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Thread: Gravity.

  1. #1
    Don't smoke, Mike. shapelike's Avatar
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    Gravity.

    Four and a halfish million years ago something the size of Mars slammed into the not-quite-finished-cooking-yet Earth and ejected enough debris to eventually form the moon. As my understanding goes, this ejected matter from the impact was drawn together out in space by the force of gravity and was also trapped in orbit around the Earth by its gravity.

    Why didn't all that matter just get sucked directly back to the Earth, since its gravity would be so much stronger than the larger moon chunks that were out there at the start, and for that matter why didn't the entire moon get sucked back into the Earth? I don't understand how gravity can cause all that minute debris in space to form together as a new body but not pull that matter into a much larger planet that's right frigging next to it*.

    Okay science people, school me.

    *Give or take three or four hundred thousand kilometers.

  2. #2
    POWERCRANK addict markhr's Avatar
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    "why doesn't the moon fall into the Earth?" by Google

    http://www.google.com/search?hl=en&q...into+the+earth
    shameless POWERCRANK plug
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  3. #3
    coffeeeeee p4nh4ndle's Avatar
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    Quote Originally Posted by shapelike View Post
    Four and a halfish billion years ago

    Okay science people, school me.
    fixed that for ya.

    oh, and if i recall correctly, the moon is slowly getting farther away from earth; it's going just a little too fast to remain in orbit indefinitely.

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    Roller Coaster ChiefCatchacold's Avatar
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    Or Earth falling into the sun. That would suck.
    Make your banana pancakes, and pretend like it's the weekend.

  5. #5
    Don't smoke, Mike. shapelike's Avatar
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    Quote Originally Posted by p4nh4ndle View Post
    fixed that for ya.

    oh, and if i recall correctly, the moon is slowly getting farther away from earth; it's going just a little too fast to remain in orbit indefinitely.
    What's a zero here or there?

  6. #6
    Videre non videri
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    Million, billion... Hell, if you ask crackpot Kent Hovind, he'll tell you the earth formed, or rather,was created, no more than about 4000 years ago...

    Good thing he's in a safe place for the next decade...

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    Hardrocker
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    Gorntastic! v1k1ng1001's Avatar
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    Quote Originally Posted by shapelike View Post
    Why didn't all that matter just get sucked directly back to the Earth, since its gravity would be so much stronger than the larger moon chunks that were out there at the start, and for that matter why didn't the entire moon get sucked back into the Earth?
    The moon's orbit is slowly decaying. Give it some time for chrissakes!

  9. #9
    The Site Administrator: Currently at home recovering from a couple of strokes,please contact my assistnt admins for forum issues Tom Stormcrowe's Avatar
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    Quote Originally Posted by v1k1ng1001 View Post
    The moon's orbit is slowly decaying. Give it some time for chrissakes!
    Actually, it's moving away at a rate of 2.54 cm/year.
    on light duty due to illness; please contact my assistants for forum issues. They are Siu Blue Wind, or CbadRider or the other 3 star folk. I am currently at home recovering from a couple of strokes. I am making good progress, happily.


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  10. #10
    Gorntastic! v1k1ng1001's Avatar
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    Quote Originally Posted by shapelike View Post
    I don't understand how gravity can cause all that minute debris in space to form together as a new body but not pull that matter into a much larger planet that's right frigging next to it*.
    You mean like when the planets formed from matter spinning about the sun rather than being pulled directly into it?

  11. #11
    Gorntastic! v1k1ng1001's Avatar
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    Quote Originally Posted by Tom Stormcrowe View Post
    Actually, it's moving away at a rate of 2.54 cm/year.
    I think you're right. I remember hearing something about this as a kid, that the moon would have taken up a huge portion of the sky millions of years ago.

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    Hardrocker
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    Forum Admin lotek's Avatar
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    One cannot catch uncle gravity sleeping and walk up walls. . .

    don't ask how I know this.
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    Señor Member USAZorro's Avatar
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    Quote Originally Posted by Tom Stormcrowe View Post
    Actually, it's moving away at a rate of 2.54 cm/year.
    Wow! That's almost an inch a year!!! Maybe if we made the Earth a little heavier...
    The search for inner peace continues...

  15. #15
    Senior Member ken cummings's Avatar
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    Folks the OP didn't ask how does it stay there now but how did all the stuff smashed off of the proto-Earth stay in orbit. Easy friend, most of it didn't. The slow stuff dropped back, the fast stuff went on out, and the stuff with the right range of speeds did go into a whole slew of orbits. Enough stuff likely was in a near circular elliptical orbit to be a focus for some of the rest to condense on. Most of the rest would be slung by near misses out into space or hit the Earth or Moon. The person who can solve the general Three Body problem may get the Nobel Prize for math. A lot of the finer stuff is still out there and can be seen under the right viewing conditions.

    The gegenschein accounts for some of it.
    This space open

  16. #16
    Dammit!
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    Quote Originally Posted by shapelike View Post
    Okay science people, school me.
    Gravity - you know, along with getting older, it's a woman's worst enemy, you know...

  17. #17
    Senior Member deraltekluge's Avatar
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    Quote Originally Posted by v1k1ng1001 View Post
    The moon's orbit is slowly decaying. Give it some time for chrissakes!
    The Moon is slowly moving away from Earth. The additional energy it takes to cause that comes from the Earth's rotation...we're gradually slowing down. It's all due to tides.

  18. #18
    Senior Member deraltekluge's Avatar
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    Quote Originally Posted by ken cummings View Post
    The person who can solve the general Three Body problem may get the Nobel Prize for math.
    Alas, mathematicians have been slighted...there is no Nobel for math.

    Awarded for Outstanding contributions in Physics, Chemistry, Literature, Peace, and Physiology or Medicine.
    The Sveriges Riksbank Prize in Economic Sciences in Memory of Alfred Nobel, commonly "identified with" the Nobel Prize, is awarded for outstanding contributions in Economics.

  19. #19
    Body By Nintendo Psydotek's Avatar
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    Quote Originally Posted by jsharr View Post
    A girl once asked me to give her twelve inches and make it hurt. I had to make love to her 3 times and then punch her in the nose.

  20. #20
    On my TARDIScycle! KingTermite's Avatar
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    LOL @ Psydotek
    Quote Originally Posted by coffeecake View Post
    - it's pretty well established that Hitler was an *******.

  21. #21
    Body By Nintendo Psydotek's Avatar
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    I do what i can.

    Quote Originally Posted by jsharr View Post
    A girl once asked me to give her twelve inches and make it hurt. I had to make love to her 3 times and then punch her in the nose.

  22. #22
    On my TARDIScycle! KingTermite's Avatar
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    Quote Originally Posted by Psydotek View Post
    I do what i can.
    Thanks for the after lunch laugh.
    Quote Originally Posted by coffeecake View Post
    - it's pretty well established that Hitler was an *******.

  23. #23
    Videre non videri
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    Quote Originally Posted by Tom Stormcrowe View Post
    Actually, it's moving away at a rate of 2.54 cm/year.
    Is it really 1.00 inch per year? Or was it actually ~1 inch/year, converted with far too much precision?

  24. #24
    Senior Member deraltekluge's Avatar
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    This item from NASA says that the increase is about 3.8 cm (1.5 inches) per year: http://sunearth.gsfc.nasa.gov/eclips...olloLaser.html

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