. “Water has its own time: the hours of high tide, the hours of low tide.” Mayakovsky .
|| trans. Decrease, decline in the development of something. "The ebb and flow of love." A.K. Tolstoy .
2. A reflection, a shade of color mixed with the main one. “The field shines with a golden tint.” Chernyshevsky . “A large black braid with a blue tint.” Nekrasov .
Ushakov's Explanatory Dictionary. D.N. Ushakov. 1935-1940.
Synonyms:
See what "LOW" is in other dictionaries:
Shade, drainage, leakage, highlight, casting, reflection, reflection, drainage, casting Dictionary of Russian synonyms. tint 1. see shade 1. 2. see reflection... Synonym dictionary
LOW TIDE, ah, husband. 1. see cast 1. 2. Periodically repeated retreat of the border of the sea, ocean. At low tide. | adj. low tide, oh, oh. II. LOW TIDE, ah, husband. Shade against the background of what n. colors. Silver o. Ozhegov's explanatory dictionary. S.I. Ozhegov, N.Yu... Ozhegov's Explanatory Dictionary
LOW TIDE 1, a, m. Ozhegov’s Explanatory Dictionary. S.I. Ozhegov, N.Yu. Shvedova. 1949 1992 … Ozhegov's Explanatory Dictionary
LOW TIDE 2, a, m. Shade against the background of what n. colors. Silver o. Ozhegov's explanatory dictionary. S.I. Ozhegov, N.Yu. Shvedova. 1949 1992 … Ozhegov's Explanatory Dictionary
A canopy designed to protect the bottom of the window and remove moisture. Source: Dictionary of architectural and construction terms... Construction dictionary
Low tide- - a visor designed to protect the lower part of the window and remove moisture... Builder's Dictionary
low tide- ebb current The reverse of the tidal current. Leads to lower sea levels. Topics oceanology Synonyms ebb current EN ebb tideebb flow ... Technical Translator's Guide
low tide- A state of the sea opposite to the climax of the tide, a decline in sea level immediately following the tide. → Fig. 103... Dictionary of Geography
Low tide- Flashing, rainproof profile - a part designed to drain rainwater and protect the window structure from its penetration. [GOST 23166 99] Term heading: Window and door blocks Encyclopedia headings: Abrasive equipment,... ... Encyclopedia of terms, definitions and explanations of building materials
Wiktionary has an entry for "low tide" Low tide: A periodic decrease in water level due to the movement of the Moon. The opposite in meaning to tide. Low tide in construction has two meanings: a metal or plastic strip, which... ... Wikipedia
Books
- Low tide. History of capricious water, Victor Kolosov. “At first you live slowly. Then you do it faster. Then you simply don’t notice that you’re alive. Then you try...
The content of the article
Ebbs and flows, periodic fluctuations in water levels (rises and falls) in water areas on Earth, which are caused by the gravitational attraction of the Moon and Sun acting on the rotating Earth. All large water areas, including oceans, seas and lakes, are subject to tides to one degree or another, although they are small in lakes.
Reversible waterfall
(reversing direction) is another phenomenon associated with tides in rivers. A typical example is the waterfall on the Saint John River (New Brunswick, Canada). Here, through a narrow gorge, water during high tide penetrates into a basin located above the low water level, but slightly below the high water level in the same gorge. Thus, a barrier arises, flowing through which water forms a waterfall. During low tide, the water flows downstream through a narrowed passage and, overcoming an underwater ledge, forms an ordinary waterfall. During high tide, a steep wave that penetrates the gorge falls like a waterfall into the overlying basin. The backward flow continues until the water levels on both sides of the threshold are equal and the tide begins to ebb. Then the waterfall facing downstream is restored again. The average water level difference in the gorge is approx. 2.7 m, however, at the highest tides, the height of the direct waterfall can exceed 4.8 m, and the reverse one - 3.7 m.
Greatest tidal amplitudes.
