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. Sanborn Chase

    B Can the Proton's 10e35 Pascals Outward Force Be True?

    I recently read the proton has an outward force of 10e35 Pascals with an equal inward force containing it. Can this be true?
  2. P

    I Neutron vs electron degeneracy pressure

    How is neutron degeneracy pressure able to support a much higher density object such as a neutron star where electron degeneracy pressure only supports a comparatively less dense object such as a white dwarf. Conceptually I would think electron degeneracy pressure to be stronger due to the...
  3. C

    Calculate Pressure vessel Collapse Pressure

    Homework Statement I have a simple cylindrical pressure vessel with thickness 100m and inner radius 254mm,.the cylnder has flat head closed ends but these are thickness 30mm. I need to calculate the pressure that would cause the vessel to collapse given material properties E=207Gpa, poissons...
  4. P

    Pressure changes of a fluid flowing through a horizontal pipe

    If we have a tube of fluid going like it is shown in the picture, and we measure pressure at two points we would get the same value. But the fluid is still going from point A to point B. So is pressure difference not necessary for fluid flow or I made some other wrong assumptions?
  5. dlgoff

    Atmospheric pressure -- Record low in Kansas?

    Here's a print screen from my weather station's computer early this morning. I've never seen this low of atmospheric pressure here in Kansas before. Shortly after midnight the pressure hit a low of 28.08 InHg. :oldsurprised:
  6. M

    Pressure on a submerged object

    New member: Stem cell biologist by training, and many years since my last physics class. Imagine I take a water balloon and fill it completely with water. I then submerge the balloon in a beaker of water and place the glass inside a sealed chamber. What forces are applied to the water balloon...
  7. T

    Atmospheric pressure per square cm

    Hi, I have a problem to understand one small thing. They say that air pressure per square cm at sea level is approximately 1 kg. So at 2 sq cm it will be 2 kg, at 3 sq cm it will be 3 kg etc. But... Here where I have a problem. The thing is that inside 2 square cm you can put 4 one square cm...
  8. S

    Calculating the time for a pressure change

    I've been searching and it seems I am not smart enough to find the solution for this... Let say I have a fully closed box made of concrete left in air. The pressure inside the box is 0.01atm. Since it is left in air, the air will come inside the box through concrete walls(since concrete is...
  9. K

    Pressure Waves in an Open Tube

    1. Problem Statement: The pressure in an gas tube of length L stretched along the x-axis is given by P(x, t) = Patm + P1(x, t) + P2(x, t) (1) where , P1(x, t) = 20 [P a] sin (−5.9 x − 1300 t ) P2(x, t) = 20 [P a] sin (5.9 x − 1300 t )One open end of the air tube is at x = 0m. By how much does...
  10. Roy S Ramirez

    How can I predict the flow rate for a real life water hose?

    Hello! I hope you are all doing well! I've been always intrigued by fluid mechanics and decided to try out a quick experiment with my water faucet. After using some equations I found online [1] [2], I plugged a hose to the faucet and let the water run. I filled a 1 quart bowl and recorded the...
  11. P

    Calculating Pressure Losses & Coefficients in Y-Junction w/Mixed Fluids

    i have a y - junction fitting (two inlets (1,2) and one outlet (3)). Two different fluids (with different densities and viscosities but same temperatures) let's say paint and other fluid comes from two inlets, mix and they will go through the outlet. and also laminar flow conditions. How to...
  12. A

    B Need Help Regarding a U Shaped tube problem

    my text box says that the pressure at point A is less than pressure at point B Are not they supposed to have same pressure as they are on the same horizontal plane ?
  13. A

    B Can the same formula be used for both water and mercury manometers?

    if we use a water manometer we get the pressure of the gas in manometer by using this forumla : Pgas = Patmosphere ± ρgh and if we use the a mercury manometer we use this formula instead : Pgas = Patmosphere ± h and here's my question : why cannot we use the first formula in both of them ...
  14. A

    B Why is the height of a liquid not affected by the radius of a U-Shaped tube

    Why the height of liquid is not affected by the radius of U-Shaped tube . ..my textbook says this and it does make sense because if increase the radius of u shaped tube the height of liquid should decrease as the liquids take shape of their container. Edit : I could not make the title longer...
  15. K

    Pressure Difference Between the Inside and Outside of a Balloon

    Hello all. I have a question about gasses and pressure: Is there a way to calculate how strong a material making up a balloon has to be to withstand a given pressure difference between the inside and outside? In other words, if I have a balloon I need to fill to a pressure of 10atm inside vs...
  16. M

    Same pressure points , 2 fluids u shaped tube

    Homework Statement see pic uploadedHomework Equations Pascal principal p = ρgh The Attempt at a Solution Pressure at C and D is the same . Pressure at A and B is the same ? I believe it is
  17. Bheshaj

    Pressure exerted by a gas (derivation using the kinetic theory of gases)

    In the derivation of finding pressure exerted by a gas using kinetic theory of gases I am not understanding why the time between two collisions is taken as the time for rate of change of momentum when a particle bounces back from the wall. please help me
  18. K

    I What is the pressure gradient towards the centre of a large planet?

