What is Atmospheric pressure: Definition and 119 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. Steve Rogers

    A water-bottle demonstration of atmospheric pressure

    I'd like to ask about an experiment on atmospheric pressure. To conduct the experiment, we need an empty PET bottle and make a small cut on the lower part of the bottle. A cut no greater than one-half the circumference is acceptable. Then, we press a table tennis ball against the cut to open the...
  2. C

    Homework Help - Fluid Statics

    For A) I used P = hpg (h=0.0125km, p=1000kg/m^3, and g= 9.8m/s^2) this gave me 122.5N/m^2 For B) I used Ptotal = Pgauge + Patm = 1.01E5 + 122.5 = 101122.5 N/m^2
  3. Lotto

    B Problem with understanding deriving Torricelli's law

    We can derive it by using Bernoulli's equation ##p_0+h_0\rho g+\frac12 \rho {v_0}^2=p_1+h_1\rho g+\frac12 \rho {v_1}^2##, where ##v_0=0## is a velocity of a water surface and ##h_0## is its height. ##h_1## is a height of the outlet above the bottom of a tank the water is in. I am confused about...
  4. P

    A How much thickness for sphere to withstand atmospheric pressure?

    Imagine a hollow sphere made of a material with high elasticity constant(e.g. steel). How much thickness should it have to prevent it from crushing when the air inside is pumped out? Is it valid to use Lame solution to quantify the answer? What about Finite Element Analysis?
  5. G

    Calculating atmospheric partial pressure of oxygen

    I study genotype-environment associations in alpine species. I frequently see altitude as the sole predictor of partial pressure of oxygen in the literature concerning hypoxia adaptations. However, I understand that partial pressure of oxygen is also influenced by temperature, humidity, and...
  6. T

    B Atmospheric pressure, vacuum, etc.

    The value of the atmospheric pressure does not seem to me to be correct 1013 HPa and can be recalculated as approx. 1kg/cm2 (is it true?), but it does not seem that such a pressure would be manifested by any resistance or any deformations, for example on a folded sheet of paper. It is possible...
  7. C

    Pressure in a gas container measured with a barometer and a U pipe

    Can someone please tell me where I am wrong, here goes the question: to a container filled with gas, U shaped pipe is attached, as shown in the picture(picture below). What is a gas pressure in the container if the height of the pillar of mercury in barometer is 740 mm? The way I solved it is...
  8. 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...
  9. C

    What does atmospheric pressure have to do with the gauge pressure?

    In this video( ) it's explained what is gauge pressure. Can someone please explain to me what does atmospheric pressure acting on a tube(in video at 3:51) has to do with displacement of a tube? I understand that the atmospheric pressure acts on the tube, but in the open space that does not...
  10. C

    Solving Fluid Statics Problem: Accounting for Atmospheric Pressure

    Hi! For this fluid statics problem, One of the answers is: However, why did they assume the pressure at the top was zero? I thought the pressure at the top would be 1 atm? So tried to take atmospheric pressure into account putting 1 atm at the top, Do you please know how to get P_0A/2 so...
  11. Galexy

    Atmospheric pressure inside a protoplanetary disc

    Summary:: Could there be a place in a newly forming protoplanetary disc where the gas pressure and temperature would be anywhere close to survivable? I am writing a fiction story that takes place there, and I want to know how far from reality this premise would be. When a protoplanetary disc...
  12. K

    B Cheapest equipment to boil water at 60℃

    Water (any liquid) in a closed container boils when the vapor pressure of water (a property that depends on its temperature) equals the surrounding pressure. The vapor pressure of water at 60℃ is about ##1.99\times10^{4}## which is roughly 150 mm Hg.This principle is so simple, and yet, it is...
  13. Krokodrile

    Hi determine the height of the mountain (using atmospheric pressure)

    i have the first convertions of the atmospheric pressure: 1872 lbf/ft^2 = 89,632.6 Pa 2016 lbm/ft^2 = 96,325.4 Pa g= 9.72 m/s^2 But, i don't have idea how pass the air density of "lbm" to international units ;,(. And other cuestion: its fine pass lbm/ft^2 and lbf/ft^2 to Pa simirlarly?
  14. 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...
  15. K

    Atmospheric pressure as a function of altitude

    Summary:: i) Set up a differential equation that describes how the pressure ##p## varies with the distance r from the center of the planet. Hint: You can base your reasoning on static equilibrium and Archimedes' principle. ii)Calculate how the atmospheric pressure p and the density of the...
  16. brotherbobby

    Pressure due to two liquids in a U-tube

    (a) Situation (2) is my answer (which cannot be in static equilibrium). The pressures in the lower dashed line (##P_2##) has to be the same on either side (for equilibrium). That means the pressure due to the red liquid is equal to the pressure due to the same length of air column (length)...
  17. T

    Impact of Atmospheric Pressure on the Water in a Tank and a Pipe

    Hello all I was hoping someone could help with understanding how fluids level out under atmospheric pressure. For example:- Below is a picture of a tank of water with a closed door at the bottom, the door leads to an inclined pipe that is closed off at the end there is another pipe connected...
  18. C

    Why is air in atmospheric pressure and room temperature a gas?

