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Balloons and pressure

  1. Dec 16, 2003 #1
    I did this experiment for school.
    A balloon is filled with water, and then a cork with a drilled hole is plugged into the end. I'm trying to find the relationship between horizonatal displacement and the size of a hole in a cork. Manipulated variable is the size of the hole in the cork. Responding variable is the water's horizontal displacement. It turns out that horizontal displacement is directly related to the diameter of the hole. In other words, the smaller the hole, the less the displacement. Why does this happen? For example if you take a hose and cover a part of it, the water will go further.
    Thanks a lot everyone!
  2. jcsd
  3. Dec 16, 2003 #2


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    Staff: Mentor

    The displacement (velocity actually) is related to pressure via Bernouli's principle. Pressure is determined by many factors, but in a hose, the pressure is limited by the flowrate. To have a higher flowrate you need less resistance at the nozzle, making for lower backpressure. By putting your thumb over the nozzle, you restrict the flow, increasing the back pressure, and increasing the throw of the water stream.

    A water balloon is more difficult because the weight of the water has as much effect on the pressure as the elasticity of the balloon itself. So it depends a lot on the geometry of the setup.
  4. Dec 16, 2003 #3
    Well I found that the volume in the balloon does not matter, as long as the balloon's total surface area is greater than its initial surface area. I supported the big ball of water with one hand, with the other I held the spout. Initially, water was coming out parallel to the ground.
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