    Given that the gravitational field falls to zero at the centre of a large body (e.g. the earth), what happens to the pressure curve? (Assuming no effects due to high temperature.) Does it ease off too? What would the curve look like and what would the formula be?
  19. D

    Pressure drop as volume changes

    I am trying to calculate pressure losses. I've attached an image to show what I mean. Starting out tank 1 is 92.8 litres at 155 psi and when the shutoff valve is open the volume goes from 92.8 to 192.8 and so I thought the pressure would drop by the same factor that the volume increased by so...
  20. Raghav Seetharamu

    Time taken for pressure equalization between two tanks

    Homework Statement How to calculate time taken (rough approximation) for pressure equalization between two tanks. Both the tanks have same fluid (Air). Homework Equations Rough equilibrium pressure can be achieved by using equations Ptot = (P1V1+P2V2)/Vtot. Thought of using exponential...
  21. D

    Misc. Hydrostatics problem in a water vessel

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  22. G

    Air flow through a hole in a submerged pressure tank

    Hello! I will try to formulate myself as clearly as possible, but english isn't my main language. I'm having trouble solving this problem that should be relatively easy to solve. Let's say we have a submerged pressure tank, constantly fed with air through a compressor, so it's maintained at a...
  23. B

    Speed of a cap when released from a pressure vessel

    Hi, Pressure vessels have caps on top of them. These caps are secured with tri clamps and if you need to remove them you have to make sure that the tank's pressure is released. If the tank is under pressure (say 10psi) and an operator removes the cap (A is known), what is the speed of the cap?
  24. C

    What causes low pressure on a wing?

    Even today there are lot of misconception about how and WHY static pressure reduce above wing. 1)Faster air velocity cause low static pressure One involves holding a piece of paper horizontally so that it droops downward and then blowing over the top of it. As the demonstrator blows over...
  25. L

    Help with formulas for calculating pressure

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  26. M

    Pressure within two connected vessels

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  27. J

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  28. Z

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  29. B

    HVAC High Flow Control with High Pressure and Temperatures

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  30. jybe

    Constant pressure heat of reaction -> constant volume q

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  31. Z

    Time till the air pressure is gone

    Hello, I have a 8 gram cartridge of N2O meant for kitchens. Long story short from what I understand it has 10 cm cube of N2O inside. I also know it has 900 psi / 60 bar of pressure inside. The cylinder is exactly like this image. I am trying to find out how much time it would take if I...
  32. hnnhcmmngs

    How Does the Equation of State for a Solid Change with Temperature and Pressure?

    Homework Statement [/B] Find the equation of state of a solid that has an isobaric expansion coefficient dV/dT = 2cT - bp and an isothermal pressure-volume coefficient dV/dp = -bT (Assume the solid has a volume Vo at zero temperature and pressure. Enter a mathematical equation. Use any variable...
  33. M

    Hydrostatics Pressure - Finding thrust and resultants

    Homework Statement I'm getting stuck with this one and in need of some direction! Obviously I'm not looking for a direct solution, but maybe a outline of what I should be doing? (I'll attach an image in a few minutes) <Image here incoming!> Known data: d2 = d1 / 2 F = thrust force (N) Pa = ρ...
  34. A

    Pressure / Volume Gas relationship Pendle Hill experiment

    I was reading about the Pendle Hill experiment by Henry Power and Richard Towneley showing the relationship between Volume and Pressure in gas that eventually became Boyle's Law. The higher they got the greater the volume became. My question is, was the gas measured in the barometer isolated...
  35. G

    I Pascal's law (fluids): Derivable from fundamental laws?

    Hi. Pascal's law states that static pressure in a confined incompressible fluid without gravity is the same everywhere. Is this law derivable from more fundamental laws? Some thoughts: Is Pascal's law part of the definition of the liquid state? If the liquid operates between two hydraulic...
  36. L

    Pressure and Volume -- are the growth/decay rates exponential?

    Homework Statement forumlate if its growth/decay is exponential I have equation that i intergrated and found Pressure over volume = work done of pressure P = 3.2c^-1.4 f(v) = -8v^-0.4 i set limits of 10x10^-6 --> 100x10^-6 and 10x10^-6 --> 100x10^-6 but i increase both values by 20x10^-6 every...
  37. Y

    How can I calculate the drop in pressure across an orifice?

