Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

How would this work on the moon? theory

  1. Apr 16, 2008 #1
    how would this work on the moon?? theory..

    i already posted this in the astrophysics forum, but i know this is visited a lot more, and this isn't that advanced. it's also kind of time-sensitive, so i figured id post here in hopes someone stumbles along and knows how to explain it.. thanks..

    basically im thinking this, if you were in a complete vacuum, say, on the moon, and held down a rope from your hand, it would be mildly pulled toward the center of the moon, but if you were to move your hand parallel to the moon's surface (like from straight out in front of you, perpendicular to your chest, and moved it ninety degrees to straight in line with your shoulders), how would the rope follow? would it follow the same as on earth? would the 'delay' be the same. as in would the top (your hand) move first and fastest and would the rest of the rope follow as what happens here?? what about a flag, or hankerchief held spread out, and you moved it closer or farther from you, like a bull-fighter, what would that motion visibly look like? how would the lack of atmosphere and wind resistance effect it??

    im more questioning the bull-fighter part. i know the flag would want to stay straight perpendicular to the moon due to gravity, but how would it's movement be effected considering there's no resistance from air, wind, or atmosphere?? thanks.
  2. jcsd
  3. Apr 16, 2008 #2


    User Avatar
    Gold Member

    Welcome to PF, Howsitwork.
    You're forgetting about inertia. Any flexible object will still follow the same basic initial pattern as it would on Earth, because the mass of the object will be reluctant to move. I can't tell you what exact pattern it will be, but I'm sure that someone else here can.
  4. Apr 17, 2008 #3

    I think you pretty much covered it. Due to lack of atmospheric drag and less gravity, the lower part of the handkerchief should "drag-along" faster than it would on Earth. As Danger already mentioned, the inertia will still make it drag along rather than moving in sync with your hand (top portion of the handkerchief). I would assume that the lack of atmosphere plays the greatest role in making the difference here since you are talking about a loose material like handkerchief.
  5. Apr 17, 2008 #4


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    I believe that in one of the videos of a moon walk you can see a flag "waving" due the effect you are asking about. The top edge of the flag is supported by a stiff wire so it hangs as if there were a strong wind, the bottom edge of the flag waves as if it were being blown, but it is just the motion of the support causing the flag to move.
  6. Apr 17, 2008 #5


    User Avatar
    Gold Member

    Yeah, that's a favourite target of the 'faked moon landing' conspiracy theorists. They can't understand why the flag was 'waving' without air.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook