An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 30 Search : moment
moment of momentum
  گشتاور ِ جنباک   
gaštâvar-e jonbâk

Fr.: moment cinétique   

Same as → angular momentum.

moment; → momentum.


Fr.: quantité de movement   

In → Newtonian mechanics, the momentum p of a body with → mass m and → velocity v is the product of these two quantities: p = mv. Momentum usually means → linear momentum as opposed to → angular momentum.

From L. momentum "movement, moving power," from movere "to move," → move.

Jonbâk, from jonb present stem of jonbidan "to move" (Mid.Pers. jumbidan, jumb- "to move," Lori, Laki jem "motion," related to gâm "step, pace;" O.Pers. gam- "to come; to go," Av. gam- "to come; to go," jamaiti "goes," gāman- "step, pac;" Mod.Pers. âmadan "to come;" Skt. gamati "goes;" Gk. bainein "to go, walk, step," L. venire "to come;" Tocharian A käm- "to come;" O.H.G. queman "to come;" E. come; PIE root *gwem- "to go, come") + -âk noun suffix.

multipole moment
  گشتاور ِ بس‌قطبه   
gaštâvar-e basqotbé

Fr.: moment multipolaire   

The quantity that gives the electric potential field due to a distribution of charges, such as a → dipole, → quadrupole, → octupole, etc. A multipole moment usually involves powers of the distance to the origin, as well as some angular dependence.

multi-; → pole; → moment.

orbital angular momentum
  جنباک ِ زاویه‌ای ِ مداری   
jonbâk-e zâviyeyi-ye madâri

Fr.: moment cinétique orbital, ~ angulaire ~   

1) Mechanics: The → angular momentum associated with the motion of a particle about an origin, equal to the cross product of the position vector (r) with the linear momentum (p = mv): L = r x p. Although r and p are constantly changing direction, L is a constant in the absence of any external force on the system. Also known as orbital momentum.
2) Quantum mechanics: The → angular momentum operator associated with the motion of a particle about an origin, equal to the cross product of the position vector with the linear momentum, as opposed to the → spin angular momentum. In quantum mechanics the orbital angular momentum is quantized. Its magnitude is confined to discrete values given by the expression: ħ &radic l(l + 1), where l is the orbital angular momentum quantum number, or azimuthal quantum number, and is limited to positive integral values (l = 0, 1, 2, ...). Moreover, the orientation of the direction of rotation is quantized, as determined by the → magnetic quantum number. Since the electron carries an electric charge, the circulation of electron constitutes a current loop which generates a magnetic moment associated to the orbital angular momentum.

orbital; → angular; → momentum.

quadrupole moment
  گشتاور ِ چهارقطبه   
gaštâvar-e cahârqotbé

Fr.: moment quadrupolaire   

A quantity characterizing an electric charge distribution, determined by the product of the charge density, the second power of the distance from the origin, and a spherical harmonic over the charge distribution.

quadrupole; → moment.

rotational angular momentum
  جنباک ِ زاویه‌ای ِ چرخشی   
jonbâk-e zâviyeyi-ye carxeši

Fr.: moment angulaire rotationnel, moment cinétique ~   

The → angular momentum of a body rotating about an axis. The rotational angular momentum of a solid homogeneous sphere of mass M and radius R rotating about an axis passing through its center with a period of T is given by: L = 4πMR2/5T.

rotational; → angular; → momentum.

specific angular momentum
  جنباک ِ زاویه‌ای ِ آبیزه   
jonbâk-e zâvie-yi-ye âbizé

Fr.: moment angulaire spécifique   

Angular momentum per unit mass.

specific; → angular; → momentum.

spin angular momentum
  جنباک ِ زاویه‌ای ِ اسپین   
jonbâk-e zâviyeyi-ye espin

Fr.: moment angulaire de spin   

An intrinsic quantum mechanical characteristic of a particle that has no classical counterpart but may loosely be likened to the classical → angular momentum of a particle arising from rotation about its own axis. The magnitude of spin angular momentum is given by the expression S = ħ √ s(s + 1), where s is the → spin quantum number. As an example, the spin of an electron is s = 1/2; this means that its spin angular momentum is (ħ /2) √ 3 or 0.91 x 10-34 J.s. In addition, the projection of an angular momentum onto some defined axis is also quantized, with a z-component Sz = msħ. The only values of ms (magnetic quantum number) are ± 1/2. See also → Stern-Gerlach experiment.

spin; → angular; → momentum.

spin magnetic moment
  گشتاور ِ مغناتیسی ِ اسپین   
gaštâvar-e meqnâtisi-ye espin (#)

Fr.: moment magnétique de spin   

The magnetic moment associated with the → spin angular momentum of a charged particle. The direction of the magnetic moment is opposite to the direction of the angular momentum. The magnitude of the magnetic moment is given by: μ = -g(q / 2m)J, where q is the charge, m is the mass, and J the angular momentum. The parameter g is a characteristic of the state of the atom. It would be 1 for a pure orbital moment, or 2 for a spin moment, or some other number in between for a complicated system like an atom. The quantity in the parenthesis for the electron is the → Bohr magneton. The electron spin magnetic moment is important in the → spin-orbit interaction which splits atomic energy levels and gives rise to → fine structure in the spectra of atoms. It is also a factor in the interaction of atom with external fields, → Zeeman effect.

spin; → magnetic moment.

wind momentum
  جنباک ِ باد   
jonbâk-e bâd

Fr.: moment angulaire de vent   

The product of the → mass loss rate and → terminal velocity used in the → radiation-driven wind theory. See also → modified wind momentum.

wind; → momentum.

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