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Passare da un riferimento all'altro

LuigiFortunati 7 Ago 2017 17:44
Prima della partenza il gemello viaggiatore si trova nel riferimento
terrestre K, poi accelera fino a trovarsi nel riferimento K'
dell'andata dove viaggia per anni a velocità inerziale.

Al termine del viaggio d'andata accelera nuovamente per invertire la
marcia fino a trovarsi nel riferimento K" del ritorno dove viaggia per
altri anni a velocità inerziale.

Infine decelera per l'ultima volta fino a fermarsi sulla Terra, nel
riferimento K dal quale era partito.

Tutti i passaggi, da K a K', da K' a K" e da K" a K avvengono con
un'accelerazione (positiva o negativa).

Vi chiedo: il passaggio da un riferimento all'altro può avvenire solo
ed esclusivamente con un'accelerazione (come in questo caso) oppure c'è
qualche altro modo per realizzarlo?

(Switch from one reference to another
   Before departure, the traveling twin is in the land reference K,
then accelerates until it is in the reference K' of the route where it
travels for years at inertial speed.
   At the end of the forward trip, accelerate again to reverse the gear
until it finds itself in the K" return point where it travels for years
at inertial speed.
   Lastly, it lasts for the last time to stop on Earth, in the
reference K from which it started.
   All passages, from K to K', K' to K", and K" to K occur with an
acceleration (positive or negative).
   I ask you: can the transition from one reference to another only be
achieved with acceleration (as in this case) or is there any other way
to achieve it?)

--
Luigi Fortunati

Credere e' piu' facile che pensare
Believing is easier than thinking
LuigiFortunati 8 Ago 2017 18:36
Jos Bergervoet alle ore 13:43:18 del 08/08/2017 ha scritto:
> [Moderator's note: The i*****syncratic characters result from not using a
> proper news client to post to sci.physics.research. In fact in my
> moderation process I always try to repair this as far this is possible
> in an automized way. hvh.]
>
> On 8/8/2017 9:36 AM, LuigiFortunati wrote:
> ...
>> =A0=A0
>> =A0=A0 I ask you:
>
> Luigi, can you please post more readable text? I do not know what
> you mean with "=A0=A0" and similar insertions.

Non sono io che inserisco questi maledetti "=A0=A0", adesso proverò a
cambiare il mio news client (MESNEWS) come suggerisce il moderatore
(userò GOOGLE GROUPS).

(I am not the one who puts these curses "=A0=A0", now I will try to
change my news client (MESNEWS) as the moderator suggests (I will use
GOOGLE GROUPS)).

>> can the transition from one reference to another only be
>> achieved with acceleration (as in this case) or is there any other way
>> to achieve it?
>
> There is no prescribed reference frame to use. Everyone is free
> to use any reference system, *also* those in which he himself is
> not at rest. So the transition to another reference frame can be
> achieved simply by a decision: "let me now use reference frame
> Y instead of X for my calculations".
>
> If, for whatever reason, you insist (unnecessarily) on using only
> the reference frame in which you are at rest, then (by your own
> choice) you need to change your velocity to be able to use another
> reference frame. But then this is just your own chosen rule.
>
> A reference frame is just a grid of coordinates. There is no law
> in physics that forces you to use any specific grid. You can even
> use arbitrarily curved coordinate lines (which were not yet
> considered in this discussion until now).
>
> Your questions are only about your own superficial choices of
> choosing some specific reference frame. You maybe have the idea
> that there is only one choice allowed, from popular descriptions
> of the theory of relativity. But those descriptions are wrong!
>
> It is *not true* that if you are moving at some speed, you're only
> allowed to use one reference frame. Please change your beliefs.

Non ho chiesto se esiste un riferimento prescritto da utilizzare per
i calcoli.

Ho chiesto se chi è in quiete in un certo riferimento K può passare
all'essere in quiete non più rispetto a K ma rispetto a un altro
diverso riferimento K' (a gamma=8 rispetto a K) senza accelerare una
qualche "astronave".

(I did not ask if there is a prescribed reference frame to use for
calculations. I asked if anyone who is at rest in a certain K can go to
being at rest no more than K but to another K' (at gamma=8 than K)
without accelering some "spaceship").

--
Luigi Fortunati

Credere e' piu' facile che pensare
Believing is easier than thinking
LuigiFortunati 10 Ago 2017 15:28
Jos Bergervoet alle ore 19:33:08 del 09/08/2017 ha scritto:
> Obviously it is important here to define 'acceleration' as the
> locally perceived (by T) acceleration. Incidentally, the other
> twin, T0, who is still on Earth, perceives an acceleration of
> 9.8m/s^2 all the time, whereas T, using the sling ******* return,
> perceives no acceleration at all during his journey.
>
> If you want to use another definition of 'acceleration' (or of
> 'transition' or of 'reference frame') the answers to your
> questions might well be different. These things are actually
> very difficult to discuss in words, without mathematical
> definitions.

L'accelerazione è la variazione della velocità in un certo riferimento.

E' rigorosa (e sufficiente) questa definizione di accelerazione?

(Acceleration is variation of velocity in a given frame.
Is this definition of acceleration rigorous (and sufficient)?).

--
Luigi Fortunati

Credere e' piu' facile che pensare
Believing is easier than thinking

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