What is Air pressure: Definition and 207 Discussions

Atmospheric pressure, also known as barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The standard atmosphere (symbol: atm) is a unit of pressure defined as 101,325 Pa (1,013.25 hPa; 1,013.25 mbar), which is equivalent to 760 mm Hg, 29.9212 inches Hg, or 14.696 psi. The atm unit is roughly equivalent to the mean sea-level atmospheric pressure on Earth; that is, the Earth's atmospheric pressure at sea level is approximately 1 atm.
In most circumstances, atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point. As elevation increases, there is less overlying atmospheric mass, so that atmospheric pressure decreases with increasing elevation. Pressure measures force per unit area, with SI units of pascals (1 pascal = 1 newton per square metre, 1 N/m2). On average, a column of air with a cross-sectional area of 1 square centimetre (cm2), measured from mean (average) sea level to the top of Earth's atmosphere, has a mass of about 1.03 kilogram and exerts a force or "weight" of about 10.1 newtons, resulting in a pressure of 10.1 N/cm2 or 101 kN/m2 (101 kilopascals, kPa). A column of air with a cross-sectional area of 1 in2 would have a weight of about 14.7 lbf, resulting in a pressure of 14.7 lbf/in2.

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  1. J

    I Trying to wrap my head around gas turbine thermodynamics

    I created a crayon drawing to aid the discussion below: Basically if you have a blower of low pressure, and you blow it through a tube which has a very hot center, when the heat is added to the air, does the pressure of the air increase after passing by the fire, or is that impossible since...
  2. S

    Air pressure changes in a vessel as the vessel volume increases

    As an example, you have a 100-gallon capacity sealed pressure vessel containing 100 psi of air pressure. What is the change in air pressure as the vessel volume is increased? If the volume is doubled is the pressure reduced to 50 pounds psi. On a graph, is the reduction rate a straight line? Is...
  3. Lotto

    B What is the pressure acting on the air?

    Let us say that the glass isn't whole under the water. If the height of the air layer under the water is ##\Delta x##, then the pressure the water acts on the gas is ##p=p_{\mathrm {atm}}+\Delta x \rho g##. But my confusion is why the "hydrostaic pressure" is ##\Delta x \rho g##, not ##L\rho...
  4. K

    B Water doesn’t fall in inverted half cup

    I just happen to see a show about air pressure host by Brian Cox. As the link:https://i.stack.imgur.com/vfZlI.jpg shows, he flipped a half-filled water cup upside down then the paper on cup doesn't drop: It puzzled me, because the cup is half-filled, the pressure shouldn't balance since inside...
  5. 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...
  6. 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...
  7. D

    B Digging Mars for Air Pressure

    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...
  8. D

    B Air pressure generated by driving at 60mph

    If I place a 5' L x 12" W open box at front and a 1/8" hole at the back of the box and drove my car at 60 mph how much psi would I generate at the 1/8" hole?
  9. 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...
  10. G

    Choosing a Flexible hose for outlet air pressure vessel

    Hi everyone, What should be the considerations to choose the proper hose (max working press) installed at outlet air pressure vessels (11 bar) for industrial purposes? Please remark source\link. Also, I've found a table which lists the max sys operating press for 4 different fluids (fuel, oil...
  11. S

    I Ceiling fan pressure increase or decrease

    Would air pressure increase or decrease due to a ceiling fan in a room?
  12. I

    B Rebound Height vs Air Pressure: A Puzzling Relationship

    Hi all I have a very quick question I'm trying to understand why a graph of Rebound height (m) vs Air Pressure (x axis) doesn't have a line of best fit which goes through the origin. I understand a basketball's bounce can be compared to the compression of a mass-spring system but then why...
  13. D

    "Air Pressure" is not "the weight of the air above you"

    All the popular definitions of 'air pressure' that I have seen say: "air pressure is the weight of the column of air above you". This seems misleading to me. - -...
  14. Theravenhouse

    Air pressure to energy, am I missing something?

    Hello! I've come across this forum looking for an answer to an odd question related to energy production. I have no intention of creating infinite energy so don't worry. Imagine a very strong balloon with a cord wrapped tightly around it. The balloon expands pulling the cord which spins a...
  15. Johnnyallen

    Water pressure affects air pressure

    In the movie The Abyss an oil rig crew works and lives at the bottom of the ocean in a deep sea structure. There is a compartment where there is an opening in the floor allowing the crew to lower a submersible craft without going through any kind of air locks etc. We all should know from high...
  16. person123

    Bernoulli Principle For Pitot Tubes

    Here is the setup: Apply Bernoulli Principle to the top (free surface) of the two pitot tubes (1 for static and 2 for dynamic with the points colored in red): $$\frac{p_1}{\rho_w g}=h+\frac{p_2}{\rho_w g}$$ The difference in air pressure would give the following:$$p_1=p_2+h\rho_{air} g$$...
  17. DrPython

