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. eddiezhang

    How does a difference in air pressure induce a force?

    Another likely very basic question from me Suppose I pinch a piece of A4 paper and pull it up, at a velocity of let’s say 1 or 2m/s (i.e. order of magnitude 10^0). The paper, of course, encounters air resistance / drag as it moves through the air, but there’s also a (larger) force that is...
  2. dadthedestroyer

    Increasing pipe size and then decreasing

    Seen a lot of videos of a guy increasing and decreasing the pipe size on YouTube and changing the flow of water or the pressure. It seems an explanation of how this works would be nice. I understand a little bit about flowing pressure. Is there any other things that involved in this?
  3. kaare_t

    I Pressure delta 1.0 bar: 0.0 to 1.0 vs 1.0 to 2.0

    Hi, New member here. I have no higher education, please excuse me if I'm asking an obvious question, and feel free to reply with more questions if my post is unclear! And please feel free to correct me if I'm using wrong term(s), or wrong assumptions. My question is related to pressure, and...
  4. Dario56

    What determines the pressure inside this experimental setup?

    I have two gas tanks of nitrogen and oxygen. Mixture of gases is created and used in the system of interest. Let's say I want to create an atmospheric conditions in my system, mass ratio of oxygen to nitrogen is 0.3 and total pressure of 1 bar (oxygen partial pressure 0.21 bar). Therefore, mass...
  5. S

    Air pressure changes in a vessel as the vessel volume increases

    As an example, you have a 100-gallon capacity sealed pressure vessel containing 100 psi of air pressure. What is the change in air pressure as the vessel volume is increased? If the volume is doubled is the pressure reduced to 50 pounds psi. On a graph, is the reduction rate a straight line? Is...
  6. B

    Volume's effect on buoyancy: Does pressure increase?

    Hey! Im currently writing a lab on how an increase in the volume of an object will result in an increase of buoyancy force acting on an object. We fully immerse different amounts of clay playing blocks into water (using a string) on top of a scale, and calculate the buoyancy force. The reasoning...
  7. ergospherical

    How does pressure balance work in the magnetosphere?

    I'm not sure how to set up the pressure balance at the magnetosphere? Maybe some energy equation relating ##\frac{1}{2} \dot{M} v^2 \sim## magnetic energy density?
  8. brochesspro

    Pressure inside a sealed container

    I do know how to solve this question: We find the equilibrium pressure due to air molecules inside the container (after water has stopped flowing). Then, assuming initial pressure of gas inside the container to be atmospheric pressure, we use Boyle's law to find the new volume of the gas and...
  9. Lotto

    B What is the pressure acting on the air?

    Let us say that the glass isn't whole under the water. If the height of the air layer under the water is ##\Delta x##, then the pressure the water acts on the gas is ##p=p_{\mathrm {atm}}+\Delta x \rho g##. But my confusion is why the "hydrostaic pressure" is ##\Delta x \rho g##, not ##L\rho...
  10. M

    B Superposed loads (gunpowder and bullets) igniting simultaneously in a barrel

    Look at this picture of two superposed loads: Imagine that each bullet weight 150 grains and each gunpowder charge 50 grains. If the rear load were to be fired first, it would be equal to firing two bullets +the weight of the front gunpowder charge. So a 350 grains bullet with a 50 grains...
  11. Lotto

    What helium mass in a balloon to make it bouyant in air?

    I suppose that the temperature is the same for the helium as well as for the air. So ##\frac 43 \pi r^3 \rho g >m_{He}g+4\pi r^2 \sigma g##. I would determine the density of air from ##p_0 \mathrm d V=\frac{\rho \mathrm d V}{M_a}RT##. So ##m_{He}<4\pi r^2\left(\frac{p_0M_a r}{3RT}-\sigma...
  12. H

    I Fluid dynamics: drag coefficient and pressure at the stagnation point.

    Hi, In my textbook the author say that the drag coefficient is the drag force divided by the pressure at the stagnation point time the area perpendicular to the stream. ##c_d = \frac{2F_d}{\rho v^2 A}## To get the pressure at the stagnation point I'm using Bernoulli for an incompressible fluid...
  13. Esref AHMETOGLU

    HVAC Pressure tank bladder replacement

    How did you find PF?: by searching If I have an old 5000 lt pressure tank and as I see it needs a change of its membrane (Bludder) what is the recommendation that must be followed and also what is the volume ratio between the membrane before using and after testing or working situations
  14. domv95

    B Pumping water upwards into a large water tank

    Hi everyone! Not sure if this is the right place, but here we go: I am layman when it comes to physics, so I might be overthinking this completely, but I need to make sure that the physics stack up before I do the actual pipes etc. I have a 1000-litre water tank and below it I have a smaller...
  15. Hak

    Is My Calculation for Bicycle Pump Pressure Incorrect?

