Two years ago I was vacationing on the coast Indian Ocean on the wonderful island of Ceylon. My little hotel was just 50 meters from the ocean. Every day I watched with my own eyes all the powerful movement and stormy life of the ocean. One early morning I stood on the shore, looking at the waves and thinking about what gives strength to such a powerful oscillation of the ocean, its daily ebb and flow.
What gives strength to the ebb and flow
Gravity affects the movement of all objects in the same way. But if gravity causes the tides in the oceans, and water causes water in Africa, then why is there no ebb and flow in the lakes? Hmm, what if we assume that everything we know is wrong. Many intelligent people from the scientific world explain it like this. The Earth's gravity at point A is weaker than at point B. The cumulative effect of the earth's gravity is stretching the ocean. After which it swells on opposite sides.
Yes, indeed the facts are real and there is a difference in the strength of the moon's gravity at points A and B.
The misunderstanding lies in the explanation of the bulges. Maybe they do not appear due to the difference in attraction. And the reasons are less obvious, and they are confused. It's more about the cumulative pressure in different places the water column. At the same time, the Moon turns the Earth into a hydraulic pump of a planetary scale, and the water swells, pressing against the center. Therefore, even the slightest influence is enough for the wave movement to begin.
A little more about the tides
But I would like to understand why they are not in another body of water:
- in the human body (it is 80% water);
- in a filled bath;
- in the lakes;
- in cups of coffee, etc.
Most likely due to less pressure than in the ocean and poor hydraulics. Unlike the ocean, these are all small accumulations of water. The area of the lake, the cup and the rest is not enough for the minimum pressure on it to change the water level, creating waves.
Large lakes can create pressure for mini tides. But since winds and surges create large ripples, we just don't notice them. The ebb and flow is everywhere, it's just very microscopic.
October 15th, 2012
British photographer Michael Marten has created a series of original shots that capture the coast of Britain from the same angles, but different time... One shot at high tide and the other at low tide.
It turned out very unusual, but positive reviews about the project, literally forced the author to start publishing the book. The book, titled "Sea Change", was released in August this year and was released in two languages. It took Michael Marten about eight years to create his impressive series of images. The time between high and low water is on average a little more than six hours. Therefore, Michael has to linger at each location longer than just a few clicks of the shutter. The idea of creating a series of such works was hatched by the author for a long time. He was looking for how to implement changes in nature on film, without human influence. And I found it by chance, in one of the seaside Scottish villages, where I spent the whole day and found the time of ebb and flow.
Periodic fluctuations in water level (rises and falls) in water areas on Earth are called ebbs and flows.
The highest water level observed in a day or half a day during high tide is called full water, the lowest level at low tide is called low water, and the moment these limit levels are reached is the standing (or stage), respectively, of high tide or low tide. Average level sea - a conventional value, above which the level marks are located during high tides, and below - during low tides. This is the result of averaging large series of urgent observations.
Vertical fluctuations in water level during ebb and flow are associated with horizontal movements water masses in relation to the shore. These processes are complicated by wind surge, river runoff and other factors. Horizontal movements of water masses in the coastal zone are called tidal (or tidal) currents, while vertical fluctuations in the water level are called ebb and flow. All phenomena associated with ebb and flow are characterized by periodicity. Tidal currents periodically change direction to the opposite, in contrast to them ocean currents moving continuously and unidirectionally, due to the general circulation of the atmosphere and cover large spaces open ocean.
The ebb and flow of the tide cyclically alternate in accordance with the changing astronomical, hydrological and meteorological conditions. The sequence of the ebb and flow phases is determined by two highs and two lows in the diurnal cycle.
Although the Sun plays a significant role in tidal processes, the decisive factor in their development is the force of the Moon's gravitational attraction. The degree of influence of tidal forces on each particle of water, regardless of its location on the earth's surface, is determined by the law universal gravitation Newton.
