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Atmospheric Pressure Question?

  1. Nov 30, 2013 #1

    vac

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    1. The problem statement, all variables and given/known data
    A scuba diver can withstand pressures up to 4 atmospheres without risk of getting the bends.


    2. Relevant equations
    What is the maximum safe diving depth?


    3. The attempt at a solution
    4 atmospheric pressure = 40 meters down in water.
    Thus the maximum safe diving depth is 40 meters.
     
  2. jcsd
  3. Nov 30, 2013 #2

    Simon Bridge

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    Interesting...
    Was there a question in all that?
     
  4. Dec 1, 2013 #3

    CWatters

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    Is that 4 atmospheres total pressure or 4 more than on the surface?
     
  5. Dec 1, 2013 #4

    vac

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    That's exactly how the question is being asked.
     
  6. Dec 1, 2013 #5

    vac

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    This is the question:
    A scuba diver can withstand pressures up to 4 atmospheres without risk of getting the bends.
    What is the maximum safe diving depth?
     
  7. Dec 1, 2013 #6

    adjacent

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    A person Underwater has pressure of Water Plus(+) Atmosphere above.
     
  8. Dec 1, 2013 #7

    vac

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    Can you please elaborate?
     
  9. Dec 1, 2013 #8

    CWatters

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  10. Dec 1, 2013 #9

    vac

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    Can you please show me how?
     
  11. Dec 1, 2013 #10

    Simon Bridge

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    So the question is: "do I have the right answer?" Is that correct?

    The weight of the water creates a pressure that varies with depth.
    But the ocean also has air pressing on it from above.
    Thus the pressure experienced by a diver is a combination of the pressure of the water alone and the pressure of the air.

    What you really need to know is the relationship between the pressure experienced by the diver and the depth of the diver. This is usually expressed as a gauge pressure - i.e. what the diver would read on the pressure gauge on his wrist.

    When the diver stands on the shore - there is pressure on his body from the air.
    How much pressure is this? (Hint: what is the atmosphere made of?)
    As he descends, the water provides some additional pressure.

    You will have had some information about this previously in your course.
    There are lots of ways this could be taught - so we are left second guessing your teachers.
    Please don't make us guess.
     
  12. Dec 2, 2013 #11

    Borek

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    Question - as asked - makes absolutely no sense. Bends have nothing to do with pressures "scuba diver can withstand". This is bad physics, bad physiology and bad medicine.
     
  13. Dec 2, 2013 #12

    Simon Bridge

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    Pressure is important to the bends [1]... and the pressure range in which the risk of the bends (on a casual ascent) is low can also be withstood by the diver. Certainly it is the rapid decompression that results in the bends and not the pressure itself [2] but I don't think the wording is so bad that it makes "absolutely no sense" at all.

    [1] http://dwb.unl.edu/calculators/pdf/bends.pdf [Broken]
    [2] http://chemwiki.ucdavis.edu/Physica...quilibrium/Case_Studies/Case_Study:_The_Bends
    http://www.bishopmuseum.org/research/treks/palautz97/phys.html

    More accessible:
    http://adventure.howstuffworks.com/outdoor-activities/water-sports/question1011.htm
     
    Last edited by a moderator: May 6, 2017
  14. Dec 2, 2013 #13

    Borek

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    Sorry, but it makes no sense at all. First of all, what does it mean "diver can withstand 4 atm"? I have friends that were below 60 meters, so 7 atm. Apparently they survived. Saturation divers routinely work in much deeper water, where they withstand tens of atm (I believe record dive was somewhere below 500 meters, so 50 atm).

    Then, bends are not directly related to the depth. Yes, the deeper you go the longer the decompression procedure (unless you are saturated, then it doesn't get any longer), but it is not depth that causes bends.

    Question is poorly worded and suggests things that are completely wrong. I am not going to change my mind.
     
  15. Dec 2, 2013 #14

    adjacent

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    I think the OP didn't intend to talk about the reality but talk about a simple pressure question.
     
    Last edited by a moderator: May 6, 2017
  16. Dec 2, 2013 #15

    vac

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    When I tried that calculator I plugged different values until come up with 30.2408 meters

    4 ATM = 30.2408

    The problem is the pressure increase is not a constant, I learn about this long ago in chemistry but I forgot how I did it :(
     
  17. Dec 2, 2013 #16

    Borek

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    Probably. But there are so many good questions and so many good ways of asking an interesting question that I start to boil when I see see a nonsensical one.
     
  18. Dec 2, 2013 #17

    Borek

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    Vac, you are forgetting person on the surface is already under a pressure.

    What is the pressure in your room right now? Approximately, I am not asking about exact value.
     
  19. Dec 2, 2013 #18

    BruceW

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    the pressure increase will be constant as long as you are swimming in a fluid. maybe it won't be pure fluid, since there will be stuff suspended in the water, but I think most seawater or freshwater will be pretty darn fluid.

    as Borek says, this is not right. decompression sickness occurs due to a quick change in the pressure. But when they say "risk of getting the bends", maybe they mean something like "If you immediately swam to the surface, are you at risk". This kindof makes more sense. But then, you're going to have other stuff to worry about anyway, like your lungs exploding.
     
  20. Dec 2, 2013 #19

    CWatters

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    The problem is the diver is subject to 1 Atmos on the surface. So at 40m he is subject to more than just the pressure due to 40m of water.
     
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