Re: What is weight? (was Re: Internal or external?)

[Cliff Parker <cparker@EMPOWERING.COM>]

Wouldn't the weight of the 100 kg body be 1000 N in all cases described.  Other
forces act on the object such as the force of the elevator or the water on the body
but the weight does not change in the conditions described.  At least not if one
uses w = mg.

Cliff Parker

John Mallinckrodt wrote:

> Here are my answers:  (And I *think* Leigh will agree even though he might
> have oversimplified a bit in his previous post.)
>
> On Sun, 10 Oct 1999, Robert Carlson wrote:
>
> > Leigh,
> >
> > To clarify your definition of weight in my mind, please tell me the weight in
> > the following cases.  I have a 100 kg mass with a density of 5000 kg/m^3.
> > The mass is placed on a bathroom scale in a tub that can be filled with
> > water.  The tub is placed in an elevator that may be accelerated and is at a
> > location where g is approximately 10 N/kg to simplify calculations.  What is
> > the weight of the mass in the following cases, first with no water in the
> > tub, and second, with enough water to completely submerge the mass?
> >
> > 1.  The elevator is at rest.
>
> 1000 N
>
> > 2.  The elevator accelerates up with a = 5 m/s/s.
>
> 1500 N
>
> > 3.  The elevator accelerates down with a = 5 m/s/s.
>
> 500 N
>
> In each case the weight is m*g where g is the local acceleration of freely
> falling frames relative to the body in question.  This will necessarily be
> the same as the magnitude of the vector sum of all "nongravitational
> forces."
>
> John