What is Pressure: Definition and 1000 Discussions

Pressure (symbol: p or P) is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled gage pressure) is the pressure relative to the ambient pressure.
Various units are used to express pressure. Some of these derive from a unit of force divided by a unit of area; the SI unit of pressure, the pascal (Pa), for example, is one newton per square metre (N/m2); similarly, the pound-force per square inch (psi) is the traditional unit of pressure in the imperial and U.S. customary systems. Pressure may also be expressed in terms of standard atmospheric pressure; the atmosphere (atm) is equal to this pressure, and the torr is defined as 1⁄760 of this. Manometric units such as the centimetre of water, millimetre of mercury, and inch of mercury are used to express pressures in terms of the height of column of a particular fluid in a manometer.

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  1. H

    Pressure variation during resonance?

    Consider a hypothetical pipe of length L and diameter d with both end closed. The pipe is filled with a some fluid. Let there be a ultrasound source of frequency f=v/2L at one end of the pipe and a sensor to measure pressure at the other end of the pipe, where v is the speed of ultrasound wave...
  2. J

    Can a piezoelectric create dynamic pressure in oil fluid for energy harvesting?

    Would it be possible to do a experimental setup where I create a dynamic pressure (10-500 Hz) of around 0.1-2 MPa, using a high force piezoelectric pushing on a piston on a Small volume of oil fluid. There is this paper, where the authors create a pressure wave of around 170 KPa using a...
  3. D

    What is the pressure in a closed container dependent on?

    Hello! I have a problem : I have an elastic container (I call it "balloon"). I fill it 100% with water (no air bubbles) and close it. There is a pressure sensor connected to the balloon to measure the pressure inside it. I would like to ask You : what factors have influence on the pressure...
  4. M

    Pressure drop across a valve in tank

    Hey I've gotten some good answers here before, so I'm giving it another try: Recently I attended a building-engineering meeting, and trying to learn something new (or refresh old knowledge in some cases..) I had a hydrodynamic question/case. My firm is engineering a concrete tank for a water...
  5. S

    A Interior Schwarzschild Metric: Pressure Dependence

    I'm looking influence of pressure on the general interior Schwarzschild metric (see for example the book by Weinberg, eq. 11.1.11 and 11.1.16. The radial component of the metric (usually called A(r)) depends only on the mass included up to radius r A(r) = \left(1-\frac{ 2G M(r)}{r}\right)^{-1}...
  6. P

    Pressure Decay from a Fixed Volume

    If an ideal gas is leaking from a fixed volume, does the temperature of the air in the fixed volume go down, or does it remain constant? We do pressure decay measurements under choked leakage flow conditions, but I wonder if our assumption of constant temperature for the gas remaining in the...
  7. V

    Magnetic Pressure: Formula Origin & Derivation

    I have seen a formula for magnetic pressure ##P_M=\frac{B^2}{2\mu_0}## Where does it come from? How my I derive it?
  8. B

    How Water Dept's of major metros maintain water pressure?

    Small towns in America frequently have water towers in which water is kept in huge tanks hundreds of feet high within water towers. I suppose that some sort of pump pumps the water entering the water tower to the tank at the top. I suppose that water pressure is maintain in these small towns...
  9. L

    Plot the contact pressure vs axe x (mm) in ansys workbench

    thanks for you sir i want to se how can i plot the contact pressure vs axe x (mm) in ansys workbench.? its very important for me
  10. Ethan Singer

    I What causes pressure in White Dwarfs and Neutron Stars?

    Before today, I'd been led to believe that collections of only one (or few) types of matter could never exist: And to my surprise it is indeed possible to have degenerate matter, resulting from the death of less massive stars! So I'm curious: If these lesser massive stars collapse due to their...
  11. B

    What is the pressure at point B in a moving liquid with density ρ?

    Homework Statement Considering the figure. The liquid has a density $$\rho$$. What is the pressure at B? http://imgur.com/HHMiWcU (I put the link because the image uploaded doesn't work) The Attempt at a Solution In a solution that I have found on internet, it is said that the pressure in B is...
  12. Vivek98phyboy

    Gas Through Porous Plug: Pressure & Temp Change Explained

    I can't understand why a gas passing through a porous plug experiences change in its pressure and why does the cooling or heating process depends upon the initial temperature
  13. Alexander350

    Understanding Liquid Pressure in a Cone: How Does It Compare to a Cylinder?

    I am confused about the pressure depending only on the depth of the liquid, particularly for a cone. Up until P=mg/A=ρVg/A I understand it, but the problem I have is cancelling the area with the volume to give the height. How does this work when the volume of the liquid in the cone is not given...
  14. T

    Compressing a gas above compressor's discharge pressure

    A 2 stage compressor has a final delivery/discharge pressure of 250 bar. hydrogen is been compressed and stored in vessels. The pressure in the storage vessel reaches the delivery pressure(i.e.250 bar) and the compressor is still running ( vessel has a safety pressure of 450 bar) and the...
  15. T

    Calculating pressure release time

    Hey people, I have a pressure vessel pressurized to say 20MPa at 33C, of which I'm working with a gas (scCO2 to be exact) which will then be released into the atmosphere (standard pressure and temperature) through a release valve; I'm wondering how long it will take for the pressure to reach...
  16. Const@ntine

    Airgun shoots ball: Pressure = ?

