Foucault pendulum in Motala, Sweden
|History of the Foucault pendulum-short version|
|Why build a pendulum?||
A Foucault pendulum is a classical, beautiful experiment in physics, showing that Earth rotates around its axis. When the experiment was performed for the first time by Léon Foucault in 1851 in Paris it was the first ocular proof for the rotation of Earth where one with own eyes could see that earth really rotates around its axis. Of course this was known at this time but an obvious proof was still missing.
The pendulum in Motala is made up of a steel bob suspended in a wire (See the picture to the right). The bob must be suspended in a perfectly symmetric way, able to swing freely in all directions if the experiment is goingbe successful. Once the pendulum is set in movement, after a while you can notice that the plane of the pendulum´s swing has changed direction clockwise. The plane of swing keep changing its direction and is making a full circle in 32 hours in Motala. Thus the velocity of the rotation is about 13 degrees an hour.
But this is an optical illusion. In reality it is not the plane of the pendulum´s swing that changes - the pendulum swings in the same direction all the time relative to distant masses of universe*). Instead it is Earth that moves under the pendulum. But for a spectator on Earth it looks like the plane of the pendulum´s swing is changing.
In 2007 Carlsund utbildningscentrum celebrated their
jubilee. The upper secondary school
then on 11 May could inaugurate a
Foucault pendulum that had been made on the school without external
sponsors. To buy a complete pendulum had been far to expensive
if possible to find a seller). The pendulum has an
electro-magnetic drive that gives the bob a little kick every time it has
passed a turning-point. In this way the pendulum keeps swinging all the time to
compensate for the air resistance. *) Strictly, this is true only at the North and South Pole. At other latitudes the motion is more complicated.
*) Strictly, this is true only at the North and South Pole. At other latitudes the motion is more complicated.
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