The world's highest tide is generated by strong currents in Minas Bay in the Bay of Fundy. Tidal fluctuations here are characterized by a normal course with a semi-diurnal period. The water level at high tide often rises by more than 12 m in six hours, and then drops by the same amount over the next six hours. When the effect of spring tide, the position of the Moon at perigee and the maximum declination of the Moon occur on the same day, the tide level can reach 15 m. This exceptionally large amplitude of tidal fluctuations is partly due to the funnel-shaped shape of the Bay of Fundy, where the depths decrease and the shores move closer together towards top of the bay.
Wind and weather.
Wind has a significant influence on tidal phenomena. The wind from the sea pushes the water towards the coast, the height of the tide increases above normal, and at low tide the water level also exceeds the average. On the contrary, when the wind blows from land, water is driven away from the coast, and sea level drops.
Due to the increase in atmospheric pressure over a vast area of water, the water level decreases, as the superimposed weight of the atmosphere is added. When atmospheric pressure increases by 25 mmHg. Art., the water level drops by approximately 33 cm. The decrease in atmospheric pressure causes a corresponding increase in the water level. Consequently, a sharp drop in atmospheric pressure combined with hurricane-force winds can cause a noticeable rise in water levels. Such waves, although called tidal, are in fact not associated with the influence of tidal forces and do not have the periodicity characteristic of tidal phenomena. The formation of these waves can be associated either with hurricane force winds or with underwater earthquakes (in the latter case they are called seismic sea waves, or tsunamis).
Using tidal energy.
Four methods have been developed to harness tidal energy, but the most practical is to create a tidal pool system. At the same time, fluctuations in water levels associated with tidal phenomena are used in the lock system so that a level difference is constantly maintained, which allows energy to be generated. The power of tidal power plants directly depends on the area of the trap pools and the potential level difference. The latter factor, in turn, is a function of the amplitude of tidal fluctuations. The achievable level difference is by far the most important for power generation, although the cost of the structures depends on the area of the basins. Currently, large tidal power plants operate in Russia on the Kola Peninsula and in Primorye, in France in the Rance River estuary, in China near Shanghai, as well as in other areas of the globe.
| INFORMATION ABOUT TIDES IN SOME PORTS OF THE WORLD | ||||
| Port | Interval between tides | Average tide height, m | Height of spring tide, m | |
| h | min | |||
| m. Morris-Jessep, Greenland, Denmark | 10 | 49 | 0,12 | 0,18 |
| Reykjavik, Iceland | 4 | 50 | 2,77 | 3,66 |
| R. Koksoak, Hudson Strait, Canada | 8 | 56 | 7,65 | 10,19 |
| St. John's, Newfoundland, Canada | 7 | 12 | 0,76 | 1,04 |
| Barntko, Bay of Fundy, Canada | 0 | 09 | 12,02 | 13,51 |
| Portland, USA Maine, USA | 11 | 10 | 2,71 | 3,11 |
| Boston, USA Massachusetts, USA | 11 | 16 | 2,90 | 3,35 |
| New York, NY New York, USA | 8 | 15 | 1,34 | 1,62 |
| Baltimore, pc. Maryland, USA | 6 | 29 | 0,33 | 0,40 |
| Miami Beach Florida, USA | 7 | 37 | 0,76 | 0,91 |
| Galveston, pc. Texas, USA | 5 | 07 | 0,30 | 0,43* |
| O. Maraca, Brazil | 6 | 00 | 6,98 | 9,15 |
| Rio de Janeiro, Brazil | 2 | 23 | 0,76 | 1,07 |
| Callao, Peru | 5 | 36 | 0,55 | 0,73 |
| Balboa, Panama | 3 | 05 | 3,84 | 5,00 |
| San Francisco California, USA | 11 | 40 | 1,19 | 1,74* |
| Seattle, Washington, USA | 4 | 29 | 2,32 | 3,45* |
| Nanaimo, British Columbia, Canada | 5 | 00 | ... | 3,42* |
| Sitka, Alaska, USA | 0 | 07 | 2,35 | 3,02* |
| Sunrise, Cook Inlet, USA Alaska, USA | 6 | 15 | 9,24 | 10,16 |
| Honolulu, pc. Hawaii, USA | 3 | 41 | 0,37 | 0,58* |
