On Friday, 23 September 2022 at 10:01:58 UTC+2, Luigi Fortunati wrote:
> In my animation
> > https://www.geogebra.org/m/dfv4bsrw
> there are two bodies next to each other, standing still without pushing
> each other (and the dynamometer proves it).
> They don't push each other because nothing pushing body A to the right
> and nothing pushing body B to the left.
> But if the two bodies A and B have electromagnetic charge (as seen by
> clicking on the "Electromagnetic interaction" button), the external
> force that pushes body A to the right and body B to the left, is there.
> In this case there is an external action (the blue electromagnetic
> attraction between the two opposite charges) that pushes the two bodies
> towards each other and all this generates an opposite internal red
> reaction (in the contact zone) direct in the opposite direction to
> contrast the approach of the two bodies.
Your blue forces should be attached to the centers, indeed they
are not "external"... That said, IMHO, the main reason why you are
not getting answers is that you keep repeating the same mistakes.
> Red forces exist as a reaction to blue forces and would not exist
> without them.
No, the red forces exist because the two bodies get in contact, and
these, microscopically speaking, are in fact electromagnetic repulsive
forces that prevent the two bodies from penetrating each other (i.e.
as long as they are not as strong as to break the molecular bonds,
then it's another regime). The point is you still miss what is action
and reaction: the two blue forces are each the reaction of the other,
while the two red forces, on the other hand, are each the reaction of
the other, not the mix of red and blue you do above and elsewhere!
And that despite there is in fact a correspondence in magnitude
between all the forces involved due to the fact that the two bodies
press on each other by the same exact amount that the two bodies
are attracting each other.
Let my try and put it this was: imagine you are pushing on a bolder
that in turn pushes by contact on a second boulder: you exert force
A and *by reaction* bolder 1 replies with -A on you, in turn bolder 1
is pushing on 2 with force B and *by reaction* bolder 2 pushes back
on 1 by a force -B... and that is about the 3rd principle, despite it is a
matter of the collinear setup that A and B will necessarily have the
same magnitude. Indeed, notice that, as soon as the pushing is not
all just collinear, the magnitudes are not anymore simply the same.
> Is it correct to say that the situation is completely analogous to the
> one seen by clicking on the "Gravitational interaction" button, where
> the reciprocal red force (of action-reaction between bodies A and B)
> exists only thanks to the blue gravitational force?
Modulo the corrections mentioned above, and having assumed the
specificities of GR don't count in this small experiment, yes, the two
situations are completely analogous.
That said, you have meanwhile also asked if the red forces are "real":
1) of course they are, just put a hand in between the two bodies,
wouldn't you feel the pressure?! 2) as long as that question still
revolves around the meaning of "apparent forces", I thought it had
meanwhile amply been explained how that "apparent" does not mean
those forces do not exist. And why should anybody be interested in
repeating things already said, to you, recently, and more than once...