Re: [Phys-l] g...

["John Clement" <clement@hal-pc.org>]

Many of the sites I have seen do not make a clear distinction between the
acceleration of a body at the surface, and the gravitational field strength.
There is a tendency to talk about how the gravitational acceleration
changes, when really they should be calling it the net acceleration changes,
and then they define the gravitational force=mg, where g is the
gravitational acceleration.  But the g they use is actually the net
acceleration, or as proposed the local free fall acceleration.

BTW how is this standard value arrived at since the local acceleration
varies by about 0.5%.  I would think that this value is merely established
for comparison purposes so one can quote measured values as differences from
it, and not as a value to be used to make exact calculations.  Or is it a
theoretical value at one point on Earth?

John M. Clement
Houston, TX

> According to NIST again, the "standard acceleration of gravity", g_n, is
> defined to be exactly  g_n = 9.806 65 m s-2
>
> The local acceleration of gravity, g, varies noticeably from this value,
> due to rotation and a non-spherical earth.  Perhaps the terms "local
> free fall acceleration" and "standard free fall acceleration" would be
> better terms,  since g at any given location include not only
> gravitational effects but also a correction for the rotation of the
> earth.