| Papeete, about. Tahiti, French Polynesia | ... | ... | 0,24 | 0,33 |
| Darwin, Australia | 5 | 00 | 4,39 | 6,19 |
| Melbourne, Australia | 2 | 10 | 0,52 | 0,58 |
| Rangoon, Myanmar | 4 | 26 | 3,90 | 4,97 |
| Zanzibar, Tanzania | 3 | 28 | 2,47 | 3,63 |
| Cape Town, South Africa | 2 | 55 | 0,98 | 1,31 |
| Gibraltar, Vlad. Great Britain | 1 | 27 | 0,70 | 0,94 |
| Granville,France | 5 | 45 | 8,69 | 12,26 |
| Leath, UK | 2 | 08 | 3,72 | 4,91 |
| London, Great Britain | 1 | 18 | 5,67 | 6,56 |
| Dover, UK | 11 | 06 | 4,42 | 5,67 |
| Avonmouth, UK | 6 | 39 | 9,48 | 12,32 |
| Ramsey, Fr. Maine, UK | 10 | 55 | 5,25 | 7,17 |
| Oslo, Norway | 5 | 26 | 0,30 | 0,33 |
| Hamburg, Germany | 4 | 40 | 2,23 | 2,38 |
| * Daily tide amplitude. | ||||
Literature:
Shuleykin V.V. Physics of the sea. M., 1968
Harvey J. Atmosphere and ocean. M., 1982
Drake C., Imbrie J., Knaus J., Turekian K. The ocean is for itself and for us. M., 1982
Ebbs and flows - natural phenomena, which many people have heard about and observed, especially those living on the seashore or ocean. What are ebbs and flows, what power lies in them, why they arise, read the article.
Meaning of the word "tide"
According to explanatory dictionary Efremova, a tide is a natural phenomenon when the level of the open sea rises, that is, it rises, and this repeats periodically. What does tide mean? According to Ozhegov's explanatory dictionary, a tide is an influx, an accumulation of something moving.
Tide - what is it?
This is a natural phenomenon when the water level in the ocean, sea or other body of water regularly rises and falls. What is a tide? This is a response to the influence of gravitational forces, that is, the forces of attraction possessed by the Sun, Moon and other tidal forces.
What is a tide? This is the rise of ocean water to its highest level, which occurs every 13 hours. Low tide is the opposite phenomenon in which the water in the ocean drops to its lowest level.
Ebb and flow - what is it? This is a fluctuation in water level that occurs periodically vertically. This natural phenomenon, ebb and flow, occurs because the position of the Sun and Moon changes relative to the Earth, along with the rotating effects of the Earth and the features of the relief.
Where do the tides occur?
These natural phenomena are observed in almost all seas. They are expressed in periodic increases and decreases in water levels. Tides occur on opposite sides of the Earth, which lie next to the line directed towards the Sun and Moon. The formation of a hump on one side of the Earth is influenced by direct attraction celestial bodies, and on the other - their least attraction. Since the Earth rotates, near the seashore at each point in one day there are two high tides and the same number of low tides.
Tides are not the same. The movement of water masses and the level to which water rises in the sea depend on many factors. This is the latitude of the area, the outline of the land, atmospheric pressure, wind strength and much more.
Varieties
Ebbs and flows are classified according to the duration of the cycle. They are:
- Half daily allowance, when there are two high tides and two low tides per day, that is, the transformation of the space of water in the ocean or sea consists of full and incomplete waters. The amplitude parameters, which alternate with each other, have practically no differences. They look like a curved sinusoidal line and are localized in the waters of a sea such as the Barents Sea, off the coast of the White Sea, and are distributed throughout almost the entire Atlantic Ocean.
- Daily allowance- characterized by one high tide and the same number of low tides during the day. Such natural phenomena are also observed in the Pacific Ocean, but very rarely. So, if the Earth's satellite passes through the equatorial zone, standing water is observed. But if the declination of the Moon occurs with the smallest index, low-power tides of an equatorial nature are observed. If the numbers are higher, tropical tides are formed, accompanied by significant strength.
