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0
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1answer
620 views

How to calculate the ship resistance caused by water viscosity

If there is a ship going in the sea at 50km/h, and a length of 5m, width of 2m, how do I calculate the ship resistance caused by water viscosity? in other words I want to calculate the drag Force that ...
0
votes
1answer
129 views

Application of Stoke's Law

I was looking at Stoke's law and it says that you use it to calculate the drag force on a sphere passing through a fluid. Can i also use this equation to calculate the drag force on a car going ...
3
votes
3answers
31 views

Why does a pot start rotating when coffee is stirred inside?

I usually make Turkish coffee as my morning coffee. I have a small somewhat rounded pot with handle on one side. I noticed that when I pour water in and start stirring, pot has a tendency to start ...
1
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2answers
187 views

Viscosity calculation of a rarefied gas

I am studying the rotational-translational relaxation of a diatomic gas (like oxygen) using a GPU in order to accelerate the calculations; during the calculations I get the translational temperature, ...
0
votes
1answer
217 views

How to calculate fluid(oil / hydrocarbon) loss under pressure

I'm trying to calculate the amount of fluid that would flow through an area dependant on the amount of pressure that there is. I'd also like to know the rate at which it would flow. Essentially I ...
0
votes
0answers
21 views

Pendulum with Viscous and Frictional Damping

I am trying to model a pendulum with both viscous and frictional (Coulomb) damping. The problem is that the viscous damping only occurs in one direction because I am modeling a dashpot that only has ...
0
votes
2answers
220 views

Viscosity for steam in the Reynolds number

In calculating the Reynolds number for a flow of steam in a pipe, this is the general formula I am trying to use: $$Re=\frac{\rho d v}{\mu}$$ with density $\rho$, pipe diameter $d$, flow steam $v$ ...
0
votes
3answers
38 views

Wind restistance as function of temperature

Is temperature-dependent wind resistance the reason there's a significant increase in fuel consumption in my Prius car when air temperature drops by 30 degrees K from 300 degrees K? I think I see a ...
0
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0answers
9 views

Is viscosity excluded by Lorentz symmetry in spatio-temporal discreteness?

"In the case of spatio-temporal discreteness, viscosity is excluded by Lorentz symmetry". This statement is from here. Can anyone explain why this is the case? I'm looking for an intuitive way to ...
1
vote
1answer
34 views

Physical reason why Prandtl number is order unity for gases?

Is there a physical reason behind the fact that for gases the thermal diffusivity is on the same order of magnitude as kinematic viscosity (and as such a Prandtl number of order unity) and if so what ...
0
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0answers
24 views

Working Out Shaft Torque in a Stirred Tank with a Cylindrical Cavern Formation (using a non Newtonian fluid)

Here is some background to the problem (in a stirred tank): "With yield stress non-Newtonian (viscoplastic) fluids, it is possible to generate an agitated volume around the impeller, defined as a ...
1
vote
1answer
68 views

Patterns in falling viscous fluids

It is a common observation that honey(or any other viscous fluid),tends to overlap/coil/wind up as it reaches the rigid surface. There is this little bend near the pile-up. Why is this so? How does a ...
0
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1answer
46 views

Ball touching the side of a tube — DOUBT

I have a small doubt in understanding a physics concept. If a steel ball is dropped in a thin tube of glycerol, it will eventually reach its maximum or terminal velocity. However, if the steel ball ...
1
vote
0answers
14 views

percolation permeability threshold in Helium before and after lambda point transition

There's an experiment demonstrating the properties of super-fluid Helium compared to normal fluid Helium, in which the Helium is put in a jar who's bottom is porous. The super-fluid can pass through ...
1
vote
1answer
32 views

Why do we need the kinematic viscosity?

Kinematic viscosity is the well known dynamic viscosity divided by density. What difference does it make to divide by density? What is so useful about this?
1
vote
1answer
39 views

Newton's second law of motion and viscosity [closed]

In a Coutte flow, the applied force on one of the plates can be expressed by $F = \eta A \frac{dv}{dz}$. F here can also be defined using Newton's second law of motion, $F = m \frac{dv}{dt}$. The ...
5
votes
1answer
41 views

How should I think of a liquid in terms of interatomic potential and molecular speed?

