Fr.: vitesse de phase
The speed at which any fixed phase (individual wave) in a → wave packet travels. It is expressed as vph = 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.
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 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.
tondâ-ye dur šodan
Fr.: vitesse d'éloignement
The velocity with which an object moves away from another object or a reference point.
Fr.: vitesse relative
For two objects A and B, the velocity which B, supposing itself at rest, assigns to A.
Fr.: vitesse relativiste
The velocity of a body when it is a significant fraction of the → speed of light.
Fr.: vitesse de rotation
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.
Fr.: vitesse spatiale
The velocity of a star relative to the Sun.
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: vt = ωr.
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.
Fr.: vitesse transverse
Same as → tangential 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.
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.
Fr.: courbe de vitesse
A plot of the radial velocity of an object against time, derived from the Doppler shift of spectral lines.
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.
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.
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.