Talk:Inertial frame of reference

message: In Misner, Thorne and Wheeler, the "inertial frame" is what the authors call a "free float frame." It's any reference frame in which Newton's laws of motion hold good, and things are weightless. Fair enough. The introduction to this article puts it a little more technically: In general relativity, in any region small enough for the curvature of spacetime to be negligible one can find a set of inertial frames that approximately describe that region. So what then are we to do with the special case of the reference frame occupied by an object in an inertial trajectory, as (for example) a body falling in a vacuum in a gravitational field? Must we say that a body on an inertial path occupies a physically accelerated reference frame that is NOT an "inertial frame"? What a pity. If free fall motion is inertial motion, why is a free-fall reference frame not an inertial reference frame? SBHarris 23:19, 27 June 2012 (UTC)
replies: text: Well for one, because if there is curvature, it is impossible to define "the" reference frame of a freely falling observer. That is, there is canonical way of extending the tangent space along the trajectory of the observer to a frame of reference in his vicinity. It help you to know, that a constant gravitational field has zero curvature.TR 14:11, 25 October 2012 (UTC)
thread_title:  Problem with this definition in GR 

message: Some time ago I proposed merging Inertial space with this article, and no discussion resulted (the original tag is still on Inertial space, but the one on this page was removed). I'd like to reopen the discussion, and this time I'll act fairly quickly if there are no objections. I haven't ever seen a formal definition of "inertial space", but informally it tends to be used for inertial frames of reference when it doesn't matter which frame you choose. It's useful terminology, but not really a distinct concept. Merging it would enhance this article because it would add a discussion of the measurement of acceleration and applications to inertial guidance systems. RockMagnetist (talk) 00:06, 30 March 2013 (UTC)
replies: text: *"Inertial space", who ordered that? By all means, go ahead and merge it into here. - DVdm (talk) 09:48, 30 March 2013 (UTC)
replies: text: I have finally done the merger. It was rather difficult to decide how exactly to do it, since much of the source material was unreferenced. I ended up dividing Separating non-inertial from inertial reference frames into Theory and Applications and writing an entirely new description of inertial navigation in the latter. I also copied a paragraph on some work by Schwarzschild into Theory. I don't really know if this work was influential enough to include on this page. Maybe someone else can figure that out. RockMagnetist (talk) 19:07, 26 October 2013 (UTC)
thread_title:  Merger proposal 

message: From this article:
:So much for fictitious forces due to rotation. However, for linear acceleration, Newton expressed the idea of undetectability of straight-line accelerations held in common:
:
::If bodies, any how moved among themselves, are urged in the direction of parallel lines by equal accelerative forces, they will continue to move among themselves, after the same manner as if they had been urged by no such forces.
::
:::—Isaac Newton: Principia Corollary VI, p. 89, in Andrew Motte translation
:
:This principle generalizes the notion of an inertial frame. For example, an observer confined in a free-falling lift will assert that he himself is a valid inertial frame, even if he is accelerating under gravity, so long as he has no knowledge about anything outside the lift. So, strictly speaking, inertial frame is a relative concept. With this in mind, we can define inertial frames collectively as a set of frames which are stationary or moving at constant velocity with respect to each other, so that a single inertial frame is defined as an element of this set.
This strongly suggests that Newton described free-fall as inertial motion. However, the Equivalence principle article states that this was an Einstein thing:
:That is, being at rest on the surface of the Earth is equivalent to being inside a spaceship (far from any sources of gravity) that is being accelerated by its engines. From this principle, Einstein deduced that free-fall is actually inertial motion. Objects in free-fall do not really accelerate.
The article on Force also says it was Einstein:
:The concept of inertia can be further generalized to explain the tendency of objects to continue in many different forms of constant motion, even those that are not strictly constant velocity. The rotational inertia of planet Earth is what fixes the constancy of the length of a day and the length of a year. Albert Einstein extended the principle of inertia further when he explained that reference frames subject to constant acceleration, such as those free-falling toward a gravitating object, were physically equivalent to inertial reference frames. This is why, for example, astronauts experience weightlessness when in free-fall orbit around the Earth, and why Newton's Laws of Motion are more easily discernible in such environments. If an astronaut places an object with mass in mid-air next to himself, it will remain stationary with respect to the astronaut due to its inertia. This is the same thing that would occur if the astronaut and the object were in intergalactic space with no net force of gravity acting on their shared reference frame. This principle of equivalence was one of the foundational underpinnings for the development of the general theory of relativity.
Is the ascription to Newton in this article a mistake?  — Preceding unsigned comment added by 50.133.145.226 (talk) 17:46, 11 October 2013 (UTC)
thread_title:  Free-fall equivalence with inertial frames: Newton, or Einstein? 