- Mixed, when semidiurnal or diurnal tides with an irregular configuration predominate in height. For example, in semi-diurnal changes in the level of the hydrosphere there is a similarity with semi-diurnal tides in many ways, and in diurnal changes - with tides of the same time, that is, diurnal, which depend on the degree to which the Moon is inclined in a given period of time. Ebbs and flows mixed type more often found in the waters of the Pacific Ocean.
- Abnormal tides- characterized by rises and falls of water that do not fit any description based on various characteristics. The anomaly has a direct connection with shallow water, as a result of which the cycle of both rise and fall of water changes. This process particularly affects river mouths. Here the high tides are shorter than the low tides. Similar cataclysms characterize certain sections of the English Channel, as well as the currents of the White Sea.
However, the tides are practically invisible in the seas, which are called internal, that is, separated from the ocean by straits, narrow in width.
What creates tides?
If the forces of gravity and inertia are disrupted, tides arise on Earth. The natural phenomenon of tides is more pronounced along the ocean coasts. Here twice a day varying degrees The water level rises and falls the same number of times. This happens because humps form on the surface of two opposite regions of the ocean. Their position is determined depending on the position of the Moon and the Sun.
Moon influence
The Moon has a greater influence on the occurrence of tides than the Sun. As a result of numerous studies, it has been found that the point on the earth's surface located closest to the Moon is influenced by external factors 6% more than the most distant one. In this regard, scientists have concluded that thanks to this demarcation of forces, the Earth is moving apart in the direction of such a trajectory as the Moon-Earth.
Taking into account the fact that the Earth rotates around its axis in one day, during this time a double tidal wave passes along the created stretch, or more precisely, its perimeter, twice. This process creates double "valleys". Their height in the World Ocean reaches two meters, and on land - 40-43 centimeters, so this phenomenon goes unnoticed for the inhabitants of the planet. We do not feel the power of the ebb and flow of the tides, no matter where we are: on land or on water. Although people are familiar with this phenomenon, observing it on the coastline. Sea or ocean waters sometimes gain quite a high altitude by inertia, then we see waves rolling onto the shore - this is the tide. When they roll back, the tide is low.
Influence of the Sun
Main star solar system located far from Earth. For this reason, its impact on our planet is little noticeable. The Sun is more massive than the Moon, if we consider these celestial bodies as sources of energy. But the large distance between the star and the Earth affects the amplitude of solar tides; it is two times less than similar processes on the Moon. When there is a full moon and the moon is waxing, the celestial bodies - the Sun, the Earth and the Moon - have the same position, as a result of which the solar and lunar tides add up. The Sun has little influence on the tides during the period when gravitational forces from the Earth go in two directions: to the Moon and the Sun. At this time, the ebb tide level rises and the tide level decreases.
Land on the planet occupies 30% of the surface. The rest is covered by oceans and seas, with which many secrets and natural phenomena are associated. One of them is the so-called red tide. This phenomenon is amazing in beauty. It occurs off the Florida Gulf Coast and is considered the largest, especially during the summer months of June or July. How often you can observe a red tide depends on a banal reason - human pollution of coastal waters. The waves have a rich bright red or orange hue. This is an amazing sight, but admiring it for a long time is dangerous for your health.
The fact is that algae give color to the water during flowering. This period occurs very intensively, plants secrete a large number of toxins and chemicals. They do not dissolve completely in water; some of them are released into the air. These substances are very harmful to plants, animals, and seabirds. People often suffer from them. Particularly dangerous to humans are shellfish caught from the red tide zone. A person who consumes them gets severe poisoning, often leading to death. The fact is that the oxygen level decreases during high tide, ammonia and hydrogen sulfide appear in the water. They are the cause of poisoning.
What are the highest tides in the world?
If the shape of the bay is funnel-shaped, when a tidal wave hits it, the shores are compressed. Because of this, the height of the tide increases. Thus, the height of the tidal wave off the eastern coast of North America, namely in the Bay of Fundy, reaches approximately 18 meters. In Europe, the highest tides (13.5 meters) are in Brittany, near Saint-Malo.
