# What is Pressure difference: Definition and 75 Discussions

Pressure measurement is the analysis of an applied force by a fluid (liquid or gas) on a surface. Pressure is typically measured in units of force per unit of surface area. Many techniques have been developed for the measurement of pressure and vacuum. Instruments used to measure and display pressure in an integral unit are called pressure meters or pressure gauges or vacuum gauges. A manometer is a good example, as it uses the surface area and weight of a column of liquid to both measure and indicate pressure. Likewise the widely used Bourdon gauge is a mechanical device, which both measures and indicates and is probably the best known type of gauge.
A vacuum gauge is a pressure gauge used to measure pressures lower than the ambient atmospheric pressure, which is set as the zero point, in negative values (e.g.: −15 psig or −760 mmHg equals total vacuum). Most gauges measure pressure relative to atmospheric pressure as the zero point, so this form of reading is simply referred to as "gauge pressure". However, anything greater than total vacuum is technically a form of pressure. For very accurate readings, especially at very low pressures, a gauge that uses total vacuum as the zero point may be used, giving pressure readings in an absolute scale.
Other methods of pressure measurement involve sensors that can transmit the pressure reading to a remote indicator or control system (telemetry).

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1. ### 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...
2. ### 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. ### Measuring Pressure on a Concrete Table

Hi guys, I am not doing homework, it is just suddenly brainstormed this question. What if I place a very small mass like 10kg on the center of a concrete 10m*10m flat table supported by the ground, then how to measure the surface pressure acting on the center and right on the edge? Or the...
4. ### Chimney effect and pressure difference

Kind of similar question was once on polish high school ("matura") exam, and the solution that the authors gave was: Pressure at the bottom of the chimney inside of it is ##p_{top}+\rho_1gh##, and outside ##p_{top}+\rho_2gh## where: ##p_{top}## is the atmospheric pressure at the height of ##h##...
5. ### Working out steam velocity with only pressure difference

I am currently doing an assignment on nuclear power and in the turbine, the steam is moving from pressure of 6Mpa to 0.008 Mpa. is there any way to work out the velocity of the steam when moving between these pressure differences?
6. ### I Volume of water consumed by vacuum

I'm trying to do the math for a backyard thermodynamic pump experiment, and getting stuck. Suppose an empty 3.79 liter container was airlocked by a vertical 25 cm long empty tube whose end sits at the top of an unlimited supply of water in a basin. The tube protrudes through the container such...
7. ### 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)...
8. ### 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...
9. ### I Was the recent ISS leak imminently dangerous?

The ISS suffered a leak apparently caused by a 1/8 inch hole left during manufacture and never repaired. On Quora, the claim has been made that such a hole with one atm of pressure difference would only cause 324 cu ft of air to rush out per hour. I don't think this is close to correct, but I am...
10. ### How long will it take for compressed air to reach 29 psi?

A large tank filled with air is compressed to 49 PSI. A valve is open and air escapes through the hole (d = 0.04 ft) to the atmosphere. How long will it take for the compressed air to reach 29 PSI. Assume constant temperature. Not exactly sure how to approach this problem since the flow rate...
11. ### Euler's equation pressure difference

Homework Statement I am after PC - PA However I must do so without breaking into components. My problem has different values L=3 H=4 SG=1.2 downward a = 1.5g horizontal a = 0.9g and my coordinate is conventional positive y up and positive x to the right cos##\theta## = 3/5 sin##\theta## =...
12. ### Pressure Difference: F=10 Tonnes, A=100 sq m - Calculate & Understand

Homework Statement [/B] A ceiling can blow off due to pressure difference between the inside and outside of the house. In a magazine, it said: "Let's have a ceiling of 100 square meters. A pressure difference of 1% of the air pressure between the two sides of the ceiling is equivalent to a lift...
13. ### How does a pressure/temperature difference cause a force?