A rather simple question for liquids specialists I guess but I have hard time finding information about this. Here is my problem. I understand the ideal gas theory and the Maxwell's speed ...
1
vote
4answers
56 views

What makes the magnitude of the force of friction velocity dependent in one scenario, but not the other?

When a solid objects makes contact with another solid object, I believe the magnitude of the force of friction between them does not depend on the relative speed of the two objects. When a solid and a ...
0
votes
1answer
49 views

Terminal Velocity in Water

Another question concerning classical physics. On Earth, the combination of air resistance and gravity interact in a way that creates the phenomenon of terminal velocity. Do other fluids (for example, ...
1
vote
2answers
10k views

Determine viscosity using falling sphere (Stokes Law, Ladenburg correction)

Introduction I am trying to determine the viscosity of a fluid. Therefore, I let a sphere of known mass m and radius r fall ...
1
vote
1answer
43 views

Free expansion of ideal gas, transient phase (3 questions)

We all know the classic scenario of free expansion. A contained gas expands into a vaccum and in the end we have $\Delta T = \Delta U = \Delta H = 0$ and $\Delta S = R \ln \frac{V_2}{V_1}$. This is ...
1
vote
3answers
115 views

Shaking water inside bowl causes waves but why does the water stabilize?

Suppose you shake water inside a container, then at first the waves goes up and down strongly but they gradually dissipate. What makes them dissipate?
0
votes
1answer
22 views

If there was an object such as a bucket travelling through the atmosphere very fast could the air caught in it transition to a liquid?

The question came to me after thinking of the pressure waves in front of a spacecraft during re-entry. Would the pressure caused by the air being compressed cause the air to liquefy and if so at what ...
0
votes
1answer
58 views

Basis for Derivation of Stokes Friction Law for Spheres

When deriving Stokes law one uses the Navier Stokes equation with the assumptions: low Reynolds number stationary flow in compressible flow leading to this version of the N.S : $$\nabla p = ...
2
votes
1answer
45 views

Effect of paint on drag force [closed]

Aerospace engineering as well as automobile engineering gives a particular significance to the shape of a vehicle to enable proper and more effective transportation.What I want to know, is, about the ...
4
votes
1answer
229 views

Explicit form of the entropy production in hydrodynamics

I'm trying to understand how hydrodynamics arise from a precise, mathematical formulation of thermodynamics, learning mostly from Landau's "Hydrodynamics". So Landau starts from formulating the ...
7
votes
4answers
5k views

Does irrotational imply inviscid?

Let us consider a 2D irrotational flow, such that $\nabla\times\boldsymbol u =\boldsymbol 0$. Defining the stream function such that $\boldsymbol u =\nabla\times\psi \boldsymbol n$ where $\boldsymbol ...
0
votes
2answers
77 views

Viscous forces with asymmetric gradient velocity in fluid mechanics

In fluid mechanics, the stress tensor writes $\sigma = -p 1 + \tau$ where the deviatoric part $\tau$ corresponds to shear. The viscous (volumic) forces are $\operatorname{div}\tau$. For a Newtonian ...
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votes
3answers
1k views

How is viscosity described on the molecular level?

What is the 'molecular' origin of the viscosity? The molecular origin of elasticity is almost clear for me: at the very bottom the 'elasticity' comes from the attraction and repulsion between atoms ...
1
vote
1answer
49 views

Derive drag coefficient of plate

There is any analytical way to derive drag coefficient of flat plate aligned perpendicular to the flow? Wikipedia says it's between 1.98~2.05 but I want to get this value in calculation, not ...
0
votes
1answer
33 views

Ratio of force of resistance due to liquid to that due to gravity

What is ratio of force of resistance due to liquid to that due to gravity? For any object for example a ball falling in a liquid with constant velocity, what will be the ratio?
2
votes
1answer
86 views

Can dynamic viscosity be measured directly and without knowing fluid density?

Can dynamic viscosity be measured directly and without knowing fluid density? If so, how? My understanding is that only the kinematic viscosity can be measured directly (with the devices that I am ...
0
votes
1answer
29 views

Without knowing fluid density, can it be correctly determined by measuring both kinematic and dynamic viscosity directly?

