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.

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  1. nduka-san

    Can I Generate Energy from Lakes to Clean and Revitalize My Backyard?

    could i convert the pressure underneath a lake around 30 feet deep and another lake that's 10 feet deep to run a boiler and then used to clean the old moldy unclean lake In my backyard and fill it with new fishes suited for the environment .cause there
  2. cwill53

    CO2 Sequestration and Cave Pressure Problem

    I've made it through the first 2 parts, it's just that part C has me stumped. I don't know how to manipulate the information I already know to figure out the total work energy required by the compressor, ##W_{compressor}##, during the process.
  3. G

    B Degeneracy Pressure: Pauli Principle & Neutron Stars

    Is degeneracy pressure created due to Pauli exclusion principle able to create some waves? Also at neutron star stage similarly are there waves created may be of higher energy? Can we talk of some harmonic motions in these stages?
  4. eleanorwest83

    Pressure relief valves & pressure regulators - What's the difference?

    What is the difference between a pressure reducing valve and a pressure relief valve? pressure-reducing/regulating/ relief/release - There are so many different options available! I read this article on Fluid Controls that did a really good job of explaining pressure regulators, but I am a bit...
  5. WMDhamnekar

    MHB Computation of the ratio of barometric pressure

    Hi, The Homestake gold mine near Lead,South Dakota is excavated to 8000 feet below the surface. Lead is nearly a mile high; the bottom of the Homestake is about 900 m below sea level. Nearby custer peak is about 2100 m above sea level. What is the ratio of barometric pressure on the top of the...
  6. WhiteWolf98

    Surface Pressure Coefficient Distribution of a Doublet in a Uniform Flow

    So, it's a long way to the solution, but I'm finding it difficult to find a starting point. I'm going to say that as a first step, I should find what the value of the stream function ##\psi## is, at the surface. In order to do this, I need to use the following equation: ##F=\phi+i\psi## If I...
  7. F

    Does Fluid Dynamics Explain Pressure Gradients in a Frictionless Tube?

    Let's start with a horizontal tube with a constant diameter. I'm not sure if it's important, but let's assume it's frictionless. I will have some fluid flowing in this tube and if it's important, we can make the fluid incompressible, inviscid, irrotational, etc. To create a flow in the tube...
  8. P

    Problem related to the Ideal Gas equation -- Nitrogen under pressure

    Solution from the textbook: My work: I constantly get 1.55kg. I also tried dividing the first and the second equation (pxV=m/M x R x T with different values). How did they come up with the equation in the solution? Also, I am sorry if I posted it in the wrong place and didn't follow the rules...
  9. T

    Conversion of high velocity airflow into a pressure

    We know blower compressors i.e. compressors that use a blower to create high velocity for injecting air/fluid to higher pressure and that's available in market. Now, suppose we have such a blower type compressor that can create a flow of air/gaseous fluid of 337 m/s. Question is, what maximum...
  10. anonymous99

    Is the pressure equal everywhere here?

  11. jaumzaum

    Pressure experiment with a burning straw protruding from a hole in a bottle

    Consider the following experiment: we have an open bottle, with a hole where we put a straw. We burn the outer side of the straw. We see smoke ascending outside and descending inside. Why is that? I would say the smoke has lower density than air outside, that's why it goes up. Inside the bottle...
  12. T

    Why does the pressure of a gas bubble change as it rises?

    The correct answer is 'C'. I'm having trouble understanding the solution shown on this link (http://www.engineeringadmissionsassessment.com/2019-solutions.html) - scroll down to Section 2, Question 8. From what I've gathered, [final pressure = initial pressure x 'R^3/r^3'], as PV must be...
  13. FEAnalyst

    Capped pressure vessel - strength and stability

    Hi, in mechanics of materials books one may easily find fomulas for stress and strain in thin- and thick-walled cylindrical pressure vessels subjected to internal pressure. However, it is assumed that they are open. So what are the formulas for stress and strain in capped vessels (with flat or...
  14. S

    Pressure at the bottom of a cube immersed in two liquids

    I am not sure about value of depth I need to use. What I did: Hydrostatic pressure at bottom of cube = hydrostatic pressure by oil + hydrostatic pressure by water = ρoil . g . d + ρwater . g . h Is it correct I use value d = 0.2 m for depth of oil and value of h = 0.02 m for depth of water to...
  15. anuttarasammyak

    Is Bernoulli's Theorem an Expression of Energy Density in Fluids?

