Re: Weight and Mass

["RAUBER, JOEL" <JOEL_RAUBER@SDSTATE.EDU>]

Thanks, Tim for a succinct summary of several iterations of discussion on
this topic.  I agree that the non-unanamous consensus was SET I.  I too am
curious if anyone sees a SET IV option that we haven't considered?

Joel


> Consider the following useful ideas (avoid/ignore buoyancy,
> holding on to
> ropes, etc, etc):
> a)   the gravitational force between you and the earth
> b)   the reading when you stand on a scale on the earth
> c)   the reading when you stand on a scale in any other
> reference frame.
>
> All of these clearly have something to do with weight, so
> which one should
> we call "the weight"?  ANY of the following sets can be logical and
> consistent names (respectively):
>
> SET I
> a)   force due to gravity
> b)   weight
> c)   weight
>
>
> SET II
> a)   force due to gravity
> b)   weight
> c)   apparent weight
>
> SET III
> a)   weight
> b)   apparent weight
> c)   apparent weight
>
>
>
> My top choice (and I *think* the consensus of the group here)
> has been the
> first.  My reasons are as follows.
> 1)  F(G) = "force due to gravity" is a perfectly good and
> clear name for
> the first concept.  Why use a second name to mean exactly the
> same thing?
>
> 2) If W == mg == m(9.81 m/s/s), then this numerically is not
> GmM/r^2, but
> rather GmM/r^2 - mv^2/r.  The standard "g" has the earth's
> rotation built
> into the definition.  What we most commonly calculate as
> weight on earth is
> the same as (b).
>
> 3)  Since weight (in in the previous point) already is the
> "apparant force
> of gravity" in the specific frame of the rotating earth, the word
> "apparant" seems implied.  So why add it specifically in some
> reference
> frames (e.g. in orbit), but not in others (e.g. on the
> rotating earth.)?
>
> Does anyone want to argue for a different set of definitions
> for the above
> concepts???
>
>
> Tim Folkerts
> FHSU