Newtonian Gravitation |

**Theory** > s.a. equivalence principle;
models of spacetime structure.

* __Idea__: Bodies interact
through a gravitational force *F*_{g}
= *G* *m*_{g} *m'*_{g}/*r*^{2}
acting at a distance, and accelerations are proportional to forces with proportionality
constant equal to the inertial mass, *a* = *F*/*m*_{i}.

* __Masses__: The force is proportional
to the gravitational masses, but as Newton knew *m*_{g} ∝ *m*_{i},
which makes gravitation similar to "inertial" forces,
in that the acceleration is independent of each body's individual characteristics.

* __Potential__: If we define Φ(**r**)
= *U*(*r*)/*r* for a test body, then the potential Φ satisfies the Poisson equation
∇^{2}Φ = 4π*G**ρ*,

Φ(**r**)
= –*G *∫ d*M * |**r**–**r**'|^{–1} = –*G**M*/*r* – *G* **D** · **r**/*r*^{3} – \(1\over2\)*G* *Q*_{ij} *r*^{i }*r*^{j} / *r*^{5} +
... ,

where **D** = ∫ d*M* **r**'
is the dipole moment of the mass distribution (always zero with respect to
the center of mass), and *Q*_{ij}
= ∫ d*M* [3* r _{i}'r_{j}'*
–

*

*U*_{self}
= \(1\over2\)∫ *ρ*(**r**)
Φ(**r**)
d^{3}*r* = (1/8π*G*)
* *∫ (∇Φ)^{3} d^{3}*r* +
* *∫ *ρ*(**r**) Φ(**r**)
d^{3}*r* .

@ __References__: Deser AJP(05)aug-gq/04 [from
field theory]; Counihan EJP(07)
[basic principles]; Yurtsever et al a1004 [inverse problem]; in Ohanian & Ruffini 13; in Poisson & Will 14.

**Special Topics** > s.a. cosmology;
gravitational constant; Newton's
Theorem; teaching [weightlessness, tides].

* __Tidal forces__: A mass *m* located
at (*x*, *y*, *z*) with respect to a frame centered
at a point a distance *r*_{0} away
from a center of attraction of mass *M*, feels a tidal force

*F*_{x} = –*x* (*GMm*/*r*_{0}^{3})
, *F*_{y} = –*y* (*GMm*/*r*_{0}^{3})
, *F*_{z} =
2*z* (*GMm*/*r*_{0}^{3})
;

In general relativity the expression is more complicated, uses the equation
for geodesic deviation.

* __Other formulations__:
A (slightly generalized) geometric version is the Newton-Cartan
theory.

__N____-body problem__: Volchan a0803 [Sundman-Weierstraß theorem of total collapse]; Farrés et al CMDA(13)-a1208 [high-precision symplectic integrators for the Solar System].

@ __Tidal forces__: Masi AJP(07)feb
[compressive radial]; Efroimsky & Williams CMDA(09)-a0803 [tidal torques]; > s.a. Love
Number.

@ __Other situations__: Odagaki & Kawai AJP(98)aug [many-particle statistics];
Beig & Schmidt PRS(03)gq/02 [self-gravitating
extended bodies]; Teixeira phy/03 [infinite
straight line of mass]; Buchert PLA(06)gq/05 [self-gravitating
dust]; Ridgely EJP(11) [in material media].

@ __Other formulations and issues__: De Pietri et al gq/92,
CQG(95)gq/94,
CQG(95)gq/94 [generalization];
Nardone JPA(98) [regularization];
Natário GRG(06)gq/04 [initial-value form, and warp drive].

**Phenomenology** > s.a. cosmological models [Newtonian cosmology];
phenomenology of gravity; modifications
and tests of newtonian gravity.

@ __Effects__: Abramowicz et al GRG(97)
[curvature of space and perihelion precession].

@ __Specific objects__: Dittrich a1609 [Dirichlet's massive homogeneous ellipsoid].

@ __Measurement__: Kulikov JMO(06)qp/05 [transparency of cold atoms];
Charrière et al PRA(12) [local *g* measurements];
Graney PT(12)sep [Giovanni Battista Riccioli];
Harms LRR(15)-a1507 [terrestrial gravity fluctuations];
> s.a. Eötvös Experiment; fifth force.

> __Related topics__: see critical collapse;
Newton's Theorem [shell theorem]; orbits in newtonian gravity.

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send feedback and suggestions to bombelli at olemiss.edu – modified 12 mar 2018