This law states that two material particles are attracted to each other with a force directly proportional to the product of the masses of both particles and inversely proportional to the square of the distance between them. It is understood that the more the mass of the bodies, the greater the force of mutual attraction arising between them (at the same density, a smaller body will create less attraction than a larger one).
The law also means that the greater the distance between two bodies, the less the attraction between them. Since this force is inversely proportional to the square of the distance between two bodies, the distance factor plays a much greater role in determining the magnitude of the tidal force than the masses of bodies.
The gravitational attraction of the Earth, acting on the Moon and keeping it in near-Earth orbit, is opposite to the Earth's gravity by the Moon, which seeks to displace the Earth towards the Moon and "lifts" all objects on Earth in the direction of the Moon.
The point on the earth's surface located directly under the Moon is only 6400 km away from the center of the Earth and, on average, 386 063 km from the center of the Moon. In addition, the mass of the Earth is 81.3 times that of the Moon. Thus, at this point on the earth's surface, the Earth's gravity acting on any object is approximately 300 thousand times greater than the Moon's.
It is widely believed that water on Earth, located directly under the Moon, rises in the direction of the Moon, which leads to an outflow of water from other places on the earth's surface, however, since the attraction of the Moon is so small compared to that of the Earth, it would not be enough to raise such huge weight.
Still oceans, seas and large lakes on Earth, being large fluids, they are free to move under the force of lateral shear, and any slight tendency to shear horizontally sets them in motion. All waters that are not directly under the Moon are subject to the action of the component of the force of attraction of the Moon, directed tangentially (tangentially) to the earth's surface, as well as its component directed outward, and are subject to horizontal displacement relative to the solid earth's crust.
As a result, there is a flow of water from the adjacent areas of the earth's surface towards a place under the moon. The resulting accumulation of water at a point under the Moon creates a tide there. The actual tidal wave in the open ocean has a height of only 30-60 cm, but it increases significantly when approaching the shores of continents or islands.
Due to the movement of water from neighboring regions towards a point under the Moon, corresponding ebb tides of water occur at two other points located at a distance equal to a quarter of the Earth's circumference. It is interesting to note that a drop in sea level at these two points is accompanied by a rise in sea level not only on the side of the Earth facing the Moon, but also on the opposite side.
This fact is also explained by Newton's law. Two or more objects located at different distances from the same source of gravity and subject to, therefore, gravitational acceleration of different magnitude, move relative to each other, since the object closest to the center of gravity is most strongly attracted to it.
The water at the sublunary point experiences more strong attraction to the Moon than the Earth below it, but the Earth, in turn, is more attracted to the Moon than water on the opposite side of the planet. Thus, a tidal wave arises, which is called forward on the side of the Earth facing the Moon, and backward on the opposite side. The first of them is only 5% higher than the second.
Due to the rotation of the Moon in its orbit around the Earth, between two successive high tides or two low tides, approximately 12 hours and 25 minutes pass at a given location. The interval between the culminations of successive ebb and flow is approx. 6 hours 12 minutes The period of 24 hours 50 minutes between two successive tides is called tidal (or lunar) days.
Inequalities in the magnitude of the tide... Tidal processes are very complex, so there are many factors that need to be taken into account to understand them. In any case, the main features will be determined:
1) the stage of development of the tide relative to the passage of the moon;
2) the amplitude of the tide and
3) the type of tidal fluctuations, or the shape of the curve of the course of the water level.
Numerous variations in the direction and magnitude of tidal forces give rise to differences in the magnitude of morning and evening tides in a given port, as well as between the same tides in different ports. These differences are called tide inequalities.
Semi-daily effect... Usually, during the day, due to the main tidal force - the rotation of the Earth around its axis - two complete tidal cycles are formed.
If you look from the North Pole of the ecliptic, then it is obvious that the Moon revolves around the Earth in the same direction in which the Earth revolves around its axis - counterclockwise. With each subsequent revolution, this point on the earth's surface again takes a position directly under the Moon a little later than during the previous revolution. For this reason, the ebb and flow of the ebb and flow every day are delayed by about 50 minutes. This value is called lunar lag.
