Why Tides Occur

The main cause of tidal ebb and flow is the gravitational pull of the moon. This pulls the water toward the moon.On the other hand, the moon and the earth are attracted by each other's gravitational pull and rotate as one unit around the same axis, but because the mass of the earth is very large compared to that of the moon (about 100 times), the axis exists inside the earth. Rotation about this common axis creates a centrifugal force that pulls water away from the axis, ie, away from the moon. This attractive force and the centrifugal force are balanced, and eventually the seawater is pulled in both directions. Since the earth itself rotates, a point on the earth passes through points a-b-c-d in one day. This is why the tides come and go twice a day.

Furthermore, this gravitational-centrifugal relationship is also affected by the gravitational pull from the Sun, though not as strongly as the Moon. At full moon and new moon, when the moon, earth, and sun line up in a straight line, the gravitational pull from the sun is added, and the tide is often pulled. On the other hand, when the moon-earth-sun are aligned at almost right angles, their gravitational pulls cancel each other out and the tides do not recede much. Therefore, the degree and time of the tide vary depending on the season, topography, longitude and latitude, etc. Therefore, it is necessary to check the exact time of low tide and how low the tide will be in the local tide table or the weather column of the newspaper.

When the sun, earth, and moon are aligned, the difference between the tides is large (spring tide), and when they are aligned at right angles, the tide is low (neap tide).