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Mercury 'surface tension' vs. density

  1. Dec 30, 2009 #1

    Danger

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    This probably belongs in one of the physics or engineering forums, but I don't know which one... so I post here with a request that it be moved if appropriate.
    Back in the early 70's, I desired to build a diorama of the Enterprise and a D7 Klingon cruiser. It would, of course, have to be fully lighted, but I wanted more.
    My idea for a photon torpedo strike, at that time, was to drop a blob of mercury (about half of what you find in a tilt switch) down a glass tube, with spotlights on it. I didn't like it, but it was the best that I could come up with at the time.
    Given my current state of unemployment and borderline boredom, I might actually be able to build the thing. Now, of course, I have to choose between a couple of dozen versions of Enterprise, but that's beside the point.
    My current thought is to drop a bead of mercury down a strand of 'invisible thread', which illusionists use for close-up magic tricks. You can't see the stuff from more than a few inches away. There will be a red laser aimed down along the thread from the firing ship, and another aimed upward from the target. That should result in a nice shimmering red object traveling from one ship to the other, and then splattering when it hits. A recycling system will then collect the mercury and return it to the torpedo reservoirs.
    What I need to know from any physicists, chemists, or engineers is whether or not mercury will actually follow a thread. My personal suspicion is that it will simply fall straight downward due to its weight, rather than follow the thread. Due to the toxic nature of the substance, I prefer to not experiment with it to find the answer on my own.
    Any help?
     
  2. jcsd
  3. Dec 30, 2009 #2
    You could try praying for it to happen.
     
  4. Dec 30, 2009 #3

    Pythagorean

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    Hey, he didn't intend this post for OT. I went through a lot of trouble refraining from making a joke about the planet mercury being too massive.

    (Can you tell that we don't know, Danger?)
     
  5. Dec 30, 2009 #4

    Astronuc

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    Given the toxicity of mercury, I'd say that it's probably not a good idea, even if the drop of mercury would adhere to a very thin wire and slide down. In addition to surface tension, it would require sufficient adhesion and resistance to shear. A small enough drop might work. The splatter would seem problematic - with dispersion of mercury.

    Nevertheless - it's a cool idea.
     
  6. Dec 30, 2009 #5
    You don't need the thread. You arrange the two ships relative to each other as you want them, then tilt the whole set and camera such that the mercury drop simply falls straight down.
     
  7. Dec 30, 2009 #6

    Danger

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    Never hold back. :biggrin:

    Zooby, I should have specified that this isn't for a photograph or movie. It's to be a permanent display in a glass showcase. The glass is partly so I don't have to dust the thing, and also to contain any vapours or droplets from the mercury.
    I'll probably never get around to building it, but I can have some fun with the design stage.
    Astro, as always you are the voice of reason. I agree that it probably isn't worth messing with mercury. Unfortunately, I can't think of any other substance that will give an approximate visual equivalent without either drying out or polluting the thread. Maybe I can string some crystal beads directly onto the thread, but that severely complicates the reloading system. Hmmm...
    Maybe I'll do some experimenting. Aluminum powder suspended in something like glycerine might be a decent starting point.

    Thanks to all for the input.
     
  8. Dec 30, 2009 #7

    Mech_Engineer

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    I too think using Mercury is a bad idea, but I like idea of a silver bead falling along the string... Or maybe just shoot a fluorescent airsoft pellet under a blacklight?
     
  9. Dec 30, 2009 #8
    Not your fault. My brain registered "diorama" as "panorama" and I assumed you meant a movie or video shot.

    The same solution might apply: since it's enclosed in glass you could set it up on a tilt so the mercury, or any liquid, need only drop, but change the angle the viewer sees with mirrors, i.e. looking into the glass one is actually looking into a mirror. I have no idea what sequence of mirrors would change the angle in the proper way, but I suspect it's possible to get any final desired angle of view.
     
  10. Dec 30, 2009 #9

    Pythagorean

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    Danger,

    how about a vortex generator and a laser?
    use a smoke generator or dry ice for the medium.
     