    As summarized.
  16. Kaguro

    Pressure at the walls of a container

    I wrote energy of each molecule is ##\frac{1}{2}mv_{rms}^2 \Rightarrow E/3 = \frac{1}{2}mv_i^2##. So total energy of each type of gas is ##E_i = N_i\frac{3}{2}mv_i^2## Now, PV=E. So total Pressure = Sum of energies/volume ##P=\frac{\frac{3m}{2}\sum_i N_i v_i^2}{V} =\frac{3m}{2} \sum_i n_i...
  17. P

    Calculating Hydraulic Press Pressure on a Skateboard :)

    Hi all, I wonder if someone can help me with a calculation/estimation? I have recently built a skateboard press to...press skateboards! My question is, how do I calculate how much pressure is being applied to the skateboard? Most presses are steel, however, not having any metal working skills...
  18. anonymous99

    Why does pressure need to be constant in all directions to maintain equilibrium?

    I don't understand how pressure must be constant in all directions to balance out the force? Arent the forces in each direction independent, so that pressure forces in the x direction and y direction and z direction can all be different to each other, as long as they are balanced in that...
  19. Mayan Fung

    Microcanonical ensemble generalized pressure

    In the discussion of the pressure in macrocanonical ensemble, I found in textbook that: ##dW = \bar p dV## (##dW## is in fact d_bar W, yet I can't type the bar) The derivation goes like: ##\bar p = \frac{1}{Z} \sum_{r} e^{-\beta E_r} (-\frac{\partial E_r}{\partial V}) = ... = \frac{1}{\beta}...
  20. WMDhamnekar

    MHB What is the final pressure of helium and neon gas mixture in this case?

    The answer given to the above question is Final pressure$=\frac{(10.0mol\times 5.00bar) + (5.00 mol \times 20.0 bar)}{(10.0 mol +5.00 mol)}= 10.0 bar$ Is this answer correct? if yes, How and why? My question is while computing this answer, the volumes of each gas is not considered. Note:-...
  21. anonymous99

    What causes pressure in a fluid from beneath?

    S
  22. B

    Calculating this gauge pressure reading

    Hi everyone! How do I go about solving this problem? I tried working out the gauge pressure using this but I have a few unknowns which won't make this possible such as what is the length of x which I labelled in the figure Any help would be appreciated! Thanks
  23. person123

    Bernoulli Principle For Pitot Tubes

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  24. Glenn Rowe

    Electromagnetic stress tensor from pressure and tension

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  25. F

    Exactly how do pressure waves work at the molecular level?

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  26. F

    Flow of air through an open tube with a balloon

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  27. person123

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  28. person123

    Inertial Force in Fluid Mechanics

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  29. S

    ASME compliance in Pressure Vessel design

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  30. S

    Pressure Switch to Diaphragm Flow Switch

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  31. WMDhamnekar

    MHB Exploring Robert Boyle's Law: Pressure and Volume of CO2

    Robert Boyle's law states that at constant temperature, the pressure of fixed amount ( i-e number of moles n) of gas varies inversely with its volume. Mathematically, it can be written as $p ∝ \frac1V $(at constant T and n) $\Rightarrow p = k_1 \times \frac1V $ where $k_1$is a proportionality...
  32. 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...
  33. Z

    Question regarding the Pressure of a gas flowing from a cylinder into balloons

    P1V1=P2V2 (2.5x10^7x4x10^4)/1.85x10^5 , V2 = 5.41x10^6 cm^3 5.41x10^6=4x10^4+7.24x10^3 N N= 741
  34. K

    Velocity, barrel length and bore volume

    Hello. How does a bullet propell inside a bore? What determine its velocity? I read that a bullet in cal .44 propelled by black powder from a 3” barrel is as powerful as a .25 ACP, however with a longer barrel, the velocity increase significant. With a 8” barrel a .44 black powder bullet is as...
  35. A

    Physical state given the critical temperature and critical pressure

    Summary:: I have two substances H2O and CH3OH given at a temperature T and pressure P. I also have critical temperatures and pressures. How can I find the physical states of these substances. My teacher recommended me to use the Antoine equation and find the saturation pressure, but I can't...
  36. cwill53

    Duct Pressure Question: Troubleshooting Complicated Units and Conversions

    These units complicate everything and I simply cannot get them to check out for the life of me. After making some conversions I got to this point:
  37. mktsgm

    Medical How are normal values of blood pressure and glucose determined?