Half-month inequality... This main type of variation is characterized by a periodicity of about 143/4 days, which is associated with the rotation of the Moon around the Earth and its passage through successive phases, in particular syzygies (new moons and full moons), i.e. moments when the Sun, Earth and Moon are located on one straight line.
So far, we have only dealt with the tidal effect of the moon. The sun's gravitational field also acts on the tides, however, although the mass of the sun is much greater than the mass of the moon, the distance from the earth to the sun is so much greater than the distance to the moon that the tidal force of the sun is less than half the tidal force of the moon.
However, when the Sun and the Moon are on the same straight line, both on the same side of the Earth, and on different sides (in the new moon or full moon), the forces of their attraction add up, acting along one axis, and the solar tide is superimposed on the lunar tide.
Likewise, the attraction of the sun intensifies the ebb tide caused by the influence of the moon. As a result, the tides become higher and the ebb tides lower than if they were caused only by the gravity of the moon. Such tides are called syzygy.
When the gravitational vectors of the Sun and the Moon are mutually perpendicular (during quadratures, i.e. when the Moon is in the first or last quarter), their tidal forces oppose, since the tide caused by the attraction of the Sun is superimposed on the ebb caused by the Moon.
In such conditions, the tides are not so high, and the ebb tides are not as low as if they were due only to the force of the moon's gravity. Such intermediate ebb and flow are called quadrature.
The range of high and low water markings in this case is reduced by approximately three times compared to the syzygy tide.
Lunar parallax inequality... The period of fluctuations in the heights of the tides, arising from the lunar parallax, is 271/2 days. The reason for this inequality is the change in the distance of the Moon from the Earth during the rotation of the latter. Due to the elliptical shape of the lunar orbit, the tidal force of the moon at perigee is 40% higher than at apogee.
Daily inequality... The period of this inequality is 24 hours 50 minutes. The reasons for its occurrence are the rotation of the Earth around its axis and the change in the declination of the Moon. When the Moon is near the celestial equator, two tides on a given day (as well as two low tides) differ slightly, and the heights of the morning and evening full and low waters are very close. However, as the Moon's north or south declination increases, morning and evening tides of the same type differ in height, and when the Moon reaches its highest north or south declination, this difference is greatest.
There are also known tropical tides, so called because the moon is almost over the Northern or Southern tropics.
The daily inequality does not significantly affect the heights of two successive low tides in Atlantic Ocean, and even its effect on tide heights is small compared to the overall amplitude of fluctuations. However, in Pacific diurnal unevenness is manifested in ebb levels three times stronger than in tide levels.
Semi-Annual Inequality... It is caused by the revolution of the Earth around the Sun and a corresponding change in the declination of the Sun. Twice a year for several days during the equinoxes, the Sun is near the celestial equator, i.e. its declination is close to 0. The moon is also located near the celestial equator for about a day every half a month. Thus, during the equinoxes, there are periods when the declination of both the Sun and the Moon is approximately 0. The total tidal effect of the attraction of these two bodies at such moments is most noticeably manifested in regions located near the Earth's equator. If at the same time the Moon is in the phase of a new moon or a full moon, the so-called. equinox syzygy tides.
Solar parallax inequality... The period for this inequality is one year. It is caused by the change in the distance from the Earth to the Sun during the Earth's orbital motion. Once for each revolution around the Earth, the Moon is at the shortest distance from it at perigee. Once a year, around January 2, the Earth, moving in its orbit, also reaches the point of closest approach to the Sun (perihelion). When these two points of closest approach coincide, producing the greatest cumulative tidal force, higher tide levels and lower ebb tide levels can be expected. Likewise, if the passage of the aphelion coincides with the apogee, less high tides and shallower ebb tides occur.