    I know the inlet pressure, temperature and density along with the massflow rate across the orifice and the orifice cross section. Is there a way for me to calculate the drop in pressure across the orifice?
  38. A

    Siphon pressure and velocity problem

    Homework Statement Homework Equations Bernoulli equation. Continuity equation The Attempt at a Solution Area of pipe is constant, so v_a = v_b = v_c = v_d.[/B] Using point on water surface and point D. Point on water surface: z = 8, v = 0, P = 0 (P_atm) Point D: z = -2, P = 0 (P_atm) v =...
  39. R

    Volume Change by Pressure: How Does Pressure Affect the Volume of an Object?

    Homework Statement It is necessary to calculate the volume of the coin which has mass 25 kg and how does change its volume when it is necessary to calculate its volume at a depth of 5000m. Compare volume change by pressure with the volume change by pressure with the Volume change by...
  40. F

    How does a metering device on an A/C lower the pressure?

    Preface: Some people call the metering device on an air-conditioner the "expansion device". When I refer to the metering device in this post, metering device is synonymous with expansion device. ______________________________________________________________________________________ I'm a...
  41. I

    Measuring Pressure For Compressible Fluid Systems?

    Is measuring pressure for a compressible fluid system angle dependent?For a compressible fluid, Bernoulli's Law gives us a relation between two points along a closed system. More specifically it gives us the relation between two cross sections belonging to two distinct points in the closed...
  42. G

    The Clausius-Clapeyron relation to study pressure cookers

    The Clausius-Clapeyron formula is given by \frac{d P}{d T} = \frac{L}{T \Delta V} where P and T are the pressure and temperature at the boiling point, respectively, and L is the latent heat per mole at the boiling point, and \Delta V is the change in the volume per mole between the gas and...
  43. T

    Stat-Mech problem: pressure from a partition function

    Homework Statement A vessel having a volume ##V## initially contains ##N## atoms of dilute (ideal) helium gas in thermal equilibrium with the surroundings at a temperature ##T##, with initial pressure ##P_{i} (T ,V ) = \frac{NRT}{V}## . After some time, a number of helium atoms adhere to the...
  44. H

    How to get the best pressure control for branches

    I am discussing with my friends to see which way is the best way to get the most stable branch outputs when one branch condition changed suddenly. There are three liquid flow branches, A, B and C, connected together with one pressure source, like this configuration: The Water Pump, #1...
  45. F

    Pressure inside the zeppelin for it to float

    Homework Statement A zeppelin of an ellipsoid shape (a=32m, b=c=a/3) iz filled with hydrogen. Pressure of the surrounding air is 100 000 Pa. Temperature of air and hydrogen is 20°C. The mass of an empty (not filled with hydrogen) zeppelin is 10 000 kg. What does the pressure of hydrogen inside...
  46. beefbrisket

    Assumed value of pressure during quasistatic compression

    My text (Ian Ford - Statistical physics) describes an ideal gas system in a piston being quasistatically compressed by a piston head of area A under external force f. It assumes the system has a uniform pressure p. All good so far. Then it says: "the force pA equals the applied external force f"...
  47. S

    Ideal Gas Law and Pressure at 80°C

    Homework Statement An ideal gas has a molar mass of 40 g and a density of 1.2 kg m-3 at 80°C. What is its pressure at that temperature? Homework Equations PV=nRT R constant= 8.314 n= number of moles T= tempreture in kelvin density=Mass/ Volume The Attempt at a Solution i simply solved it like...
  48. Logic hunter

    B How does liquid starts moving when there is Pascal's law

    Consider a conventional U-tube with both the vertical tubes having the same uniform cross section area A and the horizontal tube of length L, connecting those tubes containing an ideal liquid. Now the free surfaces in both the vertical tubes will be at the same height and will have pressure...
  49. hagopbul

    A Is the Earth's core a potential high-temperature superconductor?

    Hello to all Can we consider the core of the Earth to be a superconductor ,for example Aragon national laboratory hinted for some thing like that https://www.anl.gov/article/nickel-for-thought-compound-shows-potential-for-hightemperature-superconductivity That been said , what test could...
  50. Logic hunter

    Contradicting values of pressure for liquid cross-sections

    Consider a fixed horizontal tube of uniform cross section with pressure being 1atm at one of it's end and 5atm at the other (former due to 'open to atmosphere' and latter due to force on a piston), then liquid would flow towards low pressure end. By equation of continuity all cross sections will...
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