The influence of the moon on the ebb and flow
Tides and ebbs are periodic increases and decreases in water levels in the oceans and seas. Twice a day, with an interval of about 12 hours and 25 minutes, the water rises at the shore of the ocean or the open sea, and if there are no barriers, it sometimes pours large spaces - this is the tide. Then the water drops and retreats, exposing the bottom is a low tide. Why is this happening? This was thought of by ancient people, they also noticed that these phenomena are connected with the Moon. The main cause of the tides was first pointed out by I. Newton - the attraction of the Earth by the Moon, or more precisely, the difference between the attraction of the Moon to the whole Earth as a whole and its water shell.
Explanation of the ebb and flow of Newton's theory
The attraction of the Earth by the moon is made up of the attraction of the Moon to individual particles of the Earth. Particles that are closer to the moon at the moment are attracted to it more strongly, and more distant ones are weaker. If the Earth was absolutely solid, then this difference in the force of attraction would not play any role. But the Earth is not an absolutely rigid body, so the difference in the forces of attraction of particles near the surface of the Earth and near its center (this difference is called the tide-generating force) displaces the particles relative to each other, and the Earth, primarily its water shell, deforms.
As a result, on the side that faces the Moon and on its opposite side the water rises, forming tidal projections, and there is accumulated excess water. Due to this, the level of water in other opposite points of the Earth at this time decreases - there is an ebb.
If the Earth did not rotate, and the Moon remained stationary, then the Earth, along with its water shell, would always retain the same elongated shape. But the Earth rotates, and the Moon moves around the Earth in about 24 hours and 50 minutes. With the same period, tidal ledges follow the Moon and move along the surface of the oceans and seas from east to west. Since there are two such protrusions, a tidal wave passes over each point in the ocean twice a day at an interval of about 12 hours 25 minutes.
Why the height of the tidal wave is different
In the open ocean, the water rises when the tidal wave passes slightly: about 1 m or less, which remains almost imperceptible for seafarers. But off the coast even such a rise in water level is noticeable. In coves and narrow bays, the water level rises during the tides much higher, since the shore prevents the tidal wave from moving and water accumulates here during the entire time between the ebb and tide.
The largest tide (about 18 m) is observed in one of the bays on the coast in Canada. In Russia, the highest tides (13 m) occur in the Gizhiginskaya and Penzhinskaya Bay of the Sea of Okhotsk. In the inland seas (for example, in the Baltic or Black), tides and ebbs are almost invisible, because masses of water do not manage to penetrate into such seas, moving along with the ocean tidal wave. But still in each sea or even a lake there are independent tidal waves with a small mass of water. For example, the height of the tides in the Black Sea is only 10 cm.
In the same area, the height of the tide varies, since the distance from the Moon to the Earth and the maximum height of the Moon above the horizon change over time, and this leads to a change in the magnitude of the tide-generating forces.
Tides and the Sun
The sun also has an effect on the tides. But the tidal forces of the Sun are 2.2 times less than the tidal forces of the Moon. During the new moon and full moon, the tidal forces of the Sun and Moon act in one direction - then the highest tides are obtained. But during the first and third quarters of the moon, the tidal forces of the Sun and the Moon counteract, so the tides are smaller.
Tides in the air envelope of the Earth and in its solid body
Tidal phenomena occur not only in the water, but also in the air envelope of the Earth. They are called atmospheric tides and ebbs. Tides also occur in the solid body of the Earth, because the Earth is not absolutely solid. Vertical oscillations of the Earth's surface due to tides reach several tens of centimeters.
Practical use of tides
A tidal power plant is a special type of hydroelectric power plant that uses tidal energy, and in fact the kinetic energy of the Earth's rotation. Tidal power plants are built on the shores of the seas, where the gravitational forces of the Moon and the Sun change the water level twice a day. Fluctuations in the water level near the shore can reach 18 meters.
In 1967, a tidal power station was built in France at the mouth of the Rance River. In Russia, since 1968, there has been an experimental PES in the Kislaya Bay on the coast of the Barents Sea. There are PES and abroad - in France, Britain, Canada, China, India, the United States and other countries.
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