coefficient of viscosity همگر ِ وشکسانی hamgar-e vošksâni
*Fr.: coefficient de viscosité*
A quantity that indicates a property of fluids and
is defined by the ratio of shearing → *stress*
to the rate of change of shearing → *strain*.
It is also simply called viscosity. The coefficient of viscosity is expressed by:
*μ = (F/A) / (dv/dy)*, where *F* is the
force required to maintain a steady velocity difference *dv* between any two
parallel layers of the fluid, *A* is the area of the layers, and
*dv/dy* is the → *velocity gradient*
between two points separated by a small distance measured at right angles to the
direction of flow. The unit of viscosity is that of force times distance divided by
area times velocity. Thus, in the cgs system, the unit is 1 dyne.cm/cm^{2}.(cm/s),
which reduces to 1 dyne.s/cm^{2}.
This unit is called 1 → *poise*. → *viscosity*; → *coefficient*. |

kinematic viscosity وشکسانی ِ جنبشیک vošksâni-ye jonbešik
*Fr.: viscosité cinématique*
The ratio of the → *dynamic viscosity* (η)
to the density (ρ) of a fluid: ν = η/ρ. The unit of kinematic viscosity
in the → *SI system* is m^{2}s^{-1}. In the
→ *cgs system*, cm^{2}s^{-1}, equal to
10^{-4} m^{2}s^{-1}, is called the
→ *stokes (st)*. → *kinematic*; → *viscosity*. |

viscosity وشکسانی vošksâni (#)
*Fr.: viscosité*
The property of a → *fluid* that resists the force tending
to cause the fluid to flow. Viscosity may be thought of as the internal
→ *friction* of two fluid layers which flow
parallel to each other at different speeds. The cause of viscosity is the transport of
→ *momentum* by the molecules from one layer to the other.
Viscosity is given by *η = φ.u.λ.ρ*, where φ is a
coefficient which depends on the nature of the interaction between the molecules,
*u* is the average velocity of thermal motion of the molecules, λ is the
→ *mean free path*, and ρ the → *density*
of the fluid. Also called → *dynamic viscosity* or
→ *absolute viscosity*. See also
→ *kinematic viscosity*. Noun from → *viscous*; → *-ity*. |