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Air speed through a tube

  1. Jun 14, 2005 #1
    I was looking for the name of the principle which governs the following-

    given a constant air flow- air moves faster through a tube with a smaller diameter than a tube with a larger diameter.

    Wouldn't you like to know what this has to do with singing?

    Thank you
  2. jcsd
  3. Jun 14, 2005 #2

    Doc Al

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    equation of continuity

    The name of the principle is the equation of continuity (or the principle of mass conservation).

    The conservation of mass leads, for an incompressible fluid, to the equation of continuity: the volume flow rate must be constant at all points in an air stream. The volume flow rate is given by Volume/time = Area x Speed. Thus, for a given flow rate, air will flow faster through a tube with smaller diameter.

  4. Jun 15, 2005 #3


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    DeBruyn - Air speed in a tube is generally looked at as a phenomenon which is caused by a difference in pressure. It is not forced by some volumetric flow rate, though I suspect that's what you had in mind.

    In fact, if you have a pressure drop in a given length of pipe, say a 100 foot long section of pipe and a 5 psi drop, the larger diameter pipe will have a significantly higher velocity, even though the pressure drop and length of pipe are the same.
  5. Jun 15, 2005 #4

    One of the main aims in classical singing is to keep the muscles of the neck relaxed thereby keeping the throat open and relaxed as opposed to constricted and tense. If a singer is not providing sufficient airflow- the body will automatically try to help out in the process by constricting the throat- thus concentrating the airflow in order to make more out of the airflow which is provided. This does not create a desirable sound! Providing the correct airflow is imperative for the most efficient tone.
    Thank you for your help!!
  6. Jun 17, 2005 #5
    Blowing through a straw

    So you get a pop and straw, fill up your mouth with pop (ready to blow at someone), and blow hard. The pop spews out then it is all gone and air follows. Can you maximize the distance the pop flies out? In fluid mechanics there is a factor called a Reynolds Number. It basically talks about the size of pipe and pressure will cause the fluid to glide across fluid easily, or become turbulent and begin spiraling. Taking also into account the fact that pop is still stuck in the straw and not fixed in one point, air that follows will be interrupted. The interruption will always be changing its shape and position, so how can you maximize it? If you can get the pop to become turbulent for a while to help build up pressure, can you then increase the velocity at which it comes out of the straw, and therefore add to the distance it flies?
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