message: There was an offhand comment in the article which I removed, about the handedness of coordinate systems. Since this matters only for electromagnetism and quantum physics, and the article does not deal with those topics, I think it's preferable to ignore it. Alternatively this could be expanded later in the article, but not in the lead. Bright☀ 18:18, 5 June 2017 (UTC)
thread_title:  Removal of handedness of coordinate systems 

message: There is no experiment observers can perform to distinguish whether an acceleration arises because of a gravitational force or because their reference frame is accelerating.
— Douglas C. Giancoli, Physics for Scientists and Engineers with Modern Physics, p. 155.
Seems a little strange. Firstly gravitational fields are not homogeneous so this must be a infinitesimal situation. The field is detectable as being divergent inside the box that is accelerating.
But any geodesic like an orbit around a heavy body surely is a fall in a gravitational field, and also easily detectable not to be inertial. — Preceding unsigned comment added by Burningbrand (talk • contribs)  
:It is explained in the last paragraph of the section Inertial frame of reference#General relativity: 
: - DVdm (talk) 10:45, 15 June 2017 (UTC)
replies: text: Obviously in large enough regions it's easy enough to observe whether the acceleration is due to gravitation or otherwise because of the reasons you stated, but in principle they're equivalent, and their effects are equivalent. Perhaps the quote needs to be expanded to reflect this. Bright☀ 15:38, 15 June 2017 (UTC)
thread_title:  Enertial systems 

message: The article currently states, in relation to observations of binary star angular momentum, that: 
1) "the angular momentum of all celestial bodies is angular momentum with respect to a universal inertial space."
It also states that : 
2) "This phenomenon of geodesic deviation means that inertial frames of reference do not exist globally as they do in Newtonian mechanics and special relativity."
So, do the two sentences contradict each other?  At the very least, they seem to be potentially misleading.  
(1) states makes reference to a, presumably existent, 'universal inertial space' (one would think that this implies a fixed spatial co-ordinate system for the observable universe).  (2) states that no Global inertial frame of reference exists (presumably referring to space time).  
It might be that the two sentences are somehow logically compatible (when the whole of spacetime is taken into account), but it's not eminently clear to me how.  Any explanation of whether the two assertions contradict one another would be appreciated.  
ASavantDude (talk) 23:29, 11 January 2018 (UTC)
replies: text: Yes this needs to be fixed, thanks for pointing it out. There is no universal inertial space. There is an apparent universal inertial frame with respect to the very distant stars, I think one of the article's references already mentions this. Bright☀ 12:37, 13 January 2018 (UTC)

text: Yup, the article makes a brief mention of Mach's principle. I think the entire paragraph about double-star systems is superfluous at the moment, but I kept it in because it could be made relevant if the article is expanded. Bright☀ 13:00, 13 January 2018 (UTC)
thread_title:  (Problematic?) Mention of Universal Inertial Space

message: The article is good and useful and well-sourced, but it's written like a textbook. This is not appropriate according to Wikipedia's policies and guidelines. I will eventually overhaul it (unless someone does it before me) and this is a sort of heads-up for page-watchers (who may not have noticed the tag being put up two months ago) so they're not taken by surprise when much of the article's style and order changes. Bright☀ 09:26, 10 March 2018 (UTC)
thread_title:  Article written like a textbook, not a summary 

message: At the time of writing this, the first sentence of the article was:
"An inertial frame of reference in classical physics and special relativity is a frame of reference in which a body with zero net force acting upon it is not accelerating; that is, such a body is at rest or is moving at a constant speed in a straight line."
This is trying to invert Newton's first law and make it a definition of an inertial frame. But this is a necessary but not sufficient property. It is particularly ironic that it mentions special relativity, because if this was the definition of an inertial frame in special relativity, then ANY linear transformation from an inertial frame would satisfy the definition and SR would be falsified. I am changing the first sentence to make it clear that is a property of an inertial frame, not a definition. BunkerQ (talk) 04:54, 15 June 2019 (UTC)
replies: text: Yes, these different summaries of inertial frames (Newtonian, analitycal) were jammed together. They give a quick, if somewhat obtuse, overview of the topic. Bright☀ 15:27, 15 June 2019 (UTC)
thread_title:  Netwon's First Law alone does not define an Inertial Coordinate System 

message: The current state of the article has been flagged by wikipedia for the lack of an  encyclopedic tone. I will be working on this article for the next few weeks to meet these standards. My focus will be to make bold and frequent edits to support an encyclopedic tone and offer suggestions for wording that is too technical.  BMarie 212 (talk) 18:12, 20 February 2024 (UTC)
replies: text: I suggest that the "delete" key will be very valuable in your effort. Johnjbarton (talk) 18:32, 20 February 2024 (UTC)

text: I agree that the article is too technical. I recomend to delete or severely edit anything coming from  as it is considered one of the most technical books to learn mechanics from and mostly reserved for PhD in theoretical physics. Jafloch (talk) 05:34, 25 February 2024 (UTC)
replies: text: There are only two used of Landau and Lifshitz and neither one is complex. Johnjbarton (talk) 16:03, 25 February 2024 (UTC)
thread_title:  Article Restructure for Encyclopedic Tone/Style