What is Air density: Definition and 36 Discussions

The density of air or atmospheric density, denoted ρ (Greek: rho), is the mass per unit volume of Earth's atmosphere. Air density, like air pressure, decreases with increasing altitude. It also changes with variation in atmospheric pressure, temperature and humidity. At 101.325 kPa (abs) and 15 °C, air has a density of approximately 1.225 kg/m3 (or 0.00237 slug/ft3), about 1/1000 that of water according to ISA (International Standard Atmosphere).Air density is a property used in many branches of science, engineering, and industry, including aeronautics; gravimetric analysis; the air-conditioning industry; atmospheric research and meteorology; agricultural engineering (modeling and tracking of Soil-Vegetation-Atmosphere-Transfer (SVAT) models); and the engineering community that deals with compressed air.Depending on the measuring instruments used, different sets of equations for the calculation of the density of air can be applied. Air is a mixture of gases and the calculations always simplify, to a greater or lesser extent, the properties of the mixture.

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  1. brotherbobby

    Pressure higher up in the atmosphere

    Attempt : 1. Pressure at height ##z## : ##P(z) = P_{\text{atm}}-\rho_0 gz ##, ignoring density variation. But actually, we have ##\rho(z)<\rho_0\;\forall z>0##. Hence, we are subtracting a bigger value from ##P_{\text{atm}}## than we actually should, meaning that we would end up what a smaller...
  2. M

    Does climate change affect air density at altitude (scale height)?

    Increases in global temperature change affect the tree line and presumably comfortable habitability via temperature, and average air pressure associated with weather patterns. That's not what I mean. I'm thinking a 1/50 increase in kelvin temperature might increase the scale height of Earth's...
  3. brotherbobby

    B Variation of air density with height

    Using the ideal gas equation ##PV = nRT\Rightarrow PV = \frac{m}{M} RT## where ##m,M## are the mass and molecular weights of the gas respectively. This yields ##\frac{m}{V} = \frac{PM}{RT} = \rho##, the density of the gas at a point with pressure ##P##. If only we can obtain the variation of...
  4. CMaso

    I Air density with a significantly higher sea level

    2 scenarios: 1) Situation in the movie "2012", where volume of ocean water hasn't changed, but worldwide seismic activity has caused massive tidal waves. In one scene, a ship is sailing by Mt. Everest close to its peak. In such a scenario, I believe the air density outside the ship would the...
  5. Anand Sivaram

    I Liquid Air and Compressed Air Density

    Densities of Normal Air is 1.225 kg/m3 at STP, whereas the density of Liquid Air is 870 kg/m3. That means liquid air is 710x denser that normal air. Then suppose, we compress normal air to more than 710 atmospheric pressure, then it could have a density more than that of liquid air. Is this...
  6. arescarmen

    [Air resistance of vehicle] Can anyone me?

    I checked the answer, and it is not correct. Is it something wrong?
  7. L

    Calculating Air Density at High Elevations

    Ok, we all know that density is mass/volume. So if air is 1.22kg/m3,If we increase pressure, volume will change, therefore density can change. So how does one calculate density of air at higher elevations. Where i currently live, at 4700ft above sea lvl, I am guessing air density is not...
  8. D

    Why does a higher density slow down sound in air?

    Homework Statement Sorry, it's not an actual problem, it's just a statement I don't understand from my text - "The density of water vapor is less than that of dry air. Therefore, the higher the humidity (that is, the more water vapor there is in the air), the lower the density of the air. For...
  9. J

    Calculating a Ballistic Coefficient (BC) from two velocities

    I have been attempting to calculate a Ballistic Coefficient (BC) from two velocities of a known distance using the formula: BC = (AirDensity * Distance) / ( SQRT(Velocity0) - SQRT(Velocity1)) for example AirDensity = 0.0751265 lb/ft³ Distance = 100 yards Velocity0 = 3000 fps Velocity1 = 2772...
  10. X

    How does a pressure/temperature difference cause a force?

    Hello. I am inquiring about how a pressure difference between a hot room (roughly room temperature) and a cold room (roughly the temperature of a standard refrigerator) can cause a force inside the cold room when exposed to its hotter counterpart. More specifically, I would like to apply this...
  11. Robert James Liguori

    I What are some formulas for calculating humid air density?

    I'm trying to compile a complete list of available humid air density formulas that work with air pressure, temperature and dew point (or RH). If you know any, please advise. Thanks, Robert
  12. Zetan

    Air density, vacuum and gravity

    Hello to everyone. My first question on this forum (it was quite tricky thinking of a heading and prefix for this thread!): Imagine for a moment that there is a hot air balloon which has a strong shell forming the balloons shape rather than one made from material and it weighs the same as a...
  13. R

    How Can Physics Improve Race Car Efficiency and Fuel Consumption?

    Ï had not the slightest idea there was even a cool place to learn about science and physics and...truth! I'd usually just "Google"it and read Wikipedia. One of the main things I would like to learn about would be air pressure or flow, air density and maybe some rotational mass. So let's say in...
  14. S

    Why does air density decrease as we go higher in altitude?

    As we go higher up a mountain, the air pressure decreases. But why would that cause the air density to decrease? Since pressure is hpg, so if h decreases pressure decreases but what causes the air density to decrease as well? Thanks for the help :)
  15. J

    What is the best air density for sound quality.

