phase velocity tondâ-ye fâz Fr.: vitesse de phase The speed at which any fixed phase (individual wave) in a → wave packet travels. It is expressed as v_{ph} = ω/k, where ω is the → angular frequency and k the → wave number. See also the → group velocity. |
projected rotational velocity tondâ-ye carxeši-ye farâšândé Fr.: vitesse rotationnelle projetée The → angular velocity of a star deduced from the → rotational broadening of its → spectral lines. It is expressed as v sini, where i is the → inclination of the rotational axis with respect to the normal to the → plane of the sky. The real equatorial rotational velocity can be determined only if the inclination of the rotational axis is known. Projected, p.p. of → project; → rotational; → velocity. |
radial velocity tondâ-ye šo'â'i Fr.: vitesse radiale The component of a three-dimensional velocity vector of an object directed along the line of sight. It is measured by examining the Doppler shift of lines in the spectrum of astronomical objects. |
radial velocity curve xam-e tondâ-ye šo'â'i Fr.: courbe de vitesse radiale A curve describing the variation of the radial velocity of a star, due to the Doppler effect, under the gravitational effect of a secondary body (companion or exoplanet). The amplitude of these variations depends upon the mass of the secondary and its distance from the star. → radial velocity; → curve. |
radial velocity method raveš-e tondâ-ye šo'â'i Fr.: méthode de vitesses radiales The technique based on the analysis of the → radial velocity curve, used to detect the presence of an invisible secondary around a host star. This method holds the majority of exoplanet discoveries. → radial velocity; → method. |
recession velocity tondâ-ye dur šodan Fr.: vitesse d'éloignement The velocity with which an object moves away from another object or a reference point. |
relative velocity tondâ-ye bâzâni Fr.: vitesse relative For two objects A and B, the velocity which B, supposing itself at rest, assigns to A. |
relativistic velocity tondâ-ye bâzânigimand Fr.: vitesse relativiste The velocity of a body when it is a significant fraction of the → speed of light. → relativistic; → velocity. |
rotational velocity tondâ-ye catxeši Fr.: vitesse de rotation The velocity of a → rotational motion; same as → angular velocity. → rotational; → velocity. |
solar velocity tondâ-ye xoršid, ~ xoršidi Fr.: vitesse solaire The rate of change of the Sun's position with respect to the local standard of rest toward the → solar apex. |
space velocity tondâ-ye fazây Fr.: vitesse spatiale The velocity of a star relative to the Sun. |
tangential velocity tondâ-ye sâyâni Fr.: vitesse tangentielle 1) The instantaneous linear velocity of a body moving in a circular path.
It is equal to the → angular velocity multiplied
by the radius: v_{t} = ωr. → tangential; → velocity. |
terminal velocity tondâ-ye pâyâni Fr.: vitesse terminale 1) The constant maximum velocity reached by a body falling under gravity through a
liquid or gas, especially the atmosphere. The body ceases
to accelerate downward because the force of gravity is equal
to the opposing force of resistance by the medium. |
transverse velocity tondâ-ye tarâgozar Fr.: vitesse transverse Same as → tangential velocity. → transverse; → velocity. |
vector angular velocity bordâr-e tondâ-ye zâviye-yi Fr.: vecteur de vitesse angulaire Of a rotating body, a vector of magnitude ω (→ angular velocity) pointing in the direction of advance of a right-hand screw which is turned in the direction of rotation. |
velocity tondâ Fr.: vitesse The time rate of change of position in a given direction, measured as length per unit time. → speed. L. velocitatem (nominative velocitas) "swiftness, speed," from velox (genitive velocis) "swift." Tondâ, from tond "swift, rapid, brisk; fierce, severe" (Mid.Pers. tund "sharp, violent;" Sogdian tund "violent;" cf. Skt. tod- "to thrust, give a push," tudáti "he thrusts;" L. tundere "to thrust, to hit" (Fr. percer, E. pierce, ultimately from L. pertusus, from p.p. of pertundere "to thrust or bore through;" PIE base *(s)teud- "to thrust, to beat") + noun suffix -â. |
velocity curve xam-e tondâ Fr.: courbe de vitesse A plot of the radial velocity of an object against time, derived from the Doppler shift of spectral lines. |
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. |