    Blood glucose is measured and compared against a set of standard/normal values (like, fasting 100 mg/dL etc) to determine if a person has hyperglycemia or not. Similarly Blood pressure readings (systolic & diastolic) are also compared against another set of standard/normal values like 120/80...
  38. A

    Lateral pressure of a liquid exerted on a plunger

  39. E

    Pressure force on curved surfaces: vertical component

    hi guys, i can't understand why they calculate F yin this way, the part of floor that is the vertical proyection has less water than the floor in the left so i tought Fy would be less, please can someone explain this concept to me?
  40. P

    What is the relationship between pressure and force inside a spherical object?

    So I already have a solution available to this problem and the link for the solution is: I have understood everything in the video except the part where they are equating the force dF=GM/r²*dm According to my reasoning the inner part of the sphere (the part below the dm element we have taken)...
  41. LCSphysicist

    Thermodynamics: internal energy and pressure

    The question is simply why i can't use ∂U/∂V = -P? (
  42. N

    How to Calculate Final Pressure in a CO2-Saturated Sealed Vessel?

    I have a sealed vessel, it is 200 ml, it contains 25 ml of water which is then saturated with CO2 (bubbled through at 0.3 l/min unitil pH drops, ~ 1 h) at rt. The vessel is then heated to 130 °C. I wish to calculate the final pressure of the system. Thus far I have calculated the volume of CO2...
  43. R

    B Does the Torricelli Vacuum Experiment Prove the Strength of Vacuum Forces?

    If Evangelista Torricelli truly created a vacuum, then there would be nothing in it, yet you can see through it which means light is obviously still in there (and who knows what else), right? If there was truly nothing in it, and glass is a highly viscous fluid, and fluids conform to fill empty...
  44. D

    Phase Equilibrium of Liquid and Vapor Under External Pressure

    Suppose you have a container of water at a given temperature T (say normal room temperature) with a vacuum above it. Presumably water will evaporate until there is sufficient vapor that the pressure of it above the water is the SVP for that temperature. Now suppose that there is air above the...
  45. T

    Is this a valid way to calculate capillary force / pressure?

    When figuring out the capillary pressure on a liquid in a tube of a certain cross-section, the typical approach is to consider the Young-Laplace pressure and the curvature etc. I was looking through some of my old notes and I had an equation for the capillary force: fc = γ cosθ dS/dx where γ...
  46. brotherbobby

    Understanding Pascal's Law: Why is Force Greater in One Cylinder Than the Other?

    Answer : Using Pascal's law, this is my answer : ##\color{blue}{\boxed{\vec F_a = \vec F_c < \vec F_b}}##. Reasoning : Forces ##F_a## and ##F_c## are equal because the pressures required at the two cylinders for case (c) is the same as that required in (a). It doesn't matter how many of those...
  47. B

    Pressure generated by a force on a pump with a lever

  48. iVenky

    When a bird flaps it's wings up, doesn't the pressure drop below?

    I am trying to understand how birds fly. If you consider a plane, using it's engine & streamline shape of the wings, it can create a low pressure region above the wings and high pressure region below and this makes it fly and the upward force is proportional to the speed. Birds seem to flap its...
  49. Spinnor

    Center of Isaias passes near, pressure drop graph local weather

  50. aspodkfpo

    Pressure & Force: Gases, Liquids, Solids

    Sorry if I'm asking too many questions, but I'm currently reviewing a textbook and I'm realising quite a few things that I'm conceptually unsure of, so I'm going to be spewing out questions. If a bottle is shaken, dissolved gas comes out of solutions and builds up pressure inside a bottle. As I...
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