Talk:Density of air

message: To calculate the density of air as a function of altitude, one requires additional parameters. They are listed below, along with their values according to the International Standard Atmosphere, using the universal gas constant instead of the specific one:
*sea level atmospheric pressure p0 = 101325 Pa (= 101325 (kg/m·s2) = 1013.25 mbar or hPa = 101.325 kPa)
*sea level standard temperature T0 = 288.15 K
*Earth-surface gravitational acceleration g = 9.80665 m/s2.
*dry adiabatic lapse rate L = −6.5 K/km
*universal gas constant R = 8.31432 J/(mol·K)
*molecular weight of dry air M = 28.9644 g/mol
Temperature at altitude h kilometres above sea level is given by the following formula (only valid below the tropopause):
:T = T_0 + L \cdot h
The pressure at altitude h is given by:
:p = p_0 \cdot (1 + \frac{L \cdot h}{T_0})^\frac{g \cdot M}{R \cdot -L}
Density can then be calculated according to a molar form of the original formula:
:\rho = \frac{p \cdot M}{1000 \cdot R \cdot T}
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Finally for fun I've uploaded a javascript calculator that uses the above parameters here: http://www.geocities.com/robojojoba/air_density.html (source code in http://wikisource.org/wiki/Air_density_calculator) -Wikibob | Talk 00:24, 2005 Jan 22 (UTC)
In school i am designing a fictional planet that is completely water except for a few scattered volcanoes.  Would the air be too dense for earth like animals to survive?
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The text says:
:molecular weight of dry air 28.9644 g/mol
the number is correct, and the unit is, but that MOLAR weight each mole of that element containing N (avogadro) molecules weight 28 grams or 0.028 Kg, that not the molecular weight but "molar weight" or "molal weight". Also naturally that mol means mole and not molecule, 28 g would be very heavy one :D
Awaiting international opinions before correcting (maybe international naming is different from my national one)
Gabriele Dini Ciacci 00:03, 13 November 2007 (UTC)
replies: text: I agree. It should read "molar mass", and be linked to the appropriate wikipedia page. And 0.0289644 kg/mol should be restated as 28.9644 g/mol as you have above.Djd sd 06:13, 14 November 2007 (UTC)
replies: text: Done. Djd sd 07:54, 16 November 2007 (UTC)

text: Let's take that whole line out. It does not really fit into the article. External links should be in the "External Links" section anyway.Djd sd 06:13, 14 November 2007 (UTC)
replies: text: Done. Djd sd 07:54, 16 November 2007 (UTC)
thread_title:  Effects of altitude 

message: Does anyone think the following line should be in slugs rather then lbm?
* At standard ambient temperature and pressure (70 °F and 14.696 psia), dry air has a density of ρSTP = 0.075 lbm/ft3.
If we went to slugs, then the density would be around .00237 slugs/ft3 according to NASA
Regards Strefli3 21:23, 22 October 2006 (UTC)
thread_title: Effects of temperature and pressure

message: It seems that the following statement in the article is wrong:
"pv = is also known as satuated preaure."
Spelling mistakes aside, pv represents the partial pressure of water vapor. Saturation pressure and partial pressure should only be equal if relative humidity is 100%. I believe the correct relationship is pv=saturation pressure*relative humidity fraction. See http://wahiduddin.net/calc/density_altitude.htm as a reference. Djd sd 22:22, 19 March 2007 (UTC)
replies: text: I made the change. I'll add references when I figure out how. I tried to make the section more clear, but it still needs a cleanup. Djd sd 06:50, 26 March 2007 (UTC)
replies: text: You are correct about the saturated pressure. I have added the reference to the formula as well. Also in the first section, previously marked as confusing, the units were wrong, I fixed that. Generally it is my opinion that when the math is done using SI units, the result should be presented in those as well.  . (Larkuur 09:34, 26 March 2007 (UTC)
replies: text: Actually, it's not clear to me that units like slugs and pound-feet even belong in this article. Does anyone still learn physics in Imperial units? I realize that Americans still use sort-of-Imperial units in daily life, but I notice that car engines are specified in litres these days, not cubic inches; US scientists certainly use SI units, as does the country's military; and even drug dealers talk in grams and kilos. To me the old units seem useful for a pretty tiny number of readers, and a distraction for the large majority. Oxymetheus  —Preceding unsigned comment added by 65.38.32.131 (talk) 00:00, 1 April 2009 (UTC)
thread_title: Effect of water vapor

