Force per unit area.

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1answer
26 views

What happens to the gas in the container in this picture when the container is tilted

So the test question asked what would happen to the gas if this container were tilted on its side. The piston shown here is 10 kg and moves frictionlessly. I said that the pressure inside the ...
-1
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0answers
10 views

Partial and total pressure of gases? [on hold]

The problem statement, all given variables and data A gaseous mixture made from 10 g of oxygen and 10 g of methane is placed in a 10 L vessel at 25°C. What is the partial pressure of each gas, ...
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0answers
12 views

What is the physical explanation for the phase relationship between acoustic pressure and particle velocity in plane and spherical waves?

I've been looking around for a decent physical explanation of the differences in the phase relationships between acoustic pressure and particle velocity in different types of waves. Mathematical ...
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2answers
33 views

Dynamic water pressure from flow and diameter

I've to test some fire hydrants and need to get the dynamic pressure. For that I know I can use a Pitot tube but... I don't have. After Googling a lot, I found two formulas allowing to compute the ...
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2answers
230 views

How does train back draft work

Quoting platforms and stations : Fast trains can create a vacuum called a ‘back draft’ that can blow you over or suck you under a train. How does that work ? I thought that the volume of air ...
3
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2answers
93 views

Could Dust Equation of State have some negative pressure?

Traditionally the cosmological equation of state of cold matter (so-called dust) is simply: $$p = 0.$$ But, in Newtonian terms, each particle is gravitationally attracting every other particle. ...
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0answers
20 views

Equation of acoustic pressure in moving fluid: derivation

I'm looking for a detailed derivation of the equation of acoustic pressure with harmonic time dependence (of type $p(t,{\bf r}) = \psi({\bf r})e^{i\omega t}$) in moving fluid and under assumptions ...
2
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1answer
48 views

If hot air expands in all directions why is the balloon moving up?

A balloon is moving up. The hot air inside the balloon is expanding in all directions and cold air outside the balloon acts with force on the balloon from all directions (higher pressure force). Why ...
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0answers
9 views

How to determine the pressure of the moving water at the bottom of a vertical pipe [closed]

Water is flowing upwards in a vertical pipe with an inside diameter of 0.06 m at a velocity of 0.0152 m/s. The length of the pipe is 0.5 m. What is the pressure at the bottom of the pipe? Density of ...
3
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1answer
41 views

How to design windy area - what variables?

When you're walking around malls or parking structures, or a building corner, you'll sometimes notice areas with consistent windiness. I was wondering what positions, angles, wind direction, ...
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1answer
542 views

Why can I see my breath after I pop my ears?

I have this weird but reproducible thing that I can see my breath for less than a second even in hot/humid weather. The key to do that is to pop my ears - I have to do that often, it's like I'm on a ...
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2answers
27 views

Why does an increase in pressure raise melting point?

I've heard that if you increase pressure in a system that has ice in it, then its melting point will increase. However, I would've thought that it would decrease the melting point as the ice would ...
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1answer
25 views

Do different density objects in liquids affect net weight [duplicate]

I would test this but I have no tools to test it with. If I have a beaker of water and weigh it on a measure. Then I stick my fingers in the water (it doesn't over flow) does the weight change or ...
2
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0answers
24 views

Simple gas in cylinder modeling

I want to do a simple (physically plausible but not physically accurate) simulation of a gas in a cylinder as it works on or is worked on by a piston. Wikipedia gives a good example of an adiabatic ...
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1answer
56 views

Definition of pressure in Bernoulli's principle

I have a difficulty to understand Bernoulli's Principle which states increased fluid speed decreases the pressure. But in a wind tunnel when we measure the pressure with a pitot tube, both the ...
9
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2answers
504 views

When blowing air through a tube, why does it act differently if I press the tube against my mouth, or hold it an inch away?

