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Re: [Phys-L] weightlessness




Better late than never?



On 2012, Jun 27, , at 11:56, John Denker wrote:

On 06/27/2012 11:22 AM, Hugh Haskell wrote:
g is *not* zero at the space station. It's at least 8-9 N/kg. You
want to consider it somewhere where g is close to zero--perhaps in
deep space, where g might approach zero (but we all no that there is
nowhere where Newtonian gravity is exactly zero. If there were there
would be no galaxies or clusters of galaxies, or even superclusters
of galaxies).

Gaaack!

In all cases, g is frame-dependent. This is required by Einstein's
principle of equivalence.

a) In the frame of the space station, g *is* zero.

b) In the frame of the earth, g in the vicinity of the space station
is on the order of 9.8 m/s/s.

Talking about "the" g field without specifying which frame is being
used is ill-posed.


Perhaps I shoulda writ weightless (~ defined by the person spring scale), and isn't it assumed the frame is the station "... on the space station."

p.s. The app's (that uses the Apple Sudden Motion Detector) manual has a calibration to set g to whatever the local value is for the stationary MacBook.


Contradicting one ill-posed statement and replacing it with another is
not an improvement.
http://www.av8n.com/physics/weight.htm
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