| Chronology | Current Month | Current Thread | Current Date |
| [Year List] [Month List (current year)] | [Date Index] [Thread Index] | [Thread Prev] [Thread Next] | [Date Prev] [Date Next] |
Anthony Lapinski wrote:
> I mean that a scale does not always show your "true weight (w =
> mg). Scales show apparent weight -- how heavy you THINK you feel.
What is the difference between how heavy you feel and how heavy you
THINK you feel? And how can a scale (used properly) do anything but
show how heavy you feel?
> So when an elevator accelerates upward, you feel heavier. You feel
> more pressed to the ground, and a scale would register a higher
> reading. It seem like you are heavier, but you are not as your true
> weight has not changed (since g is still 9.8), but your apparent
> weight has.
My personal position is that a scale (properly used) shows how heavy
you ARE, i.e., your "weight." This is the result of my preferred
definitions for
1. Gravitational force, (vector): Whatever force remains when all
other forces have been identified and accounted for. That is,
gravitational force = m*a - sum of all other forces
2. Weight, (scalar): the magnitude of the gravitational force on an
object in the rest frame of the object. That is,
weight = magnitude of (sum of all nongravitational forces)
With these definitions we don't need to talk about "true weight" or
"apparent weight." There is only "weight." The only other similar
quantity of interest is the gravitational force on the object and we
can simply call it "the gravitational force."
With these definitions astronauts, like all things in freefall, ARE
weightless even though the gravitational force on them is not zero in
an earth-based reference frame.
With these definitions the weight of a person in an elevator
accelerating upward IS larger than that of the same person standing
on the ground.
John Mallinckrodt
Professor of Physics, Cal Poly Pomona
<http://www.csupomona.edu/~ajm>
and
Lead Guitarist, Out-Laws of Physics
<http://outlawsofphysics.com>
_______________________________________________
Forum for Physics Educators
Phys-l@carnot.physics.buffalo.edu
https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l