    Calculate the air pressure needed for a projectile to travel X distance

    Hello! I'm brand new to the physics forum so please excuse any mistakes I make. I'm not even sure if I'm in the right forum section lol. My goal is to create a air cannon to launch a piece of dog food (super overkill) and I have pretty much 0 background in anything post-high school physics. I'm...
  18. C

    MHB Find the probability of 1 tire with low air pressure P (1)

    1) Let X represent the number of tires with low air pressure on a randomly chosen car. The probability of distribution of X is as follows: X 0 1 2 3 4 P(X) 0.1 0.2 0.4 0.2 0,1 a) Find the probability...
  19. S

    Compressed air pressure vs hydrostatic pressure

    Hi all, I'm new on here and will start off with what I think is a simple clarification. I'm questioning my workings due to previous work being completed by another engineer and thought this was the best place to ask. Essentially we have compressed air being supplied through a hose, the hose...
  20. C

    Maintaining higher air pressure in an "open" leaky container

    Hey all, I've got a container that needs to maintain a certain amount of air pressure for the contents inside to develop correctly. However, it is an open container (like a big box with a hole in it), so without a pump constantly pushing air into it, it will rapidly drop pressure to equalize...
  21. Ayrflyer

    Need help trying to mimic a phenomenon associated with air pressure

    Good day everyone, Hope all is well. Bare with me as I am beginner in the field of understanding air pressure. But could really use help with a certain phenomena that I have been observing with an experiment I have had success with. I am then attempting to build an apparatus that mimics its...
  22. S

    Earth's Atmosphere -- Is gravity the reason we have air pressure?

    I have read an article in Quora, where a person says that "Gravity pulls the atmosphere towards itself and that's one of the reason why our Atmosphere is still this way" and also adds that, "gravity is the reason we have air pressure in the first place. Gravity pulls on the atmosphere...
  23. falcon999

    Effect on air pressure and volume in an enclosed container

    Summary: I wish to understand if bubble formation in milk while being sloshed around, or the formation of separation layers will affect both the pressure and volume of the air head space above the milk Hi all : ) I have a basic physics question and sorry if its a very silly question: Let's...
  24. Adesh

    Derivation of the change of air pressure with height

    If we take a slab of air with cross-sectional area of A and height dz in our atmosphere. Now, what we do is make an argument like this :- Pressure from below must balance both the weight and Pressure from above to keep the slab at rest. ( I have added an attachment for clarification) And...
  25. S

    Air pressure calculation

    The basic barometric formula for calculating atmospheric pressure is (Ph: pressure at height h) = (Pzero: pressure at height zero) x exp(-mgh/kT), where the height h unit is meters, P unit is pascals, m is the mass of an average "air" molecule, g is the acceleration of gravity, k is the...
  26. Dishsoap

    Why don't we take air pressure into account in calculations?

    I once was explained the answer to this question - something about both the air and the object being incompressible. However, for the life of me I cannot seem to reproduce the answer of why we ignore air pressure when doing basic calculations. If it matters, the particular system I'm interested...
  27. mateusz24052

    Calculating the air pressure exerted on the body

    Good morning all, How do you calculate the air pressure exerted on an average human of 1.9m2 I know the air pressure is 1.01kPa. Do I do, F = PA? 1.01kPa x 1.9? What are the calculations step by step? and what is it in bars? Does that mean it is 1.919 bar? Thank you,
  28. Z

    Time till the air pressure is gone

    Hello, I have a 8 gram cartridge of N2O meant for kitchens. Long story short from what I understand it has 10 cm cube of N2O inside. I also know it has 900 psi / 60 bar of pressure inside. The cylinder is exactly like this image. I am trying to find out how much time it would take if I...
  29. Poetria

    Air Pressure Conversion: Units to Meters

    Homework Statement [/B] dp/dh = -.13*p h in kilometers I should convert it into meters2. The attempt at a solution I thought it would be enough to multiply -0.13 by 1000. :( dp/dh = -130*p but it is wrong.
  30. P

    Is this kind of pressure chamber design possible?

    Hi! Given that the chamber is airtight and no air leakage occurs, is the design in the picture below possible? Can the pressure inside the chamber cause the button (black part at the top) to be "pushed"? https://imgur.com/a/wOSD30D Obviously the temperatures are over-exaggerated, but the...
  31. A

    Piezoelectric crystal and air pressure

    Will air pressure induce a voltage of a piezoelectric crystal or does it need to be mechanically compressed? My guess is that it would depend on the permeability of the crystal
  32. A

    Piezoelectric and air pressure

    I was just wondering if anyone could explain to me what would happen to a piezoelectric crystal on a closed circuit in a pressurised vessel?
  33. G

    Using Ideal Gas Law to Calculate Vertical Pressure Gradient

    Homework Statement Consider a cylindrical parcel of air of area A and infinitesimal height dz. If this air parcel is to remain stationary, the difference between the total pressure forces exerted on its top and bottom faces must be equal to its weight. Use this information and the ideal gas...
  34. SpiffyPhysics

