So How do We Know that Earth Really Rotates?

Everyone knows that Earth rotates around its axis. But have you ever wondered is there some kind of simple proof of this? The answer is yes. The famous experiment performed by Jean Foucault proved the rotation of Earth. But let's start at the beginning.

There were ideas that the Earth might be rotating around its axis since the days of Nicolaus Copernicus (1473 - 1543). However, even though it was a rational idea, backed up by great arguments in the works of Copernicus, it wasn’t experimentally proven. Thus many people in the middle ages and later epochs weren’t aware of the fact that our planet is rotating around its axis. After all, it’s really hard to believe such a thing, as we can’t feel the Earth’s rotation.

Foucalt's Pendulum in Paris:

Source

It was Jean Foucault (1819 - 1868) a brilliant French physicist, who finally proved Earth’s rotation experimentally, more than 300 years after the works of Copernicus. Foucault built a 28 kg brass-coated lead bob with a 67 meter long wire from the dome of the Panthéon, Paris, which basically worked as a huge pendulum. The idea of the experiment is very simple – as the pendulum swings, it’s clear that Earth rotates, due to the movement of the ground below the pendulum (which, to us looks like the movement of the plane of the pendulum, as we rotate with together with Earth).

This simple, yet very hard to construct, experiment, finally proved that Earth really rotates. Furthermore, it proved the rotation of our planet in a very simple way, so that even simple people, who knew nothing about science, could easily be convinced. That is why this experiment is one of the most important experiments throughout history.


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