Re: [Phys-l] Inertial frame of reference

[Brian Whatcott <betwys1@sbcglobal.net>]

Here's an operational definition - several, actually.

Intrinsic
A platform ("frame") is inertial if equipped with three force sensors 
which are not pair-wise collinear and sense no force, and if equipped 
with three angular rate sensors
which are not pairwise axially collinear and which sense no rotation... 
for the time period of interest.

More practically: substitute "reasonably mutually orthogonal" for "not 
colinear"
where this involves pairwise axial differences greater than 60 degrees.

Extrinsic
For space-born applications: substitute two optical tracking telescopes 
whose axes are not collinear [ or - reasonably orthogonal] for the three 
rotation sensors. The telescopes need to fix any star on their 
respective optical axis for the time period of interest.

Brian W



carmelo@pacific.net.sg wrote:
> Hi everyone,
>
> Does anyone know which is the best definition on inertia frame of reference?
>
> Ohanian defines "inertial reference frame" as a frame in which Newton’s
> laws of motion are valid to a first approximation.
> Ludwig Lange argued that any three material points simultaneously  
> projected from a single point, and moving freely in noncoplanar  
> directions, constitute an inertial system.
> In John Denker's website, he suggests "a freely-falling frame". (It  
> seems to suggest accelerated frame of reference.)
>
>
> Best regards,
> Alphonsus
>
> Lange, ‘‘Ueber das Beharrungsgesetz,’’ Ber. der Ko¨nig. Sachsischen
> Gesellschaft der Wissenschaften zu Leipzig, Math.-Phys. Klasse 37, 331–
> 351 ~1885!.
>
>