What is Air: Definition and 1000 Discussions

The atmosphere of Earth is the layer of gases, commonly known as air, retained by Earth's gravity, surrounding the planet Earth and forming its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing for liquid water to exist on the Earth's surface, absorbing ultraviolet solar radiation, warming the surface through heat retention (greenhouse effect), and reducing temperature extremes between day and night (the diurnal temperature variation).
By volume, dry air contains 78.09% nitrogen, 20.95% oxygen, 0.93% argon, 0.04% carbon dioxide, and small amounts of other gases.
Air also contains a variable amount of water vapor, on average around 1% at sea level, and 0.4% over the entire atmosphere. Air composition, temperature, and atmospheric pressure vary with altitude, and air suitable for use in photosynthesis by terrestrial plants and breathing of terrestrial animals is found only in Earth's troposphere and in artificial atmospheres.
Earth's atmosphere has changed much since its formation as primarily a hydrogen atmosphere, and has changed dramatically on several occasions—for example, the Great Oxidation Event 2.4 billion years ago, greatly increased oxygen in the atmosphere from practically no oxygen to levels closer to present day. Humans have also contributed to significant changes in atmospheric composition through air pollution, especially since industrialisation, leading to rapid environmental change such as ozone depletion and global warming.
The atmosphere has a mass of about 5.15×1018 kg, three quarters of which is within about 11 km (6.8 mi; 36,000 ft) of the surface. The atmosphere becomes thinner and thinner with increasing altitude, with no definite boundary between the atmosphere and outer space. The Kármán line, at 100 km (62 mi), or 1.57% of Earth's radius, is often used as the border between the atmosphere and outer space. Atmospheric effects become noticeable during atmospheric reentry of spacecraft at an altitude of around 120 km (75 mi). Several layers can be distinguished in the atmosphere, based on characteristics such as temperature and composition.
The study of Earth's atmosphere and its processes is called atmospheric science (aerology), and includes multiple subfields, such as climatology and atmospheric physics. Early pioneers in the field include Léon Teisserenc de Bort and Richard Assmann. The study of historic atmosphere is called paleoclimatology.

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  1. davenn

    B Do Objects in Free Fall Encounter Air Resistance?

    from ... www.physicsclassroom.com/class/1DKin/Lesson-5/The-Big-Misconception "Free-fall is the motion of objects that move under the sole influence of gravity; free-falling objects do not encounter air resistance. Huh ?? of course it encounters air resistance, doesnt it ? An object...
  2. hello478

    Camera drone and speed of air below it

    my answer = F = 1.6*9.81 - 1.2*9.81 = 3.924 N -> resultant force of the drone moving (weight minus the upward force) M= 1.2kg , mass of drone a= 3.31 m/s^2 , acceleration of drone u=0 m/s , initial speed of drone t=1s , time v = 3.27 m/s, final speed of drone and its not even in the options... 😶
  3. Hauzen

    Please tell me the difference in the size of the air volume

    Hi. Since I've been studying fluid mechanics, I've been asking a lot of questions Thank you all for your help! I suddenly have a problem that I want to think about while studying today. I would like to know the change of air volume according to the pipe shape as shown in the picture below...
  4. Hauzen

    I have a question about the air volume

    Hello I need your help studying hydrodynamics. I have a question about the volume of air. Assuming incompressibility, non-viscosity, there is a coefficient of tube friction, and it moves in laminar flow... The Oulet stage Fan is installed, so air moves from top to bottom. The cross-sectional...
  5. GinaMitchell

    Engineering Science Fair Air Cannon Help

    Hi - I built an air cannon to launch a fishing lure for my science fair project. The air cannon launched a 1/4 oz lure 31.4 meters. Based on this, I calculated the initial velocity to be 17.54 m/s using the formula for range of a projectile. I want to be able to launch the lure 38.5 meters. I am...
  6. F

    B Describing the cooling of a room without any electrical or mechanical devices

    Hello. I ask nothing here from a long time ago. One of my students is doing research on how to cool the air in a room without using any electrical or mechanical devices. For example: using just ice. What we need is how to solve/describe the process using math. For example: how to use/solve the...
  7. M

