Astrophysics (Index)About

gravity

(gravitation)
(theory that mass attracts)

In physics, gravity (or gravitation) is the name given to a force that attracts masses together (gravitational force) generally according to the product of their masses and the reciprocal of the square of the intervening distance (law of gravitation). It was theorized by Isaac Newton who observed the force drawing objects toward Earth and that drawing planets toward the Sun and moons toward planets could all be explained by a single law, according to his estimates of feasible masses of the Sun, planets, and moons. Newton posited it as universal, i.e., that in other situations masses would affect each other according to the same law, its effect between everyday objects being negligible because of their relatively tiny mass.

Albert Einstein recast the theory as space itself being sucked into each mass (general relativity, GR), calibrating his formula to virtually match Newton's excepting extreme circumstances, but with some consequences, such as the effect of a massive object on passing EMR: GR predicted a degree of light bending unexplainable by Newton's laws. The term Newtonian gravity is used when it is necessary to distinguish his model from GR.

These theories are phenomenally successful: for example, their reliability and precision has made space navigation as we know it possible, and the theorized degree to which it bends light has been observed. Yet they have failed to explain some observations:

Scientists have sufficient faith in gravitational theory that they cite it to assert galaxies and galaxy clusters must include matter that has yet to be detected (dark matter), and that something otherwise-undetected must be providing an outward force throughout the universe (dark energy). Alternately, attempts have been made to further refine gravitational theory to explain these observations (such as modified Newtonian dynamics and DGP gravity).


The term gravity has a different, but related use: in studies of the detail of the effects of the gravity of Earth and/or other bodies, the terms gravity and gravitation are often used with distinct meanings: gravitation to indicate the universal force and gravity to indicate a body's gravitational effects, i.e., to indicate the downward force-per-unit-mass (which amounts to acceleration) experienced at different positions in relation to the body, such as at a particular point on its surface. In this usage, the word gravity is also often meant to include the effects of inertia from the body's rotation (centrifugal force), the two together being what would be measured by an accelerometer. Gravimetry is the measurement of this acceleration.


(physics,relativity)
Further reading:
https://en.wikipedia.org/wiki/Gravity
https://en.wikipedia.org/wiki/Gravimetry
http://hyperphysics.phy-astr.gsu.edu/hbase/grav.html
https://www.britannica.com/science/gravity-physics
https://web.stanford.edu/~buzzt/gravity.html
https://phys.libretexts.org/Courses/University_of_California_Davis/UCD%3A_Physics_9HA__Classical_Mechanics/7%3A_Gravitation/7.1%3A_Universal_Gravitation
https://www.feynmanlectures.caltech.edu/I_07.html

Referenced by pages:
accretion
accretion disk
admittance
advection
alternative cosmologies
areal coordinate system
atmosphere
atmospheric escape
atmospheric tide
barrier
barycenter
baryon acoustic oscillations (BAO)
Big Crunch
bigravity
binary star
binding energy
Birkhoff's theorem
black hole (BH)
black hole thermodynamics
Bouguer anomaly
Brunt-Väisälä frequency
Bullet Cluster
Castro
Ceres
Chandrasekhar limit
ChaNGa
Chern-Simons gravity
cold dark matter (CDM)
complex crater
conic section
convection
convection zone
corotation resonance
corotation torque
cosmic string
cosmic web
cosmological constant (Λ)
cosmological model
Coulomb's law
critical density (ρc)
curvature
dark energy (Λ)
dark flow
dark matter (DM)
dark matter annihilation
dark matter detector
dark matter filament
dark matter halo
deceleration parameter (q)
DGP gravity
Doppler shift
eccentricity (e)
Eddington luminosity
Effelsberg 100-m Radio Telescope
Einstein delay
Einstein-de Sitter model
electron degeneracy
electroweak
energy
entropic gravity
escape velocity (Ve)
Europa
Europa Clipper
evaporation
extra-solar planet
f(R) gravity
field lines
free-air anomaly
free-fall time
free-floating planet (FFP)
fuzzy dark matter (FDM)
galactic tide
galaxy
galaxy cluster (CL)
galaxy interaction
general relativity (GR)
geodesic
Geroch-Bekenstein engine
giant star
Goddard gravity model (GGM)
gradient
GRAIL
gravimetry
gravitational collapse
gravitational constant (G)
gravitational field
gravitational instability (GI)
gravitational instability model
gravitational lensing
gravitational potential (Φ)
gravitational potential energy
gravitational potential model
gravitational potential well
gravitational redshift
gravitational singularity
gravitational wave (GW)
gravitationally bound
gravitomagnetic field
graviton
gravity anomaly
gravity assist
Gravity Probe B (GP-B)
gravity sounding
gravity wave
GW detection (GW)
Hale Telescope
Hayabusa2
Hill radius
homologous collapse
Hubble expansion
Hubble time (tH)
hydrodynamic equations
hydrostatic equilibrium
hypermassive neutron star (HMNS)
internal gravity wave (IGW)
inverse square law
isolation mass
J2
Jeans length
JUICE
Juno
Kelvin-Helmholtz mechanism (KH mechanism)
Kelvin-Helmholtz timescale (KH timescale)
Kepler's laws
Keplerian disk
Keplerian orbit
Lagrange stability
Lagrangian point
Lambda-CDM model (ΛCDM)
Landau damping
Lane-Emden equation
libration
Lindblad resonance
liquid mirror telescope
long-period comet
Lovelock gravity
Lunar Prospector
Mach's principle
MACHO
mass
maximum iron fraction
Maxwell-Boltzmann distribution
metallicity gradient
mirror support cell
mixing length theory
MMX
modified Newtonian dynamics (MOND)
multi-messenger astronomy (MMA)
N-body problem
N-body simulation
natural astronomical telescopes
neutron star (NS)
Newton's laws
nutation
open cluster (OC)
orbital resonance
orbital speed
parameterized post-Newtonian formalism (PPN formalism)
physical field
planet
planet formation
planetary differentiation
planetary nebula (PN)
planetesimal
pointing error (PE)
Poisson's equation
potential energy (PE)
precession of the equinoxes
primordial black hole (PBH)
Psyche
radio science
red giant
red-giant branch (RGB)
redshift (z)
reduced mass
relativity
repulsive dark matter (RDM)
Richardson number (Ri)
Roche limit
Roche lobe
Rossby radius of deformation
scalar-tensor gravity
Schrödinger-Poisson equation
sedimentation
self-gravitation
Solar and Heliospheric Observatory (SOHO)
sounder
special relativity (SR)
speed of light (c)
spiral density wave
standard gravitational parameter (μ)
star formation feedback
STARFORGE
stationkeeping
stellar cluster (SC)
stellar core
stellar dynamics
stellar evolution
stellar mass determination
stellar stream
stellar structure
string theory
strong force
strong-field gravity
supercritical fluid (SCF)
superfluid
surface gravity (g)
symmetry breaking
T-Tauri star (TTS)
Terrestrial Time (TT)
theoretical modified GR metric
Theory of Everything (TOE)
theory of figures (TOF)
tidal capture
tidal force
tidal heating
tidal migration
tide
time standard
timescale (t)
Titan
Toomre Q parameter (Q)
topological defect
Trace Gas Orbiter (TGO)
transit timing variations (TTV)
variable star
warp
wavefront error (WFE)
weak interaction
wide binaries (WB)
Wigner crystal
WIMP
wind-momentum luminosity relationship (WLR)

Index