How do tides affect the inhabitants of the planet?
Marine inhabitants are especially susceptible to these natural phenomena. The tides have the greatest influence on the inhabitants of the waters in the coastal strip. As the level of earth's water changes, organisms with a sedentary lifestyle develop. These are mollusks and oysters, for which changes in the structure of the water element do not prevent them from reproducing. This process occurs much more actively during high tides.
But for many organisms, periodic fluctuations in water levels bring suffering. It is especially difficult for small animals; many of them completely change their habitat during high tides. Some move closer to the shore, while others, on the contrary, are carried deep into the ocean by the wave. Nature, of course, coordinates all changes on the planet, but living organisms adapt to the conditions presented by the activity of the Moon, as well as the Sun.
What role do tides play?
We have explained what ebbs and flows are. What is their role in human life? These natural phenomena have titanic power, which, unfortunately, is little used at present. Although the first attempts in this direction were made in the middle of the last century. IN different countries hydroelectric power stations using the power of tidal waves have begun to be built around the world, but there are still very few of them.
The significance of tides is also enormous for shipping. It is during their formation that ships enter the river many kilometers upstream to unload goods. Therefore, it is very important to know when these phenomena will occur, for which special tables are compiled. Ship captains use them to determine the exact time of the tides and their height.
Ebb and flow
Tide And low tide- periodic vertical fluctuations in ocean or sea level, resulting from changes in the positions of the Moon and the Sun relative to the Earth, coupled with the effects of the Earth’s rotation and the features of a given relief and manifested in periodic horizontal displacement of water masses. Tides cause changes in sea level height, as well as periodic currents known as tidal currents, making tide prediction important for coastal navigation.
The intensity of these phenomena depends on many factors, but the most important of them is the degree of connection of water bodies with the world ocean. The more closed the body of water, the less the degree of manifestation of tidal phenomena.
The annually repeated tidal cycle remains unchanged due to the precise compensation of the forces of attraction between the Sun and the center of mass of the planetary pair and the forces of inertia applied to this center.
As the position of the Moon and Sun in relation to the Earth changes periodically, the intensity of the resulting tidal phenomena also changes.
Low tide at Saint-Malo
Story
Low tides played a significant role in the supply of seafood to coastal populations, allowing edible food to be collected from the exposed seabed.
Terminology
Low Water (Brittany, France)
The maximum surface level of the water at high tide is called full of water, and the minimum during low tide is low water. In the ocean, where the bottom is flat and the land is far away, full water appears as two “swells” of the water surface: one of them is located on the side of the Moon, and the other is at the opposite end of the globe. There may also be two more smaller swellings on the side directed towards the Sun and opposite to it. An explanation of this effect can be found below, in the section tide physics.
Since the Moon and Sun move relative to the Earth, water humps also move with them, forming tidal waves And tidal currents. In the open sea, tidal currents have a rotational character, and near the coast and in narrow bays and straits they are reciprocating.
If the entire Earth were covered with water, we would experience two regular high and low tides every day. But since the unimpeded propagation of tidal waves is hampered by land areas: islands and continents, and also due to the action of the Coriolis force on moving water, instead of two tidal waves there are many small waves that slowly (in most cases with a period of 12 hours 25.2 minutes ) run around a point called amphidromic, in which the tidal amplitude is zero. The dominant component of the tide (lunar tide M2) forms about a dozen amphidromic points on the surface of the World Ocean with the wave moving clockwise and about the same number counterclockwise (see map). All this makes it impossible to predict the time of tide only based on the positions of the Moon and Sun relative to the Earth. Instead, they use a "tide yearbook" - a reference guide for calculating the time of the onset of tides and their heights in various points of the globe. Tide tables are also used, with data on the moments and heights of low and high waters, calculated a year in advance for main tidal ports.
Tide component M2
If we connect points on the map with the same tide phases, we get the so-called cotidal lines, radially diverging from the amphidromic point. Typically, cotidal lines characterize the position of the tidal wave crest for each hour. In fact, cotidal lines reflect the speed of propagation of a tidal wave in 1 hour. Maps that show lines of equal amplitudes and phases of tidal waves are called cotidal cards.
