Genady

OK. How it works if the acceleration changes, for example, continuously increases?

I doubt it says that the law is not applicable if mass changes. Does it apply for constant a only?

Could you show me what exactly that physics text says?

It applies to a momentary mass, a mass at a moment in time.

I mean misunderstanding. I have four in total. But everyday language is English.

I see. When you said, 'considered for' you meant, 'relative to'. OK. Lost in translation.

Yes.

The rocket is not an inertial frame because it accelerates. Consider relative to the ground.

Constant velocity relative to the rocket, but it changes relative to an inertial frame together with a changing velocity v of the rocket. Check in your source, how that ve is defined.

In GR, free falling object considered to have a locally inertial reference frame. The things float freely inside that frame, i.e., relative to the free falling object. Relative to the outside observer who is stationary relative to the central mass, the free falling object accelerates.

Without accelerating? It will accelerate. How is it related to the space being stationary? Perhaps, we mean different things.

An example could be the spacetime around non-rotating spherically symmetrical massive body, aka Schwarzschild metric. The space there is stationary, and the spacetime is curved, isn't it?

From the event of the ship leaving to the event of the ship returning, everyone on Earth experiences 10 years, and everyone on the ship experiences 1 week. What is confusing about it?

Sorry, when I said, "I think that OP rather is about a centripetal acceleration", I meant OP in this thread we are here now, namely, Willem, https://www.scienceforums.net/topic/128865-the-earth-is-not-accelerating-upwards/

And the clock/calendar in the ship will indeed show 1 week.

What is wrong about it?

I can't come up with any caveat to add here .

But it is precisely what it means.

OK. To me, the fact that reactions involving virtual particles occur as predicted, is as good evidence as any. More generally, to me, virtual particles are as real as any, with a defining distinction that they appear temporarily and disappear during reactions.

I mean input and output in particle reactions. External legs on Feynman diagrams. Virtual particles are, by definition, internal lines in the latter.

Isn't it simply a consequence of their definition as particles that do not show in input or output? If they do show, they are not virtual, by definition.

I think that OP rather is about a centripetal acceleration.

No, space does not accelerate. The matter on the Earth surface accelerates downwards.

This is a dishonest response. He doesn't tell you to discuss the problem in terms of Variational Calculus. He tells you that F=dP/dT follows from more general principles rather than is just made up, and thus it makes no sense to claim that it is wrong, as you do.

Sure, he is.