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Thread: Tides

  1. #1 Tides 
    Forum Freshman almirza's Avatar
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    Hi,

    I just want to know when we said gravitional force of the moon affects tides on the earth, do we mean by that it causes the sea level to rise or cause it to be forwards and backwords???

    ALMIRZA


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  3. #2  
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    Its the sea level rising and falling at certain times. At a beach when its high tide the water comes more inland while at low tide the water moves futher back from the land.

    The picture basicly explains it. It looks nice.

    http://en.wikipedia.org/wiki/Tide


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  4. #3  
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    At the risk of sounding like a mongrel, the moon is a lump of rock, it has mass, thus we feel it's gravitational pull. When the moon is near to water, boom, high tide, the moon is pulling the water upwards. But why do you get two high tides a day? Because when the moon is furthest away from you, the water is not being pulled upwards; strangely the dynamic topography of the water is kind of backwards, the water is not pulled by the moon far away from it less than its surroundings, thus it you get a high tide on the 'other side' too.


    Boom boom, voom voom vomm. You know what else is weird? The mediterranean doesn't really have tides. I have no idea why, all I know is that when I did a gravity survey there, the tidal correction was minimal in fact, I probably could of got away with ignoring it all together. Bugger.
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  5. #4  
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    Don't really know much about tides, but I imagine that this is a fairly large-scale phenomenon, with the moon affecting a huge volume of water. In some sense what you're seeing at any given coast must be an accumulative dynamic effect sweeping over a sizeable part of that ocean. I am not suprised then, that the effect is smaller in small inland seas like the mediterranean or black sea, than at the coast of huge bodies of water, like the atlantic or pacific ocean. I also don't think it's just a matter of locally lifting the water level. There must be some pretty strong currents going along with that.
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  6. #5  
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    Well, I don't expect that many people here will know about gravity surveying, but the idea is that you make corrections to all your measurements to account for external factors that might influence g. The 'tidal correction' really does not care about the size of the ocean, it is merely concerned by the variation in g caused by astronomical bodies, namely the moon and to a lesser extent the sun.
    Perhaps the tidal correction is minimal everywhere? Afterall, the only place I have actually done a gravity survey was around Naples, Italy.
    I will look into it and report back.
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  7. #6  
    Universal Mind John Galt's Avatar
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    I haven't done a gravity survey since the 1960s, so I'll be bugger all use on that point.
    My understanind of the absence of readily detectable tides in the Mediterranean is the same as for the absence of such in lakes: the small volume of the water involved.
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