Tide - SpeedyLook encyclopedia

Origin of the phenomenon

The phenomenon is due to the deformation of the surface of the oceans in consequence of the attractions combined of the others celestial bodies. This movement can even destroy the star which undergoes it: if the Force of tide overrides the force of gravitation of its components, the star disaggregates (see the article Limite of Rock).

Physical phenomenon

Attraction nelle Gravitation being inversely proportional to the square of the distance, the star (mainly the Moon in the case of the Ground) more strongly attracts the masses (liquid and solid) close. In particular, the point nearest to the Moon is attracted more than the point on the other hand. If the average of the actions is made, one can break up the force into each point of the axis the Ground-Moon in two forces:

a average Attraction force,
a centripetal Force (compared to the Barycentre Ground/the Moon).

It follows a deformation of sea surface, but also of the grounds, which thus differs from what it would be without the presence of our satellite and of the sun.

For the sea, one can compare this deformation with enormous a Vague which would be of regular form if the ocean floors “were regular and if there were no coasts”.

A very widespread explanation historical adds that the Moon and the Earth turn around the center of inertia of the Ground-Moon unit and this rotation causes another deformation, by Centrifugal force, which explains why there are two tides per day.

An analysis of the phenomenon by the Newtonian Mechanical here detailed watch which no centrifugal effect is necessary to explain the phenomenon. This interpretation results from a difficulty of apprehending the fact that the Gravité of the moon decrease as one moves away from there: it is maximum at the point of the ground nearest to the moon, average in the center of the ground and minimal at the point furthest away from the moon. The ground thus becomes deformed in a corresponding way, taking a form of " balloon of rugby". At the point nearest to the moon, the rocks are raised less than water because they are attached much more rigidly to the center of the ground. As for the point furthest away from the moon, one can say that it " remain with the traîne". Being attracted less strongly than the center of the ground (and than any other point of planet), it approaches the moon less quickly than the remainder of planet, from where the " bosse" (mysterious for much of people) which is formed at this place. The rocks being attached to the remainder of planet more rigidly than the oceans, they are drawn more strongly than those in direction from the moon (which is on the other side of the ground). In this case, the tide is thus not a " montée" water, but rather a " enfoncement" ground in direction of the moon, which is under the feet of the observers! What occurs with the moon combines with a similar effect of the sun (much less extremely than that the moon). It is when the two effects are superimposed that the tides are strongest.

Spring tides

The passage of the Moon to the Meridian of the place (possibly with a certain delay in the forced Oscillations; one will call “meridian line of tide” the meridian line which corresponds to the time angle of delay of the tides) or to opposition explains the semi-diurnal cycle. The period of this phenomenon is of 0,517525050 day (12 hours 25 minutes 14 seconds), half of the duration of the lunar Jour average.

Several astronomical phenomena contribute to the variation of the amplitude of the tides:

the Syzygy of the Sun and the Moon (in other words, the news or full moon). That occurs primarily when the Longitude Sun and the Moon are close or close to the opposition one to the other, that is to say twice per month. Precisely, the period of this phenomenon is 14,7652944 days, half of the duration that one qualifies synodical Mois.
the passage of the Sun to the lunar Node, i.e. the passage of the Sun in the plan of the lunar orbit: this one occurs twice a year (with the regression of the node near), and determines the “seasons with eclipse” (it is during those that the eclipse S of sun or the moon occur). The tides are then more important in syzygy (see the preceding point) because of best alignment Ground-Moon-Sun. The precise period is 173,310038 days, half of the duration that one qualifies draconitic Année. The passage of the Sun to the lunar node for example occurred the January 25th 2000, the July 16th 2000, the January 5th 2001, the June 28th 2001 (more precisely, this are the dates of coincidence of average longitudes; in particular, the calculation of the anomalies is omitted; but one recognizes the vicinity of the moon eclipse of the January 9th 2001 and the eclipse of the sun of the June 21st 2001). As it is noted, these dates are currently close to the Solstice S but evolve/move quickly in the year during time.
the passage of the Sun in the equatorial Plane , which is done with the equinox S, therefore twice a year. The precise period is 182.621095 days, half of a Tropical year. The phenomenon of the equinoctial tides is rather difficult to include/understand and we must be satisfied to indicate some tracks. Firstly, it is about a phenomenon in bond with the position of the ground compared to the sun, in which the moon does not play any direct part (even if the effects due to the moon and those due to the sun are added, one can reason as if the moon were not there). As opposed to what believe much of people, this phenomenon does not have thus anything to see with the alignment moon-ground-sun, which takes place every two weeks with full moon and with the new moon and is carried out of as much better when it coincides with 173 days the draconitic cycle HTTP: /fr.wikipedia.org/wiki/%C3%89clipse#Principes_m.C3.A9caniques. Secondly, contrary to other phenomena, it cannot be included/understood if one reasons in a static way. One can understand very well that the alignment of the ground, the moon and the sun generates important tides even while imagining (for the needs for the demonstration) that these stars are motionless (even if it is a false reasoning, parce the water of the oceans moves with a certain delay on the stars). But in the case of the equinoxes, if one reasons with motionless stars, one concludes that there is no difference between equinoxes and solstices. It is thus essential to think of the dynamics of the tides. These two preliminaries being posed, it should be known that the sun is with the top of Ecuador at the time of the equinoxes, whereas it is with the top of the tropic of Cancer at the time of the solstice of June and with the top of the tropic of Capricorn at the time of the solstice of December. Let us recall that the effect of tide of a star is maximum at the being point of the ground the close relation of this star and at the point being most distant. At the time of the equinoxes, these two points will be permanently on Ecuador. Each point of the equator will thus be subjected for a maximum purpose of tide of the sun twice a day (one speaks about semi-diurnal wave). At the times of the solstices, one of the points where the effect of tide of the sun is maximum will be permanently on the tropic of Cancer, while the other is with the antipodes, on the tropic of Capricorn. Each point being on one of the two tropics will thus be subjected for a maximum purpose of tide of the Sun only once per day (one speaks about diurnal wave). From these facts, it is still not easy to include/understand why the equinoctial tides are stronger. But the consulted sources agree to affirm that it is this difference between diurnal and semi-diurnal waves which is at the origin of the particular force of the equinoctial tides. At this time, the diurnal term is cancelled in the calculation of the tides, and the semi-diurnal term is maximum.
the passage of the Moon to the Perigee, moment to which the forces of tide exerted by the Moon are thus most important. With the difference in the lunar node, which regresses on the ecliptic , the perigee, advances to him. Time between two passages of the Moon to the perigee is the anomalistic Mois, 27,5545499 days. The calculation of the position of the lunar perigee is subjected to enormously disturbances.
the passage of the Earth to the Perihelion, moment to which the forces of tide exerted by the Sun are thus most important. The terrestrial perihelion progresses on the ecliptic; this known as, the major part (approximately 5/6) of this progression is actually due to the regression (“precession”) of the equinox compared to fixed stars. Time separating two passages from the Earth to the perihelion is the anomalistic Année 365,259636 days. It currently occurs on January 3rd of the year.

