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Homework Help: Change in Pressure

  1. Apr 6, 2008 #1
    1. The problem statement, all variables and given/known data

    You are traveling on a train with your window open. As the train approaches its rather high operating speed, your ears "pop." Your eardrums respond to a decrease or increase in the air pressure by "popping" outward or inward, respectively. Do your eardrums "pop" outward or inward on the train? (Use Bernoulli's equation to back up your answer)

    2. Relevant equations

    P1 + .5(rho)(v1)^2 + (rho)gy1 = P2 + .5(rho)(v2)^2 + (rho)gy2

    3. The attempt at a solution
  2. jcsd
  3. Apr 7, 2008 #2

    Andrew Mason

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    Unfortunately, this is a poorly conceived question. The movement of the train through the stationary air causes turbulence around the train. It does not change the atmospheric pressure of the air outside the window (beyond the region of turbulence). Bernoulli's equation really has nothing to do with this question.

  4. Apr 7, 2008 #3
    An increase in velocity would correlate to a decrease in pressure. It's the same concept (for the purposes of this question) as blowing air over a paper strip to see that the air above the strip has decreased in pressure, which results in the paper strip being forced upwards.
  5. Apr 8, 2008 #4
    So your ears would pop out then? Because the pressure outside the window is lower? If your eardrum is like the piece of paper that is.
  6. Apr 8, 2008 #5
    I never notice such pop before in real life, perhaps the train is just too noisy for me to notice that....
    IMO, the pop depends on the orientation, wind direction, and ear shape very much. If the wind is normal to the ear-hole rather then tangential, then there can be inward pop. Of course you can consider both cases anyway. I certainly would prefer the question be more definite.:smile:
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