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From: Mikko <mikko.levanto@iki.fi>
Newsgroups: sci.physics.relativity
Subject: Re: Approximately 300,000 km/s With Respect To What?
Date: Thu, 18 Jul 2024 10:34:12 +0300
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On 2024-07-18 06:20:39 +0000, Thomas Heger said:

> Am Mittwoch000017, 17.07.2024 um 12:27 schrieb Mikko:
>> On 2024-07-16 07:26:07 +0000, Thomas Heger said:
>> 
>>> Am Montag000015, 15.07.2024 um 11:05 schrieb Mikko:
>>>> On 2024-07-15 06:26:42 +0000, Thomas Heger said:
>>>> 
>>>>> Am Sonntag000014, 14.07.2024 um 12:19 schrieb Mikko:
>>>>>> On 2024-07-13 08:08:44 +0000, Thomas Heger said:
>>>>>> 
>>>>>>> Am Freitag000012, 12.07.2024 um 11:26 schrieb Mikko:
>>>>>>>> On 2024-07-11 19:58:02 +0000, amirjf nin said:
>>>>>>>> 
>>>>>>>>> Approximately 300,000 km/s with respect to what?
>>>>>>>> 
>>>>>>>> Whenever the speec of something is measured it is measured with respect
>>>>>>>> to someting else. The report should make clear what is the reference that
>>>>>>>> is considered stationary. Usually it is the instruments used in the
>>>>>>>> measurement, and usually but not always they are at rest with restpect to
>>>>>>>> Earth surface at the place of the measurement.
>>>>>>>> 
>>>>>>> 
>>>>>>> 'Stationary' can be understood as 'not moving' and that as 'having
>>>>>>>  velocity zero'.
>>>>>> 
>>>>>> Yes, that is what the word means.
>>>>>> 
>>>>>>> But velocity would require a reference point, in respect to which the 
>>>>>>> object does not move.
>>>>>> 
>>>>>> That gives you a revefernce point: the object does not move in respect to
>>>>>> itself.
>>>>>> 
>>>>> 
>>>>> Actually I have used this setting in my 'book' and declared, that all 
>>>>> observers regard themselves as non-moving.
>>>> 
>>>> That is possible but not always the best idea. In the real world an observer
>>>> often considers oneself as moving and someting else as stationary. Often
>>>> it is better to choose samething inertial for "statinary" when the observer
>>>> is not inertial.
>>>> 
>>> Sure, but 'non-inertial observers' where not included in SRT.
>> 
>> Not intentionally but SRT can be used for calculations of what a non-inertial
>> observer would see.
> 
> Relativity is actually not a single paper, but a set of different theories.
> 
> 'SRT' is usually used for Einstein's 'On the electrodynamics of moving bodies'.
> 
> And this paper does not deal with accelerated frames of reference.

Inertial coordinate systems are the simplest to use. You may construct other
coordnate systems but they have no physical significance. Inertial coordinate
systems are sufficient for description and analysis of accelerated objects.
All that needs be known about the theory, as long as no consideration of
gravity is needed, can be found in "On the Electrodynamics of Moving Bodies".

-- 
Mikko