🚀 go-pugleaf

Joel Tassie writes:

> John said:
>
> >I think I can make a pretty good case that that's
> >exactly what a spring scale does and that, therefore, spring
> >scales measure mass.
>
> I totally disagree here.  Because if you go into outer space, where there is
> no gravitation force, then what does your spring scale read?  Zero.  Does
> that mean that the object doesn't have mass?  No.
>
> A spring scale measures the force of gravity and that will change as the
> gravitational field changes.  You don't get the same value.

To which others have in various ways written:

>Amen.

So allow me to state my position more explicitly.  I know we don't
really disagree on the pedagogical aspects of this issue:  It IS
important for students to distinguish "gravitational force" and
inertial mass.  But I'm afraid some of us are still missing the
point that neither spring scales nor balance beams directly
measure either gravitational force or inertial mass.  As I and
others have pointed out there are a lot of assumptions that go
into the interpretation of the results obtained from either
device.  And as Einstein taught us, we can "make" a 9.8 N/kg
"gravitational field" anywhere we want in the universe by simply
firing our rockets.

Now it's time to get this mass, er... that is, body to school.

John Mallinckrodt
Cal Poly Pomona
ajmallinckro@csupomona.edu