message: This article needs more real-world data points.  It is fine to be told the density of "dry air", but many readers are likely to want to know the density of the actual air around them -- so, please give some actual densities, at typical humidity, temp, elevation, pressure, etc. -69.87.199.142 23:48, 23 August 2007 (UTC)
replies: text: Agree with comment above.  Something practical might be, how much does the air in my lungs shrink when I go down to the bottom of a 12' deep pool.  Or, at what depth of water does a one gallon plastic jug of air become a half gallon?  JCW 108.23.6.178 (talk) 05:18, 12 September 2013 (UTC)

text: Agree with general comment above. I came to Wikipedia (as an engineer) looking for a quick overview and some rough numbers. I'm finding this article is very comprehensive (which is fine); HOWEVER, it too quickly bogs down in detail. Worse however, are too many spelling and grammatical errors, suggesting lack of consensus review (and perhaps technical errors?) -- all reducing my overall confidence in what's here. Perhaps, what I want is in some other "Density of Gasses" or "Properties of Air" article -- leaving the comprehensive discussion "Density of Air" here. I would edit more, but it's not my own expertise. Thanks for what we have. HalFonts (talk) 19:49, 1 March 2015 (UTC)
thread_title:  Need more real-world data points 

message: Let's stay consistent with the standard temperature and pressure values. Every so often these data points are changed, sometimes incorrectly. I just looked up the International Standard Atmosphere (as referenced in the "Effects of altitude" section), sea level pressure is 101325 Pa, and sea level temperature is 15° C (288.15 K). There are references to other standards in the "Effects of temperature and pressure" section. We should probably standardize those, too. Or we should at least provide references as to which standards are being used so that the values can be verified. Djd sd 11:40, 30 October 2007 (UTC)
thread_title:  Standard temperature and pressure 

message: I don't know if my understanding is wrong or if the article is not clear enough but to get the "density of dry air calculated using the ideal gas law" formula to work I had to make a some changes.  I see that other people in this discussion page have also done similar things ie. multiplying by 1000 etc.  I probably didn't read/think about the formula enough, but perhaps a worked through example would help instead of just the formula and the result.
To get this to work:
p = p / (R * T)
for:
"At 20 °C and 101.325 kPa, dry air has a density of 1.2041 kg/m3"
ie. 20 °C, 101.325 kPa and 287.05 J/(kg·K) do not just slot straight in to the above formula to get 1.2041.
I convert °C to Kelvins and I also multiply by 1000.  I think I am multiplying to 1000 to get Pa as opposed to kPa so I have thrown it in with the p component, however it is entirely possible this incorrect.
C/C++/Javaish/Javascriptish:
float DegreesCelciusToKelvin(float fDegreesCelcius) { return fDegreesCelcius + 273.15f; }
float GetDensityOfAirKgPerCubicMeterForPressureKPAAndTemperatureDegreesCelcius(float fPressureKPA, float fTemperatureDegreesCelcius)
{
  const float p = 1000.0f * fPressureKPA; // absolute pressure must be in Pa not KPA
  const float R = 287.05f; // specific gas constant for dry air is 287.05 J/(kg·K) in SI units
  const float T = DegreesCelciusToKelvin(fTemperatureDegreesCelcius); // absolute temperature
  return (p / (R * T));
}
Hullo exclamation mark (talk) 21:11, 9 October 2009 (UTC)
thread_title:  Implementing the formula 

message: I came to this page looking to confirm the ISA air density (1.225 kg/m3) but couldn't find it. I see this figure for the ISA temperature of 15 deg C but this requires remembering ISA conditions. Would be handy to have some aeronautics-related info if anyone has the time to put it in. Good reference is atmosphere chapter of Shevell's Fundamentals of Flight. Cheers 203.129.23.146 (talk) 22:15, 7 May 2011 (UTC)
thread_title:  ISA density for aeronautics? 

