Tides are caused by the attraction between the Earth and the Moon.
The attraction between the Earth and the Moon causes periodic movements and changes in the Earth's lithosphere, hydrosphere and atmosphere, which are called "tides" and are divided into earth tides, sea tides and air tides. .
Most of the water is seawater. The seawater is affected by the gravitational pull of the sun and the moon, and will rise and fall. Since the earth and the moon are constantly moving, the relative positions of the earth, the moon and the sun will change. There are cyclical changes taking place, so the tidal force is also changing cyclically.
Water also rotates as the earth rotates, and rotating objects are acted upon by a force. In ancient times, the upwelling of water in rivers and seas during the day was called tide, and that at night was called tide. It was customary to refer to the vertical rise and fall of the sea surface as tide. It is a natural phenomenon in coastal areas.