    This seems like a simple thermodynamics question but I would like clarification. So the absolute critical temperature is 132.5 K (-221.17 F) and the absolute critical pressure is 3.77Mpa (546.7 psi). I understand that for temperatures above the critical point, a pure substance undergoes an...
  19. dlgoff

    Atmospheric pressure -- Record low in Kansas?

    Here's a print screen from my weather station's computer early this morning. I've never seen this low of atmospheric pressure here in Kansas before. Shortly after midnight the pressure hit a low of 28.08 InHg. :oldsurprised:
  20. T

    Atmospheric pressure per square cm

    Hi, I have a problem to understand one small thing. They say that air pressure per square cm at sea level is approximately 1 kg. So at 2 sq cm it will be 2 kg, at 3 sq cm it will be 3 kg etc. But... Here where I have a problem. The thing is that inside 2 square cm you can put 4 one square cm...
  21. S

    Is atmospheric pressure gravitational or kinetic?

    I keep seeing a popular question asking about atmospheric pressure "crushing" us. The word "crush" throws me off. It is my understanding that air molecules create pressure due to collisions. In other words, the molecules exert pressure due to having kinetic energy - and the more molecules you...
  22. opus

    Atmospheric pressure- where do we get the mass?

    At sea level, we experience an external force pressing down on us at any given time which is equal to about 15 pounds per square inch. Pressure is defined as: ##P = \frac{Force}{Area}## where Force is equal to mass x acceleration. When we say that we experience this 15 pounds per square inch of...
  23. Muhammad Danish

    Pressure in Liquids: How Does It Affect Volume?

    Homework Statement Homework Equations How does atmospheric pressure affects the volume of liquid? What will be the volume of the air bubble at the bottom of the lake? The Attempt at a Solution At the surface, the volume is 6.0cm3. So at the bottom, more pressure will be exerted so it will be...
  24. PainterGuy

    Why does atmospheric pressure increase as you go closer to the Earth's surface?

    Hi, The air pressure at the surface is about 1,00,000 N/m2. It means that on average, a virtual column of air one square meter [m2] in cross-section, measured from sea level to the top of the Earth's atmosphere, has a mass of about 10,000 kilograms and weight of about 1,00,000 Newtons. That...
  25. E

    Collisional sheaths in atmospheric pressure plasma

    Hello, I'm studying dielectric barrier discharges (DBD) at atmospheric pressure. I'd like to have some references on highly collisional sheaths in radio-frequency discharges. I know the treatment becomes very complicated and one usually uses kinetic simulations, but nonetheless I'd like to see...
  26. K

    Atmospheric pressure vs elevation understanding problem

    My wife has a medical condition where her symptoms are reduced at a higher elevation. I have done some study about the relationship between elevation and atmospheric pressure. My understanding is that the higher the elevation, the lower the atmospheric pressure. Looking at a graph of elevation...
  27. Miguel Velasquez

    Forces due to atmospheric pressure won't cancel in an open tank

    Homework Statement [/B] I am trying to understand why books always point as a fact that hydrostatic force on the bottom of a open liquid filled tank doesn't depend on the force due atmospheric pressure because they these forces cancels each other. Homework Equations [/B] P=[P][/o]+ρgh F=P*A...
  28. S

    Conceptual Issue Dealing With Atmospheric Pressure

    Homework Statement A 1m^3 steel cube is to be floated on mercury (specific gravity=13.6). On each side of the cube there is a 5mm clearance. Assume that the container is open to atmospheric pressure at 100kPA. Find the mass of the mercury. Homework Equations P=F/A The Attempt at a Solution I...
  29. M

    Atmospheric Pressure: Solving with a Mercury Barometer

    Homework Statement A mercury barometer located in a room at 25°C has a height of 750 mm. What is the atmospheric pressure in kPa? Homework Equations Patm = ρ*g*H0 The Attempt at a Solution [/B] My question pertains to the units and how it ends up as kPa in the book. I have no problem with...
  30. D

    Atmospheric Pressure on Shaft of piston cylinder assembly

    Homework Statement In a vertical piston cylinder assembly, a vertical shaft whose cross sectional area is 0.8 cm^2 is attached to the top of the piston. Determine the magnitude F, of the force acting on the shaft, in N, required if the gas pressure inside the cylinder is 3 bar. The masses of...
  31. Ravi Singh choudhary

    Why atmospheric pressure does not crush us?

    1atm is typically something 101.13 kPa that means 100kN force is acting on 1 square meter surface area of our body. How we are capable for taking such high pressure? Sometime I think on 1 square cm area what immense force they are creating. I feel something is wrong with my concept of...
  32. T

    How to calculate atmospheric pressure?

    Let's say I had the composition of an atmosphere, the mass of the planet it was on, and the diameter/density of said planet. First, what else, if anything, would I need to find the atmospheric pressure? Second, what would the equation for doing so be?
  33. H

    How much atmospheric pressure is exerted on the human body?

