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. R

    Power required to move a glass bead in a viscous fluid

    Homework Statement A bead of radius R(=5 μm) is trapped by an optical beam and moved through a viscous fluid at a speed vd of 20 μms-1. If the viscous drag is given by Stokes law: F_{d}=6\pi \eta Rv_{d} obtain an expression for the laser power (intensity). If the process only has an...
  2. Soumalya

    Rate of change of Viscous Force in Couette Flow

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  3. J

    Fluid Mechanics Viscous Dissipation

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  4. W

    What's the relation of the viscous hydrodynamic forces and swirl？

    what's the relation of the viscous hydrodynamic forces and swirl？
  5. W

    Viscous Hydrodynamic Forces on Fixed Offshore Platforms

    Are the viscous hydrodynamic forces and the nonlinear viscous hydrodynamic forces applied on offshore platform in the ocean？ The platform is fixed.
  6. W

    Viscous Hydrodynamic Forces and Ship Velocity: An Analysis

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  7. D

    Euler Lagrange equations with viscous dissipation

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  8. D

    Viscously Damped System: Maximum Displacement Calculation

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  9. N

    How can I calculate the coefficient of torsional viscous damping?

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  10. B

    Dropping Marbles in Different viscous liquids

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  11. P

    Finding A_n in a Fourier-series Approach to Viscous Fluid Slowing Down

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  12. N

    Viscous Drag on a spinning shaft

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  13. M

    Understanding Viscous Stress Tensor in Incompressible Flow

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  14. I

    Numerical solution to stationary viscous flow with a Darcy term

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  15. N

    Viscous term in the Navier stoke equation

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  16. C

    Viscous fluid flow in a manufacturing process

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  17. F

    Free Fall with Viscous Friction

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  18. K

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  19. S

    High viscous fluid, how fast will a object sink?

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  20. T

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  21. G

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  22. A

    Viscous fingering and structure of space

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  23. J

    Volume Flow Rate in a Pipe for Viscous Fluid

    Homework Statement Hi, my first post here! I have a Thermodynamics resit over the summer and I'm trying to get my head around viscous flow, I'm stuck at a question and need help! Thanks :) Glycerine discharges to the atmosphere through a circular pipe 100mm in diameter. The gauge pressure 50m...
  24. B

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  25. C

    Why are gases more viscous at higher temps?

    I'd expect that since they carry more kinetic energy, they are more fluid. Thanks!
  26. M

    What is the normal viscous force(stress)?

    Hello, I understand the tangential shear stresses (or forces) acting on a fluid element due to friction between moving fluid layers, but I can't imagine how viscosity might cause a normal force (on a fluid element)...explain please!
  27. P

    Pressure drop for viscous fluid in conducts with an obstacle at the outlet

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  28. G

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  29. A

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  30. R

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  31. S

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  32. C

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  33. T

    Energy-height graph of a ball falling through a viscous fluid

    Homework Statement A ball falls from rest through a viscous fluid in a tall beaker of height H. It reaches terminal velocity at height H/2. Draw the energy-time graph for kinetic energy and gravitational potential energy on the same axes. Homework Equations F=6πηrv The Attempt at a...
  34. T

    Does Atmospheric Viscous Drag Affect Upper Atmosphere Rotation and Air Movement?

    I guess the Earth's surface pulls around the lower atmosphere with viscous drag effects? What about the upper atmosphere? Does it rotate with a slower absolute tangential velocity? If so, is there any pressure difference that caused by the difference in velocities that would cause any...
  35. N

    Frequency and viscous friction in a spring?

