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. 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)...
  2. LCSphysicist

    Thermodynamics: internal energy and pressure

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

    Pressure in a 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...
  4. 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...
  5. 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...
  6. 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...
  7. 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...
  8. B

    Pressure generated by a force on a pump with a lever

  9. 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...
  10. Spinnor

    Center of Isaias passes near, pressure drop graph local weather

  11. 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...
  12. C

    Maximizing Efficiency: Utilizing a Pressure Cooker for Cooking

  13. A

    Hydrostatic pressure of liquid in a cart on an inclined ramp

    Sorry for my English, I'm Spanish. I am not able to make the force diagram for the liquid. I am still in high school and started now little hydrostatic. If someone can give me a light, I would be very .grateful.
  14. thommy

    Why don't airplanes explode due to pressure difference?

    My question might sound trivial (I'm just a first year physics student anyways) , however I really feel the need to get an answer. Since the pressurized cabins inside an airplane are regulated at about 0.8 atm while the pressure outside doesn't surpass 0.2 atm (at 35 000+ ft of altitude)...
  15. prodigylock

    A What pressure would be needed to cause fusion of water?

    So in a DnD story, someone made a bomb by putting 3375ft^3 of water into a 0.5ft radius sphere and caused it to make a nuke. I was thinking if this was possible then what would actually happen, so I spent an afternoon looking for the answer and only got the pressure and density...
  16. R

    Explaining Pressure & Depth Relationships in Fluids Using Halliday & Resnick

    Homework Statement:: Not a homework problem. I need a conceptual explanation. Relevant Equations:: ##p_2 = p_1 + \rho g(y_1 - y_2)## (1) ## p = p_0 + \rho gh## (2) When deriving equation (1) we use the example of a submerged cylinder in static equilibrium with its top at position ##y_1## and...
  17. iVenky

    How does pressure act in all directions if gravity is downward only

    I have a fundamental question about the pressure and I am not sure if my reasoning is correct. Let's take an example of 7 stones shown below. They don't fall because the center of mass of each stone is falling right under the stone below. If I replace the same thing with a liquid, and we know...
  18. cwill53

    Calculating Pressure & Density Proportions with Changing Altitude & Temperature

    I got the correct answer to this question with the following calculations, but I do need some correction in terms of what units I'm integrating across. ρ##\rho ## is density. mtot=n##m_{tot}=nM##, where n is the number of moles of a substance and M is the molar mass of the substance...
  19. A

    Rocket propulsion explained only through pressure differential

    Fluid can exert force to object(move object) only through pressure and tangential stress caused by viscosity. if we look at balloon rocket ,here is Newton 3 law action-reaction,but this 3 law as usual don't tell nothing how fluid really exert force to the ballon.. it exert through pressure...
  20. S

    Partial pressure of oxygen at a certain altitude

    The pressure of oxygen at sea level = ##\frac{20.9}{100} ~\text{x} ~(21.2 ~\text{x} ~ 10^3) = 4430.8~ \text{Pa}## Then I do not know how to calculate the pressure at altitude 7000 m. I tried using P = ρgh (taking ρ as density of air = 1.3 kg/m3) then subtract the result from 4430.8 Pa but got...
  21. dedocta

    Plate Tectonics and Evolutionary Pressure

    I used to work with invasive species in the early 2000's. I saw firsthand the damage a single invasive species can wreak on an ecosystem (Emerald Ash Borer among other insects.) After watching videos of plate tectonics, I began to wonder what would happen to ecosystems on large scales during...
  22. J

    Understanding Vapour Pressure & Temperature Difference

    I have a problem at the very beginning. I don't know how to relate this vapour pressure to the temperature difference. I have read the hint: Recall the idea 7: for dynamical processes, at first, a mechanical equilibrium is reached, which means the equality of pressures; the other equilibria...
  23. DrPython

    Calculate the air pressure needed for a projectile to travel X distance

    Hello! I'm brand new to the physics forum so please excuse any mistakes I make. I'm not even sure if I'm in the right forum section lol. My goal is to create a air cannon to launch a piece of dog food (super overkill) and I have pretty much 0 background in anything post-high school physics. I'm...
  24. Tymofei

    Pressure Differential in Fluid Dynamics: Why More on the '+s' Side?