    Homework Statement An airgun shoots a ball made from lead, through air of high pressure that pushes the ballforward like a piston. Because this happens very quickly, Q = 0 and the process is adiabatic. The initial volume of the air is Vi = 12.0 cm3 = 12.0 * 10-6 m3, which behaves as an ideal...
  17. R

    Calculating Water Volume in a Tank Using Pressure Measurements

    Homework Statement on a flat desk is an aquarium with a volume of 640 cm3 ,t's not full of water. The pressure to the bottom of the aquarium is 3 times bigger than to one side of it, how much water is in the tank? Homework Equations is the pressure, is the normal force, is the area of...
  18. Anachronist

    Final pressure and temperature knowing only air mass outflow

    This seems simple, but I have some confusion. I'm trying to refine a numerical simulation to get away from my isothermal assumption, to account instead for isentropic temperature and pressure changes in pressure tank with an orifice. Given an insulating air tank of volume ##V##, containing air...
  19. R

    Can someone explain the vacuum pressure created by water pressure on waders?

    Hi guys! I have question regarding vacuum and underwater pressure if anyone here could help me out with it. I'm not really a physics person (my math skills suck too much, lol), but I do find it very interesting. I recently bought some breathable stockingfoot fly fishing waders and whenever I...
  20. E

    Calculate Pressure Drop through Expansion/Reduction for Gas

    Something that routinely comes up as a problem at work is when we size flow projects for piping systems. We calculate pressure drop across a length of fixed diameter for compressible gasses, but we do not calculate pressure changes through an expansion or contraction with gas (for example...
  21. S

    B Angular momentum, degeneracy pressure, and cosmic inflation

    Considering the angular momentum of a collapsing star preventing it from resulting in a black hole by degeneracy pressure, are there ekpyrotic universe models that include angular momentum and degeneracy pressure as key factors of cosmic inflation?
  22. R

    I Energy density and pressure of perfect fluid

    is there any way to derive p=rho/3 from 4 vector or stress-energy tensor?
  23. Const@ntine

    Compute the Work: Pressure analogous to Volume

    Homework Statement One mole of an ideal gas is warmed slowly, so that the pressure and volume go from (Pi, Vi) to (3Pi, 3Vi), in such a way that the pressure is analogous to the volume. a) What's the Work (W)? b) What is the correlation between the temperature and the volume during that...
  24. PainterGuy

    Pressure exerted by an ideal gas

    Hi Please have a look on the attachment. Suppose that a 0.1 kg rubber ball having velocity of 60 m/s is moving between two walls A and B, and the distance between the walls is 1 m. It is having elastic collisions with the walls. Let's focus on what is happening at wall B. The ball is moving...
  25. Const@ntine

    Finding the Remaining Pressure of a Gas After Removing 2/3rds

    Homework Statement In a container we have a gas, at P = 11.0 atm & T = 20.0 C. We remove 2/3rds of the gas and increase the temperature to T = 75.0 C.What's the pressure of the gas that remains? Homework Equations PV = nRT The Attempt at a Solution Normally this would be a regular "put...
  26. 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...
  27. G

    Can we accurately measure water pressure using DIY water towers?

    I'd like to explore water pressure by having students build water towers out of both 2-liter bottles and thinner 1 liter bottles. 1. Assuming they build towers of the same height and fill them with the same type of water, we should see the same water pressure for identical heights within the...
  28. H

    Pressure Chamber with Flat Door

    I am currently new in this forum and just a senior high graduate, so pardon me if I have some errors in writing this questions. I have a cylindrical pressure chamber with approximately 80 cm in diameter and the length of 1.5 m and metal wall 1 cm in thickness. I know most pressure chamber have...
  29. E

    Water Container Force: Impact of Finger Dip on Scale Measurement

    A container of water is sitting on a scale. I dip my finger into the water without touching the sides or bottom of the container. Is it true that the force exerted on the scale by the container will decrease because the finger creates a downward force?
  30. A

    Stagnation pressure across a normal shock wave

    A body is reentering the Earth's atmosphere at a Mach number of 20. In front of the body is a shock wave. Opposite the nose of the body, the shock can be seen to be normal to the flow direction. Determine the stagnation pressure and temperature to which the nose is subjected. Assume that the air...
  31. U

    Pressure dependence of the equilibrium constant for an ideal gas

    I read in some scripts that equilibrium constant for an ideal gas is not a function of pressure: But that is not generally true! Since: $$\left (\frac{\partial \Delta_{R} G}{\partial p} \right )_{T,\vec{n}}=\Delta_{R} V$$ and $$\Delta_{R} G^{0}=-RT\cdot \ln K$$ it should be: $$\left...
  32. P

    One question about dynamic pressure

    As per wikipedia, dynamic pressure is nothing but the expression of kinetic energy of unit volume of a fluid in motion. That's applicable to gases too. Question is, when a fluid is passed through a convergent and/or convergent-divergent nozzle, then its speed towards a specific direction...
  33. G

    Water pressure vs pressure drop

    Hi guys, I know the difference between these two things but I'm struggling with something that I hope someone could help me with. What dictates the water pressure needed for a "system" to work? I would imagine that if you've calculated your system to have a pressure drop of 1 bar (for...
  34. wolf1728

    Standard Temp and Pressure -- old values (pre-1982) still prevalent

    Okay, my topic doesn't really ask a question but it is surprising to me that the old criteria of 273.15K and 760 torr are still being reported as the standard and very few websites have the "new" criteria of 750.06 torr. Are scientists, webmasters, etc. usually this slow at adopting changes...
  35. S

    Lift equation and pressure coming out of a tube?

