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Discussion in 'Sound Science' started by steve eddy, May 9, 2014.
  1. Steve Eddy
    Ok, perhaps not so much sound-related (though there is some music playing in the background), but it's rather sciencey.
    I'd just glued some labels onto some string-tie envelopes we use for packaging and then put them back into the plastic "boxes" that we receive the envelopes in. I later noticed something moving around inside and for a moment thought some sort of bug had got inside. It turned out to be just a little round piece of kraft paper which had come out of one of the rivet holes used for the string tie discs. It eventually settled down, but when I rubbed my finger over the plastic box, it went into its little dance again. So I grabbed my iPad and shot a little video of it.
  2. ab initio
    By the way that thing is moving around, I'd say it was the complete opposite of static! [​IMG]
  3. Steve Eddy
    Ha! Point taken!

    I found it rather strange actually. Nothing else was moving. There was no air blowing over it, etc.

  4. ab initio

    Actually, now that you mention air, I rewatched the video in detail. I'm actually about 90% certain that the movement was due to air currents. The dancing motions were at best a few cm/s. The dynamic pressure of moving air is 1/2 * the density of air * (the velocity of air)^2. For 1 cm/s, the pressure you would have to feel to detect the air movement is 60 micropascal. Compare that to the dynamic pressure of a 20mph breeze (~10 m/s) which is 1 million times higher. You probably wouldn't notice breezes at 1 cm/s.
    The dancing motion you see is imparted by the piece of paper becoming entrained by passing vortices (for example, vortices shed in the wake of your fingers, hand, and arm when you wave your hand near the paper).
    The static electricity plays an important role here: the static charge make the piece of paper stand up on it's end so it can be moved by the passing  air movements.
    Even though you don't feel them, there's just about always some air currents in rooms. They can be powered thermal convection (heat from light bulbs, from your body, etc.), or due to the motion of you walking around the room, or from air currents from a central HVAC system.
    Anyway, that's my theory. Take it or leave it! :)
  5. esldude
    Not sciency at all.  Not at all.
    The Audio Gods, have blessed you with living breathing, moving, life of sound.  You have been chosen as few are to provide this to the audio elite.  No mere static this, it is a sign from the Audio Gods.  Please tell us what spiritual journey you experienced to reach this point.  No other way will help us, poor sack cloth and ashes wearing audiophiles praying for deliverance from the evil of this world.
  6. elmoe
    This kinda reminds me of the kid who films the plastic bag dancing in the wind in American Beauty.
  7. Steve Eddy
  8. Agharta
    Did you let it burn in for 400 hours first?
  9. Steve Eddy



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