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Thread: gradual reduction in rotation of the Earth

  1. #1 gradual reduction in rotation of the Earth 
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    Let's say the rotation of the earth began to slow by a 1/100 of a second per day (every day was 1/100 of a second longer than the next). What would be the effect? Would the Earth begin to drift toward/away from the sun? Would the atmosphere get damaged? What if the reduction in speed was exponential?

    And my final question is what if the Earth were to stop dead, of course there would be extreme winds and total atmosphere destruction, but would the Earth orbit the sun any differently?


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  3. #2  
    Forum Freshman Incoming Dessert's Avatar
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    I can't remember where I read it, but I've got a nagging suspicion there's something to do with the moon that means the Earth is very slowly slowing down. The Sun will turn into a red giant before anything happens though, by which point Earth will have some other issues on its hands.


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  4. #3  
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    Yes I know we're safe for the time being, but theoretically if the Earth were slowing at a much greater rate, what effect would it have on its orbit?
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  5. #4 Re: gradual reduction in rotation of the Earth 
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    Quote Originally Posted by BigGordonLips
    Let's say the rotation of the earth began to slow by a 1/100 of a second per day (every day was 1/100 of a second longer than the next). What would be the effect? Would the Earth begin to drift toward/away from the sun?
    No ...
    If you are looking to conserve the angular momentum within the system, then the changes would be to the radius of the Earth, or the radius of the Earth-Moon co-rotation - either, or both, would increase if the rotation about either, or both, axes slowed ...

    whether a slowing about the Earth rotational axis requires a corresponding change to the Earth-Moon co-rotational axis is more a question for the physicists among us, I think ...

    Quote Originally Posted by BigGordonLips
    Would the atmosphere get damaged?
    that depends on your time frame, and what you would consider to be "damaged" ...
    lengthening the "day" would decrease the coriolis effect, but increase the min-max surface temperature range - it would make weather reporting more chaotic for a while ... in the long term, assuming continued slowing of rotation, it would render "seasons" meaningless as the day-night variation becomes dominant ...

    Quote Originally Posted by BigGordonLips
    What if the reduction in speed was exponential?
    the changes would occur sooner ...

    Quote Originally Posted by BigGordonLips
    And my final question is what if the Earth were to stop dead, of course there would be extreme winds and total atmosphere destruction, but would the Earth orbit the sun any differently?
    well, that depends on what you mean by "stop dead" ...
    if you mean zero rotation, then the "day" would equal the "year" ...
    if you mean tidally locked with respect to the sun, then one side of the Earth would experience perpetual sunlight, the other perpetual "night" ...

    either way, it wouldn't be a nice place to visit, let alone live ...
    Nature abhors perfection; cats abhor a vacuum.

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  6. #5  
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    It mainly depends on where all that kinetic energy is going. The question can't be answered without explaining the mechanism responsible for the slowing.

    If the scenario is that the earth is just slowing down magically and the kinetic energy is disappearing into nothingness, I don't think it would have any major effects for a long time. It would take almost 1000 years for the days to get even 1 hour longer...
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  7. #6  
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    The Earth is indeed slowing its rotation a little bit each day. It is due to tidal drag from the moon. The moon, at the same time, is orbiting faster as the Earth's rotational energy is transferred. This means the moon is moving constantly into a more distant orbit.

    The end result of all this is that, eventually, the Earth and moon will be tide locked. The Earth's rotation will slow to a point where it spins once for each lunar month. This is not the same as solar tide lock, with the Earth rotating once per year, and having the same face always to the sun. The Earth will rotate once per 'month'. The month will be longer than a current lunar month, since the faster orbit speed of the moon means a more distant orbit.

    As far as life on Earth is concerned, there will be no major problems since the change will take so long that all life will have ample time to adapt, even though biological evolution may require many millions of years. The lunar tides will stop, though a much smaller solar tide will continue - twice for each 'day', which will equal the then (much longer) lunar month.
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  8. #7  
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    Quote Originally Posted by skeptic
    The Earth is indeed slowing its rotation a little bit each day. It is due to tidal drag from the moon. The moon, at the same time, is orbiting faster as the Earth's rotational energy is transferred. This means the moon is moving constantly into a more distant orbit.

