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Flow of Water in plastic bottle

  1. Apr 19, 2015 #1
    1. The problem statement, all variables and given/known data
    You open the plastic bottle lid to take a drink,and notice fluid flowing from a small hole in the bottom of the bottle. You put the lid back on and the flow stops.
    Explain why the flow did not start until the lid was off.
    Explain why the flow stopped when the lid was put back on.

    2. Relevant equations

    3. The attempt at a solution
    I thought that this has something to do with the pressure and the continuity of flow because liquids are non compressible but it's still not making sense to me. Could this be something about the Bernoulli effect?
  2. jcsd
  3. Apr 19, 2015 #2


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    What will happen to the air above water (volume and pressure) if some water will come off the small hole ?
  4. Apr 19, 2015 #3
    So is it that because when the lid is closed there are no air pressure acting on the water and also air pressure from outside is acting on the small hole so that keeps the water in?
  5. Apr 19, 2015 #4
    No. If some water goes out when the lid is on, a slight vacuum starts to develop in the head space.
  6. Apr 19, 2015 #5
    Can you elaborate on that? My understanding is that because the lid is on, the air pressure on the outside is equal to the air pressure inside, and because the air pressure is pushing on the bottle on all sides, thus the water stays in the bottle.
  7. Apr 19, 2015 #6
    The air pressure on the inside is less than the air pressure on the outside. This is because when some water leaves the volume of the air inside increases. So it's pressure drops.
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