Could the earth stop spinning one day??

Discussion in 'Astronomy, Exobiology, & Cosmology' started by Vega, Jul 14, 2006.

  1. MetaKron Registered Senior Member

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    5,502
    http://en.wikipedia.org/wiki/Tidal_locking

    "The angular momentum lost due to the slowdown is balanced by a speeding up along the orbit caused by the other body pulling on the bulge. Since it takes a small but nonzero amount of time for the bulge to shift position, it is always located slightly away from the nearest point to the other object. For the case of a rotation period shorter than the orbital period, this bulge is located in the direction of the rotation, pointing slightly backwards to the direction of orbital movement. Because of this misalignment a component of the gravitational attraction by the other body on the bulge is then directed along the direction of orbital motion. This steady but significant pull on the bulge accelerates the first body along its orbit, boosting its orbital angular momentum. In the opposite case of a rotation period longer than the orbital period, the moving bulge drives the body while holding its orbital movement back, and the rate of rotation is increased at the expense of orbital momentum instead."
     
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  3. URI IMU Registered Senior Member

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    >> gravitational attraction
    >> pulling on


    well well,

    sorry to upset y'all, but force can not be transferred via "pull"
    in fact nothing can "pull"
    so just a little problem with the wiki explanation of "tidal_locking"
     
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  5. phlogistician Banned Banned

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    10,342
    OK, so how would you prefer to word the results of attractive forces, such as gravity, magnetism, or electric charge on an object?
     
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  7. Laika Space Bitch Registered Senior Member

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    ???
     
  8. MetaKron Registered Senior Member

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    5,502
    It is the funniest thing to try to wrap my mind around. I knew that it was there, and I could look a little further and see who else agrees with that.

    I would not be sure whether the geological record would show the bulge that was enough to stop the Earth's rotation. You would think that it would be inevitable, but maybe you don't see it if you don't look for it. Maybe it doesn't even crack very many fault lines even though you would expect it to. Any bending of the Earth's crust for a 100 mile bulge would still seem like a nearly straight line to a ruler a mile long. The flexing could be well within the limits of elasticity of any material involved so that no damage at all need occur that way.
     
  9. Laika Space Bitch Registered Senior Member

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    Mercury shrank by a couple of kilometres early in its history, and the resultant fault system very likely stretches all the way around. The Earth's crust deforms by about half a metre with each tidal cycle, which surely is within the elastic limit of the rocks at the surface. But you propose a close encounter with a body that did in a day what will take the Moon billions of years. What's more, the angular momentum was then returned just as suddenly! The rocks at the Earth's surface are brittle because of their relatively low temperature and lack of confining pressure. The idea that such a strain as you suggest could be accommodated elastically seems incredible to me.

    Aside from this, as Eburacum45 pointed out, there would be other geological effects. The maximum tidal range exhibited by the ocean under the influence of the Moon and Sun is between 10 and 20 metres. Under the extreme gravitational conditions that you invoke, the continents would surely be inundated. Apart from the huge numbers of humans that would be killed and displaced, aquifers would be contaminated, farmland ruined, wildlife decimated. And what about the sedimentary and erosional structures that would certainly result? I would expect extensive upward-fining deposits of marine sediment and eroded and redeposited terrestrial material, both biogenic and clastic. What happened in the last few thousand years to hide it, and where is the planetary body responsible?
     
  10. MetaKron Registered Senior Member

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    5,502
    Verbal and written histories say that there was flooding and water thousands of feet in the air. A lot of humans were killed. There are sedimentary and erosional structures, and something swept Siberia and Mongolia clear of life and piled it up in different places, we still don't know what. The stuff is there.

    The planetary body responsible is orbiting in the slot between Earth and Mercury.

    I don't have all the answers, but the broad outline of a case does exist, which is far ahead of "no evidence." There are some really well-known anomalies, like what happened to the mammoths in Asia that seem to have been blown or washed hundreds of miles until they piled up against the mountains or went off into the Arctic ocean. This is painfully well documented, as is the lake Titicaca area that was at sea level 11,000 years ago. One of the reasons for the kind of rhetoric that they unleash against catastrophism is because there aren't any good ways to deny it.
     
    Last edited: Jul 26, 2006
  11. superluminal . Registered Senior Member

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    10,717
    Venus? You're a Velikovskian! I didn't know. You should have said so earlier.

    ???
     
  12. Novacane Registered Senior Member

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    512
    Just out of curiosity, how long ago was this so-called rise in sea level was to have occured? How about the Neanderthals? Must have been a lot of snorkeling going on about then. Right?

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  13. phlogistician Banned Banned

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    There isn't enough water on the planet to flood much over 200ft, if all the ice on landmasses melted. So where did the water come from and go to afterwards?
     
  14. eburacum45 Valued Senior Member

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    1,297
    If the Earth did stop spinning, the oceans would continue to rotate; so ther surface of the Earth would effectively be converted into a salt-water river. There are numerous locations where human habitation is continous during the period when Venus is supposed to have interposed itself between the Earth and the Moon; Jericho is one. There is no evidence of the oceans' superrotation; as I said before turbidites are limited to a few specific locations, but would have occured everywhere at the margins of the continents if the world really had stopped spinning. And all land life would have been scouured off the continents into the seas.

