The very excellent Jean-Pierre Messager (Python) thought he was authorized
to speak of relativistic equations.

That's fine in itself.

But if he wants to be useful, he must listen to the great, the immense,
the superb, the incomparable Richard Hachel.

What does Riri say?

Riri, he says that the theory of relativity, contrary to Einstein's
opinion, is very simple, and that it does not require advanced
mathematical training, but that it is full of little pitfalls.

There are things you can do, and things you can't do.

Strangely, I've noticed that sometimes relativists do things that
shouldn't be done, or don't do things that should be done.

Among the things that can be done, pose, brutally, the following equation:
x=(1/2)aTr².

This I can.

But I can't write x=(1/2)a'To²

Obviously.

I can write :
a'=a.[1+a²Tr²/c²]^-3/2

Or also, which is the same thing:
a'=a[1+Vr²/c²]^-3/2

Or even a'=a[1-Vo²/c²]^3/2

These equations are correct.

BUT, if I can write Vr=a.Tr, I can't write, for example: Vo=a'.To

The observable speed at a given instant in the terrestrial reference frame
is not equal to the observable instantaneous acceleration multiplied by
the observable time To.

It seems obvious if I say so. But if I don't say it, I think some people
might fall into this trap.

I remind you that the twenty equations that I have given and which deal
with accelerations in SR are correct and can be used.

With a downside however for some which, if they are correct, should not be
used for examinations.

Although correct, they could be zero, because it is not forbidden to think
that the examiner will believe that the student is mistaken. This is
particularly the case for the proper times that I gave.

As for the equation directly giving the acceleration a' as a function of
time To (two values ​​taken in the terrestrial reference frame), it is
apparently unknown to relativists but can be used if necessary, since the
numerical values will be the same as by the usual processes which are
simply longer and more complex and therefore more prone to error.

I put again this equation here:

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R.H.

--
"Mais ne nous trompons pas. Il n'y a pas que de la violence
avec des armes : il y a des situations de violence."
Abbé Pierre.
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