Re: accerelation due to gravity

[Leigh Palmer <palmer@SFU.CA>]

At 10:29 AM +0200 1/26/01, Savinainen Antti wrote:
> I just want to make a comment on the following excerpt (taken from Leigh's
> posting):
>
> > When I introduce this topic I suppress
> > mention of the centrifugal force when I introduce weight, defining it simply
> > as the reading on a scale (or spring balance). I then tell them weight is
> > the product of an object's mass and the gravitational field at the weight's
> > position, the latter being g in the laboratory on Earth's surface. In the
> > orbiting Space Shuttle the gravitational field is nearly zero, so we say the
> > astronauts inside are weightless, or very nearly so. All of these statements
> > conform to both scientific and common cultural understanding.
>
> I disagree with Leigh that the gravitational field would be zero (or very
> nearly zero) in the orbiting space shuttle.
> The very reason for the orbiting is the gravitational force exerted by the
> Earth and hence the gravitational field cannot be zero.
> Of course astronauts inside the shuttle feel apparent weightlessness because
> the satellite is in a free fall.

You don't disagree with me, you use a different convention for what you
call "weight" and "gravitational field". The convention I use is, I claim,
simpler to teach and to understand. It has the additional virtue that the
equivalence principle is already built in; the word "apparent" never, um,
appears!

Some considerable time after introducing weight in this manner it is to
be shown that weight has a centrifugal force component on Earth's surface
and in the orbiting shuttle. The latter is larger, that's all.

Leigh