    Sorry, but it didn't happen.
    And finally, the Moon's orbit and tidal locking precludes the intrusion of any planetary sized object within cislunar space in recorded history; the Moon is tidally locked, and this would have been disrupted by any intruder, and the Moon's orbit is really quite circular. Seen in its own frame of reference the Moon's orbit has a mean eccentricity of 0.055. If a planet had come into the equation then the Moon would either have been ejected, placed into a wildly elliptical orbit, or impacted the Earth (or the intruder). This hasn't happened, so there has been no intruder.
     
  15. MetaKron Registered Senior Member

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    5,502
    Not by this mechanism they wouldn't. The oceans would decelerate along with the planet, it's gravity that's doing it. You get tides, yes, and that's part of the claim. Also, you have to do the math to show that the tide went to a particular place. You've got marks in some places. How did they get there? You have proof that the impossible happened. We're now quibbling over how much of the impossible happened.

    I don't think that the Moon's tidal locking proves anything. Even if, once again, we have to have those models to use it as proof.
     
  16. Janus58 Valued Senior Member

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    1,788

    The angular momentum lost by the rotating body is not completely balanced by the gain of the orbiting body. The friction between the tidal bulge and the rotating planet (and which is what causes the bulge to lead the orbiting body) generates heat, which the planet eventually radiates away, that raditation carries away the majority of the angular momentum. This can be easily seen by comparing the energy gained by the moon as it climbs 3.8cm a year as compared to the energy lost by the rotating Earth in that same time.
    Only 8% of the energy lost by the Earth is transfered to the Moon, the rest is given up to heating the Earth.

    Using the Same mechanism to stop the Earth completely would warm the Earth by about 37°C (66°F). This doesn't seem like much, but it would completely wreck the ecology.

    But that is small potatoes to some of the other problems.

    You mention Venus as a possible suspect. Scratch it off the list.
    Venus is about 66 times the mass of the Moon, so it would have 66 times the tidal effect as the moon at the same distance. Since the Moon slows that Earth at a rate of 1.5 milliseconds/century, at the same distance Venus would slow it at 99 miliseconds/century.
    If you want Venus to slow the Earth to a stop in less than 24 hours it has to be a lot closer than the moon. How much closer? Even considering the fact that tidal forces decrease porportional to the cube of the distance (if we halve the distance, the tidal forces increase by a factor of 8), it works out that the distance between Earth and Venus (center to center) would have to be less than 1000 km to get the required tidal force. Since this is closer than the surface of the Earth, Venus is out. In fact, you couldn't pass Venus closer than twice the Earth's radius from Earth, because at that distance they will be within each other's Roche Limit and the tidal forces on both planets would be so large that they would tear both to pieces.

    Which brings up why we needn't worry about the Earth heating that I mentioned above. It turns out that the tidal forces needed to stop the Earth in less than 24 hrs through tidal braking are enough to, at the very least, strip it clean of its atmosphere, oceans, and anything else not firmly nailed down. There wouldn't be any verbal or written records because there wouldn't be anybody left to make them.
     
  17. MetaKron Registered Senior Member

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    5,502
    I don't think that you have any math to show that slowing down the Earth that way would heat it by any given number of degrees. I also don't see how you know anything about how it "turns out"? Where is the theoretical model? I think that you are just pulling numbers out of your ass. If you don't have a model, you don't know anything about the question.
     
  18. Chatha big brown was screwed up Registered Senior Member

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    1,867
    It could given the right parameters
     
  19. Avatar smoking revolver Valued Senior Member

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    19,083
    Archimedes said he could “lift the world, if I had a lever long enough.”
    Everything could be done "given the right parameters".
     
  20. Laika Space Bitch Registered Senior Member

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    638
    Oh MetaKron, you bloody hypocrite! You make these astounding claims yourself without providing a model or mathematical reasoning. So far, your strongest argument has been along the lines of "verbal and written histories say that there was flooding," and I've yet to see a source even for that! To start with, please provide some reputable references for your claims regarding Lake Titicaca, the mammoths and the sedimentary and erosional structures that you mentioned. Then, since this is now going over the same ground as the Jupiter/Venus topic, perhaps you could address the questions that you seemed to avoid in that thread.

    Returning to the issue of elastic strain accommodation, I'd like to remind you that Mars' enormous Tharsis Bulge is considerably smaller than the tidal bulge that you propose, and it formed over many millions of years. Yet the huge faults are still visible on that planet after billions of years.

    Phlogistician, it's not that the Earth's inventory of water needed to increase; MetaKron suggests that it was just redistributed temporarily.
     
  21. Janus58 Valued Senior Member

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    1,788
    Granted, I did do a "back of the envelope" calculation on some of this, but I tried to err generously on the side of your arguement as I did.

    Going back and doing a more thorough calc however just makes things worse for your side.

