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. 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...
  2. 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.
  3. 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...
  4. 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)...
  5. 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...
  6. 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...
  7. 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...
  8. 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...
  9. 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...
  10. 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...
  11. 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...
  12. 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?
  13. 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...
  14. B

    I Metal drinking cup is stuck inside a pressure cooker

    the steel glass is stuck diagonally inside the press cooker, getting it out by brute foce didn't work and neither are we able to rotate it. Washing it with soapy liquid didn't work either. Any ideas on how I can get the glass out?
  15. C

    Pressure in a gas container measured with a barometer and a U pipe

    Can someone please tell me where I am wrong, here goes the question: to a container filled with gas, U shaped pipe is attached, as shown in the picture(picture below). What is a gas pressure in the container if the height of the pillar of mercury in barometer is 740 mm? The way I solved it is...
  16. C

    Solving an Air Pressure Question: Who Is Right?

    Can someone please answer this question, so I can figure who is wrong here, me or author. Thank you.1.question (picture below): empty epruvete turned upside down is dipped in glass filled with water to the depth H. While doing that water enters the epruvete and reaches height of h. The AIR...
  17. C

    Why Water Won't Flow From Faucet with 2000 Pa Pressure?

    Picture below can someone please explain me why will the water come out of faucet with the pressure of 2000 Pa? I was expecting the answer to be "water will not come out thrugh the faucet because the pressure from the barrel is not strong enough to overcome the height of the pipe" since...
  18. C

    What does atmospheric pressure have to do with the gauge pressure?

    In this video( ) it's explained what is gauge pressure. Can someone please explain to me what does atmospheric pressure acting on a tube(in video at 3:51) has to do with displacement of a tube? I understand that the atmospheric pressure acts on the tube, but in the open space that does not...
  19. D

    I Theoretical pressure decay of a pressurised vessel

    I am looking to derive a method of plotting the theoretical pressure decay of a pressurised vessel. I would like to end up with a graph that plots internal vessel pressure against time. Is this possible? What assumptions would I need to make? The following inputs will be known. Gas: air...
  20. haha0p1

    Finding partial pressure at equilibrium

    In the coursebook the question says: The reaction below was carried out at a pressure of 10×10⁴ Pa and at constant temperature. N2 + O2 ⇌ 2NO the partial pressures of Nitrogen and Oxygen are both 4.85×10⁴ pa  Ccalculate the partial pressure of the nitrogen(ll) oxide, NO(g) at equilibrium. In...
  21. T

    How much air pressure is needed to push water up a column?

    Hello, I was creating a device to move water up a tube using air pressure, but I am not certain how much pressure I would need. I attempted to create it using 5 gallon buckets, however I was unable to apply the needed pressure needed to the airtight container. The image below is what I have...
  22. red65

    Medical Exploring Blood Pressure: Measuring Hydrostatic Pressure?

    Hello everyone, concerning blood pressure , we know that the pressure exerted by moving fluid has two components: a dynamic, flowing component that represents the kinetic energy of the system, and a lateral component that represents the hydrostatic pressure (potential energy) exerted on the...
  23. C

    Calculating pressure of air pocket in a pressurized water column

    Looking for some guidance in calculating pressure of air pocket in pressurized water column. Example: 2" vertical pipe, capped, with 2" of air and 40 psi water applied.
  24. C

    I In a closed loop system with a pump, how can we control the pressure?

    How can we control the pressure of the water inside a closed loop system (chiller system for example)? Let´s say, we have a pump curve and an system resistance curve that can be modified (through opening or closing some valves) In everywhere, what I see is that the intersection of the system...
  25. J

    Calculating Output Pressure for 15L N2/min

    Hello, i’m not good in physics so I came here for help. I have a high pressured gas tank (200 bars) and a flow rate regulator. I need to release 15L of nitrogen per minute, but my regulator only measures output pressure between 0 and 400 bars (0 - 6000 psi). How do I measure the output pressure...
  26. tracker890 Source h

