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. E

    B How to determine force based on pressure

    Hello In a pharmaceutical lab,a certain pressure is applied to IV bags using the equipment shown below.We need to calculate the force acting on the bags based on the applied pressure.I know the formula is F=PxA.But i am not sure what the surface area is.Should i take the whole surface area of...
  2. .Scott

    Impact of alcohol and reduced cabin pressure on flights?

    In a recent news article, a Frontiers Airline passenger became very unruly after two alcoholic drinks. On an airline flight, the only ones instructed on the combined effects of alcohol and altitude are the cabin crew. This is what the FAA has to say to them: Since issues related to alcohol...
  3. PainterGuy

    I The pressure exerted by radiation

    Hi, I was reading about the pressure exerted by radiation and need help with few points. I'd appreciate if you could help me. Source: Proceedings of the American Academy of Arts and Sciences, Volume 38, By American Academy of Arts and Sciences , 1903 You can check this capture for more...
  4. S

    Diesel Injector and Water Tube Boiler Back-Pressure

    Diesel injector: How much pressure relative to the maximum combustion chamber pressure during the sharpest phase of detonation does an injector need to be able to overcome to inject its full charge? How much overlap is typical between injection and detonation? Water-tube boiler: Are the water...
  5. P

    Pressure change in pipe due to sudden closure of valve

    Water is flowing in the pipe with velocity v0. Upon sudden closure of the valve at T, a pressure wave travels in the -ve x direction with speed c. The task is to find ##\alpha##, where ##\Delta P = \rho_0 c (\Delta v) \alpha##. The 1st step is to set up an equation using conservation of mass...
  6. B

    Saturated vapour pressure vapour quality and T-S diagram location

    Hi all., Just hoping to get a better fundamental insight into a few things. If we start with this: http://hyperphysics.phy-astr.gsu.edu/hbase/Kinetic/vappre.html so we have a closed container at a given temperature, then we can find it's saturation pressure. All good so far. In the following...
  7. jjirving

    I Grip Strength: Comparing Pressure Needed to Hold 20kg Weight Plate

    I am interested to compare two scenarios relating to grip strength and how much horizontal pressure will be required to hold the weight. Scenario 1: You have a 20kg weight plate in one piece. You hold the plate between your fingers. Scenario 2: You are holding a small 2X4 block of wood with a...
  8. tmalcolm

    Force pressure variance after hole is plugged?

    There is a tall cylinder filled with water. And there is a 3 in diameter hole near the bottom and water is gushing out. (assume the cylinder is continually being re-filled from the top) You work to plug the hole with a 10 inch long cylinder that is exactly the perfect diameter fit to plug the...
  9. agnimusayoti

    How to Measure Very Small Differential Pressure in a Subsonic Wind Tunnel

    I assume that air have ##1 kg/m^3## density. Therefore, using Bernoulli equation, on upside and downside of my test object, there is a differential pressure ##\Delta P##: $$\Delta P=0.5*(v_2^2 - v_1^2)$$ From cases: (a) ##v_1 = 1 m/s## and ##v_2 = 2 m/s##, then ##\Delta P = 1,5 Pa## (b) ##v_1 =...
  10. Istiak

    Calculate the volume change with gas temperature for this piston in a cylinder

    Solution attempt : Option : I am sure that my work is wrong. But, I must add solution attempt in PF that's why I just added that. How can I solve the problem?
  11. G

    I Heat capacity for a real gas using the ideal gas (zero pressure) equation

    Summary:: Heat capacity for real gas with ideal gas (zero pressure) equation I'm looking at this problem and I'm stuck. I usually question everything but this problem is confusing me. I don't know how they've made the jump from reduced properties (from generalized Cp charts(?)) to...
  12. D

    How Do You Calculate Static Pressure Drop in a Laminar Flow Channel?

    Hallo. Since I'm new in this field, I hope someone can help me. I have a laminar, steady state, incompressible flow in a channel (a fully developed). Geometry of the channel is on the photo. How should I calculate the drop of static pressure across the channel? Since I have Re, I did calculate...
  13. G

    B Pressure under the ice of Europa?

    What could be the water pressure under the ice of Europe moon? Could it be toleratable for not super expensive machines, structures?
  14. DarkoX

    Advice on pressure drop calculation

    Hello everyone, I would appreciate any help with my task I am struggling to resolve. I need to calculate or simulate pressure drop when got the following parameters: 1. Supply pressure: 45barg. 2. Pipe Length: 80 meters 3. Pipe diameter: OD - 10mm, ID - 8mm. 4. Pipe material: stainless steel...
  15. T

    B Dynamic pressure in pressure units

    We all know that a flowing fluid acquires dynamic pressure as a result of this velocity. But the pressure has been known to be the kinetic energy of unit volume of flow i.e. 0.5 times density multiplied by the square of the velocity. I just want to know how to convert that into units that are...
  16. H

    What is the relationship between pressure and flow rate?

