# Tagged Questions

Force per unit area.

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### Pressure gradient - derivation for air stream

I need help clarifying the statement made here that $$dp = l\frac{dp}{dx}$$ $\frac{dp}{dx}$ is an infinitely small change in pressure at some point x. $dp$ is the total change in pressure between ...
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### How do I calculate the weight that PSI can lift?

Imagine that there's a force that is given to you in $psi$, say $1450\ psi$. And there's some body of weight say, $100\ kg$. What I want to know is that, how much $psi$ will I need to lift the "body" ...
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### what is the pressure that a sonic wave actually creates?

We know that sonic waves across atmosphere are basically areas of high and low pressure. But I couldn't find how much is that pressure. There are online calculators to calculate the sound pressure, ...
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### what is the effect of a sound wave at the opposite side of its direction?

We know that a sound source produces a sound wave and a high pressure area is followed by a low pressure area, while they travel with 300m/s. My question is, if the sound source travels with 50m/s in ...
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### 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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### Connection between gas flow rate and diameter of tubing

First time poster, long time troller and curious student. I have a bit of a conundrum that I would love some input on... Here's the problem. I have an air flow system is under constant pressure of ....
474 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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### Question about pistons and how their volume is affected by particles?

I can't find an answer to this anywhere. When pressure is maintained in a piston and an ideal gas is injected into it (again, with no change in pressure as it is injected) the piston is displaced ...
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### 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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### Is surface tension the result of a pressure drop over the air-water interface or visa versa, for a two sphere system?

For a liquid bridge between two spheres the Young-Laplace equation states that: $\vartriangle p= \gamma\bigl(\frac{1}{R_1}+\frac{1}{R_2}\bigr)$ where $\vartriangle p$ is the capillary pressure ...
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### Is this a case of the “venturi effect”? What's behind the “Venturi effect” actually?

Some dinghy sailboats have a hole in the bottom of their deck used to automatically bail out water after a capsize. bailer of the laser sailoat The mechanism only works if the boat is moving. The ...
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### Will changing the pipe diameter reduce the pressure head loss?

I have this system installed in my house (fig 1), and I'm having problems with the shower. I want to know whether, if I change the PEX tubes shown in red from 1/2" to 1" as shown in fig 2, I will have ...
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### How to emulate 40ft (12 m) of water? [closed]

I am part of an underwater robotics team, and our next year's challenge requires us to compete at a depth of 40ft. We don't have any pools nearby to test in, so I want to emulate this 40ft of pressure ...
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### Is 0.1 bar (hydrostatic pressure) equivalent to 0.1 bar vacuum pressure (absolute pressure)?

Suppose we would like to test the ability of an object to withstand the pressure under 1 meter of water. I would like to understand how to simulate this situation using vacuum. Is the 0.1 bar (for 1 ...
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### Are there limits for the speed of sound? A maximum or a minimum only?

The speed of sound in materials of various states of matter differs a lot. But does it have fundamental limits? Is there a maximal possible speed of sound? Is there a minimal possible speed of ...
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### Few doubts about saturated vapour pressure and unsaturated vapour pressure

I have some sort of confusions towards saturated vapour pressure and unsaturated vapour pressure.. So let me give you those. What is exactly saturated vapour pressure and unsaturated vapour ...
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### Pressure - How much fluid can void support?

Please refer to the attached (terrible) drawing while reading the post ! After watching some videos about the U-tube effect in drilling, a question came to me. Imagine one fluid of heavy density ...
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### Does atmospheric pressure have a net contribution to this FBD (free body diagram)?

Pressure acting on the left and right sides of the block counteract
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### Water pressure on a floodlight in a swimming pool [closed]

I have a circular swimming pool with a diameter of $4.5\;\text{m}$. The water height usually is about 1m. Somewhere in this pool is a single floodlight, circular aswell, diameter $25\;\text{cm}$. I ...
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### Forces of suction in WIllie Wonka's Chocolate Factory (filmed 2005 starring Johnny Depp) [closed]

Before I begin the question: I am in no way judging this movie, just happened to be casually watching it and saw the scene (referred to below) and thought to post this question. The scene: Boy falls ...
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### Measuring variation of saturated vapour pressure with temperature

Is it possible to measure variation of saturated vapour pressure of water with time.I just hesitate about it.My suggested procedure which is incomplete is given below Procedure that I would like to ...
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### Pressure and humidity

Does pressure/vacuum affect water vapor differently than other gases and hence humidity? For example, imagine I have a vacuum bell at atmospheric (mean sea level) pressure and the air in it is 50% ...
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### 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).". ...
160 views

### What is dP in pressure?

I'm reading a textbook, chapter entitled "Fluid Mechanics". This section is entirely devoted to fluid statics. Assuming an element of fluid in equilibrium, Consider a thin element of fluid with ...
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### Swimming in a ball of water in space

What would I feel if I went swimming in a ball of water in space? Would I feel greater pressure as I went deeper into the sphere? What would it be like to swim in something like that? Also, let's say ...
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### How does an airlock depressurization damage a docking vessel in space?