    Confused by temperature's effects on air pressure

    Hi, I'm an instructor at an online school, and my text says “ Air pressure is the amount of pressure the atmosphere places on the surface of Earth. Air pressure is usually measured as the weight of the column of air above a square meter (N/m2). As altitude increases, air density decreases and...
  35. M

    Low Air Pressure Training (exercise)

    Looking to do a experiment on the effects of air resistance training on the body. doing basic exercises such as jogging push ups. Maybe a couple of curls ;).got facility design herewondering what your thoughts and opinions on this would be.
  36. D

    How does air behave in the daisy chaining of compressors?

    I'm working on a project involving compressing air to a desired high pressure. So far the only equation I've been paying attention to is the ideal gas law. My question is if an air compressor pump is rated to create a maximum pressure of 100 psi based on its inlet being at atmospheric pressure...
  37. G

    Air pressure holds coaster on glass: What if only half full?

    Hi. If I fill a glass with water up to the top and close it with a coaster, I can turn it upside down without the coaster falling off and spilling everything. Usually, this is explained with the atmospheric air pressure being bigger than the pressure of the water inside the glass (hence, it...
  38. OldWorldBlues

    Basic math for air pressure?

    Hiya! I'm an ameture "maker", and recently I've become interested in air pressure and such. I thought a fun project to help me learn about it would be to make one of those small air cannons that are powered by bicycle pumps (safety first and all that). One thing confuses me though: how exactly...
  39. F

    Atmospheric air pressure on the human body

    Hello, It is well known that the atmospheric air pressure is significantly strong but our body does not get crushed by it because and equal pressure pushes from the inside our body. That said, does it mean that air can exist and be diffused inside solid organs like the lungs, our heart, etc...
  40. N

    Air pressure on planes and leak-proof containers....

    On airplanes - do you know of a container or bag that will stops individual bottles with liquid from leaking/ exploding from the changes in air pressure?
  41. Builder

    Air Pressure Lift: Lifting 250 lbs 6-12

    How much air pressure, from six 1inch in diameter pipes, would it take to lift something no more then 250 pounds about six to twelve inches off the ground?P.S. This is a personal question not, homework.
  42. P

    How to measure the air pressure of a pipe without having water resistance

    Hello, I'm having a question regarding the sensors and the techniques in fluid mechanics. Since my skills are amazing in this field, here I'm asking you questions xD I want to measure the air pressure of this tube/pipe (P1,P2,P3). This pipe will be flushed with water and then with compressed...
  43. R

    Programatically measure air pressure within a piston

    I am a software engineer. I am working on an experimental project to attempt to measure in real time the variation in air pressure (relative to the ambient pressure of the room) in a piston style apparatus. In this model, I am expectant that there will be a measureable change in the internal...
  44. System1459

    Air Pressure between two air tanks

    So I am a heavy vehicle mechanic. One of my vehicles has an air starter with a separate air tank dedicated to the starter. This tank is fed from the main air tanks on the truck with a check valve to only allow air into the starter tank. The gauge on the dash only displays the pressure in the...
  45. P

    Air Check Valve: Preventing Air Pressure Backup in Lift Fans

    would an air check valve help lift by preventing air presure backup through the lift fan?
  46. person123

    Curved Tube For Constant Pressure Increase?

    My design concept stems from the fact that the pressure in a tube increases exponentially based on the length of the tube compressed. I would like to design a tube that increases pressure at a more constant rate. I would imagine that a tube curved inward toward the base would achieve this. As...
  47. T

    Testing water pipes with air pressure

    Picture a piping system made up of threaded steel pipes. It is to hold regular water at 7-10 bars. When testing the system for leaks, air is used due to a frost issue and the consequences of a larger leak with water. But what holds water doesn't hold air, and so it slowly leaks out. The question...
  48. MichaelT17

    A box Under Air Pressure -- will it blow?

    Homework Statement I'm doing a personal project to keep me busy for the winter. I grow Bonsai and I'm making a hospital for sick trees or recently collected ones from the wild that need to recover. I have constructed a 40x40 inch plywood box, 5/8 inch thick walls, air tight. The lid will be...
  49. Alfreds9

    Calculating air pressure from altitude, RH and temperature?

    Homework Statement [/B] This is a practical problem, no homework question. I'd like to determine pressure (and O2 partial pressure) at altitude, yet following a more realistic real-world calc including measured data like relative humidity (RH) and temperature at that altitude, yet all I can...
  50. G

    Buoyant force and ambient air pressure

    I wanted to inquire as to a thought I have on a situation with buoyancy and air pressure. In the first slide (slide 1), I am showing a situation where a buoyant object is pushing up on a support wall through a fixed wall that has water in it. Here are the factors: 1. The net buoyant force of...