What is Viscosity: Definition and 251 Discussions

The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water.Viscosity can be conceptualized as quantifying the internal frictional force that arises between adjacent layers of fluid that are in relative motion. For instance, when a viscous fluid is forced through a tube, it flows more quickly near the tube's axis than near its walls. In such a case, experiments show that some stress (such as a pressure difference between the two ends of the tube) is needed to sustain the flow through the tube. This is because a force is required to overcome the friction between the layers of the fluid which are in relative motion. So for a tube with a constant rate of flow, the strength of the compensating force is proportional to the fluid's viscosity.
A fluid that has no resistance to shear stress is known as an ideal or inviscid fluid. Zero viscosity is observed only at very low temperatures in superfluids. Otherwise, the second law of thermodynamics requires all fluids to have positive viscosity; such fluids are technically said to be viscous or viscid. A fluid with a high viscosity, such as pitch, may appear to be a solid.

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  1. casparov

    A Navier-Stokes solutions: Beltrami flow

    There are some known solutions for 3D Navier-Stokes such as Beltrami flow. In the literature these Beltrami flow solutions are said to not take into account viscosity, however when I read the information on Beltrami flow, they do seem to involve (kinematic) viscosity: From incompressible...
  2. X

    Viscosity by Falling Sphere Equations

    I have recently conducted an experiment to measure the viscosity of some liquids using the falling sphere method and a high-speed camera. I used different diameters of sphere starting from 2.5, 5, 10, 15 and 20 mm. What I want to prove using stokes law equation is that diameter of sphere doesn't...
  3. E

    Understanding CVT Fluid Viscosity and When to Replace: Expert Insights

    I went to Subaru for period maintenance checkup. They told me the car was due for CVT fluid replacement which was done every 5 years or 40,000 miles. It's already 7 years even if the mileage is only below 20,000 miles so I let them go ahead. The service advisor told me as time passes, the...
  4. C

    Negative sign in Newton's Law of Viscosity?

    Hi Physics Forums, I'm wondering why Newton's Law of Viscosity sometimes has a negative sign in front of the viscosity and sometimes it doesn't? Thanks for your help!
  5. A

    B Does the density of a liquid affect the braking of an object in free fall when it lands?

    In mine hypothesis I want to slow down free fall for diffrent density objects in liqudies. I have a stone wich i roughly a denisty of 2,7 g/ml and gold with 19,7 g/ml. They have the same size. Liquied glucose has the density of roughly 1,5 g/ml. In my example, I drop at the same time in a 1...
  6. DrishantMaharjan

    Viscosity and resonant frequency?

    AP french's formula -> https://docs.google.com/document/d/13j2bIFgifZFLm65f4j6Wg9CI4sFxqEoDSIMCgCrWr9o/edit?usp=sharing Temperature relation that i couldnt understand ->...
  7. M

    A Can you help to solve this integral? (resin viscosity research)

    I have tried WolfarmAlpha but it could help me. Please note this is not a homework exercise. I am a researcher and I am looking to model viscosity development of resin. there I came across with this express :) $$\int{\frac{1}{a\cdot e^{bx}+c\cdot e^{kx}}dx}$$
  8. samy4408

    I Relationship between viscosity and velocity in fluid mechanics

    hello, I read in a lecture paper about fluid mechanics that velocity is not related to viscosity, i found this odd and i think it is an error , can someone confirm that?
  9. G

    Viscosity in lubricating fluid in the bench-guide of a machine

    Figure: bench (bancada), guide (guide), oil (aceite). My attempt at a solution: $$\textrm{extension } L=0,6\, \textrm{m}$$ $$F=1500\, \textrm{N},\,\, c=0,1\, \textrm{m}/\textrm{s},\,\, h=0,0001\, \textrm{m}$$ $$v=5\, \textrm{stoke}=0,0005\, \textrm{m}^2/\textrm{s},\,\, \rho_r=0,9$$ a)...
  10. A

    Inconsistent flow rate measurements of an engine diesel fuel

    I am measuring the volumetric flow rate of a diesel fuel using "Turbines" flow meter, both in the supply and return fuel lines of an industrial diesel engine (https://www.cat.com/en_US/products/new/power-systems/industrial/industrial-diesel-engines/18398034.html – coupled with a generator for...
  11. DadoNoah

    Calculating force on a syringe plunger for a viscous fluid?

