![]() | This article is rated Start-class on Wikipedia's
content assessment scale. It is of interest to the following WikiProjects: | ||||||||||
|
(this heading was missing and needed) Kurt Artindagi ( talk) 02:44, 30 November 2013 (UTC)
Should this page be merged with Atmospheric pressure (or contrawise)? Duk 07:25, 28 Oct 2004 (UTC)
I suspect that they shouldn't be merged, because pressure and density are different concepts. As a quick example, please note that the density calculations require that local pressure be known. Alternately, pressure is an integration of density over altitude. However, the distinction may be more technical than useful, so if you would care to mention why you think there should be a merge, I may find myself enlightened.
Cheers, One-dimensional Tangent 00:36, 30 Oct 2004 (UTC)
Hmm... If you are planning on doing a page on the various models, or a page for each model, then the Density article would likely be redundant. In that case I definately see your point, and certainly have no objections.
The only thing I see in favor of keeping the Density article is that it might be simpler than MSIS-1986 and NRLMSIS-00, especially for people who only want a rough model and who don't need to know temperature, etc. However, all I know about atmospheric modelling is due to a few hours of light research, so I figure you're probably more qualified to judge this than I am.
So... I'll not take any offense at whatever you choose to do. -grin-
One-dimensional Tangent 02:40, 30 Oct 2004 (UTC)
The density formula had the wrong units, so I multiplied by M (to balance the mol and the Temperature)
and divided by 1000 (for the gram to kilogram ratio). It now reads:
However, the external link http://wahiduddin.net/calc/density_altitude.htm also looks confused with its units, the gas constant starts off as
but later uses:
This works out as the link uses M / 1000 to correct the different units, but this article appears to have forgotten them. - Wikibob | Talk 22:21, 2005 Jan 17 (UTC)
Good point, I've removed the need for the 1000 by adjusting all the units except pressure to SI base units. This means pressure is in pascals, lapse rate in kelvin per metre (looks odd), and height in metres. Although standard units, the lapse rate, height and molecular weight may look odd to some, so here is an alternative with kilometres, and grams (this brings 1000 back, but that could be removed by using kPa for pressure.)
You should point out what mean air molecular mass you are using in the number of moles -- mass conversion. I agree with the statement directly above this. There is no such thing as an 'air molecule", air is 78+% Nitrogen, 20.9% Oxygen, etc... and both N and O exist in air as N2 and O2. Thus the discussion of the effects of humidity in the air is a bit misleading, and should say an "average" value for a hypothetical "air molecule" is calculated from the relative proportions of nitrogen and oxygen in the air, and the fact that they exist as two-atom molecules, thus yielding an average molecular weight for a hypothetical air molecule of 29. — Preceding unsigned comment added by Njaimo ( talk • contribs) 22:19, 26 September 2014 (UTC)
I do not think this article needs to be merged with the one on Atmospheric pressure. Pressure and density are indeed, as already said, totally different concepts. This article maybe should be more on the concept of density of "air" as the compound of gasses commonly found in "some reference" atmosphere, i.e. sea level and some common model and in controlled systems. It may be talking about base topics and redirecting to other articles for air in complex systems. It should also treat the sea level density of air in static conditions. It could redirect to Atmospheric pressure for air in the most common earth atmospheric system (and define the system with all the temperature, gravity gradients, composition, ecc.) to explain why density is such in atmosphere. Meanwhile it could redirect to fluid flows for the concepts of density of air (as any fluid) is a fluid dynamics system. And finally redirect to density of air in chemistry and in general the concept of density for compounds of gasses (but I leave this to others as it's not my field anymore). This should turn this article in a nice, correct and tidy one that works as an access point for the many involved concepts of why air and density.
