Re: Apparent weight

[Leigh Palmer <palmer@sfu.ca>]

> What Roger says below is how I try to resolve the problem in my classes; I
> don't define weight as the force of gravity on an object, but rather as what
> the "bathroom" scale reads.

That is the only definition which will work. Anything else is magic.
That is why we draw a distinction between weight and mass, of course.
Defining weight as the force of gravity acting on an object and then
saying that there could be "another" force acting due to the
measurement of weight being done in an accelerated frame requires
the student to have some way of determining his absolute state of
motion. I think we've got away from that.

Since this definition of weight is so much simpler than the "force
of gravity" definition, why does anyone think it is conceptually
more difficult? It is most certainly simpler, and it emphasizes the
difference between the concepts of mass and weight. Do you folks who
profess to teach conceptual physics leave out any discussion of mass
and weight?

> Then there is no problem for astronaughts, they
> are weightless and there is a force of gravity acting on them, which
> provides the centripetal force that . . .

It had never occurred to me to call them "astronaughts". I guess the
very etymology of the term stems from their weightlessness.

> PS.  the above is obviously the intro  physics discussion.

I do hope so; that is the way it should be introduced.

Leigh