Tides are controlled by the effect the moon’s gravity has on the ocean and water bodies near the ocean.
According to Princeton University’s Web site, it’s as if the ocean were bulging out toward and away from the moon. The moon pulls water toward it, and this causes the bulge toward the moon. Then you have a bulge on the opposite of the earth, away from the moon, which is caused by the moon pulling the earth away from the water on that side.
Because the moon and the earth move, this bulge moves, too, from one end of the earth to another (simply put). Think about what would happen if you put a marble-sized piece of metal under a sheet and then used a magnet to move the metal under the sheet without actually touching it. As the high point moves north, say, the sheet on the south end will begin to settle back down.
It takes time for this force to move around the earth. So when the force is greatest at Masonboro Inlet, say, that bulge will take four hours 38 minutes to get to Castle Hayne on the Northeast Cape Fear. Of course, there will be variations depending on the phase of the moon, the slope of the land around the water and other factors.
The twin bulges and the moon’s rotation mean that a local body of water experiences a high tide every 12 hours and 25 minutes or so.
Of course, this explanation is over-simplified. I encourage you to check out these Web sites for a more scientific explanation on this fascinating phenomena:
Date posted: July 16, 2009
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