As for an example, a good one could be the classic pressurized piston in static condition with some defined compound of gasses we define as air and showing some calculations of elementary thermodynamics that show the link of density to temperature, (partial) pressure(s) ecc.. So the reader get the idea of why density is such and why of air. Then three links: a links to density, a link to air and a link to thermodynamics models (and maybe chemical, for partial pressure part).
Remove "air molecule" and any reference to it. Else the next step would be students looking for "air" on the periodic table for an "air atom" (and I'm citing personal experience of a student looking for water on it...) (and when you say something they will say you "It's on THE Wikipedia". Oh dear. Let's have the Wikipedia as an help and not as an issue).
Done with August rant :)
Regards
Gabriele Dini Ciacci (
talk) 11:41, 11 August 2015 (UTC)
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:
Temperature at altitude h kilometres above sea level is given by the following formula (only valid below the tropopause):
The pressure at altitude h is given by:
Density can then be calculated according to a molar form of the original formula:
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?
The text says:
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)
The link to the: eXtreme High Altitude Calculator is broken at today. if it keeps to be broken it needs to be removed
Gabriele Dini Ciacci 00:33, 13 November 2007 (UTC)
\rho~_{_{humid~air}} = \frac{p_{d}}{R_{d} \cdot T} + \frac{p_{v}}{R_{v} \cdot T} —Preceding unsigned comment added by 134.221.122.71 ( talk) 11:33, 17 February 2009 (UTC)
In my research on corona discharge, I find Peek's law (which I am writing). His book has a variable δ:
δ is the air density factor. It is calculated by the equation:
I also come across this version of "relative air density":
which looks at first glance to be the same thing with different units (kPa and K), but I am too tired to do the math. Then I find this formula which has several other variables:
RAD = Relative Air Density
BP = Barometric Pressure (inches??)
RH = Relative Humidity (percent)
T = Air Temperature (°F)
SP = Saturation Pressure (this value comes from a table included in the spreadsheet)
RAD = (1737.97 x (BP - (SP x RH/100))/(460 + T))
What is the relationship between these? Is one a standard formula that would be used in chemistry or whatever? Are b and T standard variable names for these quantities? Do the humidity values affect air density negligibly in most cases, so they are left out of the first ones? - Omegatron 02:54, August 8, 2005 (UTC)
Does anyone think the following line should be in slugs rather then lbm?
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)
There are many "standard" temperatures and pressures used. A user recently changed one of the given standards from 100 kPa to 1 Atm, but without any references or changes to the resulting value of air density. Since you can't change one without changing the other, I reverted the change. According to the linked "standard temperature and pressure" page, there are many standards. As the values listed on the page are just examples anyway, I feel the link to the appropriate Wikipedia page provides enough information to those looking for other standards. Maybe the most common should be listed, but they vary by country and industry. Otherwise we would have to list them all. Djd sd 16:04, 28 April 2007 (UTC)
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)
The second sentence in section Humid air states This occurs when the molar mass of water vapor (18 g/mol) is less than the molar mass of dry air[note 2] (around 29 g/mol). I think it would be better to change the word when with because because the molar mass of water is always 18 g/mol so, in this context, it is always less than the molar mass of dry air. However, English isn't my mother tongue so I would prefer an English editor changes it if my suggestion seems appropriate enough. -- 149.34.8.36 ( talk) 10:14, 27 October 2021 (UTC)
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)
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)
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)
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)
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)
The bot reverts the corrections someone else did to the formula - I just lost hours because the formula was wrong. Someone please correct this:
The pressure at altitude h is given by:
to
The pressure at altitude h is given by:
and
Density can then be calculated according to a molar form of the original formula:
where M is molar mass, R is the ideal gas constant, and T is absolute temperature.
