Forces of Tidal Wave Cycles

Variations in tidal range along a coastline is primarily caused by the fluctuations in external gravitational forces acting on the earth, caused in greater extent by the moon and lesser extent the sun. What are naturally observed on a coastal area over time are the changes of water level from high tide (maximum water level) to low tide (minimum water levels). However, in the correct spot and correct time period, it would be observed that the earth has two high tides (semidiurnal tide), as opposed to one high tide (diurnal tide). This second high tide is opposite on earth than the tide influenced by the moon and is caused by a combination of inertia and gravity resulting from the moon-earth system.

At any given time, the moon is applying its gravitational pull towards its center of mass on various parts of the earth. The pull it exerts on water is strongest on the side of earth facing the moon, and is at its weakest on the 'far side,' that opposite the moon. Thus, the deformation caused by the force is relative to the moons position and the rotation of the earth, which causes the tides to move around. On the side of earth facing the moon, or 'near side', the gravitational pull creates a high tide in the ocean. As mentioned, on the far side of earth the ocean water also rises for a second high tide from a combination of inertia and gravity from the moon-earth system. Since the moons mass is such a small percentage of Earths mass, they form a common centre of mass that is within the earth. Earth doesn't rotate about this point but rather displaces water as a result of centrifugal forces, leading to a greater inertia than the gravitational pull of the moon allowing the formation a far side high tide. These two high tides occur relative to the lunar day, causing earth to rotate an additional 12 degrees from its circular 360 to reach the next high tide. This extra 12 degree rotation takes the earth an additional 50 minutes, meaning the time between the high tides are 12 hours and 25 minutes apart.

The second and lesser gravitational pull causing deformation of the oceans on the earth is caused by the sun. During a lunar orbit, the sun and moon interact through phases which can result in a substantially greater pull on the earth. When the Earth, moon, and sun are in line it is called a new moon, and when the moon is on the other side of the earth but still in line with the sun it is called a full moon.

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