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From: Luigi Fortunati <fortunati.luigi@gmail.com>
Newsgroups: sci.physics.research
Subject: Re: Experiments on the validity of Relativity
Date: Thu, 23 May 2024 16:02:56 PDT
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Il 19/05/2024 22:49, Luigi Fortunati ha scritto:
> [[Mod. note --
> *Coordinate* acceleration is indeed "the variation of velocity".
> 
> But, *proper* acceleration is something different:  An observer's
> *proper* acceleration is defined as the acceleration measured by an
> (ideal) accelerometer she carries with her.  
 > ...
> -- jt]]
Relativity is wrong to trust the accelerometer.

In my animation https://www.geogebra.org/m/r9zk9smz there are two 
accelerometers that accelerate in the *same* way but the first one says 
that the acceleration is present (the EK spring contracts and the LM 
spring contracts lengthens) and the second says that it is not there 
(the springs VR and SW keep their length unchanged at rest).

This shows that the accelerometer (despite its name) does not measure 
acceleration at all but measures something else because only a *couple* 
of non-concordant forces can compress or stretch the springs and not an 
acceleration.

The difference between accelerometer 1 and 2 lies in the point of 
application of the external force.

In accelerometer 1 the red external force F acts against a single 
surface point (E) as happens in the push of a hand, while in 
accelerometer 2 it is divided into an endless number of tiny equal 
forces that act individually on each single particle (whether internal 
or peripheral), as happens in the case of gravity and electromagnetism.

In both cases, the external force generates the *same* acceleration of 
the accelerometer, however, in the first case the accelerometer 1 
measures the acceleration, while in the second case the accelerometer 2 
says that the acceleration is not present.

Why?

Luigi Fortunati


[[Mod. note --

Why would you expect accelerometer #2 to register any acceleration?

I referred to an "(ideal) accelerometer".  "Ideal" includes that
non-gravitational external forces are applied only to the outer case,
not the inner "proof mass".  Accelerometer #1 satisfies this condition,
but accelerometer #2 doesn't.

As you've described the situation, there are two possble cases for
what's going on with accelerometer $#2:
(a) The "external forces" are really a gravitational field.  In this
    case accelerometer #2 is in free-fall, and having it read
    "zero acceleration" is just what we expect -- by virtue of the
    equivalence principle, no local accelerometer can detect a
    uniform gravitational field, so an accelerometer in free-fall
    should indeed read "zero acceleration".
(b) There are no gravitational fields around, but there's an ambient
    magnetic field and the accelerometer's intern "proof mass" is
    magnetic (e.g., iron/steel) so that the magnetic field is applying
    a force to the proof mass.  In this case the accelerometer is being
    misused (and we shouldn't pay any attention to its readings): it's
    design is such that it doesn't properly measure accelerations when
    there's an ambient magnetic field, and we're trying to use it in
    an ambient magnetic magnetic field.
-- jt]]