The largest amplitudes of tides... The world's highest tide occurs with strong currents in Minas Bay in the Bay of Fundy. The tidal fluctuations here are characterized by a normal course with a semidiurnal period. The water level during high tide often rises by more than 12 m in six hours, and then decreases by the same amount over the next six hours. When the effect of syzygy tide, the position of the moon at perigee and the maximum declination of the moon fall on one day, the tide level can reach 15 m. the top of the bay. The reasons for the tides, being subject constant study for many centuries, refer to the problems that have given rise to many conflicting theories even in relatively recent times
Charles Darwin wrote in 1911: “There is no need to look for ancient literature for the sake of grotesque theories of tides”. However, sailors manage to measure their height and use the possibilities of tides without knowing the real reasons for their occurrence.
I think that we also need not bother especially about the causes of the origin of tides. Based on long-term observations, special tables are calculated for any point in the water area of the earth, which indicate the time of high and low water for each day. I am planning my trip to, for example, Egypt, which is just famous for its shallow lagoons, but try to guess in advance so that high water fell on the first half of the day, which will allow most of the daytime to fully ride.
Another tide-related issue of interest to the kiter is the relationship between wind and water level fluctuations.
A popular omen claims that the wind increases at high tide and, on the contrary, sours at low tide.
The effect of wind on tidal phenomena is clearer. The wind from the sea drives the water towards the coast, the tide height increases above normal, and at low tide the water level also exceeds the average. On the contrary, when the wind blows from the land, the water is driven away from the coast, and the sea level drops.
The second mechanism acts by increasing atmospheric pressure over a vast water area, a decrease in the water level occurs, as the superimposed weight of the atmosphere is added. When Atmosphere pressure increases by 25 mm Hg. Art., the water level drops by about 33 cm. Zone high pressure or anticyclone is usually called good weather, but not for a kiter. Calm in the center of the anticyclone. A 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 the water level. Such waves, although called tidal waves, are not actually associated with the influence of tidal forces and do not have the periodicity characteristic of tidal phenomena.
But it is quite possible that low tides can also affect the wind, for example, a decrease in the water level in coastal lagoons, leads to a greater heating of the water, and as a consequence to a decrease in the temperature difference between the cold sea and the heated land, which weakens the breeze effect.
Photo by Michael Marten
Ebb and flow are natural phenomena that many people have heard and observed, especially those living on the seashore or ocean. What is the ebb and flow, what power lies in them, why they occur, read the article.
The meaning of the word "tide"
According to explanatory dictionary Efremova, tide is a natural phenomenon when the level of the open sea rises, that is, it rises, and this is periodically repeated. What does tide mean? According to the explanatory dictionary of Ozhegov, a tide is an inflow, an accumulation of a moving one.
What is high tide?
This is a natural phenomenon when the water level in the ocean, sea or other body of water regularly rises and falls. What is the 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 the tide? This is the rise of water in the ocean to the very high level that happens every 13 hours. Low tide is the reverse phenomenon, in which the water in the ocean drops to its lowest level.
Ebb and flow - what is it? This is a fluctuation in the water level that occurs periodically vertically. This natural phenomenon, the ebb and flow, occurs because the position of the Sun, the Moon changes relative to the Earth, along with the rotating effects of the Earth and the features of the relief.
Where does the ebb and flow happen?
These natural phenomena are observed in almost all seas. They are expressed in the periodic rise and fall of the water level. There are tides on opposite sides of the Earth, which lie next to a line directed towards the Sun and the Moon. The formation of a hump on one side of the Earth is influenced by the direct attraction of celestial bodies, and on the other - their least attraction. Since the Earth rotates, two tides and the same number of ebb tides are observed at each point near the sea coast in one day.
The tides are never the same. The movement of water masses and the level to which the water rises in the sea depends on many factors. These are the latitude of the area, landform, atmospheric pressure, wind strength and much more.
Varieties
The ebb and flow are classified by cycle length. They are:
- Semi-daily, 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 at sea consists in full and incomplete waters. The amplitude parameters, which alternate with each other, have practically no differences. They look like a sinusoidal curve and are localized in the waters of such a sea as the Barents Sea, off the coast of the White Sea, and are distributed almost throughout the 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 satellite of the Earth passes through the equatorial zone, there is a standing of water. But if the declination of the moon occurs with the smallest index, tides are observed low power having an equatorial character. If the numbers are higher, tropical tides are formed, accompanied by significant force.
