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velocity dispersion pâšeš-e tondâ Fr.: dispersion de vitesses The → standard deviation of a velocity → distribution. It indicates how objects of the sample move relative to one another. Objects with similar velocities have a small velocity dispersion, whereas objects with very different velocities have a large velocity dispersion. → velocity; → dispersion. |
velocity gradient zine-ye tondâ Fr.: gradient de vitesse Fluid Mechanics: The rate at which the velocity changes with the distance across the flow. When a fluid flows past a stationary wall, the fluid right close to the wall does not move. However, away from the wall the flow speed is not zero. Therefore a velocity gradient exists, which is due to adhesive, cohesive, and frictional forces. The amount of the velocity gradient is characteristic of the fluid. |
velocity law qânun-e tondâ Fr.: loi de vitesse In the theory of → radiation-driven winds, an equation that describes the behavior of the → wind velocity of → hot stars as a function of distance from the star. This velocity β-law is given by the expression: v(r) = v_{∞}(1 - R_{*}/r)^{β}, where v_{∞} is the → terminal velocity, R_{*} is the stellar radius, and r the distance from the center. For → O-type stars, the exponent is estimated to be β = 0.8. |
velocity of light tondi-ye nur, tondâ-ye ~ Fr.: vitesse de la lumière A → physical constant which represents the ultimate speed limit for anything moving through space, according to the theory of → special relativity. It is the speed of propagation of → electromagnetic waves in a vacuum, equal to 299,792.458 km/s (nearly 3 x 10^{8} m/s). The velocity of light appears as the connecting link between mass and energy in the → mass-energy relation. Usually denoted by c, from L. celeritas "swiftness," from celer "swift," → acceleration. |
velocity pressure fešâr-e tavânik Fr.: pression dynamique |
velocity profile farâpâl-e tondâ Fr.: profil de vitesse A plot of the fluid velocity as a function of position. |
velocity space fazâ-ye tondâyi, ~ tondâhâ Fr.: espace de vitesses Of a dynamical system, a three-dimensional space which consists of the set of values that the velocity can take (v_{x}, v_{y}, v_{z}). → phase space. |
velocity-distance relation bâzâneš-e tondâ-durâ Fr.: relation vitesse-distance The linear relation wherein all galaxies are moving away from one another, with velocities that are greater with increasing distance of the galaxy. Same as → Hubble's law. |
vorticity gerdšârigi Fr.: vorticité In fluid mechanics, a measure of the rate of rotational spin in a fluid.
Mathematically, vorticity is a vector field defined as the curl of the velocity field:
ω = ∇ x v. |
wind velocity tondâ-ye bâd Fr.: vitesse de vent The speed at which the → stellar wind is forced away from the star. Wind velocities of → hot stars are directly measured from → P Cygni profiles, which indicate velocities from several hundred to several thousand km s^{-1}. See also → escape velocity, → terminal velocity, → velocity law, → radiation-driven wind, → CAK model. |
zero-velocity surface ruye-ye tondâ-ye sefr Fr.: surface de vitesse nulle In the → restricted three-body problem, a surface which limits the region of space in which a small body can move. In the expression for the → Jacobi integral, the left side value is always positive or nul; hence the particle motion is confined to the region where U ≤ C_{J}. The surface that limits this region, defined by U = C_{J}, is called the zero-velocity surface. |
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