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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: Fri, 12 Jul 2024 12:26:44 +0300
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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.

Sometimes numbers with units of speed are used for other purposes instead
of speed, for example in E = mc², where c has units of speed. In those cases
the question need not be asked.

-- 
Mikko