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Newton's shell theorem
farbin-e puste-ye Newton
Fr.: théorème de Newton
In classical mechanics, an analytical method applied to a material sphere to determine the gravitational field at a point outside or inside the sphere. Newton's shell theorem states that: 1) The gravitational field outside a uniform spherical shell (i.e. a hollow ball) is the same as if the entire mass of the shell is concentrated at the center of the sphere. 2) The gravitational field inside the spherical shell is zero, regardless of the location within the shell. 3) Inside a solid sphere of constant density, the gravitational force varies linearly with distance from the center, being zero at the center of mass. For the relativistic generalization of this theorem, see → Birkhoff's theorem.
Newton's third law of motion
sevomin qânun-e Newtoni-ye jonbeš (#)
Fr.: troisième loi newtonienne de mouvement
In a system where no external forces are present, every action force is always opposed by an equal and opposite reaction.
Fr.: formule de Newton-Leibniz
The formula expressing the value of a → definite integral of a given function over an interval as the difference of the values at the end points of the interval of any → antiderivative of the function: ∫f(x)dx = F(b) - F(a), summed from x = a to x = b.
Fr.: incompatibilité entre Newton et Maxwell
The incompatibility between → Galilean relativity and Mawxell's theory of → electromagnetism. Maxwell demonstrated that electrical and magnetic fields propagate as waves in space. The propagation speed of these waves in a vacuum is given by the expression c = (ε0.μ0)-0.5, where ε0 is the electric → permittivity and μ0 is the magnetic → permeability, both → physical constants. Maxwell noticed that this value corresponds exactly to the → speed of light in vacuum. This implies, however, that the speed of light must also be a universal constant, just as are the electrical and the magnetic field constants! The problem is that → Maxwell's equations do not relate this velocity to an absolute background and specify no → reference frame against which it is measured. If we accept that the principle of relativity not only applies to mechanics, then it must also be true that Maxwell's equations apply in any → inertial frame, with the same values for the universal constants. Therefore, the speed of light should be independent of the movement of its source. This, however, contradicts the vector addition of velocities, which is a verified principle within → Newtonian mechanics. Einstein was bold enough to conclude that the principle of Newtonian relativity and Maxwell's theory of electromagnetism are incompatible! In other words, the → Galilean transformation and the → Newtonian relativity principle based on this transformation were wrong. There exists, therefore, a new relativity principle, → Einsteinian relativity, for both mechanics and electrodynamics that is based on the → Lorentz transformation.
Fr.: méthode de Newton-Raphson
A method for finding roots of a → polynomial that makes explicit use of the → derivative of the function. It uses → iteration to continually improve the accuracy of the estimated root. If f(x) has a → simple root near xn then a closer estimate to the root is xn + 1 where xn + 1 = xn - f(xn)/f'(xn). The iteration begins with an initial estimate of the root, x0, and continues to find x1, x2, . . . until a suitably accurate estimate of the position of the root is obtained. Also called → Newton's method.
→ Newton found the method in 1671, but it was not actually published until 1736; Joseph Raphson (1648-1715), English mathematician, independently published the method in 1690.
Of or pertaining to Sir Isaac Newton or to his theories or discoveries.
Newtonian, from → Newton + -ian a suffix forming adjectives.
Fr.: approximation newtonienne
Newtonian constant of gravitation
pâyâ-ye gerâneš-e Newton
Fr.: constante de la gravitation newtonienne
Same as the → gravitational constant.
Fr.: cosmologie newtonienne
The use of → Newtonian mechanics to derive homogeneous and isotropic solutions of → Einstein's field equations, which represent models of expanding Universe. The Newtonian cosmology deviates from the prediction of → general relativity in the general case of anisotropic and inhomogeneous models.
Fr.: fluide newtonien
kânun-e Newton, ~ Newtoni
Fr.: foyer de Newton
The focus obtained by diverting the converging light beam of a reflecting telescope to the side of the tube.
Fr.: limite newtonienne
The limit attained by → general relativity when velocities are very smaller than the → speed of light or gravitational fields are weak. This limit corresponds to the transition between general relativity and the → Newtonian mechanics. See also → Newtonian approximation.
mekânik-e Newtoni (#)
Fr.: mécanique newtonienne
Fr.: potentiel newtonien
A potential in a field of force obeying the inverse-square law such as → gravitational potential.
Newtonian principle of relativity
parvaz-e bâzânigi-ye Newton
Fr.: principe de relativité de Newton
The Newton's equations of motion, if they hold in any → reference frame, they are valid also in any other reference frame moving with uniform velocity relative to the first.
Fr.: relativité newtonienne
The laws of physics are unchanged under → Galilean transformation. This implies that no mechanical experiment can detect any intrinsic diff between two → inertial frames. Same as → Galilean relativity.
durbin-e Newton, teleskop-e ~
Fr.: télescope de Newton, ~ newtonien
A telescope with a concave paraboloidal objective mirror and a small plane mirror that reflects rays from the primary mirror laterally outside the tube where the image is viewed with an eyepiece.
Immediately following in time, order, place, and so on.
M.E., from O.E. next, nehst, niehsta, nyhsta "nearest, closest," superlative of neah "nigh" + superlative suffix. Cognate with Du. naast "next," O.H.G. nahisto "neighbor," Ger. nächst "next."
Podâ, literally "placed after," from *upada-, from *upa- "near, next, after," + *dâ- "to place, put," → thesis; cf. Baluci pôši "the day after tomorrow," from pô- contraction of *upa- + *aušah- "dawn," + → aurora, + suffix -i; cf. also Baluci godâ (from *uidâ-?) "then, next;" Bašâgardi, Baluci randâ "next, then."
Fr.: NGC 1275
A → Seyfert galaxy, which is the central, dominant member of the large and relatively nearby → Perseus cluster of galaxies. A powerful source of X-rays and radio emission, NGC 1275 accretes matter (→ accretion) as intercluster material falls into it, ultimately feeding a → supermassive black hole (SMBH) at the galaxy's core. NGC 1275, hosts a narrow-line radio source, Perseus A (3C 84), which interacts with the intracluster gas through its jets and bipolar outflows.
NGC, → New General Catalogue.
Fr.: NGC 346
A prominent → star cluster, and the ionizing core of giant → H II region → N66 in the → Small Magellanic Cloud galaxy. NGC 346 hosts the largest sample of young, → massive stars in the whole SMC, containing 33 → O-type stars among which 11 are of type O6.5 or earlier. This is young massive star cluster with an estimated age of about 3 million years.
346, a serial number in the → New General Catalogue.