Synchronisation of 3 Foucault pendulums
Improbable experiment posted live….
The idea for this experiment came to me in 2002 in my studio when I saw two Foucault pendulums hanging from the same concrete ceiling, their rotations remaining perfectly synchronous for a whole month. They had been doing this for perhaps a year without me noticing. This couldn’t have happened by chance, so what was the law that made them rotate together?
So here was a triple experiment to synchronise the rotations of small Foucault pendulums swinging freely against the same wall, the aim being to discover what would happen between the 5 choices available when they were initially thrown in the same direction:
1) Anarchy: everyone goes their own way, ignoring the other.
Or
2) Love: they synchronise their rotations and always oscillate on the same parallel plane.
Or
3) Dictatorship: they start to oscillate in the same plane, then the heaviest one kills the other by successive phases and phase shifts.
Or
4) Cold war: they choose the plane of oscillation most opposed to the other (90° for 2 pendulums, 120° for 3 pendulums) and maintain it indefinitely.
Or else…
5) … There’s something else we’re going to have to find out.
Experiment n°1, December 2023
This experiment was not as pure as I would have liked because there was also the miniFoucault oscillating at the same time in the same room and the three pendulums tested were barely adjusted. Why on earth not set them better before? Simply because it would have taken me a month per pendulum to do it properly and I don’t have three months to waste. Anyway, the experiment went like this.
The experiment went like this, with a 15-second video capture taken automatically every hour for a fortnight:
Test 1: pendulum 1 & pendulum 3
Test 2: pendulum 1 & pendulum 2
Test 3: pendulum 2 & pendulum 3
Pendulum 1 (left) weighs around 10 kg for a period of one second.
Pendulum 2 (centre) weighs about 3 kg for a period of 0.88 seconds.
Pendulum 3 (right) weighs about 6 kg for a period of one second.
3 Raspberries, 1 Mac, a Siemens Logo as orchestra conductor. Behind the scenes: a real mess…
The result was a bit of a cold war, with the planes of their rotations each moving as far away from the other as possible before stabilising their rotational speeds. So it was time for a real experiment, with two cameras taking photos. One of them took a photo at the end of each rotation of pendulum n°3 and recorded the time of revolution on the digital clock. The other took a long exposure photo every hour, showing the direction of oscillation of each of the pendulums.
Experiment 2, from 31 December to 11 January.
3 January: launch of the 3 pendulums, all in the same direction.
7 January: first results… Pendulum 2 is 30° behind and pendulum 1 is 55° behind. These differences have been stable for 2 days. The rotation time of the 3 pendulums is the same for all.
8 January: production of an “angle trirapporteur” to show the different angles of oscillation of the 3 pendulums as a function of their rotation. It’s not exactly the kind of measuring instrument you’d find in a shop, but it’s very practical!
Based on the following drawing:
…and used in the following way. Sorry Apple, sorry so…
Conclusions to 11 January 2024:
Yes, the 3 clocks influence each other. They synchronise their rotations, shift a little and never leave their respective places. Two tiny but constant forces (Coriolis and a few tiny bends in a wall) interact, while other much larger forces such as the multiple air currents in my workshop have no effect.
The times for each half-rotation were:
14.17 / 14.59 / 14.54 / 14.31 / 14.53 / 14.09 / 15.35 / 14.35 / 14.19 / 15.57 / 15.01 / 16.09 / 14.54
Moral of the experiment: it’s not anarchy, love, dictatorship or the Cold War, but rather the story of an old couple who never meet.
Shift in the plane of rotation after 10 days: 61° for pendulum n°1 and 13° for pendulum n°2
Experiment 3: from 11 to 17 January, repetition of experiment 2 for confirmation.
11 January: launch of the 3 pendulums, all in the same direction.
13 December: first results… Pendulum 2 is 14° behind and pendulum 1 is 27° behind. We are moving towards the same result as experiment 2.
15 December: Pendulum 2 lags 26° and pendulum 1 lags 59°.
The times of each half-rotation were
14.33/ 14.39 / 15.25 / 14.49 / 15.22 / 14.45 / 14.34 / 15.21 / 13.45
The experiment was completed on 27 January and the measuring equipment dismantled to make way for the forthcoming Bravais pendulum.