message: Properties of sound are interesting but I see no reason why are they mentioned in the table that should show the density of air.
I suppose the extra columns could be moved elsewhere. 
Simbulu (talk) 23:04, 22 October 2011 (UTC)
thread_title:  Why are properties of sound in dry air mentioned? 

message: I can't think of ANY good reason why air's density in g/cc isn't provided here.  A large fraction of the human race uses this as the common units for density.  Its absence is embarrassing.  I'm adding it.Abitslow (talk) 13:11, 12 November 2013 (UTC)
thread_title:  g/cc 

message: :Hi 72.69.255.121
:Please see U.S. Standard Atmosphere, 1976; Table I - Geopotential Altitude, Metric units; value for: Altitude Z(m) = 0; same for ICAO Standard Atmosphere.
:note: "The International Organization for Standardization (ISO) publishes the ISA as an international standard, ISO 2533:1975.[1] Other standards organizations, such as the International Civil Aviation Organization (ICAO) and the United States Government, publish extensions or subsets of the same atmospheric model under their own standards-making authority.
:...
:The International Civil Aviation Organization (ICAO) published their "ICAO Standard Atmosphere" as Doc 7488-CD in 1993. It has the same model as the ISA, but extends the altitude coverage to 80 kilometres (262,500 feet)." see International Standard Atmosphere
RookTorre (talk) 02:07, 3 June 2014 (UTC)
thread_title:  Air density value revision 611188337 by 72.69.255.121 

message: I am by no means a style editor, but I find the second paragraph really hard to read. I made a couple changes already for misuse of plurals, "a/an", and "the" today. Since this page is frequently edited, and I don't have much expertise in Project Physics, posting it here to get some feedback before someone moves an improved version over to the main page.    
Currently the paragraph reads:
The air density is a property used in many branches of science as aeronautics;[1][2][3] gravimetric analysis;[4] the air-conditioning[5] industry; atmospheric research and meteorology;[6][7][8] the agricultural engineering in their modeling and tracking of Soil-Vegetation-Atmosphere-Transfer (SVAT) models;[9][10][11] and the engineering community that deals with compressed air[12] from industry utility, heating, drying and cooling processes[12] in industries like cooling towers, vacuum and deep vacuum processes,[5] high pressure processes,[5] gas and light oil combustion processes[5][12] that power turbine-powered airplanes, gas turbine-powered generators and heating furnaces, and air conditioning[5] from deep mines to space capsules.
I am suggesting:
Air density is a property used in many branches of science such as aeronautics,[1][2][3] gravimetric analysis,[4] atmospheric research and meteorology,[6][7][8] agricultural engineering Soil-Vegetation-Atmosphere-Transfer (SVAT) models.[9][10][11] It is used by the engineering community that deals with compressed air[12] from industrial utility, heating, drying and cooling processes,[12] vacuum and deep vacuum processes,[5] high pressure processes,[5] and gas and light oil combustion processes[5][12].  Air density is used in industrial applications like cooling towers, turbine-powered airplanes, gas turbine-powered generators, heating furnaces, and air conditioning.[5] 
Wysockat85 (talk) 17:49, 23 September 2016 (UTC)
thread_title:  First section readability

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thread_title:  External links modified 

message: If you go to the subheading dry air, it originally uses metric units, then without warning switches to imperial? This is confusing!  — Preceding unsigned comment added by 99.43.252.75 (talk) 19:01, 9 December 2020 (UTC)
thread_title:  Units are wrong 

message: This section presents formulae, then values for the titular property, with various units. As appearing, this is not trustworthy content: by Wikipedia's own rules, sources are required for all information that is not common knowledge (and these formulae and values are not common knowledge). 
Where are the formulae from? Where are the values from? (The fact that the units of the values bulleted change from line to line—why?—suggests their being drawn from sources, or possibly that plus some added calculations.) 
The guidelines and policies also state that original research is prohibited (which, even if sources for the formulae were given, would prohibit writers here from the research activity of creating spreadsheets/writing code to run numbers through formulae to calculate values—for the expertise and periodic interpretive decision-making required in calculating, rather than just reporting, property values).  — Preceding unsigned comment added by 2601:246:C700:558:64C9:EAA7:4A93:8547 (talk) 19:53, 3 November 2021 (UTC)
thread_title:  Dry air — fact or fiction?