to
Density can then be calculated according to a molar form of the original formula:
R is the specific gas constant ( J/(kg*degK) = 287.05 for dry air), and T is temperature in deg K. — Preceding unsigned comment added by 94.222.121.251 ( talk) 23:29, 7 November 2011 (UTC)
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)
What is the helicopter doing on this page? Besides the explanation is probably incorrect as well... Kotika98 ( talk) 21:17, 25 March 2014 (UTC)
remember ( isentropic process):
RookTorre ( talk) 16:14, 26 March 2014 (UTC)
Hi, I am the annon that has just removed the helicopter picture from the article. Agreeing with Kotika98, a helicopter (or any wing) flies due to pressue not density differences between upper and lower surfaces (density differences may appear above say Mach 0.6 but are not critical to the process). Regardless, I think the generation of lift is a complex topic best left to the lift (force) article. 217.109.123.82 ( talk) 09:10, 23 April 2014 (UTC)
RookTorre ( talk) 20:20, 23 April 2014 (UTC)
Hi, fair point the flow will not be perfectly incompressible like in theory. Nevertheless a helicopter is not flying because of any density differences between the upper and lower surfaces, but because of a pressure difference. Hypothetically, if it were possible for a helicopter to have high density air beneath the rotor and low density air above the rotor, but both at the same pressure- it would not fly. Therefore I propose to remove the picture again:
217.109.123.82 ( talk) 08:52, 25 April 2014 (UTC)
RookTorre ( talk) 16:09, 25 April 2014 (UTC)
RookTorre ( talk) 02:18, 29 April 2014 (UTC)
I meant generally compressibility is most noticable at transonic speeds+, as it is I don't think it reads as if I am talking specifically about the particular helicopter (Bell 47G), but if you think otherwise feel free to rephrase. For reference 213m/s + 169km/h Bell-47 top speed = 0.78 Mach on the advancing blade and that is for a slow helicopter. 217.109.123.82 ( talk) 12:07, 29 April 2014 (UTC)
RookTorre ( talk) 20:38, 29 April 2014 (UTC)
Do remove the Helicopter.
Sorry if I was polemic (I was... but it's upsetting when you see such a thing there and there is a discussion if to remove it. It's addition was more like a very successful troll edit. It did trolled me. I bear no offense to the author for the nice artwork and I really respect him. But this article is not the right place for that example. The whole point is, please, it's wrong, remove that example.
Also be careful when citing Anderson's books. He is an exceptional teacher and I know Anderson's book are very authoritative in the US, but the rest of the world also have exceptional fluid dynamicists especially on fundamental topics that maybe it's worth reading. Notice that "Introduction to Flight" is a book on that title and not about compressible and incompressible fluid flows.
Ok sorry I am trolling myself (but for the good) I really hope the Helicopter gets removed... I'll not sleep for days now...
Gabriele Dini Ciacci ( talk) 11:08, 11 August 2015 (UTC)
RookTorre ( talk) 02:07, 3 June 2014 (UTC)
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)
Hello fellow Wikipedians,
I have just modified one external link on Density of air. Please take a moment to review my edit. If you have any questions, or need the bot to ignore the links, or the page altogether, please visit this simple FaQ for additional information. I made the following changes:
When you have finished reviewing my changes, you may follow the instructions on the template below to fix any issues with the URLs.
This message was posted before February 2018.
After February 2018, "External links modified" talk page sections are no longer generated or monitored by InternetArchiveBot. No special action is required regarding these talk page notices, other than
regular verification using the archive tool instructions below. Editors
have permission to delete these "External links modified" talk page sections if they want to de-clutter talk pages, but see the
RfC before doing mass systematic removals. This message is updated dynamically through the template {{
source check}}
(last update: 5 June 2024).
Cheers.— InternetArchiveBot ( Report bug) 23:49, 8 September 2017 (UTC)
The formula makes no sense, since the result becomes imaginary as approaches . Therefore, I changed it to where . Please note I don't have any prior knowledge and haven't done research on this topic whatsoever, but this seemed to be the only appropriate change, seeing as the formula for wouldn't be there if it wasn't relevant. Feel free to change it back if you can find proof that this is incorrect.
