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Gravitationnal acceleration
g
value on the surface of some planets and stars
celestial
object

g (N/kg)

Sun

273,95

Mercury

3,70

Venus

8.87

Earth

9.8108

Moon

1.62

Mars

3.71

Jupiter

24,79

Saturn

10,44

Uranus

8,87

Neptune

11,15

Pluto

0,66

Unit
and notation
It is noted
g, always in tiny letter, not to be confused with "G", in
capital letter, which represents the universal gravitational
constant.
Its unit is
Newton per kilogram, symbol N / kg or N.k^{g1}
This unit
can easily be found using the relation g = P: m where it clearly
appears that the Gravitational Field Intensity corresponds to the
ratio of a force (in Newton) by a mass (in kg).
Note: The
Gravitational Field Intensity is equivalent to an acceleration
(sometimes called gravitational acceleration), so it is also possible
to express it in meter per second squared (m/s^{2}
or m.s^{2}).
Definition
The
Gravitational acceleration
is defined in the vicinity of a celestial object as the coefficient
of proportionality between the mass of a system and the force
intensity (the weight) applied by the celestial object on this
system. Thus for a system of mass m, of weight P on a given celestial
object where the Gravitational Field Intensity is noted g (celestial
object) we can use the following relation:
P = m. g_{(celestial object)}_{
}
Gravitational
acceleration
Intensity and gravitation
The weight
results from the gravitation force but also from the inertia force
resulting from the rotation of the celestial object, but they are
most often negligible. therefore, we consider that the Gravitational
Field Intensity is related to gravitation, and most often we
calculate the value of the Gravitational Field Intensity using
gravitational force.
g
expression on any celestial object
On the surface
of a celestial object with a mass m_{A}
and a radius R_{A},
the gravitational force applied on an object with a mass m:
If the
gravitational force is assimilated to the weight with the expression:
P
= g_{A}.
m
Then the
expression of the Gravitational Field Intensity on the surface of the
celestial object A is:
g_{A}
= 
G.m_{A}
R_{A}^{2}


Example
On
planet
Earth with the mass is M_{T} = 5.97 x 10^{24}
kg and its average radius RT
= 6370 km:
g_{T}
= 
6,67.10^{11}.5.97
x 10^{24}_{}
(6370.10^{3})_{}^{2}


g_{T}
= 9,81 N/kg
Variations
of g
The
Gravitational Field Intensity depends on the same factors as the
gravitational force:
 The mass
of
the celestial object.
 The
distance
from the center of the celestial object
This
implies
that the Gravitational Field Intensity:
 depends
on
the celestial object (and its mass)
 decreases
with increasing altitude
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