Fr.: équilibre dynamique
Mechanics: The condition of a moving mechanical system when the accelerating force is balanced by an imaginary kinetic reaction according to → d'Alembert's principle. See also → static equilibrium; → thermodynamic equilibrium.
Fr.: aplatissement dynamique
A measure of the extent to which mass has been shifted from the polar regions of a (spinning) body toward its equator (Ellis et al., 2007, Planetary Ring Systems, Springer).
Fr.: pression dynamique
A property of a moving → fluid defined by (1/2)ρv2 in → Bernoulli's law, where ρ is → density of fluid and v is → velocity. Dynamic pressure is the difference between → total pressure and → static pressure. Also called → velocity pressure. → ram pressure.
The ratio of the maximum to minimum signal levels present in an image. For instance, a true 12-bit digital camera is capable of providing a dynamic range of 4096 to 1.
Fr.: viscosité dynamique
Of or pertaining to force or power; of or pertaining to force related to motion.
Adj. from → dynamics.
Fr.: âge dynamique
Age based on dynamical properties of a system. For example, the time derived for a system to evolve from an initial state to its present state, based on velocity and dimension (size) measurements.
Fr.: rupture dynamique
Fr.: équilibre dynamique
Of a physical system, a condition in which the parts of the system are in continuous motion, but they move in opposing directions at equal rates so that the system as a whole remains in equilibrium.
Fr.: frottement dynamique
The gravitational interaction between a relatively massive body and a field of much less massive bodies through which the massive body travels. As a result, the moving body loses → momentum and → kinetic energy. An example of dynamical friction is the sinking of massive stars to the center of a → star cluster, a process called → mass segregation. Dynamical friction plays an important role in → stellar dynamics. It was first quantified by Chandrasekhar (1943).
Fr.: loi dynamique
A law that describes the motion of individual particles in a system, in contrast to → statistical laws.
Fr.: masse dynamique
The mass of an object derived indirectly from theoretical formulae based on the laws governing the behavior of a → dynamical system.
Fr.: parallaxe dynamique
A method for deriving the distance to a binary star. The angular diameter of the orbit of the stars around each other and their apparent brightness are observed. By applying Kepler's laws and the mass-luminosity relation, the distance of the binary star can be calculated.
Fr.: relaxation dynamique
The evolution over time of a gravitationally → bound system consisting of N components because of encounters between the components, as studied in → stellar dynamics. Due to this process, in a → star cluster, → low-mass stars may acquire larger random velocities, and consequently occupy a larger volume than → high-mass stars. As a result, massive stars sink to the cluster centre on a time-scale that is inversely proportional to their mass. See also → mass segregation.
Fr.: courant dynamique
A group of stars pervading the Solar neighbourhood and travelling in the → Galaxy with a similar spatial velocity, such as the → Ursa Major star cluster, The term dynamical stream is more appropriate than the traditional term supercluster since it involves stars of di fferent ages, not born at the same place nor at the same time. A possible explanation for the presence of young groups in the same area as those streams is that they have been put there by the → spiral wave associated with their formation place, while kinematics of the older stars of the sample have also been disturbed by the same wave. The seemingly peculiar chemical composition of the Hyades-Pleiades stream suggests that this stream originates from a specific galactocentric distance and that it was perturbed by a spiral wave at a certain moment and radially pushed by the wave in the solar neighbourhood. This would explain why this stream is composed of stars sharing a common metallicity but not a common age (Famaey et al. 2005, A&A 430, 165).
Fr.: système dynamique
A system composed of one or more entities in which one state develops into another state over the course of time.
Fr.: temps dynamique
The independent variable in the theories which describe the motions of bodies in the solar system. The most widely used form of it, known as Terrestrial Time (TT) or Terrestrial Dynamical Time (TDT) uses a fundamental 86,400 Systeme Internationale seconds (one day) as its fundamental unit. → Terrestrial Time; → Terrestrial Dynamical Time; → Barycentric Dynamical Time.
dynamical time scale
marpel-e zamâni-ye tavânik
Fr.: échelle de temps dynamique
1) The characteristic time it takes a protostellar cloud to collapse
if the pressure supporting it against gravity were suddenly removed;
also known as the → free-fall time.
Fr.: variable dynamique
Mechanics: One of the variables used to describe a system in classical mechanics, such as coordinates (of a particle), components of velocity, momentum, angular momentum, and functions of these quantities.
The branch of → mechanics that explains how particles and systems move under the influence of forces.