The quantitative study of how fluids (gases and liquids) move.

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1answer
494 views

Torque on a rotational cylinder in viscous fluid

I've been stuck on what I'm pretty sure is a simple part of a larger question. It's a cylinder (radius a) spinning in a viscous fluid. It's rotating at rate $\Omega$ .During this question we get that ...
-1
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0answers
24 views

Is a 3D or 2D Poisson's equation separable or non sperable? [migrated]

Can someone please explain to me if a 2/3D Poisson's equation is separable or non separable? Thank you
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1answer
29 views

can ice crystals be molded into a structural shape in space

I know that water exposed to vacuum space first boils and then turn into vapor (sublimates) . Is it possible re use this vapor say inside a pressurized membrane, to mold it into a solid ice structure, ...
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1answer
26 views

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. ...
0
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1answer
27 views

Cosmology: collisionless vs collisional fluids?

I try to understand the difference between collisionless and collisional fluids in cosmology. My first question is the following. In the context of FLRW cosmology, we suppose that the Universe can ...
0
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1answer
139 views

Orifice Jet Flow experiment

I am writing up a report on Orifice jet flow experiment in which I am required to find coefficient of flow velocity, $C_v$, and the Coefficient of discharge, $C_d$. There are couple of things that I ...
5
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2answers
271 views

How come a whistling kettle starts whistling only when water boils, and not long before - due to hot air escaping under pressure?

A whistling kettle will start to whistle when the water boils and turns into a jet of steam which then exits the small aperture in the spout. But why doesn't this happen much earlier - when the air ...
5
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1answer
215 views

Why do some impact craters have an elevation in the center?

Why do some impact craters have an elevation in the center? What processes lead to its formation?
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0answers
43 views

Is there a definite boundary between a powder and a fluid?

Given a powder of solid substance what will happen if we make the granules smaller and smaller mechanically? Will this eventually make a liquid or gas from the powder? Can there be gaseous substanse ...
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1answer
208 views

Sum of forces with liquid in rotation

It's not homework (I'm teacher). I would like to compute sum of forces on this study : The shape is symmetrical like that I'm sure the center of gravity is in the center of the shape. I compute ...
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1answer
119 views

Positions and corresponding terminology of “acoustics energy”?

From limited knowledge, decades ago, dating back to the nineteenth century: Ohm's law of specific acoustic energies was the first biological application of Fourier's theorem. Actually, it was ...
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0answers
54 views

Locomotion at low Reynolds number with Gauge Theory

I've been studying some approaches with gauge theory to some problems in Mechanics and I've found the problem of self propulsion at low Reynolds number a quite complicated one. The approach I'm asking ...
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0answers
28 views

water is dropping from car? [migrated]

I bought a car yesterday Nissan 2009 , today i have noticed that water is dropping under the front passenger seat.is there any one knows what is the problem please.
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0answers
24 views

Deceleration of spherical particle in fluid

If I know the initial velocity of a particle entering a fluid, how can I calculate its deceleration over time ? What parameters would I need to know ? Viscosity of the fluid, weight of the particle ...
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1answer
53 views

Is there a speed limit for objects falling in gases or liquids? [duplicate]

Let $o$ be a spherical object with mass $m$ and surface $s$. Let $g$ be the gravitational acceleration and $h$ the height. Let the gas where we drop $o$ in have density $d$ and pressure $p$ at ...
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1answer
42 views

Exact solution to a 2D/3D Poiseuille flow in a channel

Hi everyone and thank you in advance for any help. I am struggling to find an analytical solution to either a 2D or 3D Poiseuille flow in a rectangular duct. All I can find is 1D example. Can someone ...
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2answers
71 views

Does the definition of compressibility depend on the frame of reference?

According to many authors, a fluid is defined to be incompressible if the material derivative of the density $\frac{D\rho}{Dt}$ is zero, that is to say, that in an frame of reference following the ...
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3answers
172 views

How does vasoconstriction/vasodilation of arterioles change blood pressure?