    Using the following formulas;

    Earth's rotational energy = Mr²w²/5
    Moon's orbit energy = -GMm/2a

    Where
    M = the mass of the Earth
    r = the radius of the Earth
    w = the angular velocity of the rotaing Earth in radians/sec
    G = the gravitational constant
    m = the mass of the moon
    a = the mean orbital distance of the moon.

    And considering that the Earth increases its rotational period by 1.5 milliseconds a century and the moon recedes at 3.8 cm a year, you can find how much rotational energy the Earth loses vs. how much energy the Moon gains in the same time period. (8.91894E+21 and 3.76504E+20 Joules respectively in a century) Comparing the two, we find that the moon only gains 042.214% of the energy given up by the rotating Earth(Not the 8% I generously allowed you in the first post). The rest is lost to friction and heating. Meaning 95.886% of the Eanergy of tidal slowing goes into heating the Earth.

    Given that the kinetic energy of the rotating Earth is 2.56865E+29 Joules (as calculated form above), this means that, in stopping the Earth, 2.48867E+29 joules worth of heat are pumped into the Earth. This works out to 43026 Joules per Kg. Most common minerals in the Earth's crust have a specific heat of around .8 Kj/Kg°K (This again is another point where I was generous the first time around, I used a different value)

    Using the formula:

    Q= cm dT
    Where Q is the Heat energy added
    c is the specific heat
    m is the mass
    dT is the change of temp in Kelvin.

    You get a temperature change of actually 51.6° K

    That is just stopping the Earth, to speed it up again would heat it another 51.6°K ( the tidal forces are just as inefficient in speeding the Earth up as it is in slowing it down).

    And this does not even take into account that the majority of the heating would take place in the crust, where the friction would be greatest.

    As far as Venus goes, It has a mass of 4.87e24kg compared to the 7.35e22kg of the moon. this makes it 66 times more massive. Tidal forces are dependant on the mass of the body causing them and the distance between the two bodies. It changes porportionately to the Mass and inversely to the cube of the distance.

    At present, the moon slows the Earth by adding 1.5 millisecond to its rotatational period a century. This works out to a decrease of rotational energy of 8.91894E+21 joules/per century. Considering the total energy of the rotating Earth given above, it would take 28800000.69 centuries for the Moon to bring the Earth to a stop at this rate. This is 1.0E+12
    times longer than 24 hrs, Thus to slow the Earth to a stop in 24 hr would take a slow down rate 1.0E+12 times greater, meaning the tidal force causing the slow down would have to be 1.0E+12 times larger. The increased mass of Venus makes up for 66 time of this, but this still leaves a factor of 15927273108. Taking the cube root of this gives us how many times closer venus must be to the Earth than the moon to create this type of tidal effect.
    The cube root of 15927273108 is almost exactly 2516. 1/2516 of the Moons distance is 152.78 km. Well under the 1000 km I mentioned. this would put parts of Venus inside the Earth.

    The Roche limit.

    The Roche limit is that distance where the tidal caused by one body exceed the gravitational force holding the body together.

    For rigid objects, it can be found by

    d = (2 pM/pm)^(1/3)

    and for liquid objects:

    d = 2.423 (pM/pm)^(1/3)

    where pM is the density of the first body and pm the density of the second.

    Neither Earth or Venus are perfectly rigid or liquid, so they will fall somewhere between. Given that Earth and Venus are almost the same mass and size, they would break up about the same time.

    This puts the liquid Roche limit for them at 2.423 Earth radii. Now while the planets themselves are not liquid, the Oceans are and the atmosphere, as a gas, will tidally behave as liquid would. This means that bringing Venus in to closer than 2.423 earth radii would increase the the tidal effect of Venus on the Earth enough to strip the planet of its oceans and air.

    Now consider that in order to stop the Earth in 24 hrs, you would have to bring a Venus sized mass to within 153 km of the Earth center to genrate the needed tidal force. that is 100 times smaller than the Roche limit mentioned. Since tidal force is inversely portional to distance, this means that the tidal force needed to stop the Earth in 24 hours, is 1 million time greater than the tidal force generated by a body sitting at the Earth's Roche limit. It doesn't matter what kind of body creates the force as we are directly comparing tidal force to tidal force. the Tidal force needed to stop the Earth in 24 hrs, and the Tidal force that would rip the oceans and atmosphere clear of the Earth. The former is much greater than the second, so you could never stop the Earth in that time period without stripping it bare and making it lifeless.
     
  22. MetaKron Registered Senior Member

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    5,502
    You are reaching when you say that tidal forces would rip the air and water from the Earth.

    I don't see where you've really shown how much tidal force it takes to make the Earth seem to stand still for a day or two. I say "seem to" because it may have acquired a new mode of rotation for a short time, like tipping a gyroscope. This would fulfill the condition that the rotation was restored to something like its original rate.

    When you are trying to prove a negative, the thing slips right out from under you partly because there are too many conditions that might be able to fulfill a vague description like "the sun stood still for a day." I think that you are giving your "back of the envelope" calculations far more authority than they are worth.
     
  23. Ophiolite Valued Senior Member

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    9,232
    Some authority is better than no authority. Back of the envelope is better than back of your ass.
     

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