    Here i added a page from my fluid dynamics book where it shows particle model for deriving the equation. My question is why pressure is more at stream side aka 'positive "s" direction'.I would expected more pressure on the other side because for example when you trying to push a rigid object or...
  25. B

    Pressure loss pipe system: Conversion from known fluid1 to fluid2

    Hello, everyone, I am currently working on the following (real) problem, where I am not getting anywhere. It would be super nice if you could have a look at this. Thank you very much :-). I have a pipe system (Black Box) of which I only know the following things: At a set flow rate with a...
  26. Adesh

    How does a pressure distribution keep the fluid from moving?

    Let’s say we have a unit volume of some fluid in a column on the Earth surface. Let ##\mathbf F## be the gravitational force that acts on the unit volume of the fluid. Consider a small volume element ##\Delta \tau## in the fluid and let’s assume it to be a cuboid with dimensions ##\Delta x##...
  27. A

    Vapour pressure of water vapour in air

    Vapour pressure in a closed system. Why does the partial pressure of water vapour in air equals to the equilibrium vapour pressure of liquid?
  28. PeterDonis

    Insights Is Pressure A Source Of Gravity?

    Continue reading...
  29. R

    Calculate the Temperature and Pressure of a melting point

    Adiabatic increase in pressure implies Tds=0, can someone tell me how to proceed?
  30. T

    External pressure when internal pressure is constant

    So, when I try to solve for expansion work, I don't know nothing about Pext. I've seen multiple times that they just replace Pext with Pint but I don't really get why. I thought about a few situations and I'd like for you to correct me if I'm wrong. If the system in vaccum: the simplest one...
  31. A

    The derivative of Heat Capacity with respect of pressure

    I'm thinking about that for 1 hour. But, I could not do it.
  32. J

    Engineering Hydrostatic Pressure Sluice Gate - Civil Engineering

    Please can you help with a question I am struggling with. I have done as much working out as I could until I was completely stumped: Calculate the concrete volume that is required to keep the sluice gate AB closed, assuming that the only resisting force is the friction between the concrete...
  33. C

    MHB Find the probability of 1 tire with low air pressure P (1)

    1) Let X represent the number of tires with low air pressure on a randomly chosen car. The probability of distribution of X is as follows: X 0 1 2 3 4 P(X) 0.1 0.2 0.4 0.2 0,1 a) Find the probability...
  34. MrInventive

    Can Increasing Helium Density Affect Payload in Space?

    I don't even know where to start... could you please show me step by step
  35. I

    Chemistry What are the partial pressures of each gas in the mixture?

    I've first calculated the partial pressures of each gas: ##N_2: 0.4\times 7.4\times 10^4=3.0\times 10^4 Nm^{-2}\\## ##O_2: 0.35\times 7.4\times 10^4=2.6\times 10^4 Nm^{-2}\\## ##CO_2: 0.25\times 7.4\times 10^4=1.9\times 10^4 Nm^{-2}\\## From here, I do not know how to continue. Could someone...
  36. I

    Question about calculating the minimum temperature in hot air balloons

    First, I tried using the Archimedes principle and calculated the weight of the surrounding air displaced when taking off. ##W = 2500\times 1.29\times 9.81 = 31637.25 N## But then, I got stuck and do not know how to proceed from here on. I don't want the full solution yet but can I get some...
  37. rjomega

    Effect on Volume of a Change in the Pressure of Compressible Gas

    Will the available Volume of oxygen gas for use of patients increase when the pressure decreases from 12.4 MPa to 500 KPa? Is using boyle's law the right way to calculate the available volume?
  38. P

    Pressure required for water discharge

    Hello everyone, I am very interested in knowing the relation to determine the pressure required to push the water upstream. In the attached picture, water is filled inside a tank of volume V and air is constantly flowing inside the tank through an inlet with constant flow rate M. Water should...
  39. E

    Does pressure affect equilibrium vapor pressure (or RH)?

