Re: No definition of weight

[Roger Key <rogerk@CSUFRESNO.EDU>]

I agree:  they have enough of a problem DISconnecting the ideas
of
mass and weight, how can you not talk about weight?

I teach an introduction to physical science course that begins with
about
9 weeks of physics.  For them, solving Galileo's falling body
equation for t
is a real challenge.  One of the homework problems asks if gravity
can act
in a vacuum, and a full 1/3 of the students said yes, of course, inside a
vacuum,
gravity holds the dust down.

this is after watching a video where the term vacuum is used to
describe
an air-evacuated tube, and I use it myself in the lecture.

Anyway, if we don't specifically attack some of these misconceptions, who
will?

- Roger


At 11:48 AM 2/8/2002 -0500, you wrote:
> While I understand the reasoning
> for your concern and avoidance of the
> word "weight" it seems to me that you cannot ignor that the
> word exists
> in our students vocabulary. If  you are concerned with
> connecting their inclass learning with the world they live in, you
> have
> to find a way to connect their concept of weight with something
> that
> they talk about in class.
> Do you do that, and if so how?
>
> cheers,
>
> joe
>
>  On Fri, 8 Feb 2002, Laurent Hodges wrote:
>
> > For many years (off and on - not continuously) I have taught
> introductory
> > physics and I do it without using the term "weight" at
> all.  (Or only in
> > telling the students to ignore the term in their textbook, and
> use
> > mg/gravitational force instead.)  All my free-body diagrams
> include a
> > gravitational force mg (g being due to everything in the universe),
> and
> > that's what I call it.  No W vector, so W is only work. 
> When we discuss
> > moving and/or accelerating elevators, we may talk about the upward
> normal
> > force of the elevator floor on a person, but I don't call that
> "apparent
> > weight" either.
> >
> > I can then ask the question, what is meant in ordinary English by
> the
> > feeling of "weightlessness" in a spaceship orbiting the
> earth?  No
> > gravitational force?  No!  No normal force pushing on
> you?  Yes.
> >
> > In mechanics we find it useful to clearly define
> "velocity" and "speed" in
> > the physics sense, which may not coincide with the ordinary English
> uses of
> > these terms.  But I see no purpose in using the term
> "weight."  It
> > unnecessarily confuses students.
> >
> > Colleagues who teach with me in the same course accept this easily,
> but
> > most of my colleagues use "weight" when teaching
> introductory physics.
> >
> > Can't we get rid of the term?
> >
> >
> > Laurent Hodges, Professor of Physics
> > 12 Physics Hall, Iowa State University, Ames, IA 
> 50011-3160
> > lhodges@iastate.edu  
> http://www.public.iastate.edu/~lhodges
> >
>
> Joseph J. Bellina,
> Jr.              
> 219-284-4662
> Associate Professor of Physics
> Saint Mary's College
> Notre Dame, IN 46556

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                          Roger Key              rogerk@csufresno.edu
California State University, Fresno                phone 559-278-2728
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