    I performed an experiment where I let water flow out of a measuring cylinder through a hole at the base of the measuring cylinder. I let the water run out for 30s, recording the volume after. I did this for different heights of water in the measuring cylinder, and kept the pressure of water at...
  17. I

    Chemistry Vapor pressure of ethanoic acid vs. ethanol

    I think the answer is D because both molecules can hydrogen bond with their OH groups, but the C=O bond in ethanoic acid is polar and contributes to dipole-dipole interactions. The solution says B is the correct answer, because ethanoic acid molecules strongly hydrogen bond so that most...
  18. Krokodrile

    Chemistry Work, temperature and energy in a constant pressure process

    So, the Cp and Cv its very confusing for me. But, i understand what's its happening in this process, so, i use the logic and first i obtain a ecuation for obtain the final temperature ecuaticon: Q=m*C*△T Q=m*C*(T2-T1) T2=(Q+T1)/(m*C) If the process its in constant pressure, i use the Cp valor...
  19. Zahid Iftikhar

    Time of Impact of Gas Molecules on the Inner Wall of a Pressure Vessel

    In derivation of relation for pressure of Gas ,(see pic below) the time for rate of change of momentum of molecules should be the time for which the wall of the vessel and the molecules kept interacting with each other, not the time between successive collisions. As circumscribed below, my...
  20. M

    Bearing (surface) pressure versus load rating

    Hi, From suppliers of bearings, some of them specify the maximum bearing (surface) pressure or the maximum load rating (static or dynamic). What's the difference between this two? And which is most commonly used during selecting and calculating bearings in a mechanical design? Thanks in advance,
  21. D

    Engineering Over-consolidation pressure / negative skin friction of clay

    However, I can't find any proof on this ? Can someone help to explain this ?
  22. bubble-flow

    Where are the pressure nodes on a standing acoustic wave in water?

    I have calculated the wave length of a 36 kHz acoustic wave in 20 °C water to be around 41.16mm. Suppose I have a transducer that produces a 36 kHz acoustic wave and a small water container with a length of 41.6 mm. How will the standing acoustic wave look like, which is produced by the...
  23. D

    Water Pressure and Different Pipe Sizes

    Started an irrigation project. There are 4 points in this irrigation system; A, B, C and D. The main water line to the house is 1" diameter pipe. (Point A) The distance from Point A to Point B is approximately 30 feet. Here at Point B the pipe size is reduced down to 3/4" pipe. The distance...
  24. Dario56

    Maximum non - PV Work at Constant Temperature and Pressure and Reversi

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  25. P

    Problem on Pressure due to Surface tension

    The method to solving this is to equate forces along a portion of the balloon through which ##\sigma_L## acts, and another portion through which ##\sigma_t## acts. The former potion should be a circular cross section of the cylinder, while the latter will be a rectangular cross section. You will...
  26. 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. - -...
  27. S

    How pressure increases in centrifugal compressor?

    I have read this in my textbook about principles of operation of centrifugal compressor: "The impeller is rotated at high speed by the turbine and air is continuously induced into the center of the impeller. Centrifugal action causes it to flow radially outwards along the vanes to the impeller...
  28. C

    Pressure variations after rapid pressurization

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  29. Q

    Problem: Estimating pressure of compressive garment

    Basically, I'm working on a project to make active compression garments instead of passive. There are a few materials that can actuate with large recoverable strains, and I want to use them to create the compression. I need to estimate how much pressure they could create based on the recoverable...
  30. J

    Does the derivative of a P(V) eqn give the eqn for change in Pressure?

    I know the integral of a P(V) eqn gives an eqn for work. I was wondering if taking the derivative of a P(V) eqn gives an eqn for change in pressure?
  31. J

    How to calculate initial pressure and temperature - adiabatic process

    Im confused on working backwards so to speak to find adiabatic work. To find work for this adiabatic process, I either need to know the change in temperature OR the initial pressure (I think?). The issue is that I don't know either the initial temperature nor the initial pressure so I am not...
  32. silverrahul

    Rack of blocks held horizontally under pressure

    Let us assume that there are 5 blocks , each of weight W. The blocks are held horizontally by applying a high enough force, ( say N ) to the leftmost and rightmost blocks. Let us say the blocks are numbered 1 to 5 from left to right. So, if i try to draw the free body diagrams, then block 3 will...
  33. Lilian Sa

    Star collapse in general relativity — pressure as a function of star radius

    What I've done is using the TOV equations and I what I found at the end is: ##e^{[\frac{-8}{3}\pi G\rho]r^2+[\frac{16}{9}(G\pi\rho)^{2}]r^4}-\rho=P(r)## so I am sure that this is not right, if someone can help me knowing it I really apricate it :)
  34. lahanadar