    I'm wondering if I'm on the right track and if anyone is willing to steer me on if not: Equilibrium vapor pressure (EVP—also referred to as saturation vapor pressure) is dependent only on temperature. Outside pressure has no bearing. Now, of course, with lower external pressure (atmospheric)...
  40. Adesh

    I What is the meaning of the free surface in fluid mechanics?

    I’m currently studying Fluid Mechanics, during an analysis I came across this We now consider an example that combines centrifugal force and gravity: a liquid in a drum (centrifuge) rotates with constant angular velocity ##\omega## about a vertical axis. The centrifugal force per unit of...
  41. tanaygupta2000

    Degeneracy pressure of a White Dwarf Star

    So far, I am provided with all the required values for calculation, except N. If N = total number of electrons in star, then using N = mass of star/ mass of an electron should be no problem. Am I right?
  42. A

    How to caluculate the pressure immediately downstream of a sudden expansion

    Good day All Here is the first ligne of the exercice that might not be visible As shown in figure , water (kinematic viscosity of water v=1E-6 m2s-1)flows out of a reservoir with a sharp entrance at A. My questions is how to compute the pressure pn right down stream the sudden expansion My...
  43. Adesh

    Three doubts in a paragraph on the equilibrium of Incompressible fluids

    These are the images from Sommerfeld’s Lectures on Theoretical Physics, Vol 2 chapter 2, section 6, Equilibrium of Incompressible Fluids. Image 1 Image 2 Doubt 1 : What does it mean for a force to act on a fluid volume? Force acts on a point, force may act on a surface but I’m unable to...
  44. il postino

    Calculate the pressure using the Van der Waal equation on reduced variables

    Summary:: Find the pressure using the vdw equation in reduced variables Hi everyone! I have a doubt when I try to solve this exercise. The result was very high pressure. Calculate the pressure using the reduced variable vdW equation for a sample of 74.8 grams of ethane in a ##200 cm^3##...
  45. S

    Mercury vapor from blood pressure devices

    I came across some articles about the health hazard from broken mercury-based sphygmomanometers. This led me to think about vapor leakage from good devices during normal operation. The top of the glass tube is at ambient atmospheric pressure. There is supposed to be a membrane at the top that...
  46. K

    I What is the Ideal Plasma Pressure for Successful Fusion?

    I am trying to wrap my head around the concepts in fusion. They talk about ion density, but I don't ever see that expressed in pascals, for instance. Why is that? I understand that confinment time is also important for successful fusion and that they go hand in hand, but I'm not concerned about...
  47. anonymous99

    Why doesn't atmospheric pressure crush us?

    H
  48. OriginalH1h

    Pressure Required to propel something a long distance

    I am making this (hopefully in the correct forum) because I started debating propulsion about objects and the like. The main two questions I want to have answered if at all possible are as follows: How much pressure would be needed to send a person flying? How much pressure is needed to...
  49. Fuux

    Sticky card Application of Bernoulli / Pressure incorrect?

    After doing what the instruction did, I noticed that the card stuck to the spool, and generated the hypothesis that it was the same effect as when putting two papers together and blowing through them, the lower pressure of the faster speed of the wind makes the higher pressure outside move the...
  50. S

    Compressed air pressure vs hydrostatic pressure

    Hi all, I'm new on here and will start off with what I think is a simple clarification. I'm questioning my workings due to previous work being completed by another engineer and thought this was the best place to ask. Essentially we have compressed air being supplied through a hose, the hose...
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