Re: [Phys-L] equivalence question

[curtis osterhoudt <flutzpah@yahoo.com>]

I could: the existence of tidal forces gives it away. They don't exist in the "hurtling through space propelled by a rocket which was accelerating you at 9.8 m/s/s" scenario, but they do for the earth.  The original question didn't specify how the G-field is changed. Presumably it's changed so that it points in the same direction at all points in space, but, without loss of generality, it could be changed in some wacky ways, one of which exactly mimics the field of a point mass (zero divergence except right at the mass, and field lines which always point toward that mass). 

  
 
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"As a species, we are forever sticking our fingers into the electric socket of the Universe to see what'll happen next. It's a trait that'll either save us or kill us, but by god it's what makes us human beings. I'd rather be in the company of people who look at Mars than people who contemplate humanity's navel -- other worlds are better than fluff." ~~Terry Pratchett
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> ________________________________
> From: Paul Nord <paul.nord@valpo.edu>
> To: Phys-L@Phys-L.org 
> Sent: Thursday, September 13, 2012 2:37 PM
> Subject: Re: [Phys-L] equivalence question
>
> If you woke up inside a sealed elevator, could you tell the difference between being stationary on the surface of the earth and hurtling through space propelled by a rocket which was accelerating you at 9.8 m/s/s?  No.
>
> When you stand on the ground the force between your feet and the surface is equivalent to a vertical acceleration pushing you up and 9.8 m/s/s.  If you jump into the air your body is in free fall.  You "feel" no differential force.  Every part of your body is accelerated by gravity just exactly the same way.  When you touch down again, you feel the external force of the ground pushing you UP!
>
> This is an important distinction because it has crashed at least two space probes.  Genesis was one of these.  In their wisdom, engineers installed some accelerometers backwards.  These accelerometers were intended to trigger the parachute deployment.  Perhaps they thought that as it got close to the earth gravity would start pulling it "down."  However as it hits the atmosphere the air drag accelerates the capsule in a direction opposite to the direction of motion -- in this case, up.
>
> With your pendulum, the only force exerted on the bob is through the string.  It is along the direction of the string and away from the bob.  Accelerating the support simply changes the strength of this force.  It becomes a vector sum of gravity and whatever acceleration the support is experiencing.
>
> Here's an imponderable question for you...  Will the bob of a dropped pendulum maintain its distance from the support?
>
> Paul
>
> On Sep 13, 2012, at 4:38 PM, Bernard Cleyet wrote:
>
> > Is accelerating the support of a pendulum the same as changing the G field?
> >
> > bc  
> >
> >
> >
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