    I am making a small project at home for my solar panels. I have made a similar project when I was in school but I can't remember the equations. I want to attach an air compressor to a tube then install it on top of a solar panel, and pinch a few holes in it to clean the dust that accumulates...
  36. 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?
  37. W

    Stress and Strain Pressure Vessels

    Homework Statement E = 290 GNm-2 Yield Stress = 500 MPa Q. What pressure would a strain of 40 με indicate? Homework Equations Hoop Strain. εθ = 1/E (σθ − νσz) = 1/E (pr/t − ν(pr/2t). The Attempt at a Solution I am looking for some direction on how to determine the poisson ratio...
  38. I

    A Change of ε with pressure for Semiconductors

    In "Sado Adachi" book "Properties of Group-IV, III–V and II–VI Semiconductors" page 222, he reported that "both εs and ε∞ decrease almost linearly with increasing pressure", however i was not able to find any empirical formula to describe these relationship for materials InAs, InP, InSb, where...
  39. K

    What is the Relationship Between Gas Pressure and Fluid Column Height?

    Homework Statement I need to find the amount of H2 being lost to water by being stored underneath a column of water. About 16 mL of H2 is made and it displaces the column by 16 cm. However the total amount of water is 30 ml/30 cm. I'm not sure which relationship to use to find the pressure of...
  40. N

    Internal pressure due to vessel collapse

    Hey All, I have a plastic vessel fully filled filled with an incompressible fluid (Water), at some time this vessel is impacted and crushed on one side (say 5% of the initial volume is lost). Only, I know the volume isn't lost, the fluid (being incompressible) will exert pressure on all...
  41. chopnhack

    Gas at a constant pressure: using Cv.dT correctly

    Hello, my questions is not so much homework, but a request for a definition. When we use Cv*dT to solve for dU (internal energy) in a constant pressure example, what is the order of the temperatures entered into dT? Is one to assume its final temp minus initial temp? I ask because it leads to...
  42. Baritone

    What is the Power of Sound Waves in a Tube Filled with Helium Gas?

    Homework Statement Suppose a tube is filled with helium gas at a pressure of 0.11MPa and a temperature of 297K. If a piston of area of 400mm2 at one end of the tube creates sound by moving sinusoidally with a frequency of 60Hz, creating a wave with amplitude of 3.8mm, what power goes into (I'm...
  43. T

    Magnetic pressure on a conductor

    Homework Statement Homework EquationsThe Attempt at a Solution i have done the first two parts but the third part confuses me i am assuming the current is flowing in the z direction then current is parallel to the magnetic field then why would there be a force acting on it ?[/B]
  44. 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.
  45. TheRumpus

    Does air flowing through a tube cause a pressure change?

    I have been involved in a fairly furious debate about a fluid dynamics experiment regarding the pressure of air passing through a tube attached to a moving car. It is similar in concept to the issue of whether or not an opening in an aeroplane fuselage would suck people out, where the opening...
  46. SlowThinker

    B Pressure of Bose-Einstein condensate

    I was wondering, if cooled sodium or rubidium atoms behave as bosons, can they also occupy the same space? I tried to google a bit, but as usual, articles throw letters like ##\beta##, ##s##, ##\lambda##, ##g## around without bothering to at least give them a name so I could search deeper. I...
  47. single0speed

    Need help on this question for a project i'm making

    I worked out about 7-10psi in the pipe. What do you guys think?
  48. J

    Pressure Drop value location

    Hello, I am calculating pressure drop through a pipe using CFD, which will be validated with hand calculations and experiments for a project. When I take results from my software, I can either take the pressure at a specific point (assume the centreline of the pipe) or I can take an average...
  49. Pat Bannan

    Gas under pressure- disturbing noise recurring

    recently my neighbors and I have been awakened by a loud noise that sounds like something is being released under high pressure. An intense vibrating sound that lasts 30-45 seconds. We live across the steet from a soda manufacturer and down the road from a natural Gas transfer station. Both are...
  50. Adam Rabe

    How Can I Solve This Fluid Dynamics Homework Problem?

    Homework Statement Homework Equations AV = AV P + 1/2*p*v^2 + pgh = P + 1/2*p*v^2 + pgh The Attempt at a Solution For a.) ... divide 3 by 0.1 because of (AV = AV) = 30 ms-1. answer is right. For b.) I am stuck on this one. I tried using the 2nd relevant equation above but i can't seem to...
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