Force per unit area.

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2k views

What is the difference between stress and pressure?

What is the difference between stress and pressure? Are there any intuitive examples that explain the difference between the two? How about an example of when pressure and stress are not equal?
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2answers
112 views

Can an extremely small force lift a mountain in a hydraulic system? If not, then why not?

As you see in the picture, a car can be lifted with a small force F1. Here it is shown that 'F1 . A1 = F2 . A2'. What will happen if A1 is of the size of a pin's cross-sectional area. Can a child ...
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1answer
424 views

A water balloon in vacuum: does it boil?

If I put water in a vacuum it will boil. But what if I put this water inside a balloon ? I searched for answers and fount this video: http://www.youtube.com/watch?v=9q8F3ClUuV0 It seams that the ...
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1answer
50 views

How does pressure influence temperature in liquids?

Lets say we have a tank with a fixed mass of liquid at atmospheric pressure and room temperature. How do we influence the temperature when we exert pressure (e. g., with a piston) on the liquid? Are ...
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4answers
375 views

How does a dive computer calculate depth?

Depth is linked to pressure and water density. All depth gauges measure pressure. But is density also considered? And how? Specifically, I'd like to know: Is temperature measured? Is salinity ...
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1answer
243 views

what will happen when I continuously heat a closed heavy iron box half-filled with water?

I mean what will be the situation inside? All water vaporized, Equilibrium, Temperature-pressure situation.. boiling point increase/decrease? Thanks for your time.
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3answers
658 views

Why isn't pressure a measure of energy?

Hey guys, I'm having a problem in understanding the 1st Law of Thermodynamics. If i would increase the pressure of a closed system by compressing a gas in a cylinder isothermal, the 1.Law states, ...
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1answer
52 views

Could you blow up a barrel (closed container) using a straw and water?

Imagine you fill up a barrel with water (or any other liquid) dig a small hole at the top and place a sufficiently large straw in it, so that there is no pressure loss or anything. Then you start to ...
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1answer
208 views

Will the “Vacuum Wine Saver” suck the bubbles out of Champagne?

The "Vacuum Wine Saver" comes with the following "warning": Not for sparkling wines Intuitively and naively, I imagine that the bubbles (or the "bubble-potential"—my made-up terminology) will be ...
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3answers
559 views

A question on Bernoulli's principle

Which is more appropriate regarding Bernoulli's principle fast moving air causes low pressure or lower pressure causes fast moving air.
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1answer
1k views

How thick does steel have to be to be able to withstand 300 bar (sphere)

How thick does the material in a sphere have to be to withstand the (inner)pressure of 300 bar if the material is steel? (With an inner-radius of 2cm) Atmosphere pressure = same as 0 meter above sea ...
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2answers
439 views

Atmospheric pressure inside a rigid vessel

On a macroscopic scale one can explain the atmospheric pressure by the weight of the column of air over a given small area. If you enclose this air in rigid vessel (for example by pressing together ...
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4answers
70 views

Basic buoyancy question

If I have a cup of water filled with air at the bottom of a pool, then when the cup is "upside down" the air doesn't leave because the water pressure is pushing it up against the top of the container. ...
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2answers
289 views

The Soda Can and air pressure experiment

Yesterday, I made an experiment. I filled an empty (but contains air) soda can with a little bit of water. Then I turn on fire at the sides of the soda can so that the water starts boiling. Next, I ...
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1answer
98 views

Distribution of pressure inside a capsule

How would pressure of an ideal gas be distributed over the inside of a capsule (a cylinder with semi-spheres on the ends)? What about the strain on the material? Is there a general formula for how ...
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1answer
2k views

Calculate mass of air in a tyre from pressure

How can one calculate the mass of air inside a tyre, given a particular tyre size; a pressure, in $kPa = \frac{1000kg}{m\cdot s^2}$; and assuming room temperature, and normal air composition? I can't ...
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2answers
882 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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1answer
149 views

Non-Dimentionalization of equations

I am trying to understand a paper in which they mention; " We non-dimentionalize the problem hereafter by selecting mass, length and time units such that the fluid density $\rho\equiv1$ the ...
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2answers
64 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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1answer
48 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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1answer
118 views

How does air escape from a pneumatic tire?