    I understand that this will vary from human to human, but how much weight is exerted, in total, on the average adult human body. It would be very much appreciated if the calculations can be shown. Thanks!
  34. dmetrd

    Confused about why atmospheric pressure won't move piston

    I'm feeling pretty silly not being able to understand this. Let's say that you have a piston (red) sitting inside of a housing (black) like this Let's say that something like this was lying on its side on a flat table. By my understanding, if the contact between the piston and the housing...
  35. cyriac

    Atmospheric pressure and weight measurement

    Whats the significance of Atmospheric pressure being refereed as 100kPa ? Does that really mean 10000 kg/m2 acting upon us ? If we are measuring only collision force on the surface and not the weight of the entire column of air above us, then why figure 100kPa (100000 N force/m2) which is huge...
  36. H

    Atmospheric Pressure: Why is it Equal?

    Hello everyone! As we've known, the pressure at the bottom of a volume of gas is define by its weight times the height. So I wonder why the atmospheric pressure is equal in all direction? Many thanks
  37. P

    Gauge pressure and atmospheric pressure

    Homework Statement Objects A and B are submerged at depth of 1m in a liquid with specific gravity of 0.877. Given that density of object B is one third that of object A and that the gauge pressure of object A is 3atm, what is the gauge pressure of object B? (assume atmos pres is 1 atm and that...
  38. R

    Why does atmospheric pressure not affect SVP?

    I'm an anaesthetist... I have exams coming up... I use lots of gases and vapours and need to appreciate the associated physics. My question relates to saturated vapour pressure and ambient pressure... SVP increases with temperature - more molecules have sufficient energy to escape the...
  39. Thom_Silva

    Hydrostatic and atmospheric pressure

    So I've been wondering, 10.3 meter of water amount for one atmosphere, and according to Pascal's law pressure can compute by P=P0+ ρgh. If we have a glass with 10 cm of water inside , the pressure in the glass would be lower than atmospheric pressure and therefore when you turn the cup upside...
  40. M

    Thermodynamics: Air pressure at 3000m above sea level

    Hello all! Can you please provide some guidance with this problem? 1. Homework Statement Calculate the air pressure at 3000m above sea level assuming that the molecular weight of air is 29 and the ambient temperature is constant against height. Homework Equations Stokes-Einstein equation. In...
  41. C

    Consequences of denser atmosphere on Earth-like planet

    I made a brain storming, but hope that someone would be able to point out what I may have missed out. Assumptions - atmospheric pressure is 3 atm, but molar concentration of oxygen is comparable to earth. The rest is mostly nitrogen. (there are a few more assumptions like tidal lock, a bit lower...
  42. 2

    Finding the pressure at a given height?

    I am having trouble trying to derive the air pressure at a given height. So far, I have considered a 1m^2 patch of area, and the pressure is the weight of all of the air above this patch. So P= \int_R^{\infty}g(x)\rho(x)dx So P= GM\int_R^{\infty}\frac{1}{x^2}\rho(x)dx But then I don't know...
  43. H

    Ammonia Gas: Vapor Pressure > Atmospheric Pressure

    This is for "ammonia". The problem says that ammonia is a gas at room temperature. And that this tells us: "the fact that ammonia is a gas at room temperature tell us that vapor pressure of ammonia must be greater than atmospheric pressure". I know that for water, when the boiling point is...
  44. B

    Thermodynamics atmospheric pressure Question

    Homework Statement A liter of air, initially at room temperature and atmospheric pressure, is heated at constant pressure until it doubles in volume. Calculate the increase in its entropy during this process. so Ti= 300K, Volume which is 2Vi=Vf; Pressure is constant Homework Equations ΔS...
  45. C

    Calculating Gravity of a New Planet with a Gas Atmosphere - Homework Solution"

    Homework Statement A space-probe discovers a planet with a gas atmosphere, detects a non-zero value for speed of sound 60km relative to the surface of the planet. It measures a surface temperature of -5 degrees C and an average atmospheric molecular mass of 38 x 10 ^ -27kg. Find G_p the...
  46. F

    Drift tube ion mobility spectrometer

    Hello PF, thanks for having me here. I am working in chemistry and we are building a atmospheric pressure drift tube ion mobility spectrometer. The drift tube consists of 20 stacked stainless steel electrodes insulated by PTFE spacers connected via a resistor chain (voltage divider) to produce...
  47. H

    Vapor Pressure vs Atmospheric Pressure

    Homework Statement If the boiling point is the point at which vapor pressure > atmospheric pressure, so all of the water molecules can break free and fly into the atmosphere (i.e. overcoming the atmospheric pressure), then why is it that when atmospheric pressure > vapor pressure, the...
  48. Y

    How does atmospheric pressure work?

    From what I know, the pressure of a gas is due to the collisions of its molecules against a surface. So I don't understand why atmospheric pressure is measured by taking the weight of all the air molecules above a surface including the ones that aren't contacting it. Gases have plenty of space...