Force per unit area.

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2answers
105 views

How many psi's are in one bar?

6894.7573 bar = 100000.0 psi according to google 6894.7573 bar = 100000.0001 psi according to wolfram alpha which is it? How many psis are in one ...
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3answers
143 views

How do we measure pressure above a liquid column?

Consider this point $A$, just at the surface of any liquid exposed to atmosphere. The hydrostatic pressure exerted by this liquid of height $h$ is $h\rho g$. My confusion is tha that this pressure ...
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2answers
412 views

Calculating pressure under water

Say I were calculating the pressure under 1 foot of water, in psi. I'm thinking the pressure is force per unit area, and should be equal to the force exerted by the column of water standing over ...
2
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0answers
51 views

Would Superman's flight be damaging? [closed]

I recently asked this question on the effects of Superman's sonic booms and it's become clear that Physics.SE is better equipped to answer it. I'll set up some assumptions. Superman's travelling to ...
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1answer
56 views

Boiling is not well described? [duplicate]

It is said that boiling occurs only when the vapour pressure becomes equal to the pressure surrounding the vapour (say atmospheric pressure). Why does it take place only satisfying these conditions ...
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2answers
140 views

Why is there a limited range of possible soap bubble size?

Soap bubbles are never "too small" or "too large". What defines the range of possible diameters of a soap bubble? Related questions: Why do steam bubbles increase in size as they rise, Why is the ...
3
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1answer
158 views

What is the maximum height for a puddle of water, assuming stp?

I wonder if anyone has figured this out. Assuming, standard temperature and pressure(273 K and 1atm), what is the maximum height of a water puddle on a flat surface? There might be some other factors ...
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1answer
408 views

Calculate Compressibility of water [closed]

I have 1 litre of water on 30 celsius, and there is a pressure of 10 mega psi affects on it. I want to calculate volume decrease that caused by pressure Thanks
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1answer
125 views

Lubrication Theory

Basically, I'm modelling the flow of a "coating" process -- a fluid flow between a flat moving plane and a stationary cylinder, 2D, cartesian coordinates. Subscript 0 is the at the minimum height b/w ...
2
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1answer
128 views

Fluid flow through an orifice

Forgive me for my ignorance. What would be the method to determine the pressure a non compressible fluid creates when forced though an orifice? Keep in mind this orifice does not have a constant ...
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1answer
2k views

How does a plunger (toilet plunger) work?

I don't quite understand the physic involved in operating a plunger. I thought that using a plunger on a clogged sink, for example, would create a difference in pressure inside the tube so that, ...
6
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2answers
268 views

Why don't forces on two surfaces of a fluid need to balance?

In my textbook (Resnick Halliday Krane), the derivation for pressure in a fluid at a given depth is done assuming that the fluid is homogeneous. Thus, the book concludes that the pressure in a fluid ...
6
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3answers
968 views

The physics behind Balloons lifting objects?

Apologies for the super basic question, but we all have to start somewhere right? Can somebody please explain exactly how you would calculate the number of helium balloons it would take to lift an ...
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4answers
164 views

Mathematical Reasoning for Fluid Pressure as a Scalar

This question from a while ago and answers/comments to this question from earlier today both make heavy mention of the fact that fluid pressure is a scalar. Although this information was surprising ...
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1answer
79 views

Pressure and variation in pressure due to depth

In my class, we were shown the following problem: Using the equation $P_1$ = $P_0$ + $\displaystyle\rho$gh, where $P_1$ is the pressure at Superman's mouth and $P_0$ is the pressure at the surface ...
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2answers
239 views

Direction of pressure in fluids

ok so my friend told me that in a container, the pressure exerted by the walls on the liquid in the container act in the upward direction.Is he correct ? so what I am imagining is a cylindrical ...
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1answer
38 views

Bubble pressure ascending?

In water bubbles rise up to the surface. As it rises, does the bubble's pressure decrease or stay the same? I think stays the same.
2
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1answer
48 views

Why do tires need to be inflated when the temperature changes?