    Because obviously too much density gives terrible sound quality, like in water. So is the answer simply the density of our lower atmosphere because that is where our ears evolved? Or has this been tested and found to be a specific density?
  16. G

    [Non-uniform Air Density] Pressure problem

    Homework Statement Assume that at sea-level the air pressure is 1.0 atm and the air density is 1.3 kg/m3. What would be the height of the atmosphere if the air density decreased linearly to zero with height? Homework Equations P = ρgh The Attempt at a Solution Really not sure...
  17. A

    Calculating Time of Freefalling Sphere w/Drag and Varying Air Density

    I am looking at the problem of a freefalling sphere and want to calculate time taken to fall a distance. I want to model drag as well as take account of the varying density in the atmosphere. I am using Drag = 1/2*A*Cd*v2*ρ; A - cross-sectional area, Cd - drag coefficient, v2 - velocity...
  18. Philosophaie

    Air Density vs Height above Earth

    What is the density of Air vs Height above Earth? Air Density is 0.001275 g/cm^3 at sea level. I would like to see a graph or a table with the air density vs km above sea level.
  19. C

    Calculating the launch speed from a launch angle, distance, and air density

    Greetings to all. First off, I apologize if I come off as an idiot here who has no idea what he's talking about (probably because I don't). My career is basically as a graphics designer, programmer, and musician- in that order (I design and build iOS applications for a living). I understand...
  20. jaketodd

    Helicopter - Variable Air Density

    This is not homework. If you descend toward the ground in a helicopter, the density of the air is going to increase. I'm curious: Is the amount of energy required to turn the blades directly proportional to the density of the air? For instance: If the air density doubles, does the energy...
  21. T

    Calculating air density from a barometer?

    Homework Statement Working on a lab report, where we are asked to calculate the density of air. Ambient Temperature: 19°C Barometer (mm Hg abs): 765 There were two correction factors: 2.35 and 2.41 How do I use the above information to find the Air Density (kg/m3) ? What are the correction...
  22. P

    Calculating Density of Moist Air: Am I Doing it Right?

    Hello All, I am trying to calculate the density of moist air. Am i correct in saying... density of dry air = 1.2754 kg/m^3 Now i can convert this to mmol/m^3 and density of dry air = 4.384692933394098e+04 mmol/m^3 at a given point in time density of CO2 in air = 16 mmol/m^3...
  23. B

    Altitude, gravity, and air density effects on flight

    I'm very unfamiliar with energy-use in aviation, but I am wondering about what effect altitude has on parameters such as gravity (i.e. weight of the aircraft) and air-density, which I would think affects friction and combustion as well as lift. One thought I've had is that higher velocities...
  24. M

    How Does Air Speed Affect Aircraft Weight?

    Homework Statement Air (density= 1.29 kg/m^3) passes over the top surface of an aircraft whoe effective wing surface area is 75.5 m^2 at a speed of 255 m/s. If the air speed beneath the wings is 135 /s, what is the weight of the plane. Homework Equations W=mg The Attempt at a...
  25. P

    Air Density: How to calculate Relative Humidity

    Hi there, I'm trying to calculate air density; I noticed on http://en.wikipedia.org/wiki/Density#Density_of_air" that there is a table that makes it seem that air density is a function of temperature... I suppose I could safely say that temperature has a significant effect on air density...
  26. R

    Calculating Wind Velocity Given Force, Air Density

    If I know the force that a wind is exerting on an object, is it be possible to determine what velocity the wind is moving at? I also know the air density.
  27. S

    Calculating Air Density: A Solution for Scientists

    Hai, I have the pressure value (which is less than atm) and temperature value. How to calculate Density of the air? I calculated but the result is not satisfactory.
  28. T

    Air resistance and Air density?

    I've never worked with air resistance before so any help just getting me started would be much appreciated. Homework Statement A 20 kg object falls free from a height of 15 m. Including air resistance, what will its position be after 0.6 seconds? Air density is 1.11 kg/m^3. Homework...
  29. T

    Estimate Air Density in ICE at Different Throttle Speeds

    How would you estimate the charge density (air actually entering the cylinder) in an ICE? Assume the outside is standard pressure and temperature of 15*C (60* F) and 101.3kPa (14.7psi). At high airflow speeds (Wide Open Throttle), pressure in the manifold should approximate atmospheric...
  30. P

    Find Air Density: Pressure=1atm, T=273, RH=45%

    Homework Statement Given Pressure= 1 atm, Temperature=273, and Relative Humidity= 45%, find the density of air. Homework Equations 1. PV= nRT 2. density of air= M*P/(R*T), where M is the molecular weight of air. 3. M= 18*Y_H2O +M_dry_air *(1 - Y_H2O), where Y_H2O is the mole...
  31. M

    Calculate Air Density at 18°C with Atmospheric Pressure of 782 mmHg

    :confused: :confused: Could someone please benice and tell me how to find the air density when the temperature is 18 degrees celsuis and the atmospheric pressurew is 782 mm HG. thanks a lot:confused:
  32. N

    Calculating Air density as a function of height?

    Is it possible to calculate the air density as a function of height? We know that density is given as, p\; =\; \frac{M}{V} And that pressure is given as, P\mbox{re}ssu\mbox{re}\; =\; pgh But I am failing to see the connection to combine the two to get air density as a function of...
  33. T

    Air Density, Pressure Differentials, Vacuum ?

    I am trying to understand some effects of pressure differences and air density particularly as it relates to the good ole american made V-8. One of my questions: What is the "speed" of air when a pressure differential is equalized? Assume I have a cube that is exactly one cubic foot in...
  34. M

    Physics metal and air density problem

    a metal of density x weighs y in air,when immersed in a liquid of density z,what is it's apparent weight.please i need explanations about this
  35. W

    Air Density Formula: Find w/ Temp & Pressure-Altitude

    I'm looking for a formula that will find the air density based on a relationship between air temperature and pressure-altitude. Any help would be greately appreciated!
  36. T

    Is air density a state function?

    I know there is a simple equation using absolute pressure and absolute temperature that predicts the density air in our atmosphere. This is commonly used in weather forcasting. My question is that if air undergoes a process of compression, cooling, etc...ending up at a pressure P and a...
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