Review my explanation of references frames and the validity of Newton's 2nd Law

[moorepants]

This video by Levinson makes some critiques on how reference frames, Newtonian/inertial reference frames, and the second law are described, defined, and used. He critiques the idea of "observer" which I do use in my explanations and he brings up "absolute space" to give a word to what a Newtonian frame may represent. It made me question some of my explanations (and also worried I may end up in his next critique).

I have known that the "fictitious forces" are nonsense, but I still point to the definition in the book. Maybe I should call them out as bogus.

[moorepants]

My reference frame explanation:

In the study of multibody dynamics, we are interested in observing motion of connected and interacting objects in three dimensional space. This observation necessitates the concept of a frame of reference, or reference frame. A reference frame is an abstraction which we define as the set of all points in Euclidean space that are carried by and fixed to the observer of any given state of motion. Practically speaking, it is useful to imagine your eye as an observer of motion. Your eye can orient itself in 3D space to view the motion of objects from any direction and the motion of objects will appear differently in the set of points associated with the reference frame attached to your eye depending on your eye’s orientation.

EoM's in the inertial frame:

Here is where I state about the equations only holding in an inertial frame and I mention fictitious forces:

[Peter230655]

Dear Jason, I definitely did not send the link to you to be critical! I have listened to all of David’s lectures and he is ( like you are in your book!) very insistent that one always indicates the frame one is in. With sympy mechanics Kane’s method, one has to be, I guess. If one is consistent, it all falls in place it seems. When I studied mechanics almost 50years ago, there was always talk about Coriolis forces and the like. Peter

[Peter230655]

My reference frame explanation:

In the study of multibody dynamics, we are interested in observing motion of connected and interacting objects in three dimensional space. This observation necessitates the concept of a frame of reference, or reference frame. A reference frame is an abstraction which we define as the set of all points in Euclidean space that are carried by and fixed to the observer of any given state of motion. Practically speaking, it is useful to imagine your eye as an observer of motion. Your eye can orient itself in 3D space to view the motion of objects from any direction and the motion of objects will appear differently in the set of points associated with the reference frame attached to your eye depending on your eye’s orientation.

EoM's in the inertial frame:

Here is where I state about the equations only holding in an inertial frame and I mention fictitious forces:

Carlos Roithmayr writes in his book on page 192: Ultimately, the justification for regarding a reference frame as Newtonian can come only from experience.

I guess this is the same thing you are saying.

[moorepants]

No, I don't think I would say that.

[Peter230655]

No, I don't think I would say that.

You say, that an inertial frame is one where Netwton's First Law holds.
Whether it holds or not can only be found out by experience / experiments, not true?