What is viscous: Definition and 112 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 quantifies the internal frictional force 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. Experiments show that some stress (such as a pressure difference between the two ends of the tube) is needed to sustain the flow. This is because a force is required to overcome the friction between the layers of the fluid which are in relative motion. For a tube with a constant rate of flow, the strength of the compensating force is proportional to the fluid's viscosity.
In general, viscosity depends on a fluid's state, such as its temperature, pressure, and rate of deformation. However, the dependence on some of these properties is negligible in certain cases. For example, the viscosity of a Newtonian fluid does not vary significantly with the rate of deformation. Zero viscosity (no resistance to shear stress) is observed only at very low temperatures in superfluids; otherwise, the second law of thermodynamics requires all fluids to have positive viscosity. A fluid that has zero viscosity is called ideal or inviscid.

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  1. hello478

    Graph of viscous force and velocity

    my answer was A but i dont understand because when the viscous force equals the weight speed becomes constant but why does the viscous force needs to be equal of weight? is it weight = viscous force? or speed = viscous force?
  2. wrobel

    I A pendulum with viscous friction

    Consider the standard pendulum with a weightless rod of length b and a mass point m and mg is applied. In the hinge there is a torque of viscous friction which is proportional ##\omega^2##. Now release the pendulum from the horizontal position. What biggest height does the point m attain after...
  3. K

    B Pressure in a viscous liquid versus non-viscous fluids

    Hc verma, concepts of Physics, vol 1 pg 258 "We define pressure of fluid at the point A as : ##P= F/\Delta S## For a homogeneous and non-viscous fluid, this quantity does not depend on orientation of ##\Delta S## and hence we talk of pressure at a point". Why did the author stress that the...
  4. G

    I How to flatten the surface of a viscous gel?

    I have gel which has a specific gravity of about 0.8 and a stated viscosity of 25000 mm2/S (whatever that means). It's thicker than honey. It just sits there with an uneven top surface. About 20cc are in a container and I want to flatten the surface. The best I can do is to shake the container...
  5. abdulbadii

    How do we make our own non sticky viscous gel?

    How do we make our own non or very little sticky viscous gel as ever overheard and glimpsed a chat circle of 3-4 persons conferring one another about how making it correctly and had successfully realized one in hand of one of them But that casual time quite short so one would have no chance to...
  6. aladinlamp

    I Viscous Drag of Water: Effects & Understanding

    Hi i want to understand effects of viscious drag of water in fixed cross section open channel flow. My understanding is water viscosity and channel surface create drag opposing movement of water, changing kinetic energy of water to heat. Result is warmer water and slower water flow. If the...
  7. 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...
  8. Ophi-Siren-Kit

    Speed/Velocity and Volume Flow Rate of Viscous Fluids

    In my first attempt, I started off converting the radii of all three sections from centimeters (10, 8, 6) to meters (0.10 , 0.08 , 0.06), then used the VFR=Av formula to find the speed/velocity of section one. VFR== 0.063 m^3/s A== pi*r^2=pi*(10cm)^2=pi*(0.10)^2=pi*0.01 == 0.031415927 VFR/A=v...
  9. 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...
  10. T

    The main cause behind viscous drag

    What's the main cause behind viscosity and viscous drag? Let's see it in the molecular level. Drag occurs because one molecule attracts another. And the foremost reason for which one mass can attract other is gravity. But, it's too weak in comparison to other forces in nature and at the...
  11. ZdMh

    Viscous fluid with air bubbles

    Is a high viscosity fluid(liquid), filled with air bubbles, more or less vicious than without air? Please provide the scientific principle behind that
  12. T

    Equation of a sound wave with viscous damping in ideal gas

    How can we find a equation of a 1D sound wave in a non-differential form in an ideal gas with viscosity? How does the damping work? How does the wave lose energy at each layer as it propagates? To be clear I am looking for a simple exponential-sinusoidal function for it just in the case of...
  13. T

