Re: Weight

["Richard W. Tarara" <rtarara@saintmarys.edu>]

Unlike many on the list, I have no problem with the concept of weight being
a special name for the gravitational attraction of the earth (or other
nearby, large astronomical body) on an object.   This gravitational
attraction dominates our daily lives in a more direct way than the
electrical force--we experience gravitational effects constantly while the
(even more important) electrical ones are basically invisible to us--thus
having a special name is not unwarranted.    OK, there is a practical
problem with whether you call weight the net force towards the center of
the earth or just the gravitational attraction but the effects of the
rotating earth is usually not of major concern in an introductory course.

I also have no problem with the 'weightless' astronauts--they're NOT.  They
have no apparent weight but again I harken back to the fact that we
experience our weight 'normally' through the balancing forces that keep us
from accelerating.  In the absence of these 'upward' forces they _feel_
weightless.  

Using the apparent weight (the upwards forces) to define the term weight
does have some advantages, but the everyday concept of weight as a downward
pull would be (in my opinion) harder to overcome than adding the concept
that we experience that pull primarily through upwards forces and thus get
fooled in situations where that upwards force does not balance the
downwards pull of gravity.

Rick
----------
> From: Rauber, Joel              
>
> David wrote and Marlow cheered
>
>
> > BTW, since gravitational forces (locally) are not "real" but are
artifacts
> of
> > the use of a noninertial frame used to describe the physics, I prefer 
> *not*
> > to define the concept of "weight" as (the magnitude of) the
gravitational
> > force on an object.  Such a definition makes an object's weight depend
on
> the
> > coordinate system of the observer.  I prefer to define weight as what 
> others
> > define as "apparent weight" which is simply the magnitude of the
> > *non*gravitational force of support on a body which prevents a free
fall
> > state (or equivalently, which deflects the motion from a free fall
state).
> > This definition of weight is independent of the frame of the observer
and
> > agrees with our usual sensations of weight.
>
> I too define weight in this fashion, although for simpler reasons than 
> talking about non-inertial frames, and free-fall frames etc.
>
> Simply put, if you define weight to be the gravitational force acting on
an 
> object; how do you explain why we say astronoughts are weigtless while 
> orbiting the earth, since they still have a gravitational force acting on

> them.
>
> Therefore defining weight as the magnitude of the non-gravitational force

> present balancing the gravitational force on the scale used, relieves one

> from the above conundrum and allows one to consistantly understand the
term 
> weightless up on the space-shuttle
>
> Joel