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Questions tagged [viscosity]

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When can viscosity be ignored?

I am working on understanding the motion of a solid ball in an infinite elastic (or possibly viscoelastic) medium when subjected to a sinusoidal driving force. The frequency-dependent complex wave ...
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35 views

What Is The Lowest Temperature At Which A Fluid Will Flow?

I’m studying Hydraulics, and this week we’re talking about viscosity and fluid properties and I came across this question but I can’t find the answer anywhere in my books. Please help.
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Viscoelastic Constitutive Relation

In the Mori-Zwanzig formalism, the following identification for the generalised shear viscosity $\eta(t)$ is given: $$ \eta(t) = \frac{V}{k_B T} \langle \sigma(t) \sigma(0) \rangle, $$ identified as ...
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54 views

Non-conservative forces in Lagrangian mechanics

In the Lagrangian formalism with a dissipative frictional force $F$, we can write $$\frac{d}{dt}\frac{\partial\mathcal{L}}{\partial\dot{q}_{k}}-\frac{\partial\mathcal{L}}{\partial q_{k}}=Q^{(nc)}_{k}...
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Is the velocity gradient of a homogeneous viscous fluid constant?

The formula for the viscosity of a fluid (or even a gas) is equal to \begin{align*} \frac{F}{A} =\mu\frac{du}{dz} \end{align*} where $F$ is the force applied to the top layer of the fluid, $A$ is the ...
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Viscous fluid equivalent of hyperelasticity

A hyperelastic solid is defined as one for which the stress tensor $\sigma$ can be written as the derivative of some stored energy function $W$ w.r.t. the strain $\varepsilon$: $\sigma = \frac{\...
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41 views

Where does this equation come from?

I am investigating about viscosity of fluids and I found the following equation to calculate the viscosity: $$\nu = \frac{2(\rho_s-\rho_l)\cdot g \cdot r^{2}}{9\cdot\Delta v} $$ The experiment ...
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Kelvin solid and deformation in transverse direction with Poisson ratio

A Kelvin-Voigt material is a material with such a behavior : I'm wondering if there is a way to model in a similar way the deformation in the transverse directions $y$. Meaning we have for the ...
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1answer
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Flow through a hole in a sphere

I have a sphere of diameter $D$ (radius $R$) with a small hole of diameter $d$ (radius $a$) in it, with air flowing through the axis of the hole: I am trying to estimate the drag force due to ...
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1answer
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How does a viscous fluid flow?

In all problem involving viscosity, while applying $f=nA \frac{du}{dz}$ why do we consider velocity of the bottom layer to be zero?
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55 views

If the molecular collisions are elastic will there be any dissipation in a fluid?

Viscosity arises due to collisions of the molecules of one layer of a fluid with another in contact. But viscosity is a dissipative element leading to heating and dissipation. Where does it heat come ...
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How does the velocity of the fluid layers gradually increase towards the axis of a tube?

For a fluid moving through a cylindrical tube in a streamlined motion, a fluid layer in immediate contact with the wall of the tube remains effectively at rest. The layers away from the wall has ...
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Why does a viscous fluid tends to cling to a solid in contact with it?

My textbook says that a viscous fluid tends to cling to a solid in contact with it, and also gives a consequence of the same: "Dust particles cling to blades of a fan even when it is rotating rapidly."...
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3answers
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Are there any cases where Stokes law does not apply in viscous fluids?

A friend of mine and I are conducting an experiment to find the relationship between terminal velocity and radius of a sphere (i.e trying to confirm Stokes law). We are using spheres ranging from 1....
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4answers
113 views

Why can't liquids oppose tangential forces acting on them?

Also, when a glass of water is inclined at a certain angle, why does the surface of water continue to remain parallel to ground?
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1answer
50 views

How to improve this simple Brownian motion simulation by adding viscosity?

I've written a 0th order Brownian motion simulator to envision how a particle of smoke might appear to move under a microscope. There will be missing $\sqrt{2}$'s and $\frac{\pi}{2}$'s since I haven'...
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2answers
62 views

Stressing Over Stress Tensor Symmetry in the Navier-Stokes Equations

How do we know that the stress tensor must be symmetric in the Navier-Stokes equation? Here are some papers that discuss this issue beyond the usual derivations: Behavior of a Vorticity Influenced ...
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47 views

How can a vortex be created?

i have seen this video. https://www.youtube.com/watch?v=pnbJEg9r1o8&t=96s It is not completly clear how a difference of velocity can cause a vortex, can you explain me?
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How does one mathematically derive the damping coefficient of a theoretical viscous dashpot?