    MTW Exercise 22.7 -- Calculate the law of local energy conservation for a viscous fluid with heat flow

    I've come to a grinding halt with this and I can't see a way forward. Can someone please take a look at what I've done so far and let me know if what I have done is OK and then if it is, give me a hint on how to proceed. First up, Is ## u \cdot \nabla \cdot T = u_\alpha...
  14. M

    Finding height of buffer regions and viscous sublayer turbulent flow

    Hi, I was recently attempting a problem about the height of buffer regions and viscous sublayer. Question: A fluid flows through a smooth pipe of diameter 150 mm with flow rate, density and kinematic viscosity of 0.180 m^{3} s^{-1} and a density 700 kg and 0.40 \times 10^{−6} 𝑚^2...
  15. E

    Viscous work and dissipation of energy

    imagine two flat plates, the upper one moving with speed v in the +z direction, the lower one is stationary is the upper plate inserting work (per unit time) on the fluid system or the system exerting work on the plate? or both? why they don't cancel each other e.g if the fluid is receiving work...
  16. D

    I How viscous forces affect force transmission in hydraulic systems.

    Hi everyone, I have a question that I am struggling and need your help. So I am working on a project which is essentially two syringes, A & B, with different cross-sectional areas, A1 & A2, connected via a tube filled with water. If we assume loss-less system, Pascal's law, the input force...
  17. T

    Relationship between Drag Force & Viscous Torque on USA Football

    Hello, I am a Physics undergrad degree graduate who is attempting to do a personal project involving the projectile motion of an American football in a 2D space. I want to take into account the drag force that the ball will experience and also take into account the spin of the football (in the...
  18. Leo Liu

    Planetary motion in a viscous medium

    The answer to (c) is ##-2\pi AGMm##. Answer to (d) For sub-question d, I used a different approach and I don't know why the solution to (d) is an appropriate approximation. What I did was that I use Newton's laws to obtain two differential equation in polar coordinate, as shown: $$\text{Assume...
  19. R

    Flow of a Non Viscous Fluid Through this Nozzle

    My first post here! I have calculated everything i need, except the thickness of the second layer dZ*, therefore i can't solve V3/V2=(R2ˇ2)/(R3ˇ2) Trying for days now, i would appreciate any help.
  20. WhiteWolf98

    Flow Rate (Q) of Viscous Flow between Two Plates

    I know how to derive the formula, but I have no idea how to actually use this. Where it says ##50~cm## wide, I'm not sure if that's in the x-direction or the z-direction. ##W##, the width in the equation, is in the z-direction. ##\mu## can be calculated, but I'm not sure what the pressure...
  21. Kaushik

    Stokes' Law: Why does viscous drag depend upon the radius of the spherical body?

    Stokes' Law gives us the value fo viscous force when a spherical body is under motion inside a fluid. ##F_{viscous} = 6\pi\eta av## (where ##a## is the radius of the spherical body and ##v## is the velocity with which it is moving) What is the reason for the Viscous drag to depend upon the...
  22. IzitoI

    Physical units problem for a DC Motor with viscous friction

    Hi everyone, I'm trying to derive DC motor differential equations. I have some doubts: I have a viscous friction coefficient in terms of N*m*s. Is it possible to express it in terms of N*m*s/rad? And how? Some exercises show this value in Newton-meter-second and others in...
  23. M

    Flow through piping (a highly viscous additive)

    Dear Members Good day to all. We recently installed a piping system to transfer a highly viscous additive from an ISO tank to another holding tank by using a mono screw/lobe pump. My question to you all is,the discharge size of the iso tank is 3 inches, will my flow be effected if i change the...
  24. WeiShan Ng

    [Fluid Mechanics] Negative sign on the viscous work term

    Homework Statement I am revising on the derivation of the differential equation of energy (White's Fluid Mechanics 7th ed) and I'm having trouble understanding the sign convention used in the viscous work term. The textbook first define an elemental control volume and list out the inlet...
  25. G