Hello. I am inquiring about how a pressure difference between a hot room (roughly room temperature) and a cold room (roughly the temperature of a standard refrigerator) can cause a force inside the cold room when exposed to its hotter counterpart. More specifically, I would like to apply this...
14. ### Calculating pressure / energy difference confusion

Homework Statement The electron density per area, ##N## for a gas layer of thickness 10 cm can be determined $$n = k \times p \times 2.47 \times 10^{19}$$ For each adjacent sets of pressure data using Matlab, calculate the average energy in keV, the pressure difference in hPa, the energy...
15. ### Calculating Power of a Water Pump: Enthalpy vs Pressure Difference

Trying to calculate the power of a pump, it's pumping water. It has a flowrate in and out in kg/s. Surely I should look up the enthalpy values and just mutiply with the flow rate to get power in kW. However I know that if I convert flowrate to m3/s by dividing 1000 and multiplying by the...
16. ### Venturi meter pressure difference

Homework Statement Homework Equations p=ρgh Q=A1U1=A2U2 Bernoulli: p1+½ρU12+ρgz1=p2+½ρU22+ρgz2 The Attempt at a Solution [/B] So I got that the pressure difference is gh(ρm-ρ). So I rearranged Bernoulli for p1-p2 to get (assuming the potential is the same I eliminated it)...
17. ### Bathtub Vortex Pressure difference

The problem statement Example 1 A single particle I have a particle being forced by a radial centripetal force onto a smaller radius $$l_1=m_c.v_1.r_1$$ $$L_1=L_2$$ $$L_2=m_c.v_2.r_2$$ $$m_c.v_1.r_1=m_c.v_2.r_2$$ $$v_1.r_1=v_2.r_2$$ $$v_2=v_1\frac{r_2}{r_1}$$ Its increase from ##v_1## to...
18. ### Calculate pressure difference in current-carrying mercury

Homework Statement A vertical column of mercury, of cross-sectional area A, is contained in an insulating cylinder and carries a current I0, with uniform current density. By considering the column to be a series of concentric current carrying cylin- ders, derive an expression for the...
19. ### Calculate the pressure difference between two points

Homework Statement Need to find the pressure difference between the two water pipes. Specific gravity of water = 1000 kg/m^3, specific gravity of oil = 800 kg/m^3[/B] Homework Equations pressure = height * specific gravity * gravitational acceleration The Attempt at a Solution I think that is...
20. ### Pressure Difference: Is the Solution Wrong?

Homework Statement is the solution given wrong ? from the bernoulli's equation , (PA-PB) / ρg = hf + ZB - ZA , am i right ? P/s : the Velocity at A and B are the same , so they cancel each other ... but in the solution , the author gave (PA-PB) / ρg = hf + ZA - ZB which is 18.27 +40 , IMO , it...
21. ### Pressure Difference: Why Ignored at P1 & P2 in Energy Eqn?

Homework Statement why the author ignore the pressure difference at point 1 and point 2 in the energy equation ?pressure at pont 1 must be higher than pressure 2 , right ? as the height of P1 is higher Homework EquationsThe Attempt at a Solution
22. ### Calculating Pressure Difference w/ Bernoulli Law for Bay Inlet

I have a container with one inlet and one outlet. I have the area of the inlet, Ai, velocity vi of the air coming in, and mass flow mi (assume a plane with an air inlet to a bay). I don't know anything about the outlet (just that there is one). What I need to do is calculate the size of an extra...
23. ### Pressure Difference measurement using Pressure Sensors / Transducers

Dear All, I am not sure if this is the right place or not for this post so i apologise in advance if not. I am trying to find some pressure sensors / transducers to measure the pressure difference (with respect to static pressure) at points on a circular cylinder model installed inside a...
24. ### Fluid Dynamics Question - Pressure Difference in Horizontal Pipe

Homework Statement The Trans-Alaska Pipeline System (TAPS) carries around 100,000m3 of oil per day from the Northern Alaskan oil fields to the nearest ice-free port of Valdez, around 1300km away. The pipe has an outer diameter of 1.22m and a wall thickness of 12mm. Eleven pumping stations...
25. ### Calculating CFM due to pressure difference

I am working on plans for a portable air motor system, to power a scooter discretely. The motor I have picked out is a Gast 1UP-NRV-15, which is a vane-style oil-less motor, with the following specifications: 6000RPM (628 radians/second) Max torque 0.68 Newton-meters @ 1000RPM (6 in.-lbs) 373...
26. ### Help with measure air flow rate with pressure difference in a cylinder