    Flow rate of air through constriction

    I've been trying to find the formula(s) to determine the flow rate of air (and properties) in a pipe of varying diameters connecting two theoretical reservoirs of infinite size. The pipe is short in length so friction can be neglected. Reservoir 1 is always a higher pressure. There is no heat...
  8. Karfen

    Thermodynamics homework -- Estimate the molar specific heat of the air at constant volume Cv

    And this is the Cv graph for hydrogen: I think the Cv graph for air is similar with this graph. But I don't know the answer, can someone tell me?
  9. dpasini3

    Finding an application where an air/n-octane mixture is cooled

    For now, I just searched online for some kind of application relevant to the problem posed
  10. O

    Arcing and conductivity and object interference

    Im trying to figure out if I were to have two points with 10cm of humid ocean air between them and a fly or mosquitoes flew between the points, if they would get zapped and create an electrical arc, or if the bug would act as an insulator and be avoided by the arc? also, could the bug trigger...
  11. B

    I Absorption cross section of light in air

    When I woke up today in the morning, I had the stupid idea of trying to remember some of my knowledge from university. As it turned out, this was easier thought than done, especially given my still drowsy state of mind. I want to roughly estimate the penetration depth of visible light in air...
  12. rhmourwa

    Need help on how to find the Equivalence Ratio of combustion for plastic waste

    Hello Actually, I'd like to find the effect of different Equivalence Ratios on my gasification experiment using plastic waste as feedstock fuel but I'm confused as to how I can find the Equivalence Ratio because I don't know the exact chemical formula of plastic waste I'm using. So I'm curious...
  13. H

    B Some Questions About Drag (for ships in water and airplanes in air)

    I'm interested in the very basics of drag, both for ships in water and airplanes in air. Here's what I have so far : Flow of the medium can be laminar or turbulent. As the relative speed of the vessel increases, the more likely the flow is to be turbulent. Laminar drag increases linearly...
  14. T

    B Understanding air flow and resistance

    In a recent thread, I thought I understood what was going on but alas, I am still confused. So I offer this diagram and ask for more help please. Shown is an aircraft holding pattern. The one on the left is flown in still air. The one on the right is flown with a wind coming from the...
  15. A

    B How long does it take to reach harmful CO2 levels in a room?

    • I exhale 1 kg of CO2 per 24 hours = 41.67g/h (average) • Co2 indoors after ventilation = outdoors = 400 ppm (world average) • Co2 indoors threshold = 1000 ppm (cognitive effect) • Room volume = 32.5 m3 • Details to neglect: window and door closed tight, no HVAC system or other ventilation...
  16. Argonaut

    Maximizing Range/Time in Air of an Airplane: Solving with Calculus

    Is my solution correct? (I only have answers to odd-numbered exercises.) Is it a good solution or have I overcomplicated things? (a) The forward force provided by the engine balances the air resistance force, so ##F_{engine}=F_{air} = \alpha v^2 + \beta /v{^2}##. Let ##W_{engine}## be the...
  17. F

    I Do you think emissivity of air makes sense?

    Hello guys :)In the frame of finding a physical model for the temperature of Earth's surface, talking about the very "idealized" two-layers model of atmosphere, I ask you now the question to the other physicists or engineers: does it make sens to associate an emissivity to a layer of air (+ some...
  18. Luchee

    How do I go about the calculations for an air conveyor?

    How do I go about the calculations for an air conveyor that has the same working principle as an air hockey table? The conveyor should not he bulky seeing as it is a prototype. Please help me.
  19. Pushoam

    B Pressure of air inside a glass

    Let's consider an uncovered glass. Air particles are present in the glass. $$ P_1 = P_a$$ $$P_2 =P_1 +\rho gh = P_a +\rho g h$$where ##P_A## is atmospheric pressuere and ##\rho ## is air density. Now, if I cover the glass with a plastic card, then what is ## P_1##? $$P_2 =P_1 +\rho gh $$ 1)...
  20. Edm

    B Air tank PSI and cubic feet calculation help please

    If I have a air tank that is 1 cubic feet with the pressure gauge at 0 and I pump in air to 5000 psi how many cubic feet of a 100 psi would be in that tank? Any help would be appreciated
  21. Thomas_Kellner

    Change in temperature of air in a closed system

    Looking at the given values, I thought the specific heat formula could be used to calculate the final temperature of the air: c = Q/mΔT. Since the final temperature is the sum of the initial temperature and the change in temperature, the formula can be rearranged to ΔT = Q/m*c. Q = 30 W * 10 s...
  22. B

    Will charcoal (carbon) oxidize in the air?