- Mixed when semi-diurnal or diurnal tides with an irregular configuration prevail in height. For example, in semidiurnal changes in the level of the hydrosphere, there is a similarity with semidiurnal tides in many ways, and in diurnal - with the same tides in time, that is, diurnal, which depend on the degree with which the moon is inclined at a given time interval. Ebb and flow mixed type more common in the water area of the Pacific Ocean.
- Anomalous hot flashes- are characterized by rises and falls of water that do not fit any description for various reasons. The anomaly is directly related to shallow water, as a result of which the cycle itself of both rise and fall of water changes. This process especially affects river estuaries. Here, the tide is shorter in time. Similar cataclysms are characterized by individual sites the English Channel, as well as the current 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 causes hot flashes?
If the forces of gravity and inertia are violated, tides arise on the Earth. The natural phenomenon of tides manifests itself to a greater extent near the oceanic shores. Here, twice a day, the water level rises to varying degrees and falls as many times. This happens because humps are formed on the surface of two opposite regions of the ocean. Their position is determined depending on the position of the Moon and the Sun.
The influence of the moon
The moon has a greater influence on the occurrence of ebb and flow than the sun. As a result of numerous studies it has been revealed that the point on the earth's surface located closest to the moon external factors affect 6% more than the most distant one. In this regard, the scientists concluded that due to this separation of forces, the Earth moves apart in the direction of such a trajectory as the Moon-Earth.
Taking into account the fact that the Earth turns around its axis in one day, a double tidal wave during this time passes along the created extension, more precisely, its perimeter, twice. As a result of this process, double “valleys” are created. Their height in the oceans reaches two meters, and on land - 40-43 centimeters, so this phenomenon remains unnoticed for the inhabitants of the planet. We do not feel the power of the ebb, flow, wherever we are: on land or on water. Although a person is familiar with a similar phenomenon, observing it on the coastline. Sea or ocean waters sometimes gain a rather large height by inertia, then we see waves rolling out onto the shore - this is a tide. When they roll back - low tide.
Influence of the Sun
The main star of the solar system is 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 luminary and the Earth affects the amplitude of solar tides, it is two times less than similar processes of the Moon. When the moon is full and the moon is growing, the celestial bodies - the sun, the earth, and the moon - are in the same position, resulting in the addition of solar and lunar tides. The sun has little effect on ebb and flow during the period when gravitational forces from the Earth they go in two directions: to the Moon and the Sun. At this time, the low tide level rises, and the tide level decreases.
The land on the planet occupies 30% of the surface. The rest is covered by oceans and seas, with which many mysteries and natural phenomena are associated. One of them is the so-called red tide. This phenomenon is amazing in its beauty. It occurs off the coast of Florida Bay and is considered the largest, especially during the summer months such as June or July. How often a red tide can be observed depends on a commonplace 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 to health.
The fact is that algae give color to water during flowering. This period is very intense, the plants release a large amount of toxins and chemicals. They do not completely dissolve 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. Mollusks, which were caught from the "red tide" zone, are especially dangerous for humans. A person, using 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 the 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. So, the height of the tidal wave off the eastern shores North America, namely in the Bay of Fundy, reaches approximately 18 meters. In Europe, the highest tides (13.5 meters) are distinguished by Brittany, near Saint-Malo.
How do the ebbs and flows affect the inhabitants of the planet?
Marine inhabitants are especially susceptible to these natural phenomena. The greatest influence ebbs and flows have on the inhabitants of the waters in the foreshore. As the level of the earth's water changes, the development of organisms with a sedentary lifestyle occurs. These are mollusks, oysters, for which the change in the structure of the water element does not interfere with reproduction. This process is much more active during high tides.
But for many organisms, periodic fluctuations in water levels bring suffering. Particularly difficult for animals small size, 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 is the role of the ebb and flow?
