LEON FOUCAULT (1819- 68)

1850 – France

portrait of LEON FOUCAULT (seated) ©

LEON FOUCAULT  (Smithsonian)

‘A Foucault pendulum is a simple pendulum – a long wire with a heavy weight (bob) at the end – except that at the top it is attached to a joint which allows it to swing in any direction’

Foucault’s pendulum proved that the Earth is rotating

Once a Foucault pendulum is set in motion, it seems not to swing back and forth in the same direction but to rotate. In fact, it is the rotation of the Earth beneath the pendulum which gives rise to its apparent rotation.
The angle of rotation per hour, which is constant at any particular location, can be calculated from the formula 15 sin Φ, where Φ is the geographical latitude of the observer. At the North or South Pole, the pendulum would rotate through 360 degrees once a day. At the equator it would not rotate at all.

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