The reference is: Elements of Newtonian Mechanics by J.M. Knudsen; Springer; page 108 to 113.
My doubt is about the significance of the apparent distinction between Gravitation and Inertia. In Knudsen's book, he says that gravitation and inertia aren't different properties of matter, the by equivalence principle.
Can you give me an example that we can verify the apparent distinction of gravitation and inertia (which we can then see as different aspects of matter; different reference frames)? Why was gravity considered a particular reference frame, and why this "bored Einstein"? What exactly did Knudsen intend to say by:
Gravitation and inertia do not seem to be separate properties of matter, but rather two different aspects of a more fundamental and universal property of space and material particles.
I know the math behind this, but I have some difficultt imagining a good example beyond "Einstein's box" thought experiment and the insight that "gravity and acceleration are the same thing"
If you want to help me even more:
I really want to know why this particular idea (Equivalence principle) leads Einstein to verify the necessity for a more general framework, I mean: how can we start from Einstein's box (equivalence principle that works for a constant gravitational field--a "little laboratory") and reach the framework of Riemannian Geometry with gravity as the problem?
Please, fell free to use mathematical arguments if you like.