The moon doesn`t rotate around it`s axis.

  1. Does the moon rotate around it`s axis?
    for images see please: http://omega.webzdarma.cz/applety/moon/moon.html
    The moon doesn`t rotate around it`s axis, I think. In many books the moon does rotate around it`s axis.
    I have never undrestood why. Let mi introduce my point of wiew. We feel centrifugal force if the body does rotate. And it is evidence that body does rotate. This is only idea I used to decide if the body rotate or not.
    The train goes around circle. The merry-go-round is on wagon. The merry-go-round does rotate - the observer at centre of circle can see all merry-go-round, but we can`t see all moon. The obsever sitting on the merry-go-round feel centrifugal force - evidence of rotating.

    The merry-go-round doesn`t rotate - the observer at centre can`t see all merry-go-round.We can`t see all moon. The obsever sitting on the merry-go-round can`t feel centrifugal force to centre of merry-go-round - evidence no rotating.

    We can`t see all moon, we can see only one side of train. I can`t imagine how does the train can make at least one turn around it`s axis, going on rail. If the merry-go-round on wagon does rotate, observer at centre would see all merry-go-round, but we can`t see all moon.


    I understand that, the red point does rotate with respect to blue referece frame, and observer at centre of circle can see this point at the same position with respect to "train". But does observer sitting on merry-go-round feel centrifugal force to centre of merry-go-round if merry-go-round doesn`t rotate with respect to train?
     
  2. jcsd
  3. Doc Al

    Staff: Mentor

    Of course the moon rotates on its axis! If it didn't, we'd be able to see around it as it revolved about the earth.

    Imagine this scenario: A dog is tied to a tree but is free to run around in circles. As the dog circles the tree, does he rotate as well? Of course! Just look where his nose points: First north... then west... then south... then east... then full circle.

    The more interesting question is why does the moon rotate just enough to keep the same side towards earth as it revolves around it. (Look up "tidal locking".)
     
  4. Let we put (glue) moon on train, if moon rotates around it`s own axis , how does the train can make at least one turn around it`s axis, going on rail?
    Can train rotate going on rail?(with respect it`s own axis)
     
  5. Doc Al

    Staff: Mentor

    The rails form a circle! The train has no choice but to rotate if it stays on the rails.
     
  6. please look at http://omega.webzdarma.cz/applety/moon/moon.html for animations and pictures on this topic, thanks.
     
  7. russ_watters

    Staff: Mentor

    It sounds like you already know you are wrong:
    All of that stuff about centrifugal force is superfluous: you don't need it to see that the moon rotates and it is causing you to confuse yourself and you end up saying that the moon doesn't rotate if you rotate the reference frame with the moon. :uhh:
     
    Last edited: Mar 17, 2006
  8. russ_watters

    Staff: Mentor

    When I was in elementary school and my teacher asked how the moon could be rotating while the same side was always facing us, my response was (don't ask me how I remember this) that the pole is pointed directly at the earth. Now that would be an interesting phenomena!
     
  9. DaveC426913

    DaveC426913 16,439
    Gold Member

    I don't understand if vlado believes he's found something new and is theorizing about it, or if he's just trying to figure out how the Moon moves.

    I'll assume the latter.

    vlado: If the Moon did not rotate, then one side of it would always point toward the Sun and one part would always point away from the Sun.

    Yet, we see phases of the Moon with our own eyes. This week, the Sea of Tranquility is in sunlight, two weeks from now it will be in darkness.


    Draw a diagram showing the Earth, Moon and Sun as viewed from overhead. Show the positions of each over the course of a month. Upload it here.
     
    Last edited: Mar 17, 2006
  10. This question is important because I must answer this question, if I want to answer another : does change "g" on the Moon, as "g" changes on Earth (pole-equator)?
     
  11. DaveC426913

    DaveC426913 16,439
    Gold Member

    Well, the Moon most definitely does rotate.
     
  12. if you saw my latest animation (on my web) can the chair on merry-go-round go up? Is the latest animation correct?
     
  13. DaveC426913

    DaveC426913 16,439
    Gold Member

    1] You do realize that there is no such thing as centrifugal force? It is an illusion brought on by observation from a subjective frame of reference. There is only inertia, which is obvious from an external frame of reference. This is the flaw in your logic.

    2] You do realize that the Moon rotates so unbelieveably slowly (one rotation per month) that your experiment will completely fail to show any effect?
     
  14. HallsofIvy

    HallsofIvy 40,950
    Staff Emeritus
    Science Advisor

    No, if the moon always kept one side toward the sun, then it would be rotating at one revolution per year.
     
  15. DaveC426913

    DaveC426913 16,439
    Gold Member

    Heh. Right. Good point.

    Unfortunately, vlado seems to be confused about his own ideas. I can't tell if he's talking about rotation about its axis, or revolution about Earth.
    If the latter, I'll simply explain to him what tides are.
     
  16. Does exist different "g" on the Moon then? Bigger at pole and smaller at equator? "g-gravitation acceleration"
     
  17. HallsofIvy

    HallsofIvy 40,950
    Staff Emeritus
    Science Advisor

    Yes, the acceleration acting of a body falling at the equator of the moon would be slightly less than one falling at the pole of the moon. It would be very small- the moon only rotates at one revolution per month.
     
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