    Cause-effect relation between pressure & velocity

    For a steady, non-viscous and incompressible flow, one can apply both Bernoulli's principle (no potentials) as $$p+\frac{\rho v^2}{2} = p_t$$ where ##p##, ##\rho,##, ##v##, and ##p_t## are static pressure, density, flow velocity, and total pressure, respectively, and continuitiy principle as...
  35. 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...
  36. S

    Stiffness by pressure calculations

    Inflatable SUP boards, LEI kites, Inflatable kayaks, and so on get their stiffness by having two layers of airtight materials separated by pressurized air. And it gets stiffer the higher pressure you can contain, or by increasing the separation between the materials. The simplest way to look at...
  37. G

    Absolute zeros other than temperature (e.g. pressure)

    Hi. A version of the third law of thermodynamics states that no system can be cooled down to absolute zero temperature in finitely many steps. But what about other quantities, for example pressure: Is it possible (in principle) to evacuate a system up to the last gas particle, or would this...
  38. barryj

    Chemistry Pressure of gasoline in a closed container

    If I knew how much of the gasoline evaporated, then I could use p = nRT/V to fine the partial pressure of the gasoline and add it to the pressure of the atmosphere. So my question is, How do I find how much of the gasoline will evaporate. I would think that the gasoline would evaporate until it...
  39. G

    Pressure vessel thickness U.S. measurement

    Hi everyone, In purpose to estimate the corrosion degredation in pressure vessels it is recommended to measure the pressure vessel thickness using an U.S. device. My question is how to determine the number of test points on the shell/caps surface as a function of the pressure vessel size...
  40. H

    Calculating Pressure & Mass for Hydrogen Tank Filling

    As I stated in the summary I'd like to calculate the required pressure and mass of a tank of hydrogen that would allow me to fill a second tank with 10kg of H2 at 700bar. I am trying to get an idea of the feasibility of doing this, putting aside, for now, how the primary tank would itself be...
  41. 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?
  42. L

    Pressure profile of a gas flow through an orifice

    Hello, The question will probably be related to mechanical engineering / chemical engineering / aeronautics. I come from the field of optics and have no background at all on fluid dynamics. I'm trying to calculate the dependence of pressure on distance, i.e. P(x) in a gas flow problem: I...
  43. yourheartandsoul

    Finding blood pressure from density and height difference

    I did (1300)(9.81)(0.67) and got 8544.51 N/m^2 but unsure if that was the correct route to take. Please confirm or deny if I was approaching it in the correct way!
  44. J

    Finding area from work, pressure and volume

    So I basically took the integral and ended up with W=PVf-A(Vf^3)/3-PVi+A(Vf^3)/3 so 65.7=72*5.3-A(5.3)^3/3-72(2.4)+A(2.4)^3/3 But when I solve for A I get the wrong answer of 3.179 when the answer is suppose to be 5.05. I've checked my calculation with an algebra calculator too...
  45. E

    How pressure affects partial pressures (and dewpoint)

    I have read numerous times that equilibrium vapor pressure (EVP) is a function ONLY of temperature. This at least partly makes sense to me (so I think) given energy of molecules and movement associated with such. But apparently this is not true for the partial pressures? I once thought that...
  46. L

    Thermodynamics problem -- Pressure oscillations in a jar

    I add a Figure with the problem and solution. I have difficulty with a solution to the given problem. Why ##F=-kx=Adp##, I do not understand minus sign because we are working with scalars not vectors. It is correct to say that ##\vec{F}=-kx\vec{i}##, but is not correct to say that ##F=-kx##. Can...
  47. J

    Need help calculating pressure for a real project

    We have a product container we purge with nitrogen to create a low oxygen environment The container is roughly 12x12x12 inch. It has an exhaust port with a 1/4 inch poly line that measures 0.17 inch ID. The top of the container is a door with a rubber gasket. We are a little surprised at...
  48. A

    How to determine the pressure when you dont have the volume

    Hello! I am having trouble with this problem I found online,it was listed under the "easy" category yet I am somehow not seeing the trick. First I converted the V into m^3 so that V = 0,015 m^3,than I converted the hPa into Pa so p = 101300 Pa and now I used the fact that ##p1V1 = p2V2 ## We...
  49. J

    Finding pressure of gas in u shaped tube with liquid

    The answer is suppose to be 0.9432. Initially I thought the pressure inside the glass ball would just be the same as the atmospheric pressure because these equal pressures would cancel each other out, but obviously that's not true. I can calculate the density of the gas using the equation...
  50. J

    Finding the normal force of a block under water, under pressure

    So since the block is at the bottom there's no pressure pushing it up. To calculate the mass and force of gravity, I multiplied the density of the block by its height and cross sectional area and got 564 kg. Multiplying this by 9.8 I got the force of gravity of 5527.2 N. Now to find the force...
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