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Social Sciences

How do tides rise so high?


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In very simplistic terms, as the moon passes over the earth the moon's gravity, pulls on the Earth below. The moon's gravity is too weak to move anything solid and small, but when the Moon's small amount of gravity is exercised over a large area such as an ocean, then, as the water moves easily, the moon's gravity has a noticeable effect. So, as the moon pulls on the surface of the ocean, it moves that bit of the surface of the ocean, slightly closer to the moon. This causes a rise in the level of the ocean at that point, which means that along the shoreline, the water recedes (you can test this with a bucket full of water in a basin full of water. If you raise up the bucket of water as if the water in the bucket was being pulled up by the moon, you will see the water level in the basin will drop i.e. the tide goes out). Once the moon passes the ocean, the water drops back down again and so the tide along the shoreline floods back in. If there is no gently sloping beach where we can see the tide slowly going out, then coming back in again and we are instead watching from say a walled harbour, all we will see is that the tide goes down low, then rises high up the harbour wall. Hope this helps - KENN JOYCE