Re: A weighty subject

[Robert Carlson <Raacc@AOL.COM>]

In a message dated 10/16/99 7:06:22 PM Central Daylight Time,
ajmallinckro@CSUPOMONA.EDU writes:

> Robert Carlson wrote:
>
>  > [John Mallinckrodt]  writes:
>  >
>  > >  I see lots of potential here for confusion down the line.  I happen to
>  > >  like the identification of weight with the magnitude of m*a_freefall
>  > >  because that *is* what a scale reads (i.e., they are using my
> definition),
>  >
>  > Scales will read whatever you calibrate them to read.
>
>  I simply don't know what to make of this response in the context of our
>  discussion.  It doesn't seem intended to promote clarity.

The definition that weight is the force of gravity does not rely on any
manmade device such as a scale.  Again, this is not my definition, but I do
prefer it to yours, simply because it does not rely on a manmade device.  In
my thinking, physics is the study of nature and trying to determine the
rules.  Weight has already been defined simply as the force of gravity.  Why
introduce a manmade device into this definition?  Nature does not give a damn
about manmade devices, or whether we have figured out what she does.  She
will do what she will do, regardless of what we think she will do based on
our measuring devices.  Weight is the force of gravity is a beautiful
definition and I do not want it bastardized.

>  > >  We know and that is certainly your right.  We would have it be
> otherwise
>  > >  since there is already a perfectly good name for the force of gravity
>  > >  (i.e., "the force of gravity") and a very meaningful alternate use
for
> the
>  > >  name "weight."
>  >
>  > I prefer weight, it is much shorter than "the force of gravity."
>
>  Robert. You can believe me when I say, I know that.
>
>  > > > Would those advocating not using weight also advocate not using
>  > > > acceleration, but instead always say the time rate of change in
>  > > > velocity?
>  > >
>  > >  Why would we do that?  I see no advantage to be gained.
>  >
>  > The advantage is that it is shorter and means the same thing.  Why do
>  > mathematicians define m = (delta y)/(delta x)?  I conclude it is
shorter,
> and
>  > easier to say slope, than delta y divided by delta x.
>
>  Let me get this straight.  In response to your question (perhaps you would
>  like to read it again), I express puzzlement as to why you would suggest
>  such a thing.  Your response leaves me even more puzzled and I can only
>  read it as saying that *you* think "it" (i.e., "time rate of change of
>  velocity") is a shorter phrase than "acceleration."  I suspect that you
>  simply didn't read carefully.

I read, but simply did not get the response in the correct position.  I
meant, that physicists use acceleration in the same fashion that
mathematicians use slope, m.  It is simply more convenient to define a
shorter expression and then use it after that.  I suggest that this is the
same for the definition, weight is the force of gravity.  Once defined,
weight is sufficient and the longer expression, the force of gravity, is no
longer necessary.

>  > >  Everyone that I
>  > >  know agrees that acceleration IS the time rate of change of velocity.
>  > >  I've never heard anyone suggest a good alternate use for the word
>  > >  acceleration.
>  >
>  > Everyone would also agree that weight is the force of gravity if they
> would
>  > read their physics texts.
>
>  Correct me if I am wrong, but I sense that you are saying you really
>  aren't interested in my *reasons* for promoting a different definition.

Please tell me your reasons.  However, if you are interested in defining
something such as what a scale reads, why not call it tension, or the normal
force?

>  > It is not my definition.  I do not presume to be on the level to make
>  > fundamental physics definitions.  I will leave that to those with much
> more
>  > knowledge than myself.  Perhaps this is you John, convince me.
>
>  I have tried my best to explain rationally the reasons that I prefer a
>  different definition.  You seem to want to have it that I am simply
>  "wrong."  I see no point in beating my head against the wall.

If you wish to make definitions, then by all means do so.  But, weight is
already defined, so call whatever you are talking about by a different name.
I liken this whole discussion about weight to a whisper passed around at a
party.  The first person whispered to the second person, weight is the force
of gravity.  The ninth person whispered to the tenth person, weight is what a
spring reads.  And, I don't know where this comes from.  I think the physics
texts have done a very reasonable job of passing the first whisper along
fairly intact.

>  John Mallinckrodt      mailto:ajm@csupomona.edu
>  Cal Poly Pomona          http://www.csupomona.edu/~ajm