    The pressure in the inner tube after four transfers of air from the pump is given by the formula: \displaystyle p_C = p_A \left(\frac{V_C + V_P}{V_C}\right)^n where \displaystyle n is the number of transfers, \displaystyle p_C is the pressure in the inner tube, \displaystyle p_A is the...
  16. Aayush Verma

    Effect of relative motion on pressure of gas in a container

  17. S

    I Pressure: Sealed bottle physics

    If a bottle is partially filled with hot water and sealed, together what some air, what happens to the pressure inside the bottle as it cools to room temperature? Assumptions: The temperature of the air in the bottle will initially be about the hot water temperature as the bottle is first...
  18. J

    Pressure rate increase between two vessels

    I have to cylindrical vessels using air as a medium. I want to pressurise vessel one, release the pressure into vessel to and register a .525mbar pressure in vessel 2 - within .3s. My understanding so far, dp/dt = 175000 Pa/s required P1V1/n1 = p2v2/n2 52500 * 0.088627484 * 0.0041846 =...
  19. S

    Relationship between pressure and temperature for liquids

    ^^
  20. JABAS

    B Hydrostatic pressure on top of a cone filled with water

    Does the cone shape and extra water below the colum of water of 1 cm increase the pressure/vacuum effect at "B" or "A"? Is it simular to an inverted cone dependant on angle of sides of cones, when looking for pressure at the bottom of a cone or cylinder? In simple terms, how? Basic maths only...
  21. L

    Converting gravity into pressure inside the very center of a planet

    Gravity in the very center of the planet must be zero because all other atoms are pulling evenly around the center. We have a deap gold mine in South Africa and uranium waste storage Norway. Has the force of gravity shown change at these depths. Even at the bottom of the Pacific ocean gravity...
  22. doconnor17dan

    Calculations for Hydraulic Jacks lifting a load

    This cylinder is connected by a pipe to the larger diameter jack cylinder on the right where pressure p2 acts on the piston which has an area A2 and is able to lift a load equivalent to the force F2. The piston area of the hand pump cylinder is 2.0 cm2, the piston area of the jack piston is 10.0...
  23. P

    B Looking for help understanding scalars vs. vectors

    Why are pressure and energy not considered as vectors?
  24. MatinSAR

    Pressure in fluids and Archimedes' principle

    Hello. A: If we put this piece of wood in the emty container, the volume of displaced water will not change (because Buoyant Force has not changed), so the pressure at the bottom of the water container doesn't change and it remains constant. B: If we put the metal in the emty container, the...
  25. N

    Maximum pressure in a rubber pipe

    What maximum pressure this silicon pipe would withstand until blowing up? ID=1mm, OD=4mm, no cord or anything like that in the pipe, pure clear silicon.
  26. M

    I Find Best Water Nozzle Type & Pressure for Longest Distance

    Hello, I am trying to throw water the furthest distance possible from a garden hose and an inline water pump. The amount of water is not important - e.g. a tiny stream is perfectly fine, so long as it reachest a really far distance. I understand wind severely messes this up, so lets not worry...
  27. dylanwalt

    Fluid Dynamics - Using the Manometer Equation

    I tried to use this equation, so I isolated the delta h because that is what im solving for and then I thought because the pressure on both ends of the reservoir is both atmospheric pressure the change in pressure is 0. This makes my entire equation 0 and thus height is 0 which is definitely not...
  28. H

    Unstable Static Pressure in Exhaust Duct

    Hello, I have a system where two exhaust fans are running simultaneously. However, they both discharge to the same outlet. The suction pressure seems to be quite stable, but the discharge pressure fluctuates between 2" wc to 4" wc frequently. Below is a rough setup of my system. The rectangles...
  29. Nova_Chr0n0

    Fluids: Concept about Fluid Pressure in a relation with Force and Area

    I've already got the correct answer in letter (a), which is 17140.2 Pascals. My question will be focusing about the letter b of the question and here is my solution: (b) FORMULA: P = F/A F = P*A My understanding about this problem is I have to use the pressure that I got in letter (a) to...
  30. K

    B Pressure in a viscous liquid versus non-viscous fluids

    Hc verma, concepts of Physics, vol 1 pg 258 "We define pressure of fluid at the point A as : ##P= F/\Delta S## For a homogeneous and non-viscous fluid, this quantity does not depend on orientation of ##\Delta S## and hence we talk of pressure at a point". Why did the author stress that the...
  31. L

    Pressure, Density: Water & Oil in Glass Tube

  32. Saladsamurai

    Predicting Remaining Pressure in Compressed Gas Cylinder

    Well, it's been nearly 10 years since my last post, and it's been about that long since I've thought about ideal gases, so here we go :smile:. Description of Setup I have a system that uses compressed gas cylinders as a source to slowly purge an optical payload. The source is 12x compressed...
  33. B

    B Water surface behavior under pressure change

    Hi togehter, this may be an easy one for most, but I'm really struggling with imagining the process. Suppose we have a compressed air vessel that is half filled with water. The pressure in the vessel drops from 10 bar to atmospheric pressure within a few seconds. How does the water surface...
  34. F

