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Hydrostatic pressure on a teapot spout

  1. Apr 25, 2013 #1
    1. The problem statement, all variables and given/known data

    First of all I apologize, the question is originally in my mother language, so I will do my best to translate it. I apologize if I commit any mistakes, and feel free to tell me if something is unclear.

    The phenomenom where water flows on the outside side of a teapot spout is named "The teapot effect", and occurs due to a difference in pressure between water and the atmosphere. Consider the image of a teapot spout and order in an ascending order the pressures of points A, B, C and D.
    Teapot.PNG
    ("Bico" means "Spout", and "Água" means "Water")


    3. The attempt at a solution
    I've been kind of lost in this question due to different theories, so I'm going to arrange them into statements to make it more organized:

    1)(This doesn't alter the answer, but I wanted to know if it's correct)The whole stream of water has a lower pressure (if compared to atmospheric) because it has a certain velocity, and fluids with velocity have lower pressure;

    2)A and D must be atmospheric pressure, since they're both in direct contact with air;

    3)B must be higher than both because of Pascal's Law;

    4)C must be lower than D, but I don't have a clue why this is true. I'm assuming that because it must be the pressure difference that supports water against gravity (considering that I'm right about D being atm pressure), but that is kind of "doing the problem in reverse", what would the real reason be?
     
  2. jcsd
  3. Mar 23, 2014 #2
    Well, maybe this is a naive solution to the problem, but let me try: a is at atmospheric pressure, due contact to air, b is higher to Pascal's law. C and d are at lower positions, so they must have less potential due to gravity, and by energy conservation, have higher velocities. So, must have lower pressures, but, d must be greater than c because both Pascal's law and atmosphere contact.
     
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