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Bubbles What are Bubbles exactly?

  1. Apr 10, 2009 #1

    I am wondering what a bubble really is, considering a case of an air bubble in water as an example, what leads to the spherical appearance???

    Why it doesn't blows up within the liquid?

    thanks in advance.
    Last edited: Apr 10, 2009
  2. jcsd
  3. Apr 10, 2009 #2


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    Dearly Missed

    Have you noticed that you can put a metal needle to float upon the surface of water, although if you push it a bit down, it will inexorably sink to the bottom?

    In the interface of two fluids like air and water, there will be an ultra-thin layer of molecules that align themselves into a membrane.

    This membrane will be able to exert a force we call "surface tension", which is the "culprit" in why the needle floats. If you add a bit of soap in the water when the needle is floating, it will begin to sink, because the soap destroys the watery membrane the needle rests upon.

    As for why the air-filled bubble isn't squeezed to death, consider that as it becomes compressed, the interior pressure will INCREASE well beyond the ambient fluid pressure.

    Thus, you will reach an equilibrium, in which the surface tension and ambient fluid pressure will try to collapse the bubble, whereas the interior pressure works in the opposite direction.

    The sphericality of the bubble is mainly due to the tiny size of the bubble; the magnitude of the pressure doesn't vary much, either the internal pressure or the external pressure.

    Thus, the pressure is equal in all directions, favouring the (almost) spherical shape.
  4. Apr 10, 2009 #3


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    Bubbles aren't typically spherical unless they are very small. They aren't stationary - they rise and are therefore elongated as they travel through the water.

    I'm not sure what you mean by "blows up with the liquid". Where would it go? A bubble is trapped air. If the bubble disintegrated, the air would still be there, so you'd get a lot of little bubbles instead of one big one. What holds bubbles together (and makes them join and governs their shape) is surface tension.
  5. Apr 10, 2009 #4
    Many thanks for your replies.

    I apologize for my wrong sentence, I meant "blows up within the liquid"... which is quite answered by arildno...
  6. Apr 10, 2009 #5
    And whereas bubbles in liquids have one surface soap bubbles have two.Donald Glaser won a Nobel prize for inventing the bubble chamber.It is said that he was inspired by examining the bubbles in his beer.I get inspired by that sort of thing.
  7. Apr 10, 2009 #6


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    If that's all that it takes for a Nobel, I should have a dozen of the bloody things by now.
    (Unfortunately, most of my beer-induced ideas no longer make sense when I sober up.)
  8. Apr 10, 2009 #7


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    What, they didn't find their way to your alley?
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