Without knowing a fluid's density, can its density be correctly determined by measuring both kinematic and dynamic viscosity directly, and then dividing these values? Can one determine cStokes and ...
0
votes
1answer
45 views

Velocity of liquid molecules in turbulent flow

I was solving some questions when I came across this: what is the velocity of liquid molecules in contact with the walls of the tube? and the answer was given that it can have any velocity and then ...
0
votes
2answers
437 views

Derivation of Viscous Force

For viscous drag, the formula for the force is, $$ \mathbf F=\pm\eta A\nabla\mathbf u $$ where $\eta$ is the viscosity coefficient, $A$ the area and $\nabla\mathbf u$ the velocity gradient. How is ...
0
votes
0answers
38 views

How to determine which one is dominant shear rate vs. flow rate

I have a question for the image below. Now we have a pump connecting to a votator for transferring some slurry. The pump yields a flow rate Q, and the votator yields a shear rate 𝛾. I wanna ...
0
votes
0answers
63 views

Dissipative forces and reversible processes

A book that I have contains the following lines: For a process to be reversible, the dissipative forces such as viscosity and friction should be absent. My question is why?
1
vote
1answer
49 views

Shear stress in cylindrical coordinates?

In cylindrical coordinates the momentum flux is given by (in the $r$ direction): $$ \Pi=-\eta \frac{\partial (r\omega)}{\partial r}$$ Where $\eta$ is the viscosity. Therefore one would expect that the ...
9
votes
3answers
675 views

Derivation of viscosity using basic kinetic theory?

This question has been asked in part before in the question Kinetic theory derivation of viscosity of a gas although the given accepted answer does not give the required detail for the part of the ...
2
votes
1answer
31 views

The validity of constitutive diffusive fluxes

In transport phenomena the diffusive fluxes for mass, energy and momentum are the constitutive laws: $$\boldsymbol{j}_c=-D\boldsymbol{\nabla}c \quad \boldsymbol{j}_T=-k\boldsymbol{\nabla}T \quad ...
0
votes
0answers
19 views

Plateau–Rayleigh instability according to liquids $Ca$ number

For examining whether viscosity or surface tension dominates each other effects, we can't refer to $Re$ or $We$ numbers because they just tell us about one of them ( surface tension and viscosity ). ...
0
votes
1answer
41 views

Plateau–Rayleigh instability for liquids with low $Re$ number

I'm working on a project about Plateau–Rayleigh instability for liquids. But I've a question. we can examine the fluids with high $Re$ number that the influence of viscosity is negligible, but what ...
1
vote
1answer
70 views

Why does my coffee stop?

As I was mixing my coffee this morning, wishing that it would do it on its own, I started wondering: What makes my coffee stop swirling? I mean what exactly? Is it the walls of the cup or the coffee ...
6
votes
1answer
807 views

Kinetic theory derivation of viscosity of a gas

Encountering a lot of issues trying to understand this. The basic idea of the derivation I'm using is as follows (the image here may help): I'm going to write $\langle u_x\rangle$ as the general ...
1
vote
2answers
60 views

Viscosity forces and Depth of water

I was wondering if the viscosity force depends on the depth of water. I mean it is much more harder to swim in the ocean at a depth of 1km than swimming at the surface due to the viscosity forces ?
2
votes
1answer
135 views

Which formula is correct to find the terminal velocity of a sphere falling through a liquid?

Consider a sphere of radius $R$ & density $\rho_s$, falling through a liquid having density $\rho_l$, attains a constant terminal velocity $V_t$ then in this case the net force acting on the ...
2
votes
1answer
46 views

Would a fluid with zero viscosity reach an equilibrium

My hunch is yes, but I can't think how to prove it. An argument against this is you have a box with a divider in the middle, one side is filled up higher than the other. The divider is removed, you ...
1
vote
0answers
80 views

Explanation of the liquid rope coil effect

I was recently introduced to the liquid rope coil effect by this video: https://www.youtube.com/watch?v=zz5lGkDdk78 I noticed while the video mentioned the equations governing the motion, it didn't ...
0
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0answers
21 views

Relation between weight and friction in fluid mechanics

In case of horizontal flow of a fluid,does its weight affect its velocity? Or just the coeffecient of viscosity is sufficient to express the increase in friction with the increase of the fluid's ...
2
votes
1answer
44 views

Friction in a fluid

when an object is moving in a fluid(air for example), the air will resist the object's movement: molecules of the air will collide with the surface of the object (no slip condition) and then we will ...