Re: A weighty subject

[Timothy Folkerts <tfolkert@TIGER.FHSU.EDU>]

Leigh,

I think we are more in agreement than it might sound but let me make a
couple of points so that we understand each other.

> > Let me define two quantities
> >    g(1) = GM/R^2    = gravitational field strength
> >    g(2) = dv/dt     = acceleration of falling object in lab frame
>
> Let's make this physical. Redefine your terms as vector quantities,
> including the explicit latitude dependence for, say, a spherically
> symmetric Earth. After you go to that trouble I will point out that
> there ain't no such thing as an "official" value of g corresponding
> to physical reality. It is a quantity which varies with position on
> the Earth.

It is of course true that g=9.8 m/s^2 is NOT a uninversal truth for the
entire earth and I didn't mean to imply that.  Even ignoring elevators,
bouyancy, etc, the value clearly varies based on latitude and the local
geography.  I couldn't agree with you more here.

However, at any given point on the earth, we can define a local value for
g, which is determined by experiment.  My main question was what does this
locally defined constant correspond to?  If I drop an object and find it
falls with dv/dt = 9.80 m/s^2 should I say "I measured g = 9.80 m/s^2" or
should I say "After correcting for the local rotation of the earth, I
determined that g = 9.82 m/s^2"?  I can't seem to find any definitive
source to say which one is correct.


> Then anyone who wants to vote on a matter of physical reality may
> do so. This particular travesty on democracy, deciding matters of
> fact by opinion polls, is something I find particularly offensive
> in contemporary culture, so I won't participate. I'll be laughing
> too hard (and crying, too) to do so.

Yes, it is a travesty to use uninformed opinions to set policy.  The TV
shows that present a legal case in 1 hr and then ask the viewers to call in
with their verdicts is a particularly ourageous example.  That said, I
think that "fact" is synonymous with "opinion of the experts".  Once the
experts decide a legal case (i.e. the jury) then the outcome is a "fact",
whether it is correct or not!

Similarly, I think is it reasonable to ask the experts (physicists) to
decide whether it is a "fact" that g= gM/R^2 or a "fact" that g = dv/dt.
Either one is a perfectly reasonable definition - it's just a matter of
convention.

When I asked for a "vote", just wanted to know if the convention held by
most physicist is the same as the "standard" viewpoint. I really don't
know.

Beyond my personal edification, if there is little disagreement on the
standard definition (among the experts!), then the minority should probably
live with the standard view (at least until thety find more convincing
arguments to convince the others).  If there is significant dissagreement,
then there should be more discussion and more education.  If there is
almost complete disagreement, then perhaps the "standard" convention should
be scrapped.

Just my $0.02

Tim Folkerts