Obviously, it is caused by the difference in pressure between the inside of the tire and its surrounding environment; but how specifically is the air escaping?
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1answer
333 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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1answer
198 views

Is pressure invariant under Lorentz transformations?

In an article from the reference there are following words (page 2): "...pressure P is a Lorentz invariant... the result follows from standart properties of the relativistic stress-energy tensor...". ...
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1answer
644 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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2answers
244 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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2answers
750 views

Is it possible to calculate atmospheric pressure if given temperature (F) and elevation?

I am working on a report at work and need to determine the atmospheric pressure for small intervals over a 24 hour period. Searching Google, I've found charts which give a base pressure of 14.65 psia ...
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2answers
145 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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2answers
244 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
220 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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1answer
62 views

Pressure change due to fan removing air from a non-airtight room

The following problem occurred to me today: Suppose a $100\mathrm{cfm}$ fan is pushing air out of a large room which is airtight except for a $10 \mathrm{cm}^2$ hole. The air pressure outside the ...
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2answers
161 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
269 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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1answer
4k views
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2k 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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1answer
446 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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1answer
164 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
15 views

Decompression speed (rate)

I've heard that decompression speed or rate in which the gas will leave the greater pressured container is equal to the speed of sound. For example, if the spacecraft gets damaged the air cannot exit ...
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1answer
51 views

Water Pressure Calculation for a volume of water at a given height

I'm looking to create a rain harvesting system. I have a 275 gallon IBC tote that is 48" x 40" x 46". I have an adapter for a 3/4 garden hose at the bottom of the IBC tote. I'm trying to figure out ...
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1answer
29 views

maintaining atmosperic pressure on mars

how would mankind be able to maintain an earth like atmospheric pressure on mars since mars only has 1/3rd the mass? I am not, nor have i ever attended college, but am very curious.
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2answers
68 views

Temperature of ideal gas after volume increases in piston

A three part question, all related Part 1. My question is about an ideal gas in a rigid container with two (equal volume) compartments separated by a rigid wall. One compartment has an ideal gas at ...
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2answers
34 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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2answers
130 views

Why doesn't our body gets crushed due to the atmospheric pressure? [duplicate]

The atmospheric pressure is 101325 Pa,which is good enough to get our bones crushed.But why aren't we crushed due to it?
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1answer
63 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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1answer
85 views

Why does a microphone membrane only measure pressure and not particle velocity?

Microphones (e.g. condenser microphone) are assumed to have a voltage output proportional to the sound pressure at the diaphragm. If the operating principle is that the voltage output is proportional ...
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1answer
75 views

Inward Pressure of Gravity

We are looking at White Dwarfs in Quantum and specifically how they are stabilized between gravitation pressure inwards balanced by the Fermi pressure due to electrons. To start the problem off ...
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1answer
69 views

How to caculate the pressure of a fluid when there is no gravity

Well for example we put a ball filled with water, with a density of $1\cdot 10^3 kg/m^3$, in space. How to calculate the pressure the water is exposed to?
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1answer
90 views

Energy conservation at a the end of a hose pipe?

I am trying to figure out the energy balance at the end of a hose pipe with water pouring out. Applying Bernoulli's equation inside the pipe we have three energy terms: Kinetic energy, "pressure" ...
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1answer
235 views

Is temperature-induced change in the volume of balloons dependent on gas?

Which balloon will have higher relative change in volume, helium balloon immersed in liquid nitrogen or air balloon immersed in liquid nitrogen? Since volume is directly proportional to temperature ...
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3answers
150 views

How does a pressure suit work?

I recently learnt that a suit called pressure suit is worn by fighter plane pilots to prevent red-outs and black-outs. And it seems to be work by - "..applying pressure to selective portions of ...
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1answer
115 views

Vacuum to hold an object

How can i check and calculate if a certain vacuum pump can hold an object that weights X kg? By "hold" I mean not let that object fall to the floor due to gravity