viscosity

(noun)

A quantity expressing the magnitude of internal friction in a fluid, as measured by the force per unit area resisting uniform flow.

Related Terms

(noun)

The property of a fluid that resists the force which tends to cause it to flow.

Related Terms

Examples of viscosity in the following topics:

  • Accretion Disks

    • Without viscosity the accretion will cease, so the crucial ingredient to move further is a prescription for the viscosity.
    • Unfortunately, natural estimates for the microscopic viscosity of astrophysical gas are too small by many orders of magnitude to account for the structure of accretion disks.
    • It is likely that accretion disks are turbulent magnifying the effects of small-scale viscosity to larger scales.
    • However, without simulating the turbulence directly, it is difficult to estimate the effective viscosity.
    • Instead let's assume there is some viscosity that we don't know exact and look at the angular momentum transport needed to maintain accretion.

  • Poiseuille's Equation and Viscosity

    • Virtually all moving fluids exhibit viscosity, which is a measure of the resistance of a fluid to flow.
    • Viscosity is a basic property necessary for the analysis of fluid flow.
    • The greater the viscosity, the ‘thicker' the fluid and the more the fluid will resist movement.
    • The viscosity of the fluid is then its inherent resistance to undergo this displacement.
    • Viscosity in fluids generally decreases with increasing temperature.

  • Motionof an Object in a Viscous Field

    • Objects moving in a viscous fluid feel a resistive force proportional to the viscosity of the fluid.
    • One of the consequences of viscosity is a resistance force called viscous drag $F_V$ that is exerted on a moving object.
    • For laminar flow around a sphere, $F_V$ is proportional to fluid viscosity , the object's characteristic size L, and its speed v.
    • For the special case of a small sphere of radius R, moving slowly in a fluid of viscosity , the drag force $F_S$ is given by
    • There is a force, called viscous drag FV, to the left on the ball due to the fluid's viscosity.

  • What is a Fluid?

    • The distinction is made by evaluating the viscosity of the substance.
    • a) not resisting deformation or resisting it only lightly (viscosity), and
    • Real fluids display viscosity and so are capable of being subjected to low levels of shear stress.

  • Blood Flow

    • Typical values for the viscosity of normal human plasma at 37°C is 1.2Nsm-2.
    • The viscosity of normal plasma varies with temperature in the same way as does that of its solvent, water.
    • (a 5°C increase of temperature in the physiological range reduces plasma viscosity by about 10%).

  • Angular Momentum Transport

    • The viscous stress is proportional to the viscosity and the angular velocity gradient,
    • We can combine these two equations to yield the value of the coefficient of dynamical viscosity, $\eta$,

  • Diffusion

    • The rate of this movement is a function of temperature, viscosity of the fluid and the size (mass) of the particles.

  • Damped transient motion

    • The fluid will damp out the motion, more or less depending on whether it has the viscosity of water or honey.

  • Non-relativistic Shocks

    • In practice viscosity and thermal conduction save the day, so although the wave may get really steep, a discontinuity doesn't actually form.
    • To understand the structure of a shock, one needs to include viscosity, but one can understand the behavior of shocks without including viscosity as we shall see.

  • Application of Bernoulli's Equation: Pressure and Speed

    • (An inviscid fluid is assumed to be an ideal fluid with no viscosity. )