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The tidal force goes as ....(ignoring higher order terms).... F = GMmr/d^3......where r is earth's radius in this case. Making a ratio of Venus vs moon, the only thing that will change in the eqn. is (the M) for mass of moon vs. mass of venus, and the distance, d, of each from earth. Mass of Venus is 71 times that of the moon, but its closest distance is 107 times that of the moon. Thus; since tidal force goes as the inverse 3rd power of distance..... the tidal force of Venus = 71 X 1/(107)^3 = 58 X 10^ - 6 that of the moon. If I did it right ....that's 58 millionth of the moon's tidal force. If you think about it that rule of thumb can't be correct since the 'area' changes as inverse square of distance, whereas tidal force changes as inverse cube of distance. G^2 ![]() Last edited by Gsquare; 15-May-2008 at 06:08 AM. |
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I see the booby trap here, and I fell into it. My initial response to the aforementioned rule of thumb was "no way". Then I checked out the case of a more distant object with the same density and angular diameter, and found that its tidal force was indeed equal to that of the nearby one. In my haste I concluded that the rule of thumb was correct. Now I see that it does not hold as a general rule. At a given distance the mass, and thus the tidal force, varies as the 1.5 power of the angular area.
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Sorry to get your hopes up, Tom ![]() |
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And Fundy enjoys its exceptional tides because it happens to resonate with the 12h50m period of the lunar tides. It's presumably not going to amplify the effect of the ~12h Venusian signal to the same extent.
Grant Hutchison |
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I'll have to look into it. PS: On a google, the first page returned led me to a Fisheries and Ocean Canada website. Looking over the tides for the next week, it looks to me that the tide is around ten meters (instead of the 17 I used before) and it has a period of near 12h 20-25m! There doesn't seem to be much variance over the week, either. So, I don't know how this works. ![]() |
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I remembered to halve the 24 hours, but not the extra 50 minutes of the lunar cycle. ![]() Grant Hutchison |
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