What is the ebb and flow, we have sorted out. What is their role in human life? These natural phenomena have a 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. V different countries the world began to build hydroelectric power plants using the force of tidal waves, but there are still very few of them.
The importance of tides is enormous for shipping as well. 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 drawn up. The captains of the ships use them to determine the exact time of the onset of the tides and their height.
What causes hot flashes?
Residents of most cities and villages located on the shores of the seas and oceans can observe one of the most interesting natural phenomena twice a day - regular changes in water level, which are called ebb and flow. Such phenomena arise due to the presence of an attraction force between the Earth, the Moon and the Sun, as well as due to the centrifugal force arising from the rotation of the Earth, and therefore the Moon, around the Sun along a certain trajectory. This article will focus on the highest tides.
Ebb and flow occurs twice a day. Each such phenomenon lasts, on average, about 6 hours and 10 minutes. Having reached its maximum point (the so-called full water), the ocean level begins to gradually decrease, which also takes about 6 hours until it reaches its minimum ( low water). The ebb and flow is best seen when observing the open sea, ocean or seaside.
Tidal record holder - Bay of Fundy
Depending on the location on the planet, tides can occur with different frequencies. For example, on the coast of Central America, on island arcs, in East Asia ebb and flow occur only once a day. But the height of the tides is much more diverse than their frequency, and it depends on the set various factors... In the open ocean and near the islands, the height of the tides is relatively low: in the Hawaiian Islands, approximately 1.1 meters, on the Fiji Islands - 1.8 meters, near St. Helena - 1.1 meters. In the inland seas, the difference in water level between high tide and low tide is quite small. In the Black Sea, it is only 14 cm.
But the record holder for the height of the tides is the Bay of Fundy, washing the coast of Canada and the United States. This bay has enough large sizes: length - 300 km, depth up to 215 meters, and its widest part reaches 90 km in width. The highest tide recorded in the Bay of Fundy reached 18 meters, which is still a world record.
Port Saint John
The Port of Saint John, located in the Gulf of Fundy (formerly French Gulf), is a unique structure. It took a lot of work for the sailors to adapt to the peculiarities of the local nature, to cope with the sea. Ships can enter the port only in accordance with a strict schedule, at certain times of the day.
The highest tide off the coast of Russia was recorded in the northern part of the Sea of Okhotsk, in the Penzhinskaya Bay. Its height was 14 m. Such high figures were achieved only once, at the beginning of the last century.
There is a rise and fall of water. This is a phenomenon of the ebb and flow of the sea. Already in ancient times, observers noticed that the tide comes some time after the climax of the moon at the place of observation. Moreover, the tides are strongest on the days of new and full moons, when the centers of the Moon and the Sun are located approximately on the same straight line.
Taking this into account, I. Newton explained the tides by the action of gravity from the Moon and the Sun, namely, by the fact that different parts of the Earth are attracted by the Moon in different ways.
The Earth revolves around its axis much faster than the Moon revolves around the Earth. As a result, the tidal hump (the relative position of the Earth and the Moon is shown in Figure 38) moves, a tidal wave runs across the Earth, and tidal currents arise. When approaching the shore, the wave height increases as the bottom rises. In the inland seas, the height of the tidal wave is only a few centi-meters, in the open ocean it reaches about one meter. In favorably located narrow bays, the height of the tide increases several times.
The friction of water against the bottom, as well as deformations of the Earth's solid shell, are accompanied by the release of heat, which leads to the dissipation of the energy of the Earth-Moon system. Since the tidal hump is due to the east, the maximum tide occurs after the climax of the Moon, the attraction of the hump causes the Moon to accelerate and slow down the Earth's rotation. The moon is gradually moving away from the Earth. Indeed, geological data show that in the Jurassic period (190-130 million years ago) the tides were much higher, and the day was shorter. It should be noted that when the distance to the Moon decreases by 2 times, the tide height increases by 8 times. At present, the day is increasing by 0.00017 s per year. So in about 1.5 billion years, their length will increase to 40 modern days. The month will be the same length. As a result, the Earth and the Moon will always face each other by the same side. After that, the Moon will begin to gradually approach the Earth and in another 2-3 billion years will be torn apart by tidal forces (if, of course, by that time the Solar System will still exist).