    Beyond Viscous Drag, Cavitation, Laminar Flow, & Reynolds

    When using Computational Fluid Dynamic (CFD) modeling you are able to see incredible complexity in water energy transfer. The Thermodynamic energy transfer occurs at much higher velocity so it does not apply in most of the cases I am looking at. What are the other parasitic energy transfers that...
  26. R

    Oscillations of Spring with Viscous Medium

    Homework Statement A spring with K=12N/m and an attached bob oscillates in a viscous medium.Amplitude is 6cm from equilibrium position at 1.5 s and Next amplitude of 5.6 cm occurs at 2.5s. what is its displacement at 3s and 4.5s and t=0s Homework Equations x(t)=Xme^-bt/2m The Attempt at a...
  27. S

    Exploring the Relationship Between Velocity and Viscosity in Materials

    As I understand, viscosity characterizes the "resistance" of a material to "flow locally" as a function of the velocity of the material flow. Now my question is following, what are the physical mechanisms involved which make this "resistance" dependent on velocity of the material movement/flow...
  28. physea

    I Calculating Viscous Damper Energy in Spring-Mass Systems

    Hello, In problems that involve springs and viscous dampers, eg a mass falls on a spring that also has a viscous damper, how can we calculate the energy absorbed by the damper? I mean, we know the energy absorbed by the spring (1/2*k*x^2), we know the kinetic energy of the mass (1/2*m*u^2)...
  29. dRic2

    I Significance of the viscous stress tensor

    Hi, when working with NS equations the stress tensor can be written as ##\nabla \tau = - \nabla P + \nabla \tau_{v}##, where ##\tau_{v} ## is \begin{pmatrix} \tau_{xx} & \tau_{xy} & \tau_{xz} \\ \tau_{xy} & \tau_{yy} & \tau_{yz} \\ \tau_{zx} & \tau_{zy} & \tau_{zz} \end{pmatrix} This...
  30. 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...
  31. kostoglotov

    Viscous drag parallel to the axis of rotation: Control Systems

    Homework Statement https://i.imgur.com/WPAKuf4.png seeking G(s) = \frac{\theta_2(s)}{\tau(s)} Homework EquationsThe Attempt at a Solution What does it mean when the viscous drag is parallel to the axis of rotation?[/B] It also turns out that this system needs two equations. I can sort...
  32. dumbdumNotSmart

    Critically Damped System - Viscous force

    Homework Statement You got a plate hanging from a spring (hookes law: k) with a viscous force acting on it, -bv. If we place a mass on the plate, gravity will cause it to oscillate. Prove that if we want the plate to oscillate as little as possible (Crticial damping, no?), then $$b=2m...
  33. B

    Efficient Viscous Fluid Degassing Techniques for Epoxy Resin: Tips from Experts

    Hi all! I'm currently working with epoxies and very viscous silicone oils. The problem is when I mixing the two part epoxy, there will be a lot of bubbles in the resin. I managed using heat gun to break air bubbles near the surface, but the bubble at bottom of the mold cannot flow up. I know...
  34. E

    Manufacturing Help -- Need a highly viscous material

    First time post, I appreciate any advice! I own a small manufacturing company that makes RF connectors and adapters. Our automated machinery makes the connector bodies out of brass, and many of the parts we make have fairly delicate threads or features that are easily damaged when one part...
  35. M

    Gravity-induced viscous flow around a cylinder

    Homework Statement A viscous liquid with density and viscosity ##\rho## and ##\mu## respectively is discharged onto the upper surface of a cylinder with radius ##a## at a volume flow rate ##Q##. This is a gravity-driven flow, and it forms a film around the cylinder--see picture. What is the...
  36. J

    A Viscous fluid in granular material (DAPL)

    I saw the DAPL news story about the oil pipeline and I realized I have no idea how to analyze the problem of a fluid flowing from a boundary into granular material (or however you would classify soil). Does anyone know of any book or website that discuss the governing (or approximate) equations...
  37. MaxKang