Can someone explain the science behind this? also i feel like in movies the ship always crumples inward, but shouldn't the only force at work be the pressure from the molecules of air in one connected ...
101 views

### unchanged temperature of balloon inside freezer

I'd tried to put a balloon in the freezer and after enough time (several hours), I took it out and noticed that as I touch it that it's temperature did not drop down . I took an empty balloon ( not ...
100 views

### Impact Force/Pressure of a wave on a vertical wall given PIV velocity field

I have PIV (Particle Image Velocimetry) data of liquid sloshing on a rectangular tank which produces a wave impacting one of the vertical walls. In the picture below you can see the wave about to hit ...
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### What is the pressure at this height? [closed]

The height of a mercury barometer is h when the atmospheric pressure is 100,000 Pa. At height h/5, what is the pressure? The choices given are 20,000 80,000 120,000 180,000 The answer given is: ...
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### 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 ...
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### If pressure inside a container is lesser than atmospheric pressure, how long can the vessel resist deformation? [closed]

Is the strain caused by stress (due to the pressure difference) is negligible?
360 views

### Why do our ears pop?

Have you ever been on a train going through a tunnel or plane and your ears pop?I was wondering why this happens and I know it relates to pressure but don't know exactly the reason
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### Force exerted by pressure on projectile

Imagine a free cylindrical body around a pipe that is pressurized with air. How does one find the force exerted on the cylindrical free body at the moment this body becomes a projectile? *air ...
111 views

### Heating suprecritical water in a closed water tank

How does the pressure of water in a closed tank evolve in the following setting: - closed tank of 2 liters (filled up with water) - water initially at 25°C and pressurized to 3 bars The water is now ...
117 views

### Could atmospheric pressure provide a torque to turn a wheel?

Imagine a smooth wheel. Now imagine it is divided up into four "pizza slices". We came up with an idea where you would put the bottom two "slices" along with the top left "slice" in a very low ...
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### Can gas return back into a sparkling beverage on cooldown?

We all know that if a sparkling beverage (let's say, CocaCola) spends some time outside of the fridge and gets warm, the gas comes out of the liquid, rises the inner pressure and makes the bottle ...
100 views

### Nozzle vs Orifice Water Jug Draining

why is this happening? Water jug draining So why does the water drain faster when you drain a jug through a funnel compared to the hole you make at the bottom of a jug( the hole is the same size as ...
52 views

### Fluid flowing into small pores

I have some open porous foams with pore sizes ranging from 50-100nm. I want to flow water into this structure but even at 30 atmospheres it would NOT go in. I am looking for a way to calculate the ...
60 views

### The significance of the pressure term within the momentum-energy tensor [duplicate]

EDIT: this question is based around my notion regarding the possible role of potential energy in the momentum energy tensor T$_{\mu\nu}$, The answer below resolves the question and I have deleted ...
118 views

### Balloon aerodynamics

In this recent anime that I have seen, there is a part where an atomic bomb is sent to the stratosphere in a box, by a helium balloon. As you can see in this picture of the set-up, there is a tube ...
53 views

### Finding volume of water that emerges from opening per unit time [closed]

A rectangular opening (width w and height h2-h1) is cut into the side of an open tank. The water doesn't emerge in a uniform velocity. Assume that SA of tank >> area of opening. I'm trying to study ...
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### What is the pressure at the center of the Earth? (Or a neutron star)

The center of the Earth has microgravity and is thought to be solid and almost 6000 degrees hot. What is the pressure like there? The confusing thing, for the common man I suppose, is that there's no ...
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### How does the bulk modulus of air change with rising pressure?

I can't seem to find the answer to what should be a trivial question: I have a rigid air-tight container of fixed volume and I am pumping air inside. The pressure is increasing (very slowly) from ~...
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### Internal pipe flow - Pressure Drop

Let's say I have internal flow at some flow rate in a pipe that is 10 ft long and there are 2 straight sections and 2 bends. I am trying to determine pressure drop due to friction in the pipe. My ...
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### How to get the pressure amplitude at any spatial point?

Working on the pressure equation from the linearized euler equations, I stumble across a very simple problem : How, from the pressure solution of the specific equation (see http://www.acs.psu.edu/...
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### Static pressure in ducts and its dependency on speed flow and density

I know that depending on the duct circuit (bends, complex geometries...etc), the static pressure will be defined. If we assume air is flowing in the circuit with varying speed and/or varying density. ...
278 views

### Why is the temperature of the ice/water bath not dependent on the barometer pressure, as was the temperature of the boiling-water bath?

Part of a laboratory experiment question set. Why is it that the known temperature of the boiling bath can be accurately determined from the days atmospheric pressure but the atmospheric pressure is ...
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### Deriving pressure from a given partition function

If the partition function for some system is given as $e^{\text{$\alpha $T}^3V}$; please note note that $\alpha$ is a constant. I have computed \left[\frac{\text{$\delta$Z}}{\text{$\delta$T}}\...