Force per unit area.

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196 views

How much pressure do wheels exert on the ground?

I would like to know how much pressure 4 "rigid" wheels (as opposed to tyres) would exert on the ground; I've been on the case for hours now and the best I've come across to calculate this was the ...
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955 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 ...
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73 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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1k 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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155 views

How can a gas support tensile stresses?

In working through a rigorous derivation of the compressible Navier-Stokes equations, I find that the momentum flux in the X-direction should be driven not only by the normal pressure gradient ...
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725 views

Pressure in Fluids,in particular horizontal pressure

I am not sure about the pressure existing in fluids.If the vertical pressure acts due to gravity and the atmospheric pressure since it also changes due to height also acts due to gravity then why is ...
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48 views

water pressure in the oceans or great lakes

Is there a way to create energy from water depth pressure? Convert the pressure to any type of energy? Does there need to be movement? Can someone comment on this process? Thanks
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78 views

Do gases have a general upper limit of density?

Is there some limit for the density of gases, at which no change in condition could make it more dense without making it fluid, or solid - or something 'in between'?
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153 views

Pressure at the front and back of a fan

I have a fan which is inside a duct. When the fan is off, the pressure at the front and back of the blade remains the same. Now when it is running, the velocity of the air below will be more because ...
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194 views

What does the absence of hydrodynamic entrance effects do to the momentum conservation Equation?

I am trying to do a homework problem where we re-write the mass, momentum and energy conservation formulas for downward flow in a vertical pipe and it says "where all hydrodynamic entrance effects ...
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1k views

Hydrostatic pressure?

What what I understand, hydrostatic pressure is the "weight" of the water pushing against objects. But if this is true, why is hydrostatic pressure perpendicular to the surface it acts on instead of ...
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1k views

Pressure in Bernoulli's equation

! I've been reading an introductory physics textbook. It has a chapter on fluids which I'm finding quite confusing. Specifically, I don't understand the meaning of the pressure terms $P_0$ and $P_1$ ...
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1k views

Water pressure on slanted wall

Water pressure is simply $pgh/2$ for a vertical wall parallel to the depth of the water at exactly the half the water's depth. Suppose the wall is tapered (angled) slightly at around 2 degrees from ...
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677 views

Water draining from a height into the bottom of a reservoir

If I hang one 5 gal. Bucket directly above another, put a hole in the bottom of the upper bucket with a tube inserted just inside hanging all the way to the bottom of the lower bucket and fill the ...
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4k views

Determine the maximum height a pump can suck up water

I am working on a homework problem that presents the scenario of trying to raise water from a small reservoir of depth 8 m whose surface is 25 m below a pump that can maintain a pressure differential ...
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2answers
213 views

What is the pressure on an empty pneumatic tube?

At the residence I'm constructing a kitchen digester. The gas is to be collected into an old bicycle/scooter tube - initially as empty as may be after wringing it out.. Will the digester (total ...
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382 views

Opposing forces on an air cylinder — half force each or full force each?

If an air cylinder is pushing two platens apart with a force of $100\: \mathrm{lbs}$, do the platens need to push back at $100\: \mathrm{lbs}$ or $50\: \mathrm{lbs}$ each to keep the cylinder from ...
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1answer
372 views

How can I estimate relative humidity ($e/e_s$) from temperature and dewpoint?

Background my goal is to estimate vapor pressure deficit ($vpd$) from Relative Humidity ($rh = \frac{e}{e_s}$): $$vpd = \frac{100 - \frac{e}{e_s}}{100} e_s$$ (from Hartmann "Global Physical ...
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211 views

Height of the atmosphere - conflicting answers

Okay. I have two ways of working out the height of the atmosphere from pressure, and they give different answers. Could someone please explain which one is wrong and why? (assuming the density is ...
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1answer
625 views

How would this rapid depressurization of water really behave?

An in-development game(Starbound) recently released a demo of their water physics. At about 39 seconds into the video, a volume of water in a container is released when the cap on the container is ...
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2k views

What is the physical or mathematical meaning of the Gibbs-Duhem equation?

The Gibbs-Duhem equation states $$0~=~SdT-VdP+\sum(N_i d\mu_i),$$ where $\mu$ is the chemical potential. Does it have any mathematical (about intensive parameters) or physical meaning?
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7k views
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3k views

When a gas expands against an external pressure of 0, must the stopper on the cylinder be massless?

Basically, I need to conceptually understand why the work a gas does is the integral $\int p_\mathrm{external}dv$ and is 0 when pressure external is 0. I understand why $\mathrm{d}w = - ...
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644 views

Given two boiling temperatures and pressures, how can I find the latent heat?

I am given the fact that at a certain pressure a liquid boils at a corresponding temperature, at a different pressure it boils at a different temperature, and then I am asked to find the latent heat ...
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184 views

In a low pressure (near vacuum), -20°C vessel, would sublimated moisture rise to the top or fall to the bottom?

If I have a strong vessel that I've cooled to say -20°C, and lowered the pressure below 0.006 atmospheres, the water in food placed inside will sublimate and freeze dry the food. But what happens to ...
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1answer
68 views

Statistical Physics: How do we derive this equation?

I'm reading through Statistical Physics by F. Mandl and there is a step in arriving at an equation that I don't follow. He uses $$P = \sum_r p_r \left(-\frac{\mathrm dE_r}{\mathrm dV} \right) ...
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62 views

Static fluid pressure does *not* depend on the shape, mass, or surface area of the liquid. Huh?

