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Thread: Sea Level and Equipotentials

  1. #1 Sea Level and Equipotentials 
    Reptile Dysfunction drowsy turtle's Avatar
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    It's suddenly occurred to me that there's a discrepancy of information that crops up pretty much everywhere - multiple sources state that sea level is a gravitational equipotential (and indeed it stands to reason that it should be), but others (and sometimes the same ones) also state that gravitational field strength is up to 0.5% stronger at sea level at the poles, compared with at the equator. Which of these is true?

    I realise that at the equator centrifugal force reduces the apparent gravity, but then sea level should follow the equipotential in apparent gravity.

    It literally never occurred to me before that there was a contradiction.


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  3. #2  
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    but then sea level should follow the equipotential in apparent gravity.

    I agree to a first approximation for large areas. Of course there are a lot of other forces that influence sea level as well--Ekman, Coriolis, winds etc.


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  4. #3  
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    It's not a contradiction.

    Gravitational potential is not the same thing as the acceleration due to gravity.

    In fact gravitational acceleration is defined to be equal to the gradient of gravitational potential. Gravitational potential can be viewed as contour lines, with g being everywhere normal to those contours with a magnitude that is greater when the contour lines are close together and lesser when they are far apart.
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  5. #4  
    Reptile Dysfunction drowsy turtle's Avatar
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    Quote Originally Posted by billiards View Post
    It's not a contradiction.

    Gravitational potential is not the same thing as the acceleration due to gravity.

    In fact gravitational acceleration is defined to be equal to the gradient of gravitational potential. Gravitational potential can be viewed as contour lines, with g being everywhere normal to those contours with a magnitude that is greater when the contour lines are close together and lesser when they are far apart.
    Thanks.
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