    Wikipedia — Carbon sequestration claims that burying charcoal into the soil offsets CO2 and thus reduces the greenhouse effect: Is it a must to cover charcoal/biochar with the soil to prevent the air and rain water exposure to avoid oxidation, i.e. offset carbon dioxide? Would it otherwise...
  23. D

    I Just for fun: treadmill air conditioner efficiency calculation

    What approximate portion of generated heat from being active on the treadmill, both the person on it as well as the machines themselves would be compensated/cooled if the treadmill resistances would be disabled/removed and instead 1/2 end cylinders would be connected to an air conditioner...
  24. B

    I Time for a cold volume of air to reach a higher air temperature

    I have a cube with a volume of 1000m3 at an initial temp of 290K. The bottom side (10m by 10m) is open to the ambient air. I put this cube into a huge fridge and cool the whole volume by 5K. I close the open side by placing a cover on it. This cube has now got a volume of air at a temperature of...
  25. P

    A Too much cooling air? (Power supply failures due to condensation)

    I have a situation that I cannot explain so I need the assistance of someone with a good understanding of thermodynamics. I have 36 AC to DC power supplies located in an equipment rack. These power supplies are failing after some time. The failures appear to be moisture related. We put...
  26. Y

    Can I run cable tv signal and on air tv signal in a single coax?

    Hi I currently subscribe to Directv, the signal is from the dish and split into 4 coax to go to 4 different rooms. So each room has a coax output on the wall to hook up to the Directv receiver box. I decided to change to Dish Network. At the same time, I want to install a VHF/UHF digital tv...
  27. C

    Solving an Air Pressure Question: Who Is Right?

    Can someone please answer this question, so I can figure who is wrong here, me or author. Thank you.1.question (picture below): empty epruvete turned upside down is dipped in glass filled with water to the depth H. While doing that water enters the epruvete and reaches height of h. The AIR...
  28. S

    I Centrifugal separation into hot & cold air streams?

    I have been reading about the Ranke-Hilsch vortex tube. Details of the explanation tend to differ somewhat among different sources, but it got me thinking about the following thought experiment. Air enters a tube of about 0.5 x 4 cm cross section. It passes through a section that is channelized...
  29. C

    Where Did I Go Wrong? Solving for Angular Momentum in Air Table Puck Collision

    For part(a), The solution is, However, I made a mistake somewhere in my working below and I'm not sure what it is. Does anybody please know? Thank you! Here is a not too scale diagram at the moment of the collision, ## \vec L = \vec r \times \vec p ## ## \vec L = -y_{com}\hat j \times...
  30. S

    Possible to create laminar flow in fast moving air?

    Is it possible to create (nearly?) laminar flow in a tube with rectangular C.S. , around 1 cm X 5 cm , with air moving at around 100 to 150 m/sec? Turbulence will likely set in sooner or later, but can the laminar flow be made to last over say 20 cm?
  31. lukeskywalker52

    I'm trying to detect PFAS molecules in air samples...

    Hi there, I'm working on a project where my aim is to detect the presence of PFAS (Per- and poly-fluoroalkyl substances) in air samples gathered by a system. I've done a ton of research, but most solutions are unachievable due to price and the available space (the system should be relatively...
  32. Glenstr

    Misc. DIY combo air cleaner/humidifier

    Last winter I built a corsi-rosenthal box filter to help clean air in the house, I built it 5 sides with 20"x20" merv 13 rated filters. I was impressed with how well it worked, and am implementing two of them this winter. We have 2 dogs & 2 cats so pet dander as well as dust can build up a lot...
  33. nmsurobert

    Using air core solenoids in a lab exercise

    I found a box of air core solenoids and was hoping someone could me think of a useful lab to use them for. They are about 700 turns each. They carry 7 to 10 amps. However I think I think I would only be able to provide 3 amps because of the power supplies I have. I would like to use them to do...
  34. T

    How much air pressure is needed to push water up a column?