Background: I am coming at this question from an electrical engineering background, and I feel like I am missing certain assumptions that are going into the statement found in my physiology textbook, ...
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2answers
45 views

Will going up with a larger diameter ensure a higher water pressure in the distribution pipes? [closed]

Have a look at the drawing below describing a sample situation: a water tank a 1'' diameter pipe bringing the water down, inside the ground, arriving near the house in the house, 2 x 0.5'' diameter ...
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1answer
28 views

what force pump is needed to power [closed]

Im studying design have not got a good grasp on maths, but understand the working principles of pressure and water! my problem hopefully has included all necessary info in the image. Please help. ...
3
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3answers
120 views

Why does it seem as if big vehicles “attract” mine when I drive close to them?

When I drive a car at high speed and when I am near to another big car (like a van, or transport vehicle) I feel an attraction to or something push me toward the other big car . What's the physics in ...
3
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1answer
121 views

Nonlinear waves and shock formation

In the cases of nonlinear acoustics, why is shock formation unlikely when the dispersion is strong when compared to the nonlinearity of the wave?
3
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2answers
190 views

Speed of Sound/Push in Supersonic Flight

I've learned from things like the Veritasium Slink Drop and the old "break the speed of light by pushing on the end of a very long pole" thought experiment that objects have a "speed of push" which is ...
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2answers
179 views

Self Stirring Boiling Liquid

A couple of weeks ago, a friend and I were brewing a new batch of beer. We boil our wort in a turkey fryer. Pretty standard setup for beginners. Anyway, our wort was getting pretty close to boiling ...
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5answers
7k views

What's the surface area of a liquid? How does evaporation increase if the surface area of a liquid is increased?

Wikipedia says that a substance that has a larger surface area will evaporate faster, as there are more surface molecules that are able to escape. I think the rate of evaporation should decrease as ...
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0answers
13 views

Saturn's Hexagon [duplicate]

I am currently trying to understand the formation or indeed the explanation as to why the hexagonal north polar vortex on Saturn is exactly that: Hexagonal. I understand that the most prominent ...
0
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1answer
702 views

Pressure loss in a syringe

I'm currently working on a problem which is really giving me some issues. The problem concerns the force required to expel water from a syringe. We have a 20 ml syringe (which is $2\times10^{-5}$ ...
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1answer
39 views

Rain system movements and highways?

In my free time I sometimes enjoy watching the weather or radar and trying to predict how a rain system will move. Pretty often I notice that a small rain system or even a large one will congregate or ...
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2answers
2k views

What are the assumptions of the Navier-Stokes equations?

I wanted to model a real life problem using the Navier-Stokes equations and was wondering what the assumptions made by the same are so that I could better relate my entities with a 'fluid' and make or ...
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1answer
37 views

Derivation of the energy-momentum tensor for an imperfect fluid

In chapter 7 of the "Physical Foundations of Cosmology" Mukhanov uses this energy-momentum tensor for an imperfect fluid: $T^\mu_\nu = (\rho + p)u^\mu u_\nu - p\delta^\mu_\nu - \eta(P^\mu_\gamma ...
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2answers
187 views

Force needed to push a syringe plunger: does one add force associated with downstream back-pressure to frictional plunger force?

I am trying to figure out how much force $F$ is needed to push a syringe plunger. The plunger needs to overcome the friction force $F_1$ and (a much smaller) inertia force $F_2=ma$, giving the total ...
6
votes
1answer
179 views

Why is there no UV catastrophe (divergence) in turbulence?

I have just read that as the Reynolds number is increased, the separation of macroscopic and microscopic scales increases and that this also means that there is no UV catastrophy (or equivalently UV ...
4
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1answer
55 views

Passively moving air [closed]

I'm interested in channeling air into an underground condenser to generate water. Which of these approaches would be most appropriate, and is there a better approach I haven't considered? A: A ...
4
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1answer
179 views

Bubble in a pipeline

I am just thinking about this phenomenon: We have a horizontal pipeline with a flowing liquid, which contains a small bubble of gas. How do the dimensions of this bubble change when it reaches a ...
3
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1answer
36 views

What's the difference between “Ohmic dissipation”, “Joule heating”, “ion drag” and “resistive heating”?