I am very well aware of how to get the damping coefficient experimentally by observing a system in action. Given the dimensions and fluid properties of a theoretical viscous fluid dashpot, how does ...
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Can a water vortex (whirlpool) be used to efficiently store energy?

Either a large, constrained cylinder of water or a large volume of open water (perhaps in the ocean) could be persuaded to form a vortex by pumping energy in. The body of water would be acting as a ...
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0answers
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Formula for volume of liquid residue in containers after pouring [closed]

When trying to empty the filled containers by pouring, we will find that this is impossible to reach the "real empty" as some residual liquid should exist in the containers. Have some mathematical ...
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1answer
45 views

Why do we use $m\frac{dv}{dy} = -b(v-v_{ter})$ while determining how the terminal velocity is changing for an object falls down in linear drag force?

Why do we use $$m\frac{dv}{dy} = -b(v-v_{ter} )$$ while determining how the terminal velocity is changing for an object falls down in linear drag force . I was Jr Taylor's classical mechanics. In the ...
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Why doesn't the object slow down more after attaining the terminal velocity in liquid?

When an object falls down in a liquid it has two forces working on it one gravity and another is viscous drag . Now when these forces are same the object attains the terminal velocity in liquid. Now ...
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Why does Anderson ignore a derivative of a normal viscous stress?

I am reading "Fundamentals of Aerodynamics" 5th edition, J.D.Anderson. In part 15.6, he said: Consider a steady two-dimensional, viscous, compressible flow. The x-momentum equation for such a ...
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0answers
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What is the relationship between coefficient of discharge, Cd and the viscosity of the fluid flow?

Will an orifice’s coefficient of discharge depend on the viscosity of the fluid being used to measure it? Is Cd a geometric property or will it change for different fluids of different viscosity? ...
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1answer
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A viscosity unit [closed]

Does the viscosity unit "$\mathrm{ps}$" exist or is it a misprint and refers to poise "$\mathrm{P}$"? Thank you A liquid of $0.014\,\mathrm{ps}$ viscosity and $1.4\,\mathrm{g/cm^3}$ density ...
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1answer
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Viscosity Vs Conduction

Viscosity of a moving fluid (e.g. a gas) is commonly related to the exchange of momentum between layers of such fluid moving at different velocities. Intuitively, one could think that in a gas such ...
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2answers
89 views

Stokes's law proportionality to radius

Is there a logical explanation why Stokes's drag $F_d=6\pi R \eta v$ is proportional to the radius, $R$ of the sphere? Naively I would have expected that it is proportional to the cross section, i....
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1answer
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Melted chocolate forming fractal branches

Tree-like structure in chocolate Today I let some melted chocolate solidify in a smooth bowl in my fridge. When it had settled, I gently heated the outside of the bowl with warm water to unstick the ...
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2answers
134 views

What causes viscosity of a fluid?

Consider a fluid like water. Intuitively I would say that its viscosity is caused by intermolecular interactions among its molecules. But the Einstein-Smoluchowski relation (and the Fluctuation-...
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2answers
45 views

Force absorption properties for various fluids

I'm a high school student and we have to research a topic in physics as part of our school curriculum. Essentially, I am unable to find any text online relating to this topic, so I was wondering if ...
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1answer
38 views

Derivation of Maxwell viscoelastic material stress

I have a problem with understanding of derivation of stress equation $\sigma(t)$ for Maxwell rheological model. Below is the classic equation: $$\dot{\sigma}(t) + \sigma(t) \, \frac{E_0}{\eta}=E_0 \,...
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1answer
71 views

What properties of liquids determine the shape of the meniscus?

