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VOTE PF Photo Contest - Flag of Our Fathers

  1. nsaspook

    4 vote(s)
    33.3%
  2. maylis

    4 vote(s)
    33.3%
  3. epenguin

    2 vote(s)
    16.7%
  4. ZapperZ

    2 vote(s)
    16.7%
  1. May 2, 2015 #1

    ZapperZ

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    Staff Emeritus
    Science Advisor
    Education Advisor
    2016 Award

    Another good collection of photos for this contest. Please vote for the photo that best represents our theme on Flags.

    1. nsaspook
    proxy.php?image=https%3A%2F%2Ffarm8.staticflickr.com%2F7494%2F15671589904_8f69aafbdc_c_d.jpg


    2. maylis
    upload_2015-4-27_22-36-7-jpeg.82651.jpg


    3. epenguin
    proxy.php?image=http%3A%2F%2Fi60.tinypic.com%2F30xj6f8.jpg


    4. ZapperZ
    i115.photobucket.com%2Falbums%2Fn320%2Fzapperz%2FPF%2520Photo%2520Contest%2FIMG_5750_zpssinxjhpd.jpg


    Contest thread

    Zz.
     
  2. jcsd
  3. May 3, 2015 #2

    Borek

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    Staff: Mentor

    I love the twist of the epenguin's picture.
     
  4. May 7, 2015 #3

    ZapperZ

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    Staff Emeritus
    Science Advisor
    Education Advisor
    2016 Award

    Final day to cast your vote for this contest.

    Zz.
     
  5. May 9, 2015 #4

    epenguin

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    Homework Helper
    Gold Member

    Pics 2. and 3. reveal something I don't think you're aware of looking at a flag fluttering - those almost sharp creases and crinkles. At least I have never been aware of them before now.

    We have had two threads on the dynamics of flag fluttering. To my surprise I see that I had contributed to one of them; I'd forgotten. ((the link no longer leads to the original Economist article but you can probably find it.)


    Why does a flag ripple/wave?
    Why do flags flutter?


    I took a quick look at the of the links and found these words of wisdom:

    " Folklore attributes this instability to some combination of (i) the Bénard–von Kármán vortex street that is shed from the trailing edge of the flag and (ii) the Kelvin–Helmholtz problem of the growth of perturbations at an interface between two inviscid fluids of infinite extent moving with different velocities. "

    Oh yes, your parents and everybody tell you that when you are a kid and you never question it. And yet

    "However, a moment's reflection makes one realize that neither of these is correct. The frequency of vortex shedding from a thin flag (with an audjble... "

    Oh yes, why didn't I think of that?
     
    Last edited: May 9, 2015
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