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)
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)
![]() | This article is rated Start-class on Wikipedia's
content assessment scale. It is of interest to the following WikiProjects: | ||||||||||
|
(this heading was missing and needed) Kurt Artindagi ( talk) 02:44, 30 November 2013 (UTC)
Should this page be merged with Atmospheric pressure (or contrawise)? Duk 07:25, 28 Oct 2004 (UTC)
I suspect that they shouldn't be merged, because pressure and density are different concepts. As a quick example, please note that the density calculations require that local pressure be known. Alternately, pressure is an integration of density over altitude. However, the distinction may be more technical than useful, so if you would care to mention why you think there should be a merge, I may find myself enlightened.
Cheers, One-dimensional Tangent 00:36, 30 Oct 2004 (UTC)
Hmm... If you are planning on doing a page on the various models, or a page for each model, then the Density article would likely be redundant. In that case I definately see your point, and certainly have no objections.
The only thing I see in favor of keeping the Density article is that it might be simpler than MSIS-1986 and NRLMSIS-00, especially for people who only want a rough model and who don't need to know temperature, etc. However, all I know about atmospheric modelling is due to a few hours of light research, so I figure you're probably more qualified to judge this than I am.
So... I'll not take any offense at whatever you choose to do. -grin-
One-dimensional Tangent 02:40, 30 Oct 2004 (UTC)
The density formula had the wrong units, so I multiplied by M (to balance the mol and the Temperature)
and divided by 1000 (for the gram to kilogram ratio). It now reads:
However, the external link http://wahiduddin.net/calc/density_altitude.htm also looks confused with its units, the gas constant starts off as
but later uses:
This works out as the link uses M / 1000 to correct the different units, but this article appears to have forgotten them. - Wikibob | Talk 22:21, 2005 Jan 17 (UTC)
Good point, I've removed the need for the 1000 by adjusting all the units except pressure to SI base units. This means pressure is in pascals, lapse rate in kelvin per metre (looks odd), and height in metres. Although standard units, the lapse rate, height and molecular weight may look odd to some, so here is an alternative with kilometres, and grams (this brings 1000 back, but that could be removed by using kPa for pressure.)
You should point out what mean air molecular mass you are using in the number of moles -- mass conversion. I agree with the statement directly above this. There is no such thing as an 'air molecule", air is 78+% Nitrogen, 20.9% Oxygen, etc... and both N and O exist in air as N2 and O2. Thus the discussion of the effects of humidity in the air is a bit misleading, and should say an "average" value for a hypothetical "air molecule" is calculated from the relative proportions of nitrogen and oxygen in the air, and the fact that they exist as two-atom molecules, thus yielding an average molecular weight for a hypothetical air molecule of 29. — Preceding unsigned comment added by Njaimo ( talk • contribs) 22:19, 26 September 2014 (UTC)
I do not think this article needs to be merged with the one on Atmospheric pressure. Pressure and density are indeed, as already said, totally different concepts. This article maybe should be more on the concept of density of "air" as the compound of gasses commonly found in "some reference" atmosphere, i.e. sea level and some common model and in controlled systems. It may be talking about base topics and redirecting to other articles for air in complex systems. It should also treat the sea level density of air in static conditions. It could redirect to Atmospheric pressure for air in the most common earth atmospheric system (and define the system with all the temperature, gravity gradients, composition, ecc.) to explain why density is such in atmosphere. Meanwhile it could redirect to fluid flows for the concepts of density of air (as any fluid) is a fluid dynamics system. And finally redirect to density of air in chemistry and in general the concept of density for compounds of gasses (but I leave this to others as it's not my field anymore). This should turn this article in a nice, correct and tidy one that works as an access point for the many involved concepts of why air and density.
