Tysk. “It’s great to be involved and personally contribute to this with a donation!”

The new buildings at Ångström Laboratory are intended to strengthen the intellectual environment and encourage social meetings between students, teachers and researchers from different subject areas.

“It is important to remember the social aspects,” says Johan Tysk. “That’s why I especially enjoy being involved in placing a pendulum in the centre of the new atrium in Building 10. It will be a focal point with a constant flow of people passing by. Maybe the pendulum will cause people to stop and reflect on science and technology.”

It will take a while before anyone can experience the pendulum swinging in the Ångström Laboratory. Building 10 with Foucault’s pendulum will not be finished until the spring of 2022.

“But we hope that many will come to watch it then. Maybe we can invite guests and school classes so that, aided by the pendulum, they can learn a little more about how the Earth spins and nature works,” says Tysk.

Anna Malmberg

About the Foucault pendulum

Jean-Bernard-Léon Foucault
Jean-Bernard-Léon Foucault (1819–1868).
Photo: Wikipedia.

The Foucault pendulum is named after French physicist Jean-Bernard-Léon Foucault (1819–1868). The pendulum consists of a weight attached to a long cable suspended from a ceiling or the like so that it can swing and rotate with as little friction as possible. After a while it will no longer move in the same direction as when it first began swinging. This is because the Earth has rotated around its axis as time passed.

How much the pendulum moves as a result of the Earth’s rotation depends on the latitude. At both poles it rotates 360 degrees in 24 hours, while at the equator it does not rotate at all but continues to oscillate in the same direction from the point of view of a terrestrial observer.

These days, the device is usually equipped with an electromagnetic drive to supply energy that compensates for energy lost through friction in the suspension and air resistance.


Watch a video showing the Foucault pendulum at the Panthéon in Paris.

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