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How does a bong/hookah work?

  1. Jul 8, 2011 #1
    I was watching my friends smoke hookah last night thinking about how it works. I drew this simplified figure to help for anyone who doesn't know what a bong or hookah looks like. I know that it works on the principle of suction, but what IS suction?

    1. Why do different results occur when I suck on the top with my lips fully around the opening (insert sex joke here) aka creating a suction, compared to when I just suck in air with my mouth very close to the opening?
    2. Why does sucking air from the taller tube cause air from the smaller tube to enter the the water?


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  2. jcsd
  3. Jul 8, 2011 #2

    Drakkith

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    Staff: Mentor

    When you suck in on anything, such as a straw, hookah, whatever, you reduce the pressure in your mouth. On the other side of the straw or hookah the air pressure around you is pushing down and in. Since there is a difference in pressure the air is pushed from one end, through the water, and into your mouth/lungs finally.
     
  4. Jul 8, 2011 #3
    I believe the heat from the lighter/charcoals has a lot to do with the pressure created.
     
  5. Jul 8, 2011 #4

    Mapes

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    I don't buy it. For one thing, the resistance when sucking air isn't any different whether the contents are on fire or at room temperature. Also, any pressure change caused by natural convection from the hot contents would suck air up through the smaller tube, which is the wrong direction.
     
  6. Jul 8, 2011 #5
    Why does the pressure in your mouth have anything to do with this system? I understand that breathing in decreases the pressure in the tube you are taking in air from, but how does that affect the other side of the tube? There is a pressure difference between the two volumes, but how do they directly experience each other when there is a body of water in between them? My view is clearly wrong because a bong does work, however I find this dilemma is comparable to two rooms of different pressures that are separated by a brick wall. Does the gas exchange take place through the water because the pressure differential force is greater than any resistant forces created by the water?

    You can still suck air from one tube to the other even when nothing is lit.
     
  7. Jul 9, 2011 #6
    Awesome question, and even awesome-er picture. I'm glad I'm not the last person who uses mspaint.

    When the entire hole is covered, air from the room cannot get in to equalize the pressure.

    The way this was explained to me in school was as follows: there is always a great deal of air pressure (well, ~ 1 atmosphere of pressure, which is about 15 lbs per square inch, which sounds like a great deal to me at least) pushing on everything from all sides -- this is usually demonstrated by taking two halves of a globe and evacuating all of the air from them; the "suction" that keeps them together is really just the lack of air inside "pushing back". So the same thing happens with the bong -- you lower the pressure at the top of the container, so that pressure isn't there to push the water back down against the air pushing at the lit part, so air enters there.

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