Pressure Definition and 999 Threads

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.

View More On Wikipedia.org
Recent contents Top users
  1. B

    Pressure gradient along a streamline using CV analysis

    Homework Statement Use a CV analysis to show that an element of fluid along a streamline gives \[\partial p/\partial x=-\rho u\partial u/\partial x\] Homework Equations \[\sum F=\oint_{CS}^{ } \rho \overrightarrow{V}(\overrightarrow{V_{rel}}\cdot \overrightarrow{n})\] The Attempt at a...
  2. R

    Follow-up Question to: The Concept of Pressure in Bernoulli’

    I have been looking all over the net for answers for the unintuitive relationship between pressure and velocity in Bernoulli's equation and this thread (https://www.physicsforums.com/threads/the-concept-of-pressure-in-bernoullis-principle.585231/) answered most of my questions. I have one last...
  3. V

    How to make a customized pressure cooker?

    I just want to make a pressure cooker for rice cooking with variable liters on demand changing. Can you give me some ideas how to make it ?
  4. B

    Pressure increase required for 1 Joule of work

    Homework Statement Estimate the pressure increase required to impart one joule of mechanical work in reversibly compressing 1 mol of silver at room temperature. Same process for alumina. Homework Equations W=-PdV dV=V(alpha)dT-V(beta)dP dT=0 The Attempt at a Solution I used the work...
  5. A

    Reverse-acting proportional pressure controller

    Homework Statement [/B] A 5 to 20 bar reverse acting proportional pressure controller has an output of 4 to 20 mA. The set point is 11 bar. Determine: (a) the measured value pressure which gives an output of 15 mA when the proportional band setting of the controller is 40% (b) the proportional...
  6. A

    Why does lifting an IV bag increase pressure?

    I understand that you need to increase the pressure in an IV bag to overcome the pressure in a vein so fluid pumps into it. But why does lifting the bag at some height increase the pressure?
  7. J

    How much time would the Pressure of both tanks be Equal?

    Hello, I need help for my thesis project. Lets say We have two tanks. Tank 1 is filled with methane and Tank 2 is empty Tank 1: V = 30L T = 40C P = 40psi Tank 2: V = 20L T = 25C P = 14.7psi Two tanks are connected by a pipe with 2inch diameter (a valve in the middle is closed at first). Then...
  8. M

    Osmotic Pressure vs Vapor Pressure

    If I were asked to calculate the vapor pressure, and I calculated the osmotic pressure and converted it to mmHg, Would I get the right answer?
  9. K

    How does the capillary tube in refrigerators work?

    How does the capillary tube decrease the pressure on the liquid when its diameter is smaller? How small diameter of capillary tube is helpful in causing more pressure drop? And how, when pressure drops, the liquid instantly cools down?
  10. I

    Hydrostatic pressure (infinitesimally small column of water)

    This is a hypothetical question: since hydrostatic pressure is calculated as depth of water times its density, would a column of water less than a square foot in cross section still have a pressure at the bottom of depth*density of water? For example, if I had a 1" thick by 1ft wide by 5' tall...
  11. H

    Fluid Statics- u-tube displacement

    Homework Statement A uniform U-tube is partially filled with water (ρH20 = 1000 kg/m3). Oil, of density 750 kg/m3, is poured into the right arm until the water level in the left arm rises 30 mm. The length of the oil column is then: (Answer: 40mm) Homework Equations P = pgh Pressure = density...
  12. J

    Best Pressure Sensor for 125°C, 3 bar Environment: Options and Considerations

    I'm trying to find a small pressure sensor for an environment that will be between 1 and 3 bar absolute, 10 to 125°C, and 100% humidity. By small I mean a port that's no larger than about 1/4" (sorry for mixing unit systems). Ideally I'd like to have a digital interface but it's not critical...
  13. N

    How do you control an Electronic Butterfly Valve with PID

    The butterfly valve I have is controlled by sending voltages to it. It accepts 0-10V and maps a specific voltage to a specific position from completely closed (zero degrees) to completely closed (90 degrees). To clarify/reiterate it is not controlled by a servo motor. I am using this valve to...
  14. S

    Liquid temperature under pressure

    Hello, I have a question regarding bath pasteurising cider in bottles. The bottles are carbonated with CO2 and capped, I heat the water up to a temperature of 70deg.C I use a test bottle filled with water and with a cork in the top, I use this to monitor the temperature inside the bottle. So my...
  15. B

    Understanding Fluid Statics: Solving Gage Pressure Problems

    Homework Statement All over the place here so bare with me, I'll get the hang of it eventually. -----For these types of problems.. can you start at either the top of the tank or from point a? -----Given specific Gravity, you need gamma of the unknown fluid so you multiply it by the density...
  16. yecko

    Isentropic process (temperature and pressure relationship)

    Homework Statement for isentropic process, which of the following is true about the relationship of temperature and pressure? (1): P2/P1=(T2/T1)^[γ/(γ-1)] (2): P2/P1=(T2/T1)^[(γ-1)/γ] where γ = 1.4 for air Homework Equations stated above The Attempt at a Solution I have found equation (1)...
  17. yecko