It is possible to have rather good conjunctions between all these phenomena.

Tides

See also: Calculation of tide

For the Ground, only the the Moon and the Sun have significant impacts, which are added or opposed according to the respective positions of the Earth, the Moon and the Sun. In fact, the Moon is much closer to the Earth than the Sun, but has also a mass much smaller, so that their attractions are comparable orders of magnitude: that of the Sun is approximately half of that of the Moon. The other celestial bodies are too distant so that their influence is sensitive. Historically, Bernardin of St-Pierre had persuaded the Academy of Science of the time that it was not the Moon but the cast iron (alternate with night freezing) of the Glacier S which caused the tides. Pushing until the end its reasoning, the great amplitude of the equinoctial tides was justified by the combined action of the glaciers Arctique S and the Antarctic S. In antiquity, Plato thought that the tides were caused by oscillations of the Earth. Later, Galileo, basing itself on work of Copernic, described the origin of the tides like resulting from the rotation of the Earth and its revolution around the Sun.

The phenomenon of tides is due to the combination of the attraction exerted by the moon and that (weaker) exerted by the Sun on the mass of the oceans. This combined attraction is however disturbed or even sometimes opposed by other physical phenomena like the inertia of the water masses, the shape of the coasts, the current sailors, the depth of the seas, or the direction of the local wind.

; Marine currents: The Earth moves during its convolution between two lines of Circonférence forming a crown whose spacing is the diameter of the Earth, approximately 12 756 km. This leads us to note that the interior circumference is shorter than the external one. This difference results in 80 150 km in 1 year are approximately 220 km per day and a little more than 9 km/h which correspond to the difference in rate of travel in space between the interior and outside of the crown, that is to say the face midday and the face midnight of our terrestrial sphere. This difference is at the origin of the marine currents with misinterpretation of rotation along the equator.

; Inertia: It is a force which is opposed to the movement of a mass that one wants to move (increase speed) or to stop (reduction speed). When the mass is important, the Inertie is important. It is the case of the water mass of all the oceans of the sphere, which tries to oppose the movements to which it is subjected by combined attraction of the moon and the sun.

There are generally two cycles of tide per day (there are exceptions) whose moments of open sea and basic sea vary with the moon (dominating attraction).

The tide appears primarily on the maritime coasts, where the sea goes up or is withdrawn according to a bound cycle, on the one hand with the rotation of the Ground and its revolution around the Sun, on the other hand with the rotation of the the Moon around the Earth. This complete cycle (low tide and high tide) lasts approximately 12 hours 25 minutes.

; The piston effect: When the coasts are tightened in funnel , as in the content of some bays (bay of Mount-Saint-Michel, Baie of Fundy, etc) there is amplification height of the tides which can exceed 14 Mètre S between low waters and high waters. It also produced there a progressive time delay as in Handle of the entry with Dunkirk.

The inland seas are not very prone to the tides because the water masses and the distances between the coasts concerned are much lower than in the Océan S. It is in particular the case of the the Mediterranean, where the narrowness of the Straits of Gibraltar prevents the passage of the tidal wave.

It should be noted that the ground is subject to also the influence of the Moon, or at least of the tides, the continents float on a coat of magma liquid and of this fact move like the oceans. With Paris at the hours of high tide one is approximately 30 centimetres higher than at the hours of low tide.

Marling

Coefficient of the tide

Remarkable places of tides

With the Canada, in the Baie of Ungava marling can reach 17 or 20 meters and in the Baie of Fundy up to 16 meters. These bays are the two places where the most important tides in the world take place. According to the sources, one allots to one or the other the record of marling.
the Channel of Bristol-board (Great Britain) with 15 meters of marling.
strongest of France (up to 14 meters of marling) in bay of the Mount-Saint-Michel, where it is traditionally known as that “the sea goes up at the speed of a horse to the gallop”.
the Saltstraumen in Norway, filling a Fjord of 400 million cubic meters.
Horizontal Falls in Western Australia, area of Kimberley (10 meters of marling approximately).
Pondichéry and certain ports of the Vietnam where there is only one tide per day.

Models of tides

August 1st

See too

tide|tide

Force of tide
Calculation of tide
Estran
tidal Power plant of Rancid the

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