I came across this figure that I'm currently unable to accept. I've come up with a thought experiment. Please point out my error: Assume zero atmospheric pressure and no boundary effects of the ...
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31 views

Nonzero stress on crystal at equilibrium volume?

Using a first principles computational method such as DFT, you can calculate the energy of a unit cell at different volumes to obtain a parabolic energy vs. volume curve. The minimum of this curve ...
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40 views

why doesn't water in a inverted tumbler with its mouth covered with a porus cloth fall down ?

Is it due to the greater external atmospheric pressure acting upwards on the molecules or due to surface tension ?
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1answer
21 views

Does moving air suck in air from left and right of its path? [closed]

When air is made to move (e.g. by a fan) it has a lower pressure than when it is still. Essentially, this moving air should become a low pressure zone relative to the static air around it and the ...
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1answer
30 views

How can I apply a certain “pressure” (g/cm²) to the ground by dropping a weight?

I'm trying to find a way to apply 100g/cm² to the ground (substrate = snow) by dropping a weight from a particular height. If I drop 250g weight (80cm² area) from 1m, I'll get a velocity of 4.43m/s² ...
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52 views

How to calculate the pressure inside hose subjected to weight? (Example)

Example: Suppose we have a garden hose laid on a concrete floor. This garden hose is made out of rubber and is sealed on both sides. It is completely filled with water with no air bubbles whatsoever. ...
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45 views

Pressure gradients at two different sized holes separating 2 chambers at different pressures [closed]

Why is the pressure gradient by the simplified Bernoulli equation higher at the smaller hole?
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24 views

Coherence of pressure and mass flow in a pipe [closed]

What is the coherence of pressure and mass-flow in a horizontal pipe? Let's assume I have just one pipe with pressure = 1.5 bar at the input and through pressure-losses 1.2bar at the output. Is there ...
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38 views

Do liquids creep from cold to hot like gases?

Consider the U-tube water experiment below with the left red block at 10C and the right red block at 90C. I think the right level will become about 3% higher than the left level simply because hotter ...
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48 views

Volume integral of pressure interpretation

If you have a fluid with with pressure field $p$ what is the physical significance of the the volume integral of the pressure $\int_V p dV$?
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1answer
111 views

Why did my bag of chips expanded in airplane and didn't get back to normal after landing?

I bought a usual bag of chips and took the plane. In the air, it seemed that it was pretty much expanded, as if it was going to explode. I thought to myself : ok that's normal, the pressure in the ...
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1answer
43 views

Density profile in the atmosphere, which equations to use…? [closed]

I came across the following density profile in the atmosphere: ...
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1answer
40 views

How much carbon dioxide do we actually ingest from a can of coke?

On this most trustworthy page it states that a 355 mL can of coke contains on average about 2.2 grams of carbon dioxide. As far as I know, this carbon dioxide can exist in solution as carbonic acid, ...
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1answer
69 views

Putting an open can of soda into a loose plastic bag to preserve its fizz?

A friend insists that, to preserve the fizz in an open can of soda, you just put it in the refrigerator inside an unsealed plastic bag. The theory is not that the bag preserves the pressure in the ...
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1answer
98 views

Find the separation distance for a line of oil being squashed between two flat plates [closed]

I was wondering if someone could give me some help on how to start this problem, I'm really struggling to get my head around it. A long line of oil is being squashed between two flat plates of length ...
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1answer
2k views

water fountain with a pipette

if you get some hot water in a pipette an put the pick of it on the top the water will jump out f pipette and make a fountain.I wondered if any one could tell me what is the reason?
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113 views

Can you blow bubbles on top of Mount Everest?

Can you blow bubbles on top of Mount Everest? How would they be different in low temperatures and pressures?
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977 views

How do I keep the temperature constant in a Boyle's Law experiment?

I'm trying to get a head start on our lab experiment next week about Boyle's Law. The set-up is we have an air chamber can immersed in a pot of boiling water (which is kept boiling over an electric ...
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1answer
495 views

How do I calculate the maximum pressure a container can withhold?

Say I have a spherical container with a certain gas inside, heated to a very high temperature, and thus a very high pressure. The gas will exert a force radially outwards onto the container, and at ...
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1answer
37 views

sound waves and atmospheric pressure

Is it possible to use sound waves (ultrasound/infrasound or whatever) in order to make some space have lower atmospheric pressure? Or maybe another way to achieve this? I was thinking that maybe sound ...
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1answer
353 views

Determine fan sound (dB) based on its rotational speed (RPM)

I am trying to find the sound amplitude or level produced by a fan, knowing its RPM. Is there a simple formula for it? What other parameters does it depend on? Assume I have all the fan properties, ...
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3answers
233 views

Calculate pressure with the ideal gas law or $\rho gh$?

In a container the pressure on the walls due to a gas can be calculated using the ideal gas law $\bigl(pV=NRT\bigr)$. However, for a column of water, or the pressure at earth's surface due to a ...
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528 views

Direction of pressure forces on a control volume (surface)

According to http://www.mne.psu.edu/cimbala/Learning/Fluid/Pressure/pressure_basics.htm, "Pressure always acts inward normal to any surface (even imaginary surfaces as in a control volume).". ...
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134 views

Can pressure be negative? [duplicate]

From Wiki and from physics fundamentals lections I received info that pressure is scalar value. But in definition you have relation between projections of two vector values to normal axe-force and ...