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Thermodynamics problem, nonsense

  1. Nov 1, 2013 #1
    I was struggling to solve a thermodynamics problem, until I looked up the page with solutions and found something that makes absolutely no sense to me.

    Basically, I'm given a balloon with a certain volume, pressure and amount of hydrogen. The amount of hydrogen is then reduced, as well as the pressure. Temperature is constant.

    Now, what would make sense to me is that, if I had a balloon with a certain volume, pressure and amount of substance, and if I reduced the substance and the pressure - volume would also be reduced, if the temperature is constant.
    Since the gas is what keeps the balloon bloated, if you have less of it and it makes smaller pressure to the balloon, I guess that the volume would also lessen. But no, the solution says that the volume is also constant, together with the temperature.

    Can somebody explain to me how is this possible? Or is it a mistake in the textbook?
  2. jcsd
  3. Nov 1, 2013 #2


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    A balloon made of Mylar will maintain an approximately fixed volume over a significant range of pressure.
  4. Nov 1, 2013 #3


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    Does the problem indicate that the pressure is reduced inside or outside of the balloon? Silly question perhaps, but lowering the pressure of the environment outside the balloon could produce no change in the volume it occupies.
  5. Nov 1, 2013 #4
    Dear infdst. Welcome to Physics Forums!!!

    If the book says that the volume was constant, the only way this could happen is if the balloon is rigid (or close to it, as jbriggs444 is suggesting). Does the exact problem statement (word for word) imply that the balloon is rigid or its volume is constant?

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