Fête de la science 2018: Les chercheurs face à l’erreur

COMUE Lille Nord de France, CNRS Nord – Pas de Calais et Picardie, Université de Lille
Gare Saint Sauveur, Lille – October 13 and 14, 2018

Stand L’erreur de Galilée: l’origine des marées
Stefano Berti and Enrico Calzavarini

Tides are variations of the height of seas and oceans. The cycle of rise and fall of seawaters typically takes place twice per day (semidiurnal tide) but, depending on the location on Earth, it can also occur once (diurnal tide), or it can be of mixed type. Tides are complex phenomena. Explaining them has for long time represented a scientific challenge. 
Galileo’s explanation was based on innovative concepts for his period. According to him, the tidal cycle was due to the composition of the rotation and revolution movements of Earth. In fact, such movements are responsible of the appearance of forces in the reference frame of Earth, known as fictitious, such as the centrifugal force and Coriolis force. However, this mechanism would give a 12-hour period only for the alternation of high and low tides.
According to the correct explanation, based on the theory of gravitation first developed by Newton, tides are mainly caused by a real physical force, the gravitational attraction (and particularly the reduction of its intensity with distance) exerted by the Moon on the solid Earth and on its oceans. Inertial (or fictitious) forces, even if present, play a secondary role.
Finally, tides also depend on the Sun (they are more or less intense as a function of the alignment of the Moon and the Sun), on the depth of ocean floors and on the shape of the considered basin. 

More details in our poster [pdf]

The hall of Gare Saint Sauveur hosting Fête de la science seen from a stand (Atelier de construction) close to ours.
Myself illustrating how the gravitational attraction exerted by the Moon can account for the correct periodicity of tides.
A movie showing our demonstrator of Coriolis force, which was designed and realized by Marine Le Breton, a last-year student in Mechanical engineering at Polytech’Lille, during her final-year project together with our colleague Thomas Dienne.
A movie showing the effect of centrifugal force on water masses, from which Galileo Galilei got inspired to construct his theoretical explanation of tides.
Myself coordinating people testing the effect of Coriolis force through our demonstrator.
Enrico explaining Galileo’s idea through our centrifugal force demonstrator.
Myself illustrating further effects on tides, like the modulation of their intensity due to the gravitational attraction exerted by the Sun.
Our team at Gare Saint Sauveur. This year Himani Garg (on the left) and Yoann Requile (on the right), both PhD students at our lab (Unité de Mécanique de Lille) joined us providing essential help to welcome people curious to learn about tides and to explain them the basic mechanisms governing this phenomenon.