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History of mathematics ‒ the Foucault pendulum. (English)
Parabola 49, No. 1, 6-15 (2013).
From the text: Foucault pendulums may be classified into two distinct types: the free and the driven. A free pendulum is simply that: a straightforward pendulum. Such a pendulum is well suited to experimental work such as that carried out by Kamerlingh Onnes, but is not always seen as well adapted to the demands of public display. The reason is that frictional effects will eventually bring the pendulum to rest (‘running down’). Such a pendulum must be restarted at frequent intervals (and, as will appear below, this can be rather tricky). The driven pendulum has a supply of energy to keep it going, so that the need for constant restarting is eliminated. However, it is important to supply this energy in such a way that the Foucault effect is not thereby disturbed. When a pendulum is set up for the purpose of experiment, then the question of running down is not especially important. However, if the principal purpose is display, then the preference is for a driven pendulum ‒ although some displays use a free one and make a ceremony of starting it afresh each day! Apart from the matter of running down, however, there are other problems confronting the would-be pendulum constructor. One is to design a pivot that does not itself affect the direction of swing. However the worst problem is that of ‘ellipsing’, to which I now turn.
Classification: M50 A30
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