Path: ...!eternal-september.org!feeder3.eternal-september.org!fu-berlin.de!uni-berlin.de!news.dfncis.de!not-for-mail
From: Luigi Fortunati <fortunati.luigi@gmail.com>
Newsgroups: sci.physics.research
Subject: Re: Equivalence principle
Date: 11 Jun 2024 07:05:55 GMT
Organization: A noiseless patient Spider
Lines: 15
Approved: hees@itp.uni-frankfurt.de (sci.physics.research)
Message-ID: <v47map$k0f3$1@dont-email.me>
References: <lcnnfcFr1a7U1@mid.dfncis.de> <v46hf4$bc49$1@dont-email.me> <lco7poFtcpjU1@mid.dfncis.de>
X-Trace: news.dfncis.de P5XicDZwH6jXIrZAtHZl1wzeglIwnTkHmah5zv2QpYvywjBKd4jl/+nI6fJnETsYuY
Cancel-Lock: sha1:AXG57XsZDtIwEgeYM9Ab9Ae05vw= sha256:QwnwMsfwvtLkT+ApJ3z1UV2fYWyeZ69/QzaHy1L+HAo=
Bytes: 1718

Hendrik van Hees il 10/06/2024 14:10:37 ha scritto:
> Or to put it simpler. In a local inertial reference frame, realized by a point-like non-rotating body in free fall, you observe (e.g., by using pointlike test particles) only the "true gravitational forces", i.e., the tidal forces.
>
> If you sit on the surface of a planet, you are not in free fall, because there are (electromagnetic) forces keeping you there.
>
> That's why the accelerometer of your smart phone at rest on Earth shows an acceleration of 9.81 m/s^2, because it measures accelerations relative to a local inertial frame of reference! See, e.g.,

Your reasoning is based on two preconceptions.

The first is that the accelerometer measures accelerations (and instead
it only measures forces) and the second is that free fall is an inertial
reference system despite its very evident mutual acceleration towards
the other body (also) in free fall.

Luigi Fortunati