Re: "acceleration due to gravity"

[Leigh Palmer <palmer@SFU.CA>]

At 12:16 AM -0500 1/26/01, Hugh Haskell wrote:
> Herb Gottlieb wrote:
>
> > Kindly help me understand the difference between
> >          F=ma and F=mg.
> >   In the first equation  "a" stands for any
> > acceleration regardless of the force or mass
> > that may be involved?   In the second equation
> > "g" stands for the acceleration due to a
> > gravitational force resulting from a position
> > of a mass in a gravitational field?
>
> Let me have a go at that, Herb. Basically, F=ma, is a law whereby we
> can determine the dynamics of an object of mass m if we know the
> (net) force F applied to it. F=mg is a rule for calculating the force
> on an object of mass m due to the gravitational interaction of the
> earth and the object, after correcting for the rotation of the earth,
> and all the other corrections Leigh talked about in his post on the
> subject.

My point has been missed entirely. I did not talk about corrections
at all. In my picture g is the quantity by which one multiplies the
mass to find what I call the weight. There are no corrections. g is
what is measured by a gravimeter, or it is the initial acceleration
of an object released from rest in any frame whatever. I do not
separate out "the gravitational interaction of the earth and the
object". All those parenthetical items I mentioned are *included*
in g, and there is no practical way to separate them; they are not
of any concern whatever to the student. They don't even have to be
mentioned when the concepts of weight and acceleration of a falling
object are introduced. It's simpler that way. *That* is my point.

Leigh