The following terms are sometimes used to refer to ... more or less ... the same thing by different people and in different contexts (electronic circuits vs. plasma physics, etc.): Ohmic ...
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1answer
18 views

Bubbly Flow and two phase flow modelling

When we pour vine or some other drink why bubbles move upward and what law they follow or what is the law that describe that motion? One other question If we consider a simple two phase flow between ...
2
votes
1answer
36 views

Reynolds number of airfoil in a pipe

As part of a physics high school paper I am writing, I need to build a wind tunnel. As part of my calculations, it appears that Reynolds number is very relevant in aerodynamics (specifically for ...
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0answers
18 views

What is the viscous force acting on a cube?

I'm aware of the viscous drag formulae to calculate the drag force acting on a moving sphere inside a viscous fluid. But how do you improve the formulae to get the force acting on a cube with side ...
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2answers
6k views

How do you calculate vortex shedding frequency?

I am attempting to try to find out if there is any effect of Von Karman vortices on a group of wind speed readings where it is presumed that due to a mountain nearby the data collection spot Von ...
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4answers
986 views

When pressure is exerted on parallel hydraulic pistons, do they start extending at the same time?

If there are two hydraulic cylinders connected in parallel, each with a different load (shown in the picture below), will they start extending at the same time? I'm having a disagreement with my ...
6
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1answer
2k views

Drag on a spinning ball in fluid

I am a physics newbie (high school level) and I am wondering what happens when a spherical object is spinning on the spot in a bunch of gas (no gravity here, just an imaginary physics sandbox). Am I ...
0
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1answer
28 views

Fluids in motion and pressure

We are taught in the lessons of fluid mechanics that for an ideal non compressible and non viscous fluid $at-rest$, the pressure at any point within the fluid is independent of the direction. But I ...
3
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1answer
101 views

How does a hollow-point bullet move smoothly through the air, presenting a 'cup-shaped' nose instead of an actual sharp-point to the fluid?

Hollow-point rounds move smoothly through the air when presenting a 'hollow cup-shape' instead of a traditional 'sharp point' to the fluid air. Does this mean the air trapped, and at some assumed ...
2
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1answer
37 views

Unsmooth behavior of water waves

I happened to come across this rather interesting picture of a very deformed (or perhaps intricate) wave. The structure looks like it illustrates a superposition of multiple waveforms, as intuitively ...
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3answers
10k views

About an upside down cup of water against atmosphere pressure

There is an experiment we learned from high school that demonstrated how atmosphere pressure worked. Fill a cup of water and put a cardboard on top of it, then turn it upside-down, the water will not ...
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2answers
38 views

What is the physical meaning of $v\times n$?

What is the physical meaning of $v\times n$, where $v$ is a velocity vector and and $n$ is a unit normal vector of a interface? Why at the free surface between two fluids, $$v^{(1)}\times ...
0
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1answer
45 views

Why does plugging a hole in an airplane's fuselage result in a huge (10x) atmospheric pressure spike?

While reading about uncontrolled decompression, I came across one famous airline incident, Aloha Airlines Flight 243, where the article I was reading discussed a 1-square-foot hole created in the ...
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4answers
138 views

What is the friction force at terminal velocity?

As terminal velocity is inversely proportional to viscosity or fluid friction, then my question is: at terminal velocity, the fluid friction is maximum or zero?
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2answers
41 views

Using fluid mechanics to show that force is directly proportional to velocity

So I am writing a paper about viscous dampers in harmonic oscilators, however I was looking at some old fluid mechanic notes and I thought I had come across what I needed although I have gotten stuck. ...
0
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1answer
28 views

How to make a structure of which water flows out at a constant rate? [closed]

Is there any way to make a structure of which water flows out of at a constant rate? Any way could be used to build the structure, including 3D printing.