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What does gravity have to do with sea level?
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[QUOTE="Bandersnatch, post: 6644846, member: 399360"] [USER=702249]@mark2142[/USER] The video goes into detail about this, so you may need to be more specific about the point of your question. But maybe rephrasing what it said will help. It's not true that 'The level of sea is same everywhere around the world because its all connected'. There are places where strength of the gravitational field is a bit higher or lower, and the water pools (i.e. raises higher) in the places that have a bit higher gravity (because e.g. the crust is denser below that spot, or there's the mass of a continent pulling on it). So you can have actual sea at different levels in different places, even after taking tides into account, even though it's all connected. In yet another words, the fact of 'being connected' doesn't equalise the level to some idealised surface, but to the actual shape of the gravitational equipotential. Which can be bumpy. After all, you don't want to use some global average and end up telling somebody on an actual beach somewhere that they're below or above sea level. (might still happen with tides, but let's ignore them) Say, if you were to imagine a perfect sphere made of some relatively non-dense material, for example silica (or even iron) somewhere in space. You drop some water on this sphere, and it forms a perfectly even sea level everywhere - same distance from the centre of the sphere. If you then bury a huge lump of lead at one spot - even if you did this in such a way that the ideal shape remains unchanged - the water on the surface of such a sphere would flow a bit more towards the spot with the denser lump underneath it. You'd have a spot with sea level above the global average. The video makes a point that even in places where there is no water, the sea level is defined along the surface where water >would< flow if it could - i.e. a gravitational equipotential surface. [/QUOTE]
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What does gravity have to do with sea level?
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