  11. Dec 30, 2009 #10
    oil will certainly follow a thread, or at least a wire. about 30 or more years ago, there were these popular tacky home decorations with beads of oil running down wires around a statue or something. maybe you could get something like a suspension of gold powder going.
     
  12. Dec 31, 2009 #11

    Danger

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    To the last 3 respondents....
    Zooby... I like that mirror idea, but it wouldn't be my first choice. Definitely something to keep in mind, though.
    Python (I hope you don't mind me calling you that; it's sort of my pet name for you.) Dry ice is sort of eliminated as a possibility simply due to this being a closed system. If, by vortex generator, you reference a glycol-based smoke machine... cool idea, but it will conflict with the original idea of the display. (I am willing to compromise, though, so I'm not discounting your idea out of hand.)
    Proton Soup... that must have been during one of my hibernation periods. I sort of went from lava lamps to plasma globes with no clue as to what went between. I've never heard of the oil/string stuff that you referred to. Still, it's something to keep in mind.
     
  13. Dec 31, 2009 #12

    Borek

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    I doubt mercury will stick to the thread. It is not surface tension that counts, but http://en.wikipedia.org/wiki/Wettability - if it won't wet the surface, it won't stick. And my bet is it won't wet, it is not called quicksilver without a reason.

    --
     
  14. Dec 31, 2009 #13
    What's the reason?
     
  15. Dec 31, 2009 #14

    Borek

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    Mobility. Most liquids wet most of the surfaces to some extent, so they stick to them; that slows their motion. Mercury dosn't stick to surfaces, so it moves very fast and easily.

    --
    methods
     
  16. Dec 31, 2009 #15
    http://www.merriam-webster.com/dictionary/quick

    I think the "quick" in "quicksilver" refers either to definition 1 or 3: "living silver" or "flowing silver". I don't think it means "fast silver"
     
  17. Dec 31, 2009 #16

    Pythagorean

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    The vortex generator itself is pretty simple and can be built easily (I'm thinking of a vortex ring generator, specifically. I thought it was the Romulans or the Klingons that fired ring-shaped rounds).

    Anyway, there are many simple ways to build the vortex generator itself, but you can't actually see the vortex without a medium like smoke or steam. Here's one made out of a soup can:
    http://www.eskimo.com/~billb/amateur/vortgen.html

    You can get one of those ultrasonic humidifiers and have cold steam for a medium, but then you'd have to have a place to put water into your device, and an outlet for moisture to escape. That may be a little more open than you'd hoped for.
     
  18. Dec 31, 2009 #17

    Danger

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    Borek, thank you for that link. It pretty much cleared up my questions. While I don't consider Wikipedia to be the ultimate answer to everything, it is very useful.
     
  19. Dec 31, 2009 #18

    Borek

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    English is my second language, so I can be wrong, but my feeling is that it refers to the second meaning, especially:

    If you have ever played with the mercury that pretty well describes its behavior.

    Could be I am skewed by the fact that in Polish it is sometimes called "żywe srebro" - "żywe" means

    (see 4th) and srebro is silver.
     
  20. Dec 31, 2009 #19
    In English we have this old phrase "the quick and the dead", in which "quick" means "living":

    http://www.indepthinfo.com/mercury/quicksilver.shtml

    "Fast" verses "slow" silver doesn't make much sense, but "living" and "flowing" verses "dead" and "static" (i.e.solid) silver does.
     
  21. Dec 31, 2009 #20

    lisab

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    When I was a young, a neighbor kid had some mercury that we all played with. Yes, we handled it, tried not to drop it...poured it from hand to hand.

    In my experience, it's called "quicksilver" because it's 1) silver colored, and 2) very "fast" in your hand...think of wiggly jello that has no adhesion to what it's sitting on. The way it moves, it's almost as if it's alive.

    Sigh...I often wonder how I survived my childhood :biggrin:.
     
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