So I have a tube of wrapping paper. It's at least a couple of feet long and maybe two inches wide. If I press one end of the tube firmly against my mouth and blow, I barely feel warm air come out ...
3
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1answer
41 views

Sound pressure and velocity pressure concepts vs loudness

Here is my understanding and question: Atmospheric pressure is around 101325 Pa. Our ear drum is exposed to this pressure from both sides so total pressure is zero. But when we hear sound, ear drum ...
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0answers
135 views

Pressure and Buoyancy [closed]

It is well known that you can trap water in a drinking straw by placing the tip of your finger over the top while the straw is in the water, and then lifting it out. The inner diameter of the straw is ...
3
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0answers
41 views

How would water drain out of a sealed pipe?

While hiking through the Grand Canyon, I started wondering. Say we have a pipe for the purpose of transporting water across a canyon, with the bottom submerged in a pool of water. Like the blue line ...
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2answers
43 views

U.S. Standard Atmosphere

My textbook states that "Ideally, we would like to have measurements of pressure versus altitude over the specific range for the specific conditions (temperature, reference pressure) for which the ...
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2answers
53 views

Why there is no pressure regulator on helium/hydrogen tanks?

So I've had people filling party balloons for me with helium tanks which had no regulators. Lately I've also seen local meteorologists filling large weather balloons from hydrogen cylinders (180 atm) ...
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0answers
48 views

How do I enforce the no-slip boundary condition in time dependent incompressible pipe flow?

This is a technical problem which must have been solved already. It won't be in beginners textbooks but there should be a solution somewhere. I welcome reading suggestions. Maybe someone with ...
1
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1answer
57 views

How to measure the pressure on the walls of a potential box by a particle inside?

Consider a quantum particle inside a 3D potential box. One can compute the pressure that it exerts on the walls, it's OK. But what puzzles me is how do we actually measure such a pressure? If we take ...
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1answer
39 views

Why is water vapor released when an empty water bottle is squeezed?

I recently came across this tutorial and wondered why vapor will come out when the cap comes off. Heres the Tutorial
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0answers
38 views

Static,total and velocity pressure at a point

I have a past exam question that I am stuck on. $200$m$^3/s$ of air is entering a shaft of $5m$ diameter, the density is $1.18$kg/m$^3$, and I have shock loss of factor $X=.5$ I want static, ...
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2answers
53 views

25 cm of vacuum correspond to what pressure?

I the following (american) test Vacuum testing consists of placing samples from the packiging operation into a jar filled with water. A lid is placed over the samples to fully immerse them in the ...
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0answers
38 views

How to get the pressure? [closed]

A system of solar panels are fixed on top of a large water tank of height $40m$ and area $10m^2$. Atmospheric pressure is $100kPa$. What is the pressure at the bottom of the tank? The density of water ...
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1answer
17 views

Does the pressure in a pressure tank depend on the amount of air?

I have a pressure tank which is filled with water and air. What want to know is: if I change the ammount of air in the tank would the ammount of water that leaves the tank, when pressurized, change? ...
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0answers
30 views

Why does the perforated tin foil on a shisha pipe rise when smoking?

Imagine this setup (just without the windguard): When applying negative pressure at the hose, I can observe the perforated tin foil separating the charcoal from the bowl rise a few millimeters, ...
22
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7answers
3k views

Does car tire pressure change with weight of car load?

Does tire pressure measured by a meter on tire gauge change with load? (I am not interested in pressure produced by car tires onto the road). Car spec usually says "inflate to 220kPa normal load, ...
3
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2answers
208 views

How to calculate pressure loss due to water leakage from a hole in a pressurized unit

I am trying to develop a method for calculting the rate of pressure loss from a small hole in a pressurized vessel full of water (small air pocket likely at top of vessel). I've found a formula for ...
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1answer
25 views

Variable area manometer duct

How does one measure the pressure at the end of the manometer tube when the manometer tube itself is having a variable area?
5
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1answer
79 views

