Foucault Experiment
By Mathieu Paquette
Observations: At night, it is observable that the stars move.
Problem: What makes them change position?
Hypothesis: The Earth is rotating on itself, thus making stars appear to be moving.
Experiment: In February 1851, Jean Bernard Léon Foucault tried to demonstrate the
rotation of the Earth by making a pendulum. This pendulum was installed in the Panthéon
in Paris with a 28-kilogram bob hanging from a 67-meter-long wire.
Prediction: The pendulum will swing in its own plane, which means that the rotation of the
Earth will not affect the plane in which it swings. With that assumption, if the Earth truly
does rotate, the pendulum will seem to rotate over time since the observers will be moving
with the Earth.
Data: The pendulum did in fact appear to change trajectory over time. It then confirms the
hypothesis that the Earth rotates, and is explained by physics models as well as simple
math equations. The time that the pendulum takes to rotate can be calculated using the
latitude at which it is placed with the following equation:
𝑅=
23ℎ56′
𝑠𝑖𝑛𝜙
In this equation, 𝑅 is the time taken for the rotation, 23ℎ56′ stands for the time in a day
on Earth, and 𝜙 corresponds to the latitude of the pendulum.
For example, the demonstration of Léon Foucault took place at a latitude of 48° N (𝜙),
which, when computed, gives around 32 hours.
With the same equation, it can be predicted
that a pendulum set on the north pole, which
would have 𝑠𝑖𝑛90° 𝑁 = 1, would take exactly
one day to complete the rotation.
The same principle applies for a pendulum
set at the equator, which would not rotate,
since the sine of 0° is 0.
https://www.schoolphysics.co.uk/age1416/Astronomy/text/Foucaults_pendulum/index.html
Peer Review: The recreation of the experiment is common in museums nowadays and
produce the same results. It has even been tested on the south pole and confirmed that
it took 24 hours for the plane to complete a full rotation.