    Q：Hydrostatic Pressure vs. Energy Conservation Equation

    Please help me to understand which ans is correct. To determine the ##P2##. $$ h_{LM}\ne 0 $$ Method 1： $$dP=\frac{\partial P}{\partial x}dx+\frac{\partial P}{\partial y}dy+\frac{\partial P}{\partial z}dz$$$$\phantom{\rule{0ex}{0ex}}\rho \overset\rightharpoonup{a}=-\triangledown p+\rho...
  27. D

    B Investigating the Impact of Chips on Packaging Pressure Differential

    Hello, I hope this is the right area to post this question. We are having a debate at my workplace and was hoping there was someone more qualified to settle the debate. We are a packaging company and have setup an experiment to test the pressure differnential from sealiong at 1800m vs. Sea...
  28. D

    B Could Nuclear Powered Bulldozers Create a Habitable Cavity for a Mars Colony?

    Digging 8km under the lowest point on Mars will get us Mount Everest conditions for air pressure. I was thinking of two ways of doing said title: Nuclear powered bulldozers working around the clock to clear away dirt on a low point on Mars such as...
  29. bigmike94

    Need help with understanding this solution (fluid pressure problem)

    So here’s the question (I am only talking about the pressure at point B, the other 2 I can understand.) And here is the solution Here is what I am not understanding, why is the pressure due to the water negative and the oil positive, and why are all measurements only made from where the...
  30. A

    Does water electrolysis work efficiently under high pressure?

    One of the stages in hydrogen production after electrolysis is to run the hydrogen through a compressor and that can take a lot of energy. Would it be possible to run an electrolysis setup inside an already high pressure hydrogen tank so that the hydrogen being separated during the electrolysis...
  31. P

    Vapor pressure -- How does water still boil at 100°C in an open pot?

    Vapor pressure is the pressure of the vapor when it is in equilibrium with its liquid. This only happens when the container where the liquid is present is closed. Indeed, when the container is open, this liquid-vapour equilibrium is never reached, because the partial pressure of the vapor (at a...
  32. C

    Solving Fluid Statics Problem: Accounting for Atmospheric Pressure

    Hi! For this fluid statics problem, One of the answers is: However, why did they assume the pressure at the top was zero? I thought the pressure at the top would be 1 atm? So tried to take atmospheric pressure into account putting 1 atm at the top, Do you please know how to get P_0A/2 so...
  33. P

    I Is RMS speed dependent on pressure?

    As it is clear from the formula for r.m.s speed ,it is only dependent of temperture for a particular gas,I think the answer should be "No change happens".But I wonder whether there is more insight to this.And is my assumption true?
  34. V

    Calculating Pressure in a Flowing Liquid

    According to what I get, the problem clearly says that ##p_2= 500 ## kPa. I can also see that ##p_1 > p_2## since higher velocity means lower pressure in a flowing liquid and we can say that ##v_1<v_2##.
  35. P

    Static hydraulic pressure in a pipe

    My Question: Two pipes filled with water and caped at one end, they have the same diameter, but different lengths. One pipe is 10 feet long and the other pipe is 1,000 feet long. At the other end of both pipes a piston applies an equal amount of pressure on the water in the pipes...
  36. C

    What is the change in internal energy after two processes?

    So the question goes like this: find change in internal energy in process 1->2 using diagram. And offered solutions a)-400J b)400J c)600J d)800J. First I found T1 and T2 using (P*V)/T=R and got T1=24K and T2=72K. Then I found n(number of moles) using PV=nRT and got n1=1mol, n2=1mol. Then I...
  37. D

    B Air pressure generated by driving at 60mph

    If I place a 5' L x 12" W open box at front and a 1/8" hole at the back of the box and drove my car at 60 mph how much psi would I generate at the 1/8" hole?
  38. O

    Converting Force Measurement to Pressure

    I have a zip-tie like structure, which when pulled, squeezes an elastic part. Think of it like a having a zip-tie around your finger. I can measure a force that is related to the squeezing pressure. This relationship between force and pressure is quite linear. I would now need to create a...
  39. G

