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Smoke Rising

  1. May 21, 2015 #1
    Hi all,
    I have what I believe is a simple physics question. I was burning a sprig of incense in my apartment, and noticed that the smoke was rising from the burning section perfectly straight up into the air for a good meter, and then started to dissipate into the air. I know that a gas will disperse into the air, but I was slightly puzzled because the smoke is a solid. My question is if there was a room with perfectly still air, would the smoke rise straight up all the way to the ceiling, or would it behave more like a gas and dissipate into the air regardless? Also, what properties would explain this?
    Thanks!
    CR
     
  2. jcsd
  3. May 21, 2015 #2

    russ_watters

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    Staff: Mentor

    Welcome to PF!

    This is actually an interesting demonstration of laminar vs turbulent flow. Most fluid flow streams (the smoke is a fluid -- it's air and exhaust gases that you can see because of suspended ash particles in it) start of laminar (linear/coherent) and after a while transition to turbulent. The distance until transition is actually highly predictable and depends on velocity, size/length of the flow stream, and the properties of the fluid. It is also an important part of our understanding of how air behaves as it flows over a wing.

    Here's more on the phenomena:
    http://profs.sci.univr.it/~zuccher/research/blstability/

    Here's the number/equation that characterizes the behavior of a flow stream:
    http://en.wikipedia.org/wiki/Reynolds_number
     
  4. May 21, 2015 #3
    Very interesting, thank you very much!
     
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