    I'm currently working on a precise glue/resin dispenser, and I'm trying to derive an equation for the force one must exert on a syringe plunger as a function of the desired flow rate Q, and also accounting for the fluid viscosity and the syringe barrel and needle geometry. I've attached a scan...
  12. G

    I Analytically Solving the Magnus Effect with Viscosity in Ball Flight Simulation

    I am trying to add to a problem of mine the viscosity parameter, simulating the fly of a ball. However I obtain the following equations d^2V_z/dt^2 = WdV_z/dt - dV_x/dt and d^2V_x/dt^2 = WdV_x/dt - dV_z/dt where W is a function linearly dependant to t. Any ideas how I could analytically solve...
  13. Y

    B Terminal Velocity Equation in vertical cylinder with some fluid

    I just have a question that could you guys make an equation that expresses the terminal velocity based on followed condition? - When diameter increase, velocity decrease - velocity should change depending on both cylinder and sphere's diameter - We know every variable - The sphere is in...
  14. Dario56

    I Fluid Viscosity & Viscous Friction Between Plates

    When fluid is placed between two parallel plates such that one plate is moving and other is stationary, fluid will start flowing. Between plate and the fluid there is viscous friction given by equation: $$ F = -\eta A \frac {dv} {dy} $$ where $ \eta $ is fluid viscosity, $A$ is area of a plate...
  15. S

    B How Does Viscosity and Turbulence Affect Fluid Flow Between Plates?

    https://openstax.org/books/university-physics-volume-1/pages/14-7-viscosity-and-turbulence I am trying to understand the derivation from Figure 14.36 which starts with " The fluid to be measured is placed between two parallel plates. The bottom plate is held fixed, while the top plate is moved...
  16. chaksome

    Can turbulence help measure liquid viscosity more accurately?

    Hi, all. Recently I plan to participate in an physics competition which focuses on viscosity measurements of liquid~I’ve investigted some kinds of methods such as capillary viscometers, Rotational viscometers, Vibrating Viscometers, co-flowing laminar viscometers and so on. I hope to find a...
  17. Will26040

    How do I get the viscosity of a mash mixture in brewing?

    Hi, I am designing a mash tun to produce beer. I have 1300kg of malted barley (at a known density) and 3250kg of water. Please could someone outline a method I could use as I am really struggling. One of the main problems I am having is accounting for the density change of the malt when it...
  18. J

    Finding the coefficient of viscosity

    "Calculate the gradient (or slope) of the line and use this and the equation above to calculate the value for the viscosity, η. You MUST use the gradient to calculate the viscosity." here are the results: I'm not sure if it's just me who finds this confusing
  19. archaic

    Density from a viscosity experiment

    The body is a small ball. The experiment consists in dropping this ball, while varying the diameter each 3 trials, in a viscous liquid and measuring its falling time: ##D_i\sim t_1,\,t_2,\,t_3##. The equation we are using is: $$\frac{\Delta x}{\Delta...
  20. tahskanaij

    B Do fluid oscillation characteristics depend on the viscosity of a fluid?

    This is my first thread here, so let me know if I didn't adhere to a format i was to follow. I'm in the middle of a project depicting the change that an oscillation of fluid inside a drinking straw faces depending on the viscosity of the liquid. For reference, this is exactly the same example...
  21. CanFan

    B What sort of can would roll the fastest?

    Hello, I'm new here so apologies if this is in the wrong place! I was wondering, hypothetically, what sort of canned food would roll the fastest (assuming the ramp remained constant and the can couldn't be altered)? I've been looking this up and I know a solid can would roll faster than an...
  22. George5356

    Dynamic Viscosity in Reynolds Number

    I am trying to run a calculation to work out the overall heat transfer coefficient of an arbitrary ten plate exchanger where the fluid is not determined using Re=puD/mu where mu is dynamic viscosity. When mu is such a strong function of temperature how should I determine which valye to use, say...
  23. JF001

    I How is the viscosity of a plasma produced?