    Reduce the pressure in an air reservoir

    TRANSITIONAL REGIME: ##\dot{V}=90\, \textrm{L}/\textrm{min}=0,0015\, \textrm{m}^3/\textrm{s}## $$\dfrac{d}{dt}\int_{VC}\rho\, dV=\dot{m}\rightarrow \dfrac{d}{dt}\rho V=\dot{m}\rightarrow $$ $$\boxed{\rho_{\textrm{air}}}\rightarrow pV=R'T\rightarrow \rho =\dfrac{p}{R'T}\rightarrow 287$$...
  40. G

    Resultant force and centre of pressure in a tank

    Figure: a) CASE A ##\rightarrow p_a=101300\, \textrm{Pa}## $$F_{\textrm{res}}?,\,\, y_c-y_{cg}=y_{cp}$$ We find ##h_{cg}\rightarrow h_{cg}=3+h## $$h=0,75\cdot \sin (30)=0,375\, \textrm{m}\rightarrow h_{cg}=3,375\, \textrm{m}$$ $$p_{cG}=\rho_{H2O}gh_{cg}=33108,75\, \textrm{Pa}$$ We calculate...
  41. Induana

    B Hydrostatic pressure in a bottle of water on ISS

    Hello, I am new in physics but I really like it so far. I have a question about hydrostatic pressure. I know that hydrostatic pressure equals (height)x(density)x(g). Am I right if I say that hydrostatic pressure in a bottle of water on ISS (state of weightlessness) will be zero ? Thank you for...
  42. samy4408

    About the binding of O2 to Hemoglobin molecules

    Hello, I just learned about the binding capacity of Hemoglobin (Hb) and that it is proportional to the partial pressure of O2 in the blood here is the curve : it does have a sigmoidal shape, but here is the problem: in the lecture, it's said that Hb has an increasing affinity to O2 the more...
  43. S

    Hydrostatic pressure at a point inside a water tank that is accelerating

    I draw this diagram: The formula for hydrostatic pressure is: ##P=\rho g h## so I just plug everything $$P=1000 \times 9.8 \times 0.1=980 Pa$$ Will the acceleration of the cart affect the hydrostatic pressure? Another thing that came to my mind was there would be extra force coming from...
  44. M

    A Calculate work done by a time-dependent pressure to a spherical hole

    Hello, Suppose I have a spherical hole in a elastic infinite space. I apply a time-dependent pressure to the inner surface of the spherical hole. I know p = f(t). If I only consider this as an elastic problem, no failure happened, how can I calculate the work done by p during the time from 0...
  45. N

    Effects of extreme pressure on materials

    This is a project I gave myself at work, really just to improve things. It didn't come from above but from myself. However I went the route of biological and computer sciences not engineering. Without going into excruciating detail essentially a plastic "tube" will be going into an oil well...
  46. Superlieutenant1

    Physics of Blood Pressure and Blood Energy

    Hello I am a physiology student who is curious about the physics underyling blood flow and pressure. I have taken physics classes however at the elementary level the focus is on ideal fluids in systems with no friction. I would appreciate any answers or if you could point me in the right...
  47. M

    A Calculate the work done by pressure rupturing a spherical containment

    I am post-processing a simulation. A spherical is meshed by many little triangles. A time-dependent pressure (p=10*t) is equally applied to the inner surface of a spherical in the normal direction all the time. After t1=0.1s, the spherical is broken, and each little triangle is disconnected...
  48. Sphere

    B Why does increasing the height of a water tower increase water pressure?

    Hello, I was wondering, for a fixed amount of water, why when the height of a water tower increases, the water pressure at the outlet of the pipe at the base of the tower increases ? I have often read on the internet that it would be caused by the weight of the water above the water at the base...
  49. Z

    How to solve for face pressure on Roller 3 using the force pushing 1

  50. S

    Engineering Looking for calculations I could apply to a vacuum-forming machine

    So far I have determined the evacuation time, a basic heat transfer between the heating element and plastic sheet, and a hold down force of the forming bed.
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