As for an example, a good one could be the classic pressurized piston in static condition with some defined compound of gasses we define as air and showing some calculations of elementary thermodynamics that show the link of density to temperature, (partial) pressure(s) ecc.. So the reader get the idea of why density is such and why of air. Then three links: a links to density, a link to air and a link to thermodynamics models (and maybe chemical, for partial pressure part).
Remove "air molecule" and any reference to it. Else the next step would be students looking for "air" on the periodic table for an "air atom" (and I'm citing personal experience of a student looking for water on it...) (and when you say something they will say you "It's on THE Wikipedia". Oh dear. Let's have the Wikipedia as an help and not as an issue).
Done with August rant :)
Regards
Gabriele Dini Ciacci (
talk) 11:41, 11 August 2015 (UTC)
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:
Temperature at altitude h kilometres above sea level is given by the following formula (only valid below the tropopause):
The pressure at altitude h is given by:
Density can then be calculated according to a molar form of the original formula:
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?
The text says:
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)
The link to the: eXtreme High Altitude Calculator is broken at today. if it keeps to be broken it needs to be removed
Gabriele Dini Ciacci 00:33, 13 November 2007 (UTC)
\rho~_{_{humid~air}} = \frac{p_{d}}{R_{d} \cdot T} + \frac{p_{v}}{R_{v} \cdot T} —Preceding unsigned comment added by 134.221.122.71 ( talk) 11:33, 17 February 2009 (UTC)
In my research on corona discharge, I find Peek's law (which I am writing). His book has a variable δ:
δ is the air density factor. It is calculated by the equation:
I also come across this version of "relative air density":
which looks at first glance to be the same thing with different units (kPa and K), but I am too tired to do the math. Then I find this formula which has several other variables:
RAD = Relative Air Density
BP = Barometric Pressure (inches??)
RH = Relative Humidity (percent)
T = Air Temperature (°F)
SP = Saturation Pressure (this value comes from a table included in the spreadsheet)
RAD = (1737.97 x (BP - (SP x RH/100))/(460 + T))
What is the relationship between these? Is one a standard formula that would be used in chemistry or whatever? Are b and T standard variable names for these quantities? Do the humidity values affect air density negligibly in most cases, so they are left out of the first ones? - Omegatron 02:54, August 8, 2005 (UTC)
Does anyone think the following line should be in slugs rather then lbm?
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)
There are many "standard" temperatures and pressures used. A user recently changed one of the given standards from 100 kPa to 1 Atm, but without any references or changes to the resulting value of air density. Since you can't change one without changing the other, I reverted the change. According to the linked "standard temperature and pressure" page, there are many standards. As the values listed on the page are just examples anyway, I feel the link to the appropriate Wikipedia page provides enough information to those looking for other standards. Maybe the most common should be listed, but they vary by country and industry. Otherwise we would have to list them all. Djd sd 16:04, 28 April 2007 (UTC)
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)
The second sentence in section Humid air states This occurs when the molar mass of water vapor (18 g/mol) is less than the molar mass of dry air[note 2] (around 29 g/mol). I think it would be better to change the word when with because because the molar mass of water is always 18 g/mol so, in this context, it is always less than the molar mass of dry air. However, English isn't my mother tongue so I would prefer an English editor changes it if my suggestion seems appropriate enough. -- 149.34.8.36 ( talk) 10:14, 27 October 2021 (UTC)
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)
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)
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)
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)
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)
The bot reverts the corrections someone else did to the formula - I just lost hours because the formula was wrong. Someone please correct this:
The pressure at altitude h is given by:
to
The pressure at altitude h is given by:
and
Density can then be calculated according to a molar form of the original formula:
where M is molar mass, R is the ideal gas constant, and T is absolute temperature.
