Re: summary of weight

[John Denker <jsd@MONMOUTH.COM>]

At 05:51 PM 10/16/99 -0400, Bob Sciamanda wrote:
> OK, John.  This makes sense and I can buy it.  This is what I mean when I
> insist that the orbiting astronaut is not weightless!

The language here is stronger than it should be.  You can insist that the
astronauts are not *necessarily* weightless, but be careful because they
might be weightless depending on the choice of reference frame.

At 06:17 PM 10/16/99 -0400, Bob Sciamanda also wrote:
> In evaluating the weight of an orbiting astronaut relative to an
> earth-bound frame, is the vector g evaluated on the earth surface (and in
> the earth surface frame)

No...

> or at the astronaut's position (and in the earth
> surface frame)?  I guess I require a specification of the word "colocated"
> (to the object or to the frame).

Yes, both!  The measurement is colocated with the object, in the earth frame.

One way to do it is to imagine super-tall scaffolding reaching from the
floor of the lab to where the astronaut is.  The position, velocity, and
acceleration of the framework is determined by the fact that it is rooted
in ("bound to") the lab, but the object's weight should be measured where
the object is.

(For a typical 100-mile-high orbit, the velocity and acceleration at the
top of the scaffolding is not significantly different than at the bottom
anyway.  So I assume that you are envisioning a higher orbit.)

Arguably an even better way to do it would be to imagine super-tall
scaffolding on rails, moving westward relative to the earth's surface so as
to nullify the earth's rotation.

______________________________________________________________
copyright (C) 1999 John S. Denker             jsd@monmouth.com