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Moon's Gravitational Pull?

  1. Apr 4, 2010 #1


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    We know that waves of the sea are caused by the gravitational pull of the moon. But if this is true, why doesn't this happen with lakes or cups of water? What about things like molecules in the air?

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  3. Apr 4, 2010 #2


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    The ocean tides are affected because there is water available (from the rest of the planet). Waves are something else (wind primarily). There is no reservoir of water to fill cups or lakes. Large lakes may have waves (from wind).
  4. Apr 4, 2010 #3


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    Hello FeDeX_LaTeX! :smile:

    Most waves in the sea, even the amazingly big ones, are caused by wind etc.

    All the Moon does is raise the water level in the open sea by a few inches (and when this tiny wave reaches the continental shelf, the shallower water makes this Moon-wave larger).

    This few inches (I forget the exact figure) is the maximum difference in height between the actual (Moony) line of equal gravitational potential joining opposite sides of an ocean, and the perfectly circular arc centred on the centre of mass of the Earth.

    For the width of yer average ocean, that's a few inches.

    For lakes or cups of water, it's proportionately smaller. :smile:
  5. Apr 4, 2010 #4

    D H

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    More than a few inches, tiny-tim. Its about a meter, peak-to-trough.
  6. Apr 4, 2010 #5
    Curious, does this effect also influence the human circulatory system?
    (Sorry for being slightly off-topic)
  7. Apr 4, 2010 #6

    D H

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    Well, jeez. "No" is too short an answer.

    No, tides do not affect human circulation.
  8. Apr 4, 2010 #7
    Earth's gravity is one g (depending on where you are). Now, a variation in acceleration (such as riding up and down in an elevator) can cause more or less blood to flow from your heart to your brain.

    However, the acceleration due to the Moon, on Earth's surface, is typically around a ten millionth of a g. I think it's safe to say that the Moon's gravity has little, if any, effect on the human circulatory system.
    Last edited: Apr 4, 2010
  9. Apr 4, 2010 #8
    Dang, I can't blame my transient bizzare behavior on a full moon. :mad:
  10. Apr 4, 2010 #9

    it would be foolish to say 'No.' sure, the effect of the tidal force of the moon on your circulatory system is immeasurably small, but to say it has no effect is denying that two numbers no matter how similar, are different. 2.000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001 and 2 are two completely different numbers, to deny that is to devalue math to the level of smashing rocks together.
  11. Apr 4, 2010 #10


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    Which would be great - if this were a math question. :uhh: But it's not; it's a physio-biology question.

    And the answer is still no, there is no measurable effect whatever of the moon on the human circulatory system.
  12. Apr 4, 2010 #11
    Thanks, Dave.
    I had posted my side-question not to be funny(though my response was), rather that some people believe tidal effects affect human behavior. So I was genuinely curious.
    You and others cleared-up that myth, at least for me.
    So, back to topic!
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