Tide height- difference between highest level water at high tide (high water) and its lowest level at low tide (low water). The height of the tide is not a constant value, but its average is given when characterizing each section of the coast.
Depending on the relative position Moon and Sun small and large tidal waves can reinforce each other. Special names have historically been developed for such tides:
- Quadrature tide- the lowest tide, when the tidal forces of the Moon and the Sun act at right angles to each other (this position of the luminaries is called quadrature).
- Spring tide- the highest tide, when the tidal forces of the Moon and the Sun act along the same direction (this position of the luminaries is called syzygy).
The lower or higher the tide, the lower or higher the ebb.
Highest tides in the world
Can be observed in the Bay of Fundy (15.6-18 m), which is located on the east coast of Canada between New Brunswick and Nova Scotia.
On the European continent, the highest tides (up to 13.5 m) are observed in Brittany near the city of Saint-Malo. Here the tidal wave is focused by the coastline of the peninsulas of Cornwall (England) and Cotentin (France).
Physics of the tide
Modern formulation
In relation to planet Earth, the cause of tides is the presence of the planet in the gravitational field created by the Sun and Moon. Since the effects they create are independent, the impact of these celestial bodies on Earth can be considered separately. In this case, for each pair of bodies we can assume that each of them revolves around a common center of gravity. For the Earth-Sun pair, this center is located deep in the Sun at a distance of 451 km from its center. For the Earth-Moon pair, it is located deep in the Earth at a distance of 2/3 of its radius.
Each of these bodies experiences tidal forces, the source of which is the force of gravity and internal forces that ensure the integrity of the celestial body, in the role of which is the force of its own attraction, hereinafter called self-gravity. The emergence of tidal forces can be most clearly seen in the Earth-Sun system.
The tidal force is the result of the competing interaction of the gravitational force, directed towards the center of gravity and decreasing in inverse proportion to the square of the distance from it, and the fictitious centrifugal force of inertia caused by the rotation of the celestial body around this center. These forces, being opposite in direction, coincide in magnitude only at the center of mass of each of the celestial bodies. Thanks to action internal forces The Earth revolves around the center of the Sun as a whole with a constant angular velocity for each element of its constituent mass. Therefore, as this element of mass moves away from the center of gravity, the centrifugal force acting on it increases in proportion to the square of the distance. A more detailed distribution of tidal forces in their projection onto a plane perpendicular to the ecliptic plane is shown in Fig. 1.
Fig. 1 Diagram of the distribution of tidal forces in projection onto a plane perpendicular to the Ecliptic. The gravitating body is either to the right or to the left.
The reproduction of changes in the shape of bodies exposed to them, achieved as a result of the action of tidal forces, can, in accordance with the Newtonian paradigm, be achieved only if these forces are completely compensated by other forces, which may include the force of universal gravity.
Fig. 2 Deformation of the Earth’s water shell as a consequence of the balance of tidal force, self-gravitational force and the force of reaction of water to compression force
As a result of the addition of these forces, tidal forces arise symmetrically on both sides of the globe, directed in different directions from it. The tidal force directed towards the Sun is of gravitational nature, while the force directed away from the Sun is a consequence of the fictitious force of inertia.
These forces are extremely weak and cannot be compared with the forces of self-gravity (the acceleration they create is 10 million times less than the acceleration of gravity). However, they cause a shift in the water particles of the World Ocean (the resistance to shear in water at low speeds is practically zero, while to compression it is extremely high), until the tangent to the surface of the water becomes perpendicular to the resulting force.
As a result, a wave appears on the surface of the world's oceans, occupying a constant position in systems of mutually gravitating bodies, but running along the surface of the ocean together with the daily movement of its bottom and shores. Thus (ignoring ocean currents), each particle of water undergoes an oscillatory movement up and down twice during the day.
Horizontal movement of water is observed only near the coast as a consequence of a rise in its level. The more shallow the seabed is, the greater the speed of movement.