    Hi. may i ask the relationship(formula) between frequency and viscous friction in a spring?
  36. N

    Calculating Viscous Friction Coefficient b

    hi.. may i ask what is the relationship(formula) between the viscous friction and the frequency? if i know the value of k(spring constant), M(mass), and f(frequency), am i able to find out friction coefficient, b?
  37. B

    Sphere falling through viscous material - velcoity calc

    I'm dropping a sphere from a known height, and it enters a viscous fluid. I know the initial velocity as it enters the fluid, from there I need the velocity as it falls through the fluid (as a function of time). I know it should approach it's settling velocity (terminal velocity) and from...
  38. A

    Calculating Viscous and Pressure Drag On A Sphere

    I've been doing some research on sphere aerodynamics, in particular that of soccer balls, and was wondering if there was any way to separately calculate the pressure / form drag, and also the surface / viscous / skin drag. I know that Stoke's Law of F=6(pi)RnVc, where R is the radius of the...
  39. M

    Translating cylinder in viscous fluid

    Homework Statement I have a cylinder of radius R translating (in radial direction) with velocity U in a viscous fluid at Re<<1. Find the force exerted on the cylinder per unit lengthHomework Equations Re<<1 so the Navier-Stokes equation simplifies to the Stokes equation: \nabla P=\mu \nabla^2 v...
  40. P

    Viscous Drag and Terminal Velocity

    Homework Statement Droplets in a deodorant spray have mass of about (4x10^-12) kg and a radius of about 0.1mm. Estimate the terminal velocity of the droplets in Air of Viscosity (2x10^-5)Nsm^-2. Homework Equations Stoke's Law, F = 6pi rvu where r = radius, v = velocity and u = viscosity...
  41. I

    Viscous Friction: Exploring the Drag Force on a Sphere

    When a sphere radius r has a velocity v in a liquid .It will has a drag force exerted on the sphere. The drag force is equal to 6\pi\etarv (Stoke's law) where \eta is the fluid's dynamic viscosity Where the drag force comes from ? How does this force occur?
  42. T

    Finding Viscous Damping Constamt

    Homework Statement I am working with a problem of damped harmonic motion. I am given that the motion is in a medium that exerts a force of 2N when the speed is 4 cm/s. The mass is 5kg. Homework Equations C = F/v The Attempt at a Solution I thought that the viscous damping...
  43. U

    Which fluid is more viscous

    Homework Statement Which fluid is more viscous at moderate to high Reynolds number if used in this situation? Air or Water? The flow is incompressible and has velocity V and size L. Homework Equations Re = inerial forces/viscous forces = rho*V*L / mu as Re approaches infinity...
  44. S

    Viscous Flow and Pressure Coefficient

    Homework Statement What effect does a large positive dCp/dX have on the real viscous flow? This is for an airfoil design project using thin airfoil theory + vortex panel method. The Attempt at a Solution As far as I know Viscosity is independent of pressure, so the only thing I can...
  45. S

    Viscous Flow and Pressure Coefficient

    I am doing a project for my aerodynamics class, basically its a simplified version of the thin airfoil theory + vortex paneling method; and I have been asked the following the question: What effect does a large positive dCp/dX (Cp=Pressure Coefficient, x=position) have on the real viscous flow...
  46. T

    How to calculate viscous damping properties of air in loudspeaker design

    In the design of a loudspeaker, one intuitively seeks a critically damped alignment. We must consider the electrical resistance of the coil, magnetic field strength, mechanical resistance, mechanical compliance, and mass (diaphragm + acoustic load) of the system. The electrical resistance...
  47. N

    Is There Detailed Information on the Physics of Objects in Viscous Fluids?

    Hey all, I am looking into the physics of an object moving through a viscous fuild. I have had a look searching google, but it only comes up with articles relating the terminal velocity of an object. Are there any detailed sources that anyone knows about? If so please post a link...
  48. A

    Incompressible viscous liquid questions

    Which of the following is true in a streamlined flow of incompressible viscous liquid? A) When a fluid is in streamlined flow then there is transport of energy from one layer to another. B) The speed of flow at all points in space is necessarily same. C) The velocity of the liquid in contact...
  49. J

    Inviscid flow and viscous flow

    viscous flows are always rotational because of shear stress that is exerted on the fluid element due to viscosity. what about the inviscid flows? can they be rotational ? if yes then what are the factors which makes the inviscid flows rotational?
  50. M

    Difference between incompressible viscous and incompressible inviscid flow.

    The Navier-stokes equations have no definite understanding of how it works; does the incompressible viscous and inviscid flow have a definite understandings (Hannah and Stephens)
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