    Difference between normal viscous stress and pressure

    Hello, I came to know that a normal component of the viscous stress can exist at a solid surface for unsteady, compressible flows(though even in that case, the normal component of the viscous stress is typically much smaller than the tangential component). I tried googling it myself but could...
  38. F

    Placing a highly viscous liquid drop on a solid surface

    Hi I'd like to ask how you would put a droplet at high viscosity (say 2.5 million times more viscous than water) on a solid surface? The droplet would have to be small (volume less than 10uL, r<1.34mm).. Thanks!
  39. S

    I Manometer reading doubt in the case of viscous fluid

    I wonder if it is correct to read an open air manometer in the case of viscous fluid in the following (usual) way. Consider the situation showed in the picture where a viscous fluid is flowing, in fact ##z_C <z_A##. The reading of the manometer would be ##p_a=\rho g z_a##, ##p_b=\rho g z_b##...
  40. D

    What is the relationship between viscosity and irrotationality in fluid flows?

    Hi, I am trying to clear the mess of the terms used in fluid mechanics and get a clearer relationship between them. So I have summarized in the table below the relationship between viscosity and irrotationality of fluid flows. Can somebody tell me if I got this right? Thanks.
  41. Jaime ortega

    I Bubbles travelling through viscous liquids

    Hi, Im doing a Invesitgation of bubbles traveling through liquids. I am blowing bubbles of fixed volume up different viscous liquids. I seem to have got a anomaly but I can't explain it When recording one of the repeats in the foam bath I saw that the bubble rushed up the liquid. It took 1.4...
  42. vktsn0303

    What does this mean? (equation for viscous flows)

    While reading a textbook on viscous flows, I came across the following interpretation of an equation: where, v is the vertical component of the free stream velocity and y is the vertical distance from the surface of a solid and Re is the reynolds number. Can someone please help me understand...
  43. C

    Thermal B.L Vs Viscous B.L

    How can I get the same properties of viscous B.L using thermal boundary layer as I am making a flow visualization for flow transition to turbulent using Schlieren Technique for flat plate? And also how can I compare between them in this situation?
  44. S

    Viscous Disc Paradox: How Does Friction Operate?

    Which way does friction in a viscous disc operate? Imagine a ring consisting of ringlets. First consider a case of a pair of nearby ringlets - in the same plane, both circular orbits. If all particles of both ringlets are in circular orbits in the same plane, then they can never collide and...
  45. K

    Change in gauge pressure using viscous flow through a pipe.

    Homework Statement Water flows at 0.25 L/s through a 9.0-m-long garden hose 2.0 cm in diameter that is lying flat on the ground. The temperature of the water is 20 ∘C. What is the gauge pressure of the water where it enters the hose? Side question: does the velocity of the water flow need to...
  46. A

    The velocity profile for viscous and non-viscous fluids

    I want to know if the velocity profile is uniform for viscous fluids or not ?
  47. B

    Thermofluids, Viscous Flow Problem

    Homework Statement Q.2 One type of bearing that can be used to support very large structures is shown below. Here fluid under pressure is forced from the bearing midpoint (A) to the exterior zone B. thus a pressure distribution occurs as shown. For this bearing which is 30cm wide, what...
  48. Feodalherren

    Fluid Mechanics: viscous flow in pipes

    Homework Statement Homework Equations ρ=789, μ=.0012 The Attempt at a Solution From the energy equation we get hf=0.9 We know that hf=f(L/D)(V^2)/(2g) [sorry don't know how to use latex after they removed the bar on the right] Now I can substitute V for Q, but I'm stuck with f and Q as...
  49. B

    Viscous damping acting on rotating disk

    I am looking for a way to calculate the torque, hence the viscous damping coefficient per T = c*w, acting on a rotating metal disk in an oil sump. How can I go about it? Thanks! PS. I am not a ME so please forgive my ignorance.