Titanic Question

I was reading this question: Was Titanic's captain's decision correct? @oakad commented about a Russian vessel keeping itself afloat by going in reverse, using hydrodynamic pressure to keep ...
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2answers
71 views

Breathing Air Underwater From A Car Tyre

I've seen in many movies and programs the event where a car plummets off the road and in to a body of water, sinking rapidly. The car slowly fills with water as it sinks and the occupant(s) don't ...
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1answer
79 views

Simple expression for transitional pressure force

Consider a simple, circular orifice with an upstream, high gas pressure and downstream, normal atmospheric pressure. Consider also a flat circular plate that can be positioned anywhere along the ...
3
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0answers
25 views

Is there a material with non-monotone density dependence on pressure?

Is there a material with such non-linear effects (including chemical reactions, phase transitions etc ...) so that there would be range where pressure increase would yield density decrease? What ...
2
votes
1answer
144 views

Calculate flow rate of air through a pressurized hole

I was wondering about this: If there is a pressurized container, like a tank of compressed air at some pressure that is greater than the ambient air pressure, and this tank of air has a hole in it, ...
0
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2answers
45 views

Given a slanted pipe

Question: I have a pipeline that is tilted. I know the length of the pipeline, and the pressure (90psi) that is felt at the very bottom. I'm trying to find out how much liquid has leaked out if the ...
3
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1answer
45 views

Pressure at a bend in a pipe

This is a question from a study guide for a military officer exam: I have fluid flowing through an elbow in a pipe (the elbow is in the shape of an upside down and backwards "J") and the flow goes ...
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2answers
116 views

Relations between pressure and temperature

I have several questions concerning thermodynamics and I order them in 4 points that may be related: What's the difference between heat and work at the atomic level? Isn't heat simply work between ...
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2answers
94 views

Why can I move through air?

Forgive me if this a simple question with an obvious answer I can't see. I was thinking about pressure and air pressure and how we have thousands of pounds of air pressing down on us. What I'm ...
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2answers
61 views

Why do liquids boil when their vapor pressure equals the ambient pressure?

Given that the boiling point of a liquid is the temperature at which the vapor pressure is equal to the ambient (surrounding) pressure, what significance does a liquid's vapor pressure have in the ...
5
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1answer
57 views

Why do some pressure cookers initially leak

Why do some pressure cookers initially leak steam from the sides and after a while settle down and don't leak? Is it a positive feedback mechanism from the building steam which makes the sealing ...
7
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1answer
769 views

Do we breathe air by creating a vacuum?

How do we suck air into our lungs, are we generating a vacuum?
2
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2answers
79 views

Do we hear sounds differently on the highest mountains?

Some searching gives that above 6,000 meter altitude the air density is less than half of that at sea level. Speed of sound is about 15-20% slower and "acoustic impedance" seems to change too. Do ...
0
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1answer
46 views

hydraulic scissor jack lifting capacity

Can you please assist with a really simple question? I have a hydraulic scissor jack table with the following: 2 hydraulic cylinders, each with a cylinder stroke of 240mm, a cylinder bore of 50mm ...
3
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2answers
62 views

Why doesn't water in water barometer boil?

I have read that the pressure in a water barometer at the top of the water column is around 0.5 psi and at such low pressures water should boil at around ~26°C (Room temperature). [1] [2] How ...
2
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1answer
35 views

Effect of aircraft speed on barometer

Many aircrafts depend on several types of static pressure sensors (barometers) to find the altitude. I assume this sensor need to be located outside the aircraft main body, so that it has a contact ...
3
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4answers
494 views

Calculate water flow rate through orifice

I'm not very good with fluid physics, and need some help. Imagine the following setup with water contained in-front of a wall with an opening on the bottom: How do I calculate the water flow $Q$?. ...
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1answer
100 views

Calculation of pressure from flow rate of water

Anybody kindly help me to find how to calculate pressure in bar from flow rate. I have a pipe and from that I am transferring water at a constant flow rate of 5ml/min. At this flow rate, with a 0.5 cm ...