Hi, I've got a horizontally moving piston in a pneumatic cylinder, the piston is moving backward to suck the air into the cylinder from a hole at one end, this will lead to an air flow rate. I would like to measure the air flow rate at that instant. I was thinking of with a pressure sensor...
27. ### Suction force and pressure difference

I am doing a study to see whether suction force can act as a mechanism to compress air. Let's say I have a normal syringe, which consist of the small cylindrical tip at the top of syringes where you attach the needle. Then there is the larger middle barrel for the liquid, medication, etc. Lastly...
28. ### Pressure difference in decreasing diameter tube

Homework Statement Helium at 20°C passes through a pipe with an initial diameter of .3 meters decreasing to .25 meters. The helium flows at .30 kg/s and an initial pressure of 200 kpa. Find the difference in pressure ΔP across the decreasing section. Assume incompressible and inviscid flow...
29. ### Questsion involving pressure difference due to submarine diving

Homework Statement A submarine maintains 100 kPa inside it and dives 250 m down in the ocean having an average density of 1030 kg/m^{3}. What is the pressure difference between the inside and the outside of the submarine in kPa?Homework Equations The Attempt at a Solution I am quite confused...
30. ### Pressure difference when height changes

Homework Statement Calculate the difference in pressure (in atmospheres) that the blood vessels in a giraffe's head have to accommodate as the head is lowered from a full upright position to ground level for a drink. The height of an average giraffe is about 6m. (Note I'm currently only...
31. ### Air pressure difference between floor & ceiling

Can't figure out how to get my digital manometers to read the pressure difference between the air near the floor vs. at the 8' high ceiling. It reads 0 IWC no matter how I do it. One of my instruments is a micromanometer (reads as low as .001 IWC pressure differential), and it reads 0 IWC...
32. ### Pressure difference in a horizontal constant area pipe

Homework Statement see attachment Homework Equations not sure if these are applicable because i don't think its steady state anymore mass flow in=mass flow out sum of forces in x direction= rate of momentum in-rate of momentum out bernoulli's p+0.5ρ(v^2)= constant The Attempt at a...
33. ### Creating electricity through pressure difference

Now i am a refregration apprentice so by know means am i qualified or mabe have no idea what i am talking. now i belief that by heating a gas you increase the pressure it is putting on the object contianing it and by cooling it you reduce that pressure. So is it possible to cool the gas at...
34. ### Pressure difference between two bulbs measured by a mercury manometer

The setup is a particular gas thermometer constructed of two gas containing bulbs, each of which is put into a water bath on adjacent sides. The pressure difference between the two bulbs is measured by a mercury manometer. Appropriate reservoirs maintain constant gas volume in the two bulbs...
35. ### Poiseuille's law - Need help determining pressure difference

Homework Statement The problem is if i have a barrel of water, and at the bottom there is a pipe sticking out going horizontally (leading to an open end), how do i determine the pressure difference?. I think I am right in saying the pressure at the end of the pipe would be pressure from the...
36. ### Bernoulli's principal and pressure difference due to altitude

Bernoulli's principal states that as velocity of a fluid increases, the static pressure decreases. I wonder if the reverse order can also happen. For example, if there is a pipe laid on the side of a mountain that is 3000 ft high. The bottom end of the pipe would be exposed to pressure at sea...
37. ### Calculating Pressure Difference Between Sections 1 and 2

Trying to calculate pressure difference between sections 1 and 2. 1=32mm 2=20mm density = 1000 kg/m^3 I have done P1-P2 = 1/2 density x (vi^2 - vj^2) Is this right? How do I now find head loss if difference between 1 and 2 were 45mm ? 45/density x gravity ? Thanks,
38. ### Venturi tube help needed in determining pressure difference

Homework Statement Water flows through venturi tube at 0.3 litres/s. Diameter of venturi tube is 32mm to 20mm to 32mm and the water density is 1000kg/m^3. Homework Equations a) Assuming head loss is neglible, what is pressure difference between 1 and 2. b) If pressure head...
39. ### Resultant Force and CP of Window @ -40C

