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how much does air weigh?

Discussion in 'Basic Scuba Discussions' started by H2Andy, Feb 26, 2007.

  1. Don Burke

    Don Burke Loggerhead Turtle

    # of Dives: 200 - 499
    Location: southeastern Virginia
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    Normally a whisker more, but not enough for most to notice.
    It weighs less for most mixes; it would be difficult to notice it in air.
     
  2. omar

    omar Solo Diver

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    Just to be a physics nit...

    pounds is a measure of force (i.e. mass * acceleration) the slug is the measure of mass in imperial units. This is another wonderful example of why SI units make more sense.

    Now taking this a little bit further [in deference to the pranksters] ... if you dive over an area where there is a gravity anomaly the “weight” of the tanks and air will be more or less depending upon the type of gravity anomaly.

    But anyway the density of dry air for us imperial oafs is 0.08071 lb/cuft. at 0 degC; 760 mmHg ---> 1.2928 g/L
     
  3. Rick Murchison

    Rick Murchison Trusty Shellback Staff Member ScubaBoard Supporter

    # of Dives: 2,500 - 4,999
    Location: Gulf of Mexico
    13,348
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    Just so.
    Rick
     
  4. Rick Murchison

    Rick Murchison Trusty Shellback Staff Member ScubaBoard Supporter

    # of Dives: 2,500 - 4,999
    Location: Gulf of Mexico
    13,348
    552
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    Omar's really shaving nits here :) and he is correct. The apparent discrepancy in mass from what I posted above is because the molecular weight (and when we use the popular term "molecular weight" we really mean average molecular mass, which takes into account the various isotopes and their percentages that occur in nature) of Nitrogen and Oxygen in the air is slightly greater than their respective atomic numbers would indicate.
    Are we havin' fun yet???
    I am!
    Rick :D
     
  5. dive_lover88

    dive_lover88 Great White

    # of Dives: 50 - 99
    Location: Singapore...(A nice city where i'm loving it!!)(".
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    do you need to factor in the gravitational pull of the earth?
     
  6. OHGoDive

    OHGoDive Barracuda

    # of Dives: 50 - 99
    Location: OH, USA
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    If you're going to do that, maybe we should measure the weight of air in a vacuum. :D
     
  7. dive_lover88

    dive_lover88 Great White

    # of Dives: 50 - 99
    Location: Singapore...(A nice city where i'm loving it!!)(".
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    maybe we could do both and see what is the difference.
     
  8. Rick Murchison

    Rick Murchison Trusty Shellback Staff Member ScubaBoard Supporter

    # of Dives: 2,500 - 4,999
    Location: Gulf of Mexico
    13,348
    552
    113
    It's included in the definition of a pound, so yes, we do, but not as an addition to what we've already done since it's already in there :D
    Rick
     
  9. Warren_L

    Warren_L Instructor, Scuba

    # of Dives: 2,500 - 4,999
    Location: Toronto, Ontario, Canada
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    Depends on the mix of nitrox. Oxygen weighs more than nitrogen, so enriched air should weigh more than air, and hypoxic mixes should weigh less.
     
  10. H2Andy

    H2Andy Blue Whale

    # of Dives: 200 - 499
    Location: NE Florida
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    without reading the responses, i would guess that yes, there is a difference in weight as the gas composition changes

    but for practical purposes, it's the same thing


    [edit] ok ... i more or less got it right
     

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