What is the relationship between high tide and low tide and the moon?

When the earth is close to the moon, the mutual attraction between the earth and the moon is great, so the tides rise, and vice versa.

Considering the earth and the moon as particles and saying that the moon moves in a circle around the earth is actually that both the moon and the earth move in a circle around their concentric centers, but the circular orbit of the earth is much smaller. (The circular orbits of two planets with similar mass in a binary star are approximately equal) Taking the center of the earth as a non-inertial reference, the attraction of the lunar particles to the earth particles is the centripetal force of the earth particles moving around the homogeneous * * * central circle, and the corresponding inertial forces of this centripetal force are equal in magnitude and opposite in direction. Therefore, the attraction of the moon particles to the earth particles and this inertia force cancel each other out.

Since the earth is regarded as a particle, the trajectory and dynamics of objects on the earth can be regarded as exactly the same as the earth particle. In this way, the gravity of the moon and the corresponding inertia force cancel each other out.

In fact, the earth is very large. On the ground closest to the moon, the orbital radius of an object moving around the center of the earth and the moon is obviously smaller than that of a particle on the earth, and the attraction of the moon to the object will be greater than the corresponding inertial force. These two forces can no longer be offset, and their resultant force is opposite to the direction in which the object is attracted by the earth, which makes the gravity of the object obviously smaller.

If the "object" is the seawater here, then there will be a climax here. Using the same method to study the objects on the ground farthest from the moon, the gravity of the moon is less than the corresponding inertia force, and their resultant force is opposite to the gravity of the earth, which also makes the gravity of the objects obviously smaller. Therefore, the part of the sea farthest from the moon will also have a climax. This makes the sea level, which should be spherical, slightly spindle-shaped.

Tidal phenomenon is a natural phenomenon in coastal areas, which refers to the periodic movement of seawater under the tidal force of celestial bodies (mainly the moon and the sun). Traditionally, the vertical fluctuation of sea surface is called tide, while the horizontal flow of sea water is called tide. Our ancestors called the high tide in the morning and the high tide in the evening as high tide to indicate the moment of tide. This is the origin of the name Chao.

According to the tidal cycle, the extended data can be divided into the following three categories:

Semidiurnal tide type: A lunar day has two high tides and two low tides. The tidal difference between pre-high tide and post-high tide and post-low tide is almost the same, and the time of high tide and low tide is almost the same (6 hours, 12.5 minutes). The Bohai Sea, the East China Sea and the Yellow Sea are semi-diurnal tides in most parts of China, such as Dagu Lake, Qingdao and Xiamen.

Diurnal tide type: A lunar day has only one high tide and one low tide. Such as Shantou in the South China Sea and Qinhuangdao in the Bohai Sea. Beibu Gulf in the South China Sea is a typical diurnal tide area in the world.

Mixed tidal pattern: there are two high tides and two low tides on some days of 1 month, but the tidal range between the two high tides and low tides is quite different, and the time of high tides and low tides is not equal; On other days, there are high tides and low tides. Most parts of the South China Sea belong to mixed tidal type. For example, in Yulin Port, there is a diurnal tide on 15 days, and the other days are irregular semidiurnal tides with large tidal range. No matter what kind of tide, there will be a big tide with the largest tidal range within two or three days after the first and fifteenth day of each month in the lunar calendar, when the tide rises highest and falls lowest.

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