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
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.
The hall of Gare Saint Sauveur
de la science seen from a stand (Atelier de construction) close to ours.
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.
people testing the effect of Coriolis force through our demonstrator.
Galileo's idea through our centrifugal force demonstrator.
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