I recently purchased a little e-cig type device that operates on these "pods," they look like this: Now, as you puff on the device, the liquid is consumed and starts to go lower in the pod, at which ...
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1answer
29 views

Tracking down a citation for the dynamic viscosity of sea-water

I inherited some computer code that estimates the dynamic viscosity of sea-water from the water's temperature. The formula in the code uses is $$\mu = 2.414 \cdot 10^{-5} \cdot 10^{\frac{248.8}{T+133}...
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1answer
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Applied physics to “fill the jar” problem [closed]

I think that the most of you are familiar with similar kind of problems / riddles: I always said that it depends upon the velocity with which the fluid comes out from the faucet. It doesn't seem ...
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Can the effective viscosity perpendicular director of a nematic liquid crystal be smaller than that in the parallel direction?

For common nematic liquid crystals (LCs), e.g., pentylcyanobiphenyl (5CB) and p-methoxybenzylidene-p-butylaniline (MBBA), the ratio of the effective viscosities $\eta_\perp^\mathrm{eff} / \eta_\...
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1answer
137 views

Drag Force VS Stoke's Force

Drag force reads $$F_d = \frac{1}{2}\rho_F v^2 \mathcal{C} A$$ Where the letters have the usual meaning (respectively: fluid density, velocity relative to the fluid, drag coefficient, front area of ...
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1answer
340 views

Are all Irrotational Flows Frictionless and Laminar?

A I understand, Irrotational flows are also inviscid (have zero viscosity). This would lead me to assume that these kind of (purely fictional) flows would be well ordered (Laminar) and be frictionless....
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1answer
74 views

Viscous force and it's proportionality constant

"Introduction of Mechanics" states: $F_v = −Cv$, where $F_v$ is viscous force and $C$ is a constant that depends on the fluid and the geometry of the body. For objects of simple shape moving slowly ...
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1answer
61 views

Maxwell material response to step strain - initial condition

A Maxwell material is a model material obtained by connecting a perfectly elastic solid and a Newtonian liquid in series. Let $\sigma$ be the stress, $\gamma$ the shear strain, $G$ the shear modulus ...
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Fluid flow through a tank with multiple holes and a viscous solution

I'm working on a project and I need to figure out the flow rate of a system where the liquid is draining through multiple holes. The liquid is slightly viscous (1% sodium alginate solution, don't know ...
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508 views

Terminal velocity and radius relationship in Millikan's oil drop experiment?

After some research, I can see that Millikan (his original experiment) calculated the terminal velocity of oil droplets, and then used it to calculate the radius of since they were too small to ...
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80 views

Is a bowl of soup “harder” to spill than a bowl of water?

Is it really harder to spill a bowl of soup (water + stuff) than a bowl of water of the same quantity? Explanation: Intuitively, one would think that spilling soup requires additional clumsiness, ...
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2answers
70 views

Is the drag force on a thrown object higher in hot or cold air?

Increased temperature lowers viscosity of gases like air but also decreases density. So then drag force would be lower if an object is thrown in higher temperatures but what about viscosity? I thought ...
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1answer
41 views

Heat dissipated by a splash of water and energy of splash

I am trying to figure out the energy of the sound generated when a droplet of water hits a glass full of water. So, I initially thought that it's potential energy would then completely be transfered ...
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95 views

Is drag coefficient in fluid dynamics a constant in every direction?

I am referring the book 'Stochastic Processes in Cell Biology'. In this book the author says that Fokker Plank equation in isotropic diffusion: $$\frac{\partial p(x,t)}{\partial t}=-\frac{F}{\gamma}\...
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1answer
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heat generation due to viscosity in a 3D fluid flow

Consider an arbitrary 3D fluid flow: $$\vec{\nu}=\vec{V}\left( \vec{x} ,t \right) \tag{1}$$ where velocity at each point $\vec{\nu}$ is a function $\vec{V}$ of position $\vec{x}$ and time $t$ (non-...
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1answer
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SPH “normal viscosity” prevents rigid body rotation

I am making a half simulator and half game with fluid simulation, using smoothed particle hydrodynamics (SPH) as the model. I was using "artificial viscosity" as my viscosity mainly to dampen ...
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0answers
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Where have I gone wrong in my determination of dynamic viscosity?

For my high school physics project I am trying to determine the viscosity of water at different temperatures using an oscillating spring. However, for water at $21^oC$ I am getting a value of about $0....
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66 views

Is viscosity additive?

If I know the viscosity of liquid A and that of liquid B, will the viscosity of liquid C equal the sum of the viscosities of liquids A and B? If not, how would I go about calculating the viscosity of ...