The gravitational constant is given the symbol "G". It is a
measured value used in the force equation for gravity (see below).
F = Gm1m2 / r2
The m units are masses of two bodies which are separated by a distance r.
By rearranging the equation, we have G (see below).
G = Fr2 / m1m2
The gravitational force, F, was measured between two masses to arrive at G.
At various times, the laboratory equipment and methods were improved to arrive at more
accurate values for G. The physics texts were not usually updated for the
new values because (1) the changes were not great enough to justify the added expense to
the texts, and (2) the changes were happening frequently enough to make each text obsolete
before it arrived in the hands of students. Consequently, there are numerous
variations of G to be found, but the differences between them are slight.
There are many systems of weights and measures used in physics. Fundamental constants
such as G often have two values according to the measuring system used. When
two such units are mixed to arrive at subsidiary units such as the planck length, the
result is a completely erroneous value along with units of measure which do not apply.
Consequently, it is important to convert the various units of the fundamental constants
used to the same system of units. In may instances of late, this has not been done.
Finally, there is human error involved in copying from an old text to create a new next.
This means that it is wise to check various texts to see if they all agree (they
usually don't), and decide what is correct and what is not correct.
For G, the following was discovered.