Tidal potential
(concept of acad. Shuleikina)
Neglecting the size, structure and shape of the Moon, we write down the specific gravitational force of the test body located on Earth. Let be the radius vector directed from the test body towards the Moon, and let be the length of this vector. In this case, the force of attraction of this body by the Moon will be equal to
where is the selenometric gravitational constant. Let's place the test body at point . The force of attraction of a test body placed at the center of mass of the Earth will be equal to
Here, and is understood as the radius vector connecting the centers of mass of the Earth and the Moon, and their absolute values. We will call the tidal force the difference between these two gravitational forces
In formulas (1) and (2), the Moon is considered a ball with a spherically symmetrical mass distribution. The force function of attraction of a test body by the Moon is no different from the force function of attraction of a ball and is equal to. The second force is applied to the center of mass of the Earth and is a strictly constant value. To obtain the force function for this force, we introduce a time coordinate system. Let's draw the axis from the center of the Earth and direct it towards the Moon. The directions of the other two axes will be left arbitrary. Then the force function of the force will be equal to . Tidal potential will be equal to the difference of these two force functions. We denote it , we obtain The constant is determined from the normalization condition, according to which the tidal potential in the center of the Earth is equal to zero. In the center of the Earth, It follows that. Consequently, we obtain the final formula for the tidal potential in the form (4)
Because the
For small values of , , the last expression can be represented in the following form
Substituting (5) into (4), we get
Deformation of the planet's surface under the influence of tides
The disturbing influence of the tidal potential deforms the leveled surface of the planet. Let us evaluate this impact, assuming that the Earth is a ball with a spherically symmetrical mass distribution. The unperturbed gravitational potential of the Earth on the surface will be equal to . For point . , located at a distance from the center of the sphere, the gravitational potential of the Earth is equal to . Reducing by the gravitational constant, we get . Here the variables are and . Let us denote the ratio of the masses of the gravitating body to the mass of the planet by a Greek letter and solve the resulting expression for:
Since with the same degree of accuracy we obtain
Considering the smallness of the ratio, the last expressions can be written as follows
We have thus obtained the equation of a biaxial ellipsoid, whose axis of rotation coincides with the axis, i.e. with the straight line connecting the gravitating body with the center of the Earth. The semi-axes of this ellipsoid are obviously equal
At the end we give a small numerical illustration of this effect. Let's calculate the tidal hump on Earth caused by the attraction of the Moon. The radius of the Earth is equal to km, the distance between the centers of the Earth and the Moon, taking into account the instability of the lunar orbit, is km, the ratio of the Earth's mass to the Moon's mass is 81:1. Obviously, when substituting into the formula, we get a value approximately equal to 36 cm.
see also
Notes
Literature
- Frisch S. A. and Timoreva A. V. Course of general physics, Textbook for physics-mathematics and physics-technical faculties of state universities, Volume I. M.: GITTL, 1957
- Shchuleykin V.V. Physics of the sea. M.: Publishing house "Science", Department of Earth Sciences of the USSR Academy of Sciences 1967
- Voight S.S. What are tides? Editorial Board of Popular Science Literature of the Academy of Sciences of the USSR
Links
The water surface level in the seas and oceans of our planet changes periodically and fluctuates in certain intervals. These periodic oscillations are sea tides.
