The high tide and associated low tide are caused by the gravitational force acted by the Earth and the Moon on each other. Thanks to this force, the Moon orbits around us and does not fly away. This gravitational effect is also responsible for the fact that the Moon does not rotate on its axis, so that it always faces us on the same side. Manifestations of gravity that cause high tide and low tide and are also responsible for the fact that the Moon does not rotate around its axis are called tides.

Gravitational force depends on the mass of the bodies acting on each other and on their distance. If the Earth were a small sphere, the gravitational force of the Moon influencing it would be the same everywhere (but then the sea would certainly not fit on it and ultimately neither would the people observing the high tide and low tide). But the Earth is quite large, so the part of the Earth that is facing the Moon is attracted more than the part of the Earth that is further away from the Moon. Because water is liquid, it can easily change its shape and overflow, so it will begin to move in the direction of the gravitational force and so there will be a high tide on the side facing the Moon. But where will the low tide be? Quite possibly surprisingly, it won't be on the side of the Earth away from the Moon — there will also be a high tide. Why even the farthest from the Moon? Since the most distant part of the Earth has the least attractive force, the water is also least attracted there and therefore a high tide will arise there as well. Low tide will occur in the areas between these locations — the water that creates the tide overflows from these locations.

A large amount of energy is associated with the movement of such a mass of water, so we can convert this water energy into electrical energy thanks to tidal power plants. But a high tide and a low tide are also important for flora and fauna. The high tide cleans the banks and water, allowing aquatic animals to find places to live.