    The end result of all this is that, eventually, the Earth and moon will be tide locked. The Earth's rotation will slow to a point where it spins once for each lunar month. This is not the same as solar tide lock, with the Earth rotating once per year, and having the same face always to the sun. The Earth will rotate once per 'month'. The month will be longer than a current lunar month, since the faster orbit speed of the moon means a more distant orbit.

    As far as life on Earth is concerned, there will be no major problems since the change will take so long that all life will have ample time to adapt, even though biological evolution may require many millions of years. The lunar tides will stop, though a much smaller solar tide will continue - twice for each 'day', which will equal the then (much longer) lunar month.
    First of all, a orbit with greater distance would be slower, not faster. Second of all, the moon doesn't technically orbit the earth. They both do a dance in the same orbit around the sun. I forget the correct name for it, but since the moon change relative orientation with the sun and earth about 13 times a year, it's orbit is more like what a spiral-graph does.

    From Discover Magazine:

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    Cobra

    Lets not quibble. What you say about the orbital dance is correct (though your diagram massively exaggerates the degree). However, it is easier to imagine the moon orbiting the Earth than running sine wave curves in solar orbit, especially in relation to this concept.

    And the Earth is throwing the moon into a more distant orbit all the time. Strictly you are correct about slower orbital speeds. I got briefly confused between kinetic and potential energies. The Earth's rotational energy is being lost by passing it to the moon, throwing it into a wider orbit. Ultimately, the end result will be Earth/moon tide lock. I am not sure if there is time for that to happen before the sun expands and engulfs Earth and moon both. Certainly it is going to take a long time.
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  10. #9  
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    Quote Originally Posted by skeptic
    Cobra

    Lets not quibble. What you say about the orbital dance is correct (though your diagram massively exaggerates the degree). However, it is easier to imagine the moon orbiting the Earth than running sine wave curves in solar orbit, especially in relation to this concept.

    And the Earth is throwing the moon into a more distant orbit all the time. Strictly you are correct about slower orbital speeds. I got briefly confused between kinetic and potential energies. The Earth's rotational energy is being lost by passing it to the moon, throwing it into a wider orbit. Ultimately, the end result will be Earth/moon tide lock. I am not sure if there is time for that to happen before the sun expands and engulfs Earth and moon both. Certainly it is going to take a long time.
    It made me remember that 30 year or so piece of knowledge. I know that many here probably didn't realize it, so I couldn't help myself.

    Yes, the orbit is exaggerated and it doesn't show the earth's path either. The article says as much, exaggerating it for illustration. A true scale would be pointless now, right?
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    Quote Originally Posted by Wild Cobra

    Yes, the orbit is exaggerated and it doesn't show the earth's path either. The article says as much, exaggerating it for illustration. A true scale would be pointless now, right?
    Wildly exaggerated. The center of gravity of the earth-moon system is off the center of the earth center by several thousand km, but still under the earth's surface. It's so minor compared to the orbital scale of the moon's orbit, that you couldn't illustrated the effect with a true scale picture.

    --
    It's my understanding that earth will be consumed by the sun before we reach the point where its tidally locked with the moon.

    The original question of the thread is rather silly but important over the evolutionary history of the planet. Our early planet probably had tides hundreds of feet high, a considerably shorter day and a much closer and visibly larger moon in the night sky. Fun to think about.
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  12. #11 Re: gradual reduction in rotation of the Earth 
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    Quote Originally Posted by BigGordonLips
    And my final question is what if the Earth were to stop dead, of course there would be extreme winds and total atmosphere destruction, but would the Earth orbit the sun any differently?
    If the Earth suddenly lost all momentum, it would drop into the sun.
    "The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at or repair." ~ Douglas Adams
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