to
Density can then be calculated according to a molar form of the original formula:
R is the specific gas constant ( J/(kg*degK) = 287.05 for dry air), and T is temperature in deg K. — Preceding unsigned comment added by 94.222.121.251 ( talk) 23:29, 7 November 2011 (UTC)
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)
What is the helicopter doing on this page? Besides the explanation is probably incorrect as well... Kotika98 ( talk) 21:17, 25 March 2014 (UTC)
remember ( isentropic process):
RookTorre ( talk) 16:14, 26 March 2014 (UTC)
Hi, I am the annon that has just removed the helicopter picture from the article. Agreeing with Kotika98, a helicopter (or any wing) flies due to pressue not density differences between upper and lower surfaces (density differences may appear above say Mach 0.6 but are not critical to the process). Regardless, I think the generation of lift is a complex topic best left to the lift (force) article. 217.109.123.82 ( talk) 09:10, 23 April 2014 (UTC)
RookTorre ( talk) 20:20, 23 April 2014 (UTC)
Hi, fair point the flow will not be perfectly incompressible like in theory. Nevertheless a helicopter is not flying because of any density differences between the upper and lower surfaces, but because of a pressure difference. Hypothetically, if it were possible for a helicopter to have high density air beneath the rotor and low density air above the rotor, but both at the same pressure- it would not fly. Therefore I propose to remove the picture again:
217.109.123.82 ( talk) 08:52, 25 April 2014 (UTC)
RookTorre ( talk) 16:09, 25 April 2014 (UTC)
RookTorre ( talk) 02:18, 29 April 2014 (UTC)
I meant generally compressibility is most noticable at transonic speeds+, as it is I don't think it reads as if I am talking specifically about the particular helicopter (Bell 47G), but if you think otherwise feel free to rephrase. For reference 213m/s + 169km/h Bell-47 top speed = 0.78 Mach on the advancing blade and that is for a slow helicopter. 217.109.123.82 ( talk) 12:07, 29 April 2014 (UTC)
RookTorre ( talk) 20:38, 29 April 2014 (UTC)
Do remove the Helicopter.
Sorry if I was polemic (I was... but it's upsetting when you see such a thing there and there is a discussion if to remove it. It's addition was more like a very successful troll edit. It did trolled me. I bear no offense to the author for the nice artwork and I really respect him. But this article is not the right place for that example. The whole point is, please, it's wrong, remove that example.
Also be careful when citing Anderson's books. He is an exceptional teacher and I know Anderson's book are very authoritative in the US, but the rest of the world also have exceptional fluid dynamicists especially on fundamental topics that maybe it's worth reading. Notice that "Introduction to Flight" is a book on that title and not about compressible and incompressible fluid flows.
Ok sorry I am trolling myself (but for the good) I really hope the Helicopter gets removed... I'll not sleep for days now...
Gabriele Dini Ciacci ( talk) 11:08, 11 August 2015 (UTC)
RookTorre ( talk) 02:07, 3 June 2014 (UTC)
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)
Hello fellow Wikipedians,
I have just modified one external link on Density of air. Please take a moment to review my edit. If you have any questions, or need the bot to ignore the links, or the page altogether, please visit this simple FaQ for additional information. I made the following changes:
When you have finished reviewing my changes, you may follow the instructions on the template below to fix any issues with the URLs.
This message was posted before February 2018.
After February 2018, "External links modified" talk page sections are no longer generated or monitored by InternetArchiveBot. No special action is required regarding these talk page notices, other than
regular verification using the archive tool instructions below. Editors
have permission to delete these "External links modified" talk page sections if they want to de-clutter talk pages, but see the
RfC before doing mass systematic removals. This message is updated dynamically through the template {{
source check}}
(last update: 5 June 2024).
Cheers.— InternetArchiveBot ( Report bug) 23:49, 8 September 2017 (UTC)
The formula makes no sense, since the result becomes imaginary as approaches . Therefore, I changed it to where . Please note I don't have any prior knowledge and haven't done research on this topic whatsoever, but this seemed to be the only appropriate change, seeing as the formula for wouldn't be there if it wasn't relevant. Feel free to change it back if you can find proof that this is incorrect.
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)
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)