Problem States If the air pressure inside the plane is atmospheric, what is the resultant force on the window (assume a rectangle) and where is the CP if the outside air temperature is -40 C. Ideal gas law, P = ρRT Window is 350mm * 450mm My work P inside = Atmospheric = 101325Pa Pc...
40. ### Calculating Pressure Difference for CFM & Hole Size

Hey its been a while since I took thermo and I am pretty rusty. I am trying to figure out a system with differential pressures. I can find the temperature difference pretty easy but finding the exact pressure difference is a bit more complicated then I remember. Situation: I have a small...
41. ### Pressure Difference in Test Tube w/ Air Flow Rate

lets say if i have a test tube (diameter 3cm and height 30cm) seal with a rubber. in the test tube there 100ml of water = around 10 cm height. if air was flow into the test tube with flow rate around 20L/min, and after a few sec, the rubber was push out. in general i understand that the pressure...
42. ### Calculating Pressure Difference in Two Tanks

Homework Statement Two tanks, one containing SAE Grade 30 oil (density of 890 kg/m3) and the other containing carbon tetrachloride (density of 1,590 kg/m3) , are connected through a differential manometer as shown in the figure. Calculate the pressure difference between chambers A and B...
43. ### How does the pressure difference over a NACA 0012 affects its characteristics?

I wanted to know how does the pressure difference (on the upper and lower surface) affect the performance of the airfoil? That is, if the pressure difference is high/low, how does that affect the characteristics of the airfoil, taking naca 0012 as example, for increased angle of attack, the...
44. ### Is this a reasonable approach to calculating pressure difference?

Homework Statement What is the pressure difference between points A and B (point where glycerol and air heads meet) in the picture, if d1 = 0.50 meters, d2 = 0.25 meters, and d3 = 0.71 meters and d4 = 0.86 meters. (ρH2O= 1.00 x 10^3 kg/m^3, ρgly = 1.25 x 10^3/m^3)...
45. ### Pressure Difference to Make Blood Flow Thru Artery

Homework Statement What is the pressure difference required to make blood flow through an artery of inner radius 2.0 mm and length 0.18 m at a speed of 5.6 cm/s?Homework Equations P1-P2 = Q8nL/pi*r fourth or P1-P2 = velocity*8*viscosity of blood*L/rsquared viscosity of blood = 4 x 10e-3 r = 2.0...
46. ### Blood Pressure Difference between Aorta and Aneurysym

Homework Statement Blood flowing thru aorta (radius 1.2 cm) enters aneurysym of radius 3.1 cm. How much on average is blood pressure higher inside the aneursym than the pressure in the unenlarged part of aorta? Average flow rate of blood thru aorta is 110 cm cubed/secHomework Equations Q =...
47. ### Find out the correct pressure difference if the level of the liquid

Homework Statement The limbs of a manometer consist of uniform capillary tubes of radii 1.4 x 10^-3 m and 7.2 x 10^-4 m. Find out the correct pressure difference if the level of the liquid (density 10^3 kg/m^3 and surface tension 72 x 10^-3 N/m) in narrower tube stands 0.2 m above that in the...
48. ### Flow rate calculation using pressure difference and time

I am a second year engineering student out on my first co-op work term. My supervisor's first task for me was to calculate the flow rate of one of his parts that he will use on a system that he is designing. I hooked up the part to a compressed nitrogen tank initially at 6,000psi. I cracked open...
49. ### Pressure difference in two pipelines

Homework Statement A water manometer is connected to the wall of two pipelines in order to measure pressure difference between the pipes. Manometer shows a 0.5m height difference, pipe B is 3m higher than pipe A. Find pressure difference between pipes...
50. ### Work Done by Air pressure difference

Work Done by Air "pressure difference" Homework Statement Air that initially occupies .14 m^3 at a gauge pressure of 103.0kPa is expanded isothermally to a pressure to 101.3 kPa and then cooled at constant pressure until it reaches its initial volume. Compute the work done by the air. (Gauge...