    Summary: I'm interested in knowing more about instabilities within plasma. Is the viscosity of plasma produced by thermal, magnetic, or gravitational effects (or even something else)? I had the opportunity to talk with multiple Ph.D. students during the summer and was especially interested in...
  24. taktoa

    A Navier-Stokes with spatially varying viscosity

    Does anyone know of a differential equation, similar to Navier-Stokes, that encompasses incompressible fluid flow with spatially varying viscosity? Viscosity is treated as a global constant in NS; I've found some papers online that address NS with viscosity as a function of velocity, but I can't...
  25. person123

    I Viscosity Term in Navier-Stokes Equation

    I'm a bit confused about the viscosity term in the Navier-Stokes equation; my intuitive understanding of what it would is different from what it actually is. I took the z component of the stress on an infinitesimal cube, but the same approach should apply in the x and y direction. I think my...
  26. S

    I Adhesive force between cutting oil and metal chips?

    I am working on a project to remove cutting oil from waste metal chips. I need to know the retationship between viscous force of oil and centrifugal force required to remove oil from chips, so that I can calculate the RPM P.S Design is attached
  27. C

    I Trying to better understand what viscosity really is

    I'm trying to get a better handle on the actual physical phenomena underlying viscosity (for Newtonian fluids). Something I could word in the format of "this happens (and this and this), and so the fluid resists flow." What I've found online is that when gasses are at higher temperatures, they...
  28. A

    What is the dynamic viscosity of air?

    Homework Statement Considering an airfoil (a flat plate) flying at 100 m/s under sea-level conditions, so the density is 1.225 kg/m3 and the length being 1 m, what is the dynamic viscosity of air? The problem is that I have two variables in one formula, Reynolds number and the viscosity...
  29. A

    Scattering dynamics and viscosity

    I have been studying the statistical mechanics' viewpoint of fluid dynamics by considering the derivation of Navier-Stokes' equations from the Boltzmann equation involving the whole Chapman-Enskog expansion. It is clear that through this process, it is possible to account for the dependence of...
  30. Polyamorph

    A Viscosity from DFT (VASP) using the Green-Kubo relation

    Hello! In this paper https://pdfs.semanticscholar.org/e8a2/02f25555cd8c4f947bbbdff5a61a0ea0efd2.pdf the authors use VASP to determine MgSiO3 viscosity using the Green-Kubo relation ## \eta = \frac{V}{3k_{\rm{B}}T}\int_{0} \left<\sum_\limits{i<j}\sigma_{ij}(t+t_{0}).\sigma_{ij}(t_{0})\right>dt##...
  31. JTC

    What causes pressure in form drag?

    Consider a ball flying through the air. When there is turbulence, and the flow separates, say on a SMOOTH ball, then in the rear, there is circulation in the wide wake. There is pressure on the front, but no pressure on the rear due to the fact that the fluid is "busy" circulating around. So...
  32. P

    A Measuring Viscosity via the Speed of Sound

    Hello, I am on the search for papers, books, etc. on how one can measure the viscosity of viscous materials via the speed of sound. I've searched for a while now and haven't been able to find much on this topic. Any help is greatly appreciated.
  33. P

    Speed of sound: viscosity dependece in liquids and solids

    Hello, Wikipedia gave me prior hints as to how the speed of sound depends on viscosity but after searching on Google scholar and Google, I have yet to find any direct equations/findings that give a direct relationship of the speed of sound to the visocisty of fluids and solids outside of...
  34. felipe de carli

    Torque lost using Newton's law of viscosity

    Homework Statement Two circular plates, as indicated in the figure, slide one over the other. Calculate the torque lost in this situation. The rotation w of the internal radius of the plates R1, the outer radius of the plates R2, the absolute viscosity of the lubricant between the plates (η)...
  35. A

    Viscosity & Temperature - Linearisation and glycerine?

    Hey all, I'm new to the forums and had a quick question: (please tell me if this is the wrong topic under which I posted, please move it if needed! @mods) I am doing a lab report investigating the effect of temperature (˚C) on the dynamic viscosity (Pa s) of glycerin. I am timing the time it...
  36. wildonion

    Kinematic viscosity for water on Mars

    Hi - I am trying to understand the relationship between atmosphere pressure, viscosity, and density - specifically water. Is there are way to estimate a range of dynamic viscosity and density values based on varying atmospheric pressures and/or temperature that I could use on any planet. Thanks...
  37. WhiteWolf98

    Determining the coefficient of viscosity of water (Graph Problem)

