# An Etymological Dictionary of Astronomy and AstrophysicsEnglish-French-Persian

## فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

### M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 5 Search : viscosity
 absolute viscosity   وشکسانی ِ اوست   vošksâni-ye avastFr.: viscosité absolue   Same as → viscosity and → dynamic viscosity.→ absolute; → viscosity. coefficient of viscosity   همگر ِ وشکسانی   hamgar-e vošksâniFr.: 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/cm2.(cm/s), which reduces to 1 dyne.s/cm2. This unit is called 1 → poise.→ viscosity; → coefficient. dynamic viscosity   وشکسانی ِ توانیک   vošksâni-y tavânikFr.: viscosité dynamique   Same as → viscosity and → absolute viscosity.→ dynamic; → viscosity. kinematic viscosity   وشکسانی ِ جنبشیک   vošksâni-ye jonbešikFr.: 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 m2s-1. In the → cgs system, cm2s-1, equal to 10-4 m2s-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.