The influence of the moon on tide
Consider, following Newton, in more detail the tides caused by the attraction of the Moon, since the influence of the Sun is significantly (2.2 times) less.
Let us write expressions for the accelerations caused by the attraction of the Moon for different points of the Earth, taking into account that for all bodies at a given point in space, these accelerations are the same. In the inertial frame of reference associated with the center of mass of the system, the acceleration values will be:
A A = -GM / (R - r) 2, a B = GM / (R + r) 2, a O = -GM / R 2,
where a A, a O, a B- accelerations caused by the attraction of the moon at points A, O, B(fig. 37); M- the mass of the moon; r- Earth radius; R- the distance between the centers of the Earth and the Moon (for calculations, it can be taken equal to 60 r); G- gravitational constant.
But we live on Earth and all observations are carried out in a frame of reference connected with the center of the Earth, and not with the center of mass of the Earth - the Moon. To go to this system, it is necessary to subtract the acceleration of the center of the Earth from all accelerations. Then
A ’A = -GM ☾ / (R - r) 2 + GM ☾ / R 2, a’ B = -GM ☾ / (R + r) 2 + GM / R 2.
Let's perform the actions in brackets and take into account that r little in comparison with R and in sums and differences it can be neglected. Then
A 'A = -GM / (R - r) 2 + GM ☾ / R 2 = GM ☾ (-2Rr + r 2) / R 2 (R - r) 2 = -2GM ☾ r / R 3.
Acceleration a’A and a’B equal in magnitude, opposite in direction, each directed from the center of the Earth. They're called tidal accelerations... At points C and D tidal accelerations, smaller in magnitude and directed to the center of the Earth.
Tidal accelerations are the accelerations arising in the frame of reference associated with the body due to the fact that, due to the finite dimensions of this body, its different parts are differently attracted by the disturbing body. At points A and B the acceleration of gravity turns out to be less than at the points C and D(fig. 37). Therefore, in order for the pressure at the same depth to be the same (as in communicating vessels) at these points, the water must rise, forming the so-called tidal hump. Calculations show that the rise of water or tide in the open ocean is about 40 cm. In coastal waters it is much higher, and the record is about 18 m. Newtonian theory cannot explain this.
On the coast of many outer seas, you can see a curious picture: along the coast, not far from the water, there are fishing nets. Moreover, these nets were not supplied for drying, but for fishing. If you stay on the shore and watch the sea, then everything will become clear. Now the water begins to arrive, and where there was a sandbank just a few hours ago, waves splashed. When the water receded, nets appeared, in which the tangled fish sparkled with scales. The fishermen, going around the nets, took the catch. Material from the site
This is how an eyewitness describes the onset of the tide: “We got to the sea,” a fellow traveler told me. I looked around in bewilderment. There really was a coast in front of me: a trail of ripples, a half-buried seal carcass, rare pieces of fin, fragments of shells. And then there was an even space ... and no sea. But three hours later the motionless line of the horizon began to breathe, became agitated. And now the sea swell sparkled behind her. The tide shaft rolled uncontrollably forward across the gray surface. Overtaking each other, the waves ran ashore. One after another, the distant rocks sank - and only water is visible all around. She throws salt spray in my face. Instead of a dead plain, the water surface lives and breathes in front of me. "
When a tidal wave enters a funnel-shaped bay in the plan, the shores of the bay compress it, as it were, causing the tide height to increase several times. So, in the Bay of Fundy off the eastern coast of North America, the tide height reaches 18 m. In Europe, the highest tides (up to 13.5 meters) are in Brittany near the city of Saint-Malo.
Very often, a tidal wave enters the mouths of rivers, raising the water level in them by several meters. For example, near London at the mouth of the Thames River, the tide height is 5 m.