Geoscience Reference
In-Depth Information
important constant, see http://physics.nist.gov/cuu/constants. (For other
constants we have a relative accuracy of 10
−
7
and better.) For comparison
of experimental results see the internet.
Although the masses
m
1
,m
2
attract each other in a completely symmet-
rical way, it is convenient to call one of them the attracting mass and the
other the attracted mass. For simplicity we set the attracted mass equal to
unity and denote the attracting mass by
m
. The formula
F
=
G
m
(1-3)
l
2
expresses the force exerted by the mass
m
on a unit mass located at
P
at a
distance
l
from
m
.
We now introduce a rectangular coordinate system
xyz
and denote the
coordinates of the attracting mass
m
by
ξ, η, ζ
and the coordinates of the
attracted point
P
by
x, y, z
. The force may be represented by a vector
F
with magnitude
F
(Fig. 1.1). The components of
F
are given by
P
l
F
¯
Y
||
y
m
y
-
´
z
P xyz
(,,)
||
z
l
F
z
-
³
°
Z
m(,,)
»´³
¯
||
y
X
®
x -
»
||
x
y
x
Fig. 1.1. The components of the gravitational force; upper figure
shows
y
-component
