[time-nuts] FW: Pendulums & Atomic Clocks & Gravity

Didier Juges didier at cox.net
Wed May 30 07:22:04 EDT 2007


Ulrich,

Yes, but your use of the term "system" instead of "frame of reference"
confused me instead of helping. 
It sounded like you were talking about different cases, instead of the
same case under different viewpoints.
I did not understand what you meant.

That's OK, I believe I got it now.

Thanks

Didier KO4BB

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Ulrich Bangert
Sent: Wednesday, May 30, 2007 12:37 AM
To: 'Discussion of precise time and frequency measurement'
Subject: Re: [time-nuts] FW: Pendulums & Atomic Clocks & Gravity


Didier,

my first posting to that topic contained the semtences:

> Centrifugal forces are so called fictitious forces
> which are only observed from within accelerated systems. 
> Normal physics is done in inertial systems.

Is that not pretty much what you have found out after all?

73s and my best regards
Ulrich, DF6JB

> -----Ursprüngliche Nachricht-----
> Von: time-nuts-bounces at febo.com
> [mailto:time-nuts-bounces at febo.com] Im Auftrag von Didier Juges
> Gesendet: Mittwoch, 30. Mai 2007 02:35
> An: Discussion of precise time and frequency measurement
> Betreff: Re: [time-nuts] FW: Pendulums & Atomic Clocks & Gravity
> 
> 
> James,
> 
> Where were you all week-end?
> 
> Your explanations are so clear, it makes sense now. Thank you
> very much.
> 
> I understand now that centrifugal forces are necessary to
> explain the behavior of objects when an accelerating frame of 
> reference is used, but not necessary (actually 
> counter-productive) to explain the behavior of the same 
> objects when an inertial frame of reference is used.
> 
> That solves my problem and the apparent contradiction that
> sometimes the centrifugal force is necessary and sometimes 
> not, because I did not appreciate the effects of changing the 
> frame of reference.
> 
> Thanks a lot again.
> 
> I had no idea time-nuts would drive me to brush-up on physics :-)
> 
> Didier KO4BB
> 
> ---- James Maynard <james.h.maynard at usa.net> wrote:
> 
> > The reason that the frame of reference matters is that gravity is 
> > indistinguishable from acceleration. (This is an assumption that 
> > Einstein made when deriving his general theory of
> relativity. It seems
> > to work.)
> > 
> > An "inertial" frame of reference is a non-accelerating frame of 
> > reference. In an inertial frame of reference, Newton's laws
> of motion
> > work -- if you use Newton's gravitational relationship, that the
> > gravitational force (weight) that each of two bodies exerts 
> on the other
> > is proportional to both their masses, and inversely
> proportional to the
> > square of the distance between them.
> > 
> > In an accelerating frame of reference (either linear
> acceleration, or
> > rotational acceleration, or both) additional forces,
> technically called
> > "fictitious" forces, must be introduced in order to explain
> the motions
> > of bodies with Newtonian mechanics. The "fictitious" forces
> on a body
> > are also proportional to the body's mass. (A body's mass is just a
> > measure of its inertia: to accelerate at an acceleration 
> "a", a force
> > "F" must be applied, and the mass "m" is just F/a.)
> ......
> 
> 
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