Why do tides appear in the sea?

Video: Why are there ebbs and flows?

Ebb and flow are regularly recurring water movements in the oceans. The ebb describes the period in which the water sinks, the high tide the period in which the water rises. This happens every 12 hours and 25 minutes. The oceans rise and fall by up to 20 meters. In Germany, the phenomenon of tides can be observed particularly on the coasts: the North Sea has two high tides and two low tides within a day. The difference between high and low water, measured in meters, is called the tidal range.

The moon causes ebb and flow

The moon determines the tides with its attractive effect on the earth. The moon acts like a magnet and pulls the water away from the earth. This creates a flood mountain on the side of the earth facing the moon, as well as on the side facing away from the moon. Both flood mountains are about half a meter high. In between there are two ebb valleys. Within a day the earth rotates beneath the two flood mountains.

Attraction and centrifugal force determine the tides

Two forces are responsible for the development of ebb and flow: the gravitational forces of the moon and the centrifugal force. Both forces work in interaction with the earth-moon system, which rotates around a common center of gravity inside the globe: on the side facing the moon, the gravitational pull of the moon has a stronger effect, on the opposite side, the centrifugal force dominates. This creates mountains of tides on both sides of the earth.

Influence of the sun

Depending on its position, the sun can also influence the play of the tides and increase the power of the moon. At full and new moon, the sun and moon work together: the result is strong flooding, a so-called spring tide. At a half moon, the ebb and flow of the tide are less pronounced, as the forces of the sun and moon point in different directions. This phenomenon of "low water" is called nipptide.