    Specific heat at constant pressure formula help

    Homework Statement https://i.imgur.com/f2vSXtq.png Homework Equations https://i.imgur.com/Kjy1Tzh.png The Attempt at a Solution In this question, the pressure is different at different point, in other words it is not constant throughout the system. Why the solution use c(p) (or "enthalpy" h...
  18. R

    Size expansion vessel to reduce pressure loss

    Hi all, Given: I have a pressure vessel of 1000M^3 filled with water with 8 bar pressure. On this pressure vessel I have installed a valve and a expansion vessel on top of the pressure vessel. The expansion vessel is prepressurized to 8 bar as well. Question: when I open the valve i lose 20...
  19. A

    Pressure drop over double parallel system

    I have a system where pipes run 24l L/min of water @60 degrees through 3 manifolds and those manifolds distribute the water over 8 heat exchangers. Every heat exchanger requires 1 L/min, and has a resistance of about 1.333 KPa per heat exchanger at that flow (2 meter @ 9mm diameter + 2...
  20. T

    Relationship between the pressure gradient and mass flow of a gas

    Hi everyone, I would like to know how to calculate the diameter of a pipe when we know the desired mass flow, the gas type, and the pressure at both end. I have these requirements : Gas : O2 Molecular weight : 0.032 [kg / mol] Desired mass flow : 0.32 [kg / s] Pressure in the gas tank : p1 =...
  21. T

    Pore pressure at different point ( seepage in soil)

    Homework Statement I am not sure how to get Nd in this question ( circled part) I am not sure the exact location of the point where the author want to find the pore pressure . Can someone help ? This notes is confusing Homework EquationsThe Attempt at a Solution I think the Nd can be only...
  22. J

    Simple Gas Pressure Question - Combined Chambers Final Pressure

    Before anything, my apologies for offering such an elementary question about gas pressure. Any help would be appreciated. 1. Homework Statement There are two chambers. One is 100 L, containing air at a pressure of 200 kPa. The other, joined to it, is 10 L and contains air at a pressure of 20...
  23. T

    Pore pressure due to capillary rise

    Homework Statement Why there's no pore pressure due to capillary rise at point A and point D ? There's only pore pressure due to capillary rise at B .. Homework EquationsThe Attempt at a Solution i think the author is wrong . There's should be also ore pressure due to capillary rise at A and D...
  24. B

    Hydrualic pressure moving plug in pipe

    Homework Statement A plug with a given mass is placed in the end of a horizontal pipe to hold water at a given pressure behind it. Is there any way to calculate how far this plug would move in the x-axis if it suddenly lost it's grip against the pipe wall, and it was situated a given height...
  25. W

    How Does Specific Gravity Impact NPSH in Centrifugal Pumps?

    Head psa(suction surface pressure) = 2.31xP/specific gravity This is one of the factors to calc NPSH. Shows how much head is pushing liquid through the pump. What does the specific gravity have to do with surface pressure of a liquid before it goes into the pump? Isn't it just involving the...
  26. N

    Pressure at the center of an accelerating sphere

    Homework Statement Consider a glass sphere completely filled with water except for a small air bubble at 1 atmosphere. The sphere is accelerating to the right. What is the pressure at the center of the sphere? Let Pe = Atmospheric pressure r = radius of sphere pw = density of water a =...
  27. N

    Installing Chemical Storage Tank: Pressure of Liquid or Gas?

    Hello Forum, I'm looking to install a new chemical storage tank at my site. The tank itself is not rated for vacuum. We will have proper ventilation and nitrogen pumping into the tank to compensate when we are pumping out of the bottom. However, I do want to include a pressure transmitter on...
  28. D

    Pressure Halfway through a planet

    Homework Statement "In a galaxy far far away, a planet composed of an incompressible liquid of uniform mass density ρ has mass mplanet and radius R. Determine the pressure midway between the surface and the center of the planet." I used M=mass of planet, m=mass of shell, R=radius of planet...
  29. T

    Manometer finding absolute pressure at P1

    Homework Statement https://imgur.com/a/nxWvK this is the problem Homework Equations P=Patm + dgh The Attempt at a Solution I really just need to check if i did this right. I converted the densities to kg/m^3 and did p1= ((1121.689)(9.8)(.15) + ((1019.717)(9.8)(.04)) which gives 2048.61 Pa +...
  30. C

    I Does moisture escaping from powders decrease chamber vacuum?

    I'm drying some wet powders using vacuum oven and start seeing some condensation on the window after few minutes. The vacuum level stays pretty constant which puzzles me as i thought that the moisture escapes from the powder into the air will increase the chamber pressure or decrease the vacuum...
  31. 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...
  32. 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...
  33. 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...
  34. 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...
  35. 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}...
  36. 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...
  37. 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?
  38. 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...
  39. 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
  40. 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...
  41. 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...
  42. 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
  43. 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...
  44. 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...
  45. 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...
  46. 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...
  47. 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...
  48. 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...
  49. 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...
  50. 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...
Back
Top