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Re: [Phys-l] Weightless (running around in circles)



John,

Thanks for the reply, I see that your "weight" definition is frame
independent in the same way that proper time is frame independent for an
object.

________________________
Joel Rauber
Department of Physics - SDSU

Joel.Rauber@sdstate.edu
605-688-4293



| -----Original Message-----
| From: phys-l-bounces@carnot.physics.buffalo.edu
| [mailto:phys-l-bounces@carnot.physics.buffalo.edu] On Behalf
| Of John Mallinckrodt
| Sent: Wednesday, November 22, 2006 9:40 AM
| To: Forum for Physics Educators
| Subject: Re: [Phys-l] Weightless (running around in circles)
|
| Joel wrote:
|
| > I'm having trouble reconciling some of the statements made
| by John D.
| > and John M. Whose opinions on the weighty matters I thought
| > corresponded;
| >
| > I think John M.'s definition of "gravitational force" below
| and John
| > D's definition of weight are the same??
|
| I think that's right. As I understand it from reading the
| first part of <http://www.av8n.com/physics/weight.htm>, JD
| would define both "weight" as mg where g is the local
| acceleration of a freely falling
| object. That corresponds exactly with my preferred definition of
| "gravitational force." On the other hand, I see no need to
| waste the perfectly good word "weight" by making it mean the
| same thing. I would prefer to let weight be the MAGNITUDE of
| the gravitational force IN THE REST FRAME OF THE OBJECT. It
| seems to me that this agrees far better with the use of the
| word in common parlance. With these definitions,
| "gravitational force" is manifestly a frame- dependent
| vector, while "weight" is, even more manifestly, a frame-
| independent scalar.
|
| For example, if I find that my weight is zero, then EVERYONE
| must agree that my weight is zero. At the same time, they
| may find that the gravitational force on me is 200 pounds
| directed toward the center of Earth, or 3 tons directed
| toward Alpha Centauri depending only on the acceleration of
| THEIR reference frame.
|
| > But I'm confused by what John M. is saying is frame
| dependent and what
| > isn't
|
| I hope this helps!
|
| John Mallinckrodt
|
| Professor of Physics, Cal Poly Pomona
| <http://www.csupomona.edu/~ajm>
|
| and
|
| Lead Guitarist, Out-Laws of Physics
| <http://outlawsofphysics.com>
|
|
|
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