Picture of sea tides
To visualize picture of sea ebbs and flows, imagine that you are standing on the sloping shore of the ocean, in some bay, 200–300 meters from the water. There's a lot on the sand various items- an old anchor, a little closer a large pile of white stone. Now, not far away, lies the iron hull of a small boat, fallen on its side. The bottom of its hull in the bow is badly damaged. Obviously, once this ship, being not far from the shore, hit an anchor. This accident occurred, in all likelihood, during low tide, and, apparently, the ship had been lying in this place for many years, since almost its entire hull had become covered with brown rust. You are inclined to consider the careless captain to be the culprit of the ship's accident. Apparently, the anchor was the sharp weapon that the ship that had fallen on its side struck. You are looking for this anchor and cannot find it. Where could he have gone? Then you notice that the water is already approaching a pile of white stones, and then you realize that the anchor you saw has long been flooded by a tidal wave. The water “steps” onto the shore, it continues to rise further and further upward. Now the pile of white stones turned out to be almost all hidden under water.Phenomena of sea tides
Phenomena of sea tides people have long been associated with the movement of the Moon, but this connection remained a mystery until the brilliant mathematician Isaac Newton did not explain on the basis of the law of gravity he discovered. The cause of these phenomena is the effect of the Moon’s gravity on the Earth’s water shell. Still famous Galileo Galilei connected the ebb and flow of the tides with the rotation of the Earth and saw in this one of the most substantiated and true proofs of the validity of the teachings of Nicolaus Copernicus (more details:). The Paris Academy of Sciences in 1738 announced a prize to the one who would give the most substantiated presentation of the theory of tides. The award was then received Euler, Maclaurin, D. Bernoulli and Cavalieri. The first three took Newton's law of gravitation as the basis for their work, and the Jesuit Cavalieri explained tides based on Descartes' vortex hypothesis. However, the most outstanding works in this area belong to Newton and Laplace, and all subsequent research is based on the findings of these great scientists.How to explain the phenomenon of ebb and flow
How most clearly explain the phenomenon of ebb and flow. If for simplicity we assume that earth's surface everything is completely covered with a water shell, and if we look at the globe from one of its poles, then the picture of sea ebbs and flows can be imagined as follows.Lunar attraction
That part of the surface of our planet that faces the Moon is closest to it; as a result, it is exposed to greater force lunar gravity, than, for example, the central part of our planet and, therefore, is pulled towards the Moon more than the rest of the Earth. Because of this, a tidal hump is formed on the side facing the Moon. At the same time, on the opposite side of the Earth, which is least subject to the gravity of the Moon, the same tidal hump appears. The Earth therefore takes the form of a figure somewhat elongated along a straight line connecting the centers of our planet and the Moon. Thus, on two opposite sides of the Earth, located on the same straight line, which passes through the centers of the Earth and the Moon, two large humps are formed, two huge water swellings. At the same time, on the other two sides of our planet, located at an angle of ninety degrees from the above points of maximum tide, the greatest low tides occur. Here the water drops more than anywhere else on the surface of the globe. The line connecting these points at low tide shortens somewhat, and thus creates the impression of an increase in the elongation of the Earth in the direction of the maximum high tide points. Due to lunar gravity, these points of maximum tide constantly maintain their position relative to the Moon, but since the Earth rotates around its axis, during the day they seem to move across the entire surface of the globe. That's why in each area there are two high and two low tides during the day.Solar ebbs and flows
The Sun, like the Moon, produces ebbs and flows by the force of its gravity. But it is located at a much greater distance from our planet compared to the Moon, and the solar tides that occur on Earth are almost two and a half times less than the lunar ones. That's why solar tides, are not observed separately, but only their influence on the magnitude of lunar tides is considered. For example, The highest sea tides occur during full and new moons, since at this time the Earth, Moon and Sun are on the same straight line, and our daylight increases the attraction of the Moon with its attraction. On the contrary, when we observe the Moon in the first or last quarter (phase), there are lowest sea tides. This is explained by the fact that in this case the lunar tide coincides with solar ebb. The effect of lunar gravity is reduced by the amount of gravity of the Sun.Tidal friction
« Tidal friction", existing on our planet, in turn affects the lunar orbit, since the tidal wave caused by lunar gravity has a reverse effect on the Moon, creating a tendency to accelerate its movement. As a result, the Moon gradually moves away from the Earth, its period of revolution increases, and it, in all likelihood, lags a little behind in its movement.The magnitude of sea tides
In addition to the relative position in space of the Sun, Earth and Moon, on the magnitude of the sea tides in each separate area are influenced by the shape of the seabed and the nature of the coastline. It is also known that in closed seas, such as the Aral, Caspian, Azov and Black seas, ebbs and flows are almost never observed. It is difficult to detect them in the open oceans; here the tides barely reach one meter, the water level rises very little. But in some bays there are tides of such colossal magnitude that the water rises to a height of more than ten meters and in some places floods colossal spaces.
