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