    I Calculating Pressure Change Filling Gas Cylinders

    I want to work out how to calculate the pressure change in a gas cylinder if it is used to fill another cylinder to a lower pressure. For example, if a 50 litre gas cylinder initially at 200 bara is used to fill a 600 litre cylinder from atmospheric pressure to 1.5 Bara. What would the change...
  35. M

    Pressure at bottom of three differently shaped cylinders

    For this problem, The solution is, However, I thought the answer would be (b) and (e). I choose (b) because from the formula ##P = \frac{F}{A}## then since the vessel A has more water, then the water will have a larger weight ##W_A > W_C > W_B##, therefore from##P = \frac{mg}{A}## we conclude...
  36. D

    Is There a Solution to My Pressure Cooker Problem?

    **Question:** Why do these two different approaches lead to the same result in this case? Is one of them more appropriate or valid than the other? I am looking for an explanation and clarification on this matter.Thank you in advance for your insights.
  37. chocopanda

    Mixing two ideal gases with different V, T at constant pressure

    To be honest, thermodynamics is really not my strong suit and I get confused when and how to apply formulas. My thought process is as follows: - there are two ideal gases (ideal gas law applies) - the pressure remains constant (isobaric process), so p1= p2 = p - I imagine there being two...
  38. Pushoam

    Surface Tension and Pressure Balance in a Spherical Water Drop

    Taking the shape of water drop to be spherical with radius R and ignoring the gravity, three forces acting on the surface of the water drop are 1) force ##F_o## in radially inwards direrction due to the outside pressure ##P_o## 2) force ## F_{in}## in radially outward direction due to the...
  39. T

    What is the pressure difference?

    TL;DR Summary: Which gas has a higher pressure and why? School has provided answer which I disagree. Like to hear comment from others.
  40. bruhtation

    B Gas cylinder at constant pressure being exposed to atmosphere, how?

    im learning thermodynamics and currently in a lesson about thermal processes. one process has constant pressure and before diving into equations or any proof the book provides a figure of a gas cylinder. the cylinder has a movable piston/lid on one side. the book then says "...and the piston end...
  41. Pushoam

    B Pressure of air inside a glass

    Let's consider an uncovered glass. Air particles are present in the glass. $$ P_1 = P_a$$ $$P_2 =P_1 +\rho gh = P_a +\rho g h$$where ##P_A## is atmospheric pressuere and ##\rho ## is air density. Now, if I cover the glass with a plastic card, then what is ## P_1##? $$P_2 =P_1 +\rho gh $$ 1)...
  42. T

    Cubical Pressure Vessel - Maximum Pressure Computation

    Hello everyone - this is my first post on the forum and this would be for a real world application. I have no mechanical engineering experience. We plan to build a cubical aluminium (6082 grade) pressure vessel. The total external dimensions are 540mm x 400mm x 75mm. The aluminium wall...
  43. R

    Hydrostatic pressure in a narrow container

    I understand that pressure increases with depth regardless of the shape of the container. However, this doesn't sit well with me. Imagine a container: 8' tall x 1" wide x 1' long. The pressure at the bottom of the container is 8' x 62.4 pcf = 499.2psf. However, the weight of the water in the...
  44. Bike Mi Vie

    B Negative pressure in a car to power it

    My father has an idea is powering vehicle using negative pressure. I'm trying to explain to him that I don't think that can work. He is saying that imagine you're in space and you try create negative pressure by keep on removing and the only thing that's preventing the collapse of the material...
  45. F

    Calculating pressure from a known equation of energy

    My attempted solution is as follows: Obviously the heat transfer happens during transitions 1->2 and 3->1. It's also clear that P1 = P3 V1 = V2 E2 - E1 = Integral[T dQ , from state 1 to state 2] E3 - E2 = - Integral[P dV , from state 2 to state 3] E1 - E3 = Integral[T dQ , from state 3 to...
  46. F

    B Acoustic levitation: high or low pressure?

    So the video I'm referring to is the second in this webpage. Around time stamp 3:55 mr Wolfgang, the demonstrator, says that the little balls settle down at the high-pressure areas, which are signaled by the bright bands in the Schlieren image. We understand this by noticing that the area near...
  47. 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...
  48. L

    Pressure vessel wall thickness ASME BPVC VIII vs AS1210

    The ASME BPVC formula is t=PR/(SE-0.6P) where P = pressure , R = inside radius, S = allowed material design stress and E = joint efficiency factor. the AS1210 formula ,(equivalent nomenclature) is t=PR/(SE-P). This makes 1210 more conservative when using the inside radius . I suspect the pure...
  49. Steven Bolgiano

    I Pressure Required to Circulate Liquid in a Closed System?

    Example: 3/4 pvc in closed circuit with pump. Linear distance of pipe=30ft / head 8ft .... so not counting friction, what general description of force can describe what's required to make the liquid circulate?
  50. 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...
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