    Hello, I was creating a device to move water up a tube using air pressure, but I am not certain how much pressure I would need. I attempted to create it using 5 gallon buckets, however I was unable to apply the needed pressure needed to the airtight container. The image below is what I have...
  35. S

    Why does decreasing evaporator airflow impact an air conditioner's performance?

    The other day I read on a website that a lower evaporator airflow causes lower low pressure side saturation temperatures and higher delta T on an air-conditioner. Now I think I know why a lower evaporator airflow would cause a high delta T. If there is less air moving over the evaporator, the...
  36. F

    I Heat transfer via air cooling -- which airflow direction is best?

    I'm using a stainless steel pan and a fan to cool my coffee down as quickly as possible. Usually, I have the fan blowing down towards the coffee, but this morning I flipped it over to suck the heat out of the coffee and I'm wondering which of the two is the most efficient, especially as, in the...
  37. C

    Calculating pressure of air pocket in a pressurized water column

    Looking for some guidance in calculating pressure of air pocket in pressurized water column. Example: 2" vertical pipe, capped, with 2" of air and 40 psi water applied.
  38. DaveC426913

    Plotting My Air Flight Path from Photos

    I expected this to be challenging but it's turning out to be much harder than I expected. I just flew back from Cuba to Toronto, got in at 315AM. It was a beautiful, clear and I had the window seat, so I took a bunch of pics. Now I'm plotting the flight path by analyzing the photos. It's super...
  39. T

    Total force from air spring model (double acting piston)

    Hi everyone, I'm an electrical engineer working on making a linear model for a power take-off system. I've gotten inertial, friction, and hydraulic/electric components done, but what is really confusing me is the gas system; I haven't taken ANY thermodynamics. To simplify it, it is modeled as a...
  40. Some1WhoNeedsHelp

    Calculating the motion of air cylinder

    I am stuck at A, how do you calculate the motion of the air? I know ρ=m/V but what is the mass of the air, or I got that question wrong? Thanks
  41. D

    B Could Nuclear Powered Bulldozers Create a Habitable Cavity for a Mars Colony?

    Digging 8km under the lowest point on Mars will get us Mount Everest conditions for air pressure. I was thinking of two ways of doing said title: Nuclear powered bulldozers working around the clock to clear away dirt on a low point on Mars such as...
  42. V

    Why does less dense air rise and more dense air come down?

    My answer given below seems incomplete. Since warm air causes the air to expand in volume, so its density becomes less as compared to the colder air at the top of the room. After this, I generally find all books saying the less dense air rises and more dense air from top comes down and...
  43. daanisrael

    I How is the damping of sound (over distance) affected by air properties?

    Hey all, For my physics major I need to quantify the acoustic effect of sunfields. I'm trying to do this by measuring the sound level before and after a sunfield, and after that by measuring a comparable situation, only without a sunfield. By comparing the results of the two measurements I'll...
  44. Some1WhoNeedsHelp

    Need Help to Understand an Equation for Air Resistance

    I don't understand what the gamma letter in the equation is supposed to represent.
  45. B

    Calculating the speed air comes out of a fan

    Hi, I have a task where i have to calculate the speed of which the air is flowing out of a drones propeller fan. This is all i have been given: The mass of the drone m = 0.42kg, There are four propellers the lenght of each blade d = 0.21m, the air density is 1.3 kg/m3 and g=10 m/s^2y. And the...
  46. M

    Calculating turbine RPM in a pipe with known air velocity and diameter

    Hello, I am trying to calculate the turbine RPM for a turbine in a closed pipe. I know the air velocity and pipe diameter. Can this be done?
  47. Lotto

    B Can we use molecular speed of gas formula also for the air?

    Molecular speed of gas is generally $$v=\sqrt{\frac{3RT}{M}},$$where R is gas constant and M is molecular mass. Can we use this formula for the air as well, when the air is a mixture of different gasses?
  48. Gustavo Reis

    I Air Resistance: Exploring Hooke's Law

    Basically the air works like a spring, it always tries to get back to its resting state. And it's like Hooke's law, the more it deforms the more elastic potential energy it has. That's why the faster you are, the air resistance is greater. Thinking in this way, I imagine that in fluid mechanics...