Focault's pendulum

In the lobby of the University of Tartu Museum there is the Focault's pendulum which makes the rotation of the Earth visible.

It is named after French physicist Leon Foucault (1819-1868) who constructed the first one for the observatory of Paris in 1851.

The fact that the Earth is rotating was known long ago. Similar experiments with pendulums were done in the past, for example by the Italian physicist Vincenzo Viviani in 1661. Foucault however was able to take advantage of the external effect of this phenomenon and since then such pendulums have been popular throughout the world.

How does a pendulum work? The inertia makes each freely hanging and swaying pendulum to maintain its vibratory target. If the pendulum is heavy and long enough to overcome air resistance and its movement can be monitored closely then you can see how the Earth rotates underneath it. In addition, the movement of the pendulum depends on latitude (formula: T = 24 / sinφ, T is time, and φ is the latitude). At the North Pole the visible path of the pendulum would make a full circle clockwise in 24 hours (actually the Earth rotates making a counterclockwise circle around its own axis). At the equator you would see no effect.

Tartu is located at 58° 23' north latitude and it is suitable to monitor the movement of the  pendulum.

In the image underneath the pendulum there is a geographical map dating from 1849. The map area is chosen so that the viewer has a clear understanding of the approximate location of the pendulum and the direction of movement over its location towards the North Pole.

The Focault pendulum now in the museum was originally created for the physics department building of the University of Tartu at Tähe street. The pendulum was opened on 6th November 1999. Due to the relocation of the physics department into a new building the pendulum was brought over to the of the University of Tartu Museum in 2014.

The pendulum was designed by Imbi Kruuv and executed by Hando Kruuv.