    Homework Statement So, the question is based around an experiment to determine the coefficient of viscosity for water (by capillary flow). Part of the experiment involved producing a graph of Q against h. This graph is supposed to be linear, and is supposed to pass through the origin. As can be...
  38. I

    Hydrodynamic forces on a foil, Reynolds number, viscosity

    Hi! I know little about physics, but I am very well educated , with an inquisitive mind. First the context, then my specific question A. Context The practice of windsurfing has brought me to try and understand the principles of hydrodynamics, in order to make my sailing more efficient. As...
  39. M

    Exploring Reyleigh-Taylor Instability with Variable Density and Viscosity

    Homework Statement import time import numpy as np from Output import * from PoissonSolver import * tmps1=time.clock() # Physical parameters Re = 10. # Numerical parameters CFL = 0.9 dt = 0.001/4 t = 0.0 tmax = 1.5 # Make mesh from MeshGeneration import * mesh = Mesh(2.0,1.0,50,25) #...
  40. dRic2

    Viscosity and thermal diffusivity in liquids and gases

    Hi PF, I was wondering about this for some time and I can get my head around it. Viscosity ##\mu## is a "measure" of the momentum flux Thermal diffusivity ##\alpha## is a "measure" of the heat flux (kinetic energy of molecules) In gases both viscous stresses and heat flux take place due to...
  41. F

    Understanding Viscosity: Solving a Fluid Mechanics Problem

    Homework Statement the picture has all the information Homework Equations I am assuming we will be needing the viscosity equation, tao= mue(dv/dy) where v is velocity The Attempt at a Solution I do not know how to approach this exercise.
  42. C

    Does electron gas in metals experience viscosity?

    Does electron gas in metals experience viscosity? Also, does highly charged plasma experience viscosity?
  43. Perodamh

    Find Viscosity of Fluid on an Inclined Plane

    Homework Statement A plate having an area of 0.6m^2 is sliding down the inclined plane at 30 degrees to the horizontal with a velocity 0.36 ms^-1. There is a cushion of fluid 1.8mm thick between the plate and plane. Find the viscosity of the fluid if the weight of the plate is 280N.Homework...
  44. P

    Motion of a particle in a magnetic field and viscous medium

    Homework Statement In a homogeneous, non-magnetic, highly insulating and viscous medium, a moving particle experiences a viscous drag given by the law f→=−bv→. Here b is a positive constant. A particle having charge q is projected with an unknown velocity from a point in the medium. It almost...
  45. M

    Estimating density, viscosity and thermal conductivity

    Homework Statement Hi there, I am designing a heat exchanger and I am really struggling to find out how to fairly accurately estimate the density, viscosity and thermal conductivity of a gaseous mixture at ~~20bar. There is 8 components in the mixture: methane, ethane, ethene, ethlyene oxide...
  46. B

    Finding torque in rotating cylinder (viscosity )

    Homework Statement Homework Equations τ= η* (dv/dy) The Attempt at a Solution so dA= 2π* r * dr T = ∫ τ * r * dA T = ∫((0.01* r* 2*π * 450 /60)/(5*10^-3) ) * r * 2π* r *dr = (592.1762)*(r^4/4) T = 0.11 Nm is this correct?
  47. J

    Inviscid flows and the turbulent (eddy) viscosity

    Hello, After Favre averaging the momentum equation for an inviscid flow, the following can be obtained: $$\frac{\partial}{\partial t} \left(\overline{\rho}\tilde{u}_i \right) + \frac{\partial}{\partial x_j}\left( \overline{\rho}\tilde{u}_i \tilde{u}_j \right) + \frac{\partial...
  48. Gabriel Ulisses

    B What property of a fluid determinates rising and sinking Velocities

    If we have a bottle with a fluid A of X density, and in the bottom of this bottle it magically spawns the same amount of fluid B with X/2 density, fluid B should rise in fluid A until they both change positions and fluid B floats in A. Wich property of the fluids are the ones that determinates...
  49. N

    How sodium alginate changes the viscosity in water?

    Hello everyone. I have a question about the sodium alginate (NaC6H7O6)n. Recently, sodium alginate is widely used for fabricating edible bottle. And I also try to utilize sodium alginate for controlling the viscosity of water. I found that with small amount of sodium alginate powder in DI water...