Why do you need to add air to your tires when the temperature drops? The temperature inside and outside of the tire is the same (let's assume that you aren't currently driving, and your car has been ...
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0answers
31 views

Strange Spurting of Water

Yesterday, I punctured the base of a partially drunken 50cl bottle of Badoit sparkling water with a compass (the one used for geometry). For someone reason, a stream of water started spurting out of ...
2
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1answer
76 views

Effect of gravity on large tower with reduced air pressure

Suppose I built a 5km high building. The pressure of the air at the top would be around 50% compared to the pressure at the ground (I assume that the exact values don't matter in my case). Now ...
0
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1answer
156 views

Pressure inside a plastic bottle filled with water and squeezed by X weight?

I'd like to know how it'd be possible to calculate the pressure inside a plastic bottle filled with water and squeezed by say 20 kg sitting on the bottle, which is lying on its side (so that ...
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0answers
41 views

Airfield Windsock

Why don't windsocks collapse? It would seem Bernouilli would say otherwise. But we know empirically that they don't. Proof:Visit any airfield. So the air in the sock must be going slower right? I ...
2
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0answers
120 views

Calculating PSI generated by water entraining air as it flows down a pipe

This is the concept used in a trompe. Basically, the idea is that if we allow water to flow down a pipe and if that pipe has inclined air intake orifices near the top where the water enters, then the ...
3
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4answers
1k views

Why does filling a compressed air cylinder produces heat?

And the opposite follow-up question: why does opening the air cylinder makes the air cooler? What I know is that I can't find these answers using the ideal gas law, because that is an equation of ...
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1answer
61 views

Is there an equilibrium for water and air in a tank?

I'll try my best to explain my question with examples because I don't have much knowledge on the theory. So say that I had a block of water in air, a cube of water, that is dropping. If the cube ...
5
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4answers
177 views

why is the force on the side of a very narrow tank independent of the volume of water?

I building a tank for water 2ft high, 2ft wide (front to back), 8 feet long (left to right) Common formulas dictate the total force on the long sides is approx 1000lbs (w x h x .43). Where .43 is psi ...
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0answers
26 views

Distribution of refractive index of water when applied pressure wave

I was wondering when applying pressure wave, ultrasonic sound waves, under water, how I would be able to measure the distribution of the refractive index.
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1answer
1k views

Would you die before reaching the ground?

If you were to jump off a tall building, let's say Burj Khalifa, is it true that the pressure difference would be so strong as to kill you before reaching the ground?
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3answers
204 views

Why does the air pressure at the surface of the earth exactly equal the weight of the entire air column above it

Why does the air pressure at the surface of the earth (resulting from collisions of molecules on the surface of the earth which has to do with the velocity of the particles) exactly equal the weight ...
1
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1answer
2k views

Work Done in a Thermodynamic System (Cylinder with Piston) [closed]

Heated Piston A cylinder of cross-sectional area 0.0314m^2, filled with argon (a monatomic ideal gas), is sealed with a piston of mass M=25kg that is free to move up and down. The piston is ...
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0answers
415 views

Pressure required on a wing to lift a plane and the speed required to create this pressure difference [closed]

An aircraft has a single wing with a total area of A =1 2.6 m2 (assume that the thickness of the wing is negligible). When in motion, the air flows under the wing at the velocity that the aircraft ...
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0answers
46 views

Functional relationship of pressure and position(1d)

so today I started doing my research on oscillations in a course on advanced mechanics. The experiment was to mathematically model the speed of sound in air and experimentally prove the usability of ...
4
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3answers
354 views

How do gas molecules constantly bounce without losing energy?

From a related question (How does pressurized gas constantly push?), i asked myself this: How do gas molecules constantly bounce off each other without losing energy? If you drop a ball, it bounces a ...
2
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1answer
123 views

Rigorous definition of pressure in a fluid

We briefly introduced some terms at the start of my Fluids class, and one of them was pressure. I'm looking for a rigorous definition of pressure. Wikipedia gives this definition for pressure: $p = ...
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1answer
60 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 ...
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0answers
103 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 ...
2
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2answers
322 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 ...
5
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2answers
539 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 ...
4
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2answers
162 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. ...
2
votes
1answer
205 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 ...
2
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1answer
68 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, ...
4
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1answer
625 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 ...
2
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2answers
2k 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 ...
1
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1answer
260 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
101 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 ...
0
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2answers
174 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 ...
10
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2answers
833 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
votes
1answer
86 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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1answer
250 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
102 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 ...