Talk:Non-inertial reference frame

Is this correct in general?

the article states:

"A non-inertial reference frame is a frame of reference that is undergoing acceleration with respect to an inertial frame.[1]"

but in general relativity theory we call accelerating systems (like free falling elevators) "locally inertial". So maybe we should start the sentence with "in classical mechanics a non-inertial frame is..."?--Pokipsy76 (talk) 15:40, 29 October 2019 (UTC)

Untitled

Hi, CH! You asked me to discuss this article on the talk page, so here I am.  :)

First off, thanks for your nice note on Inertial frame of reference! I made the re-reversion you suggested, which (I'll confess) made me very happy. But please let me know if you think there should be other refinements of the article.

I'm keenly aware that my version of this article ("non-inertial reference frame") wasn't all that great, especially on the delicate "gravity is a fictitious force" issue from general relativity. But I also feel that the older version needed to be clarified. For example, the opening line

In such a frame, despite no real force acting on a body at rest, it might move; or one that was already moving come at rest or change it's direction of motion.

seemed too colloquial and diffuse (also, it's "its" ;). The later link to geeforces suggests that they're related to gravity rather than fictitious forces. Finally, the old version of the general-relativity issues seems a little diffuse and, perhaps, too long relative to the Newtonian section? I think we should give more weight (i.e., length) to the Newtonian definition of non-inertial reference frame, since that's the most common usage -- don't you agree? Please let me know what features you'd like to see in this article! WillowW 09:40, 8 June 2006 (UTC)

Hi, would like to discuss the italicised sentence that was actually put by me once before. A non inertial frame is one that basically violates Newton's Law of inertia, that is his first law. Hence, in a non - inertial frame a body can move...even when there is apparently no cause for it. I suggest we remove the concept of something accelerating with respect to something else for the definition of inertial; that might give readers the impression that what is inertial or not depends on some other frame. The question as to whether a frame is inertial or not has nothing to do with another frame; it is a simple question of whether the laws of Newton work in that frame or not. If the laws do, then the frame is inertial, if it does not, then it is not.

Curvilinear coordinates

Curvilinear coordinates are a general form of coordinate system. The topic of coordinate systems is basically a mathematical topic, and has no necessary relation to physics.

The topic of non-inertial reference frames, in contrast, is a purely physics-based idea related to the state of motion of an observer and the form of physical laws. Basically, there are two sets of frames in the universe: the inertial frames where the physical laws are simply stated and transform simply from one inertial frame to another; and those frames where this is not so, the non-inertial frames.

Curvilinear coordinate systems can be used in either type of frame, according to the convenience of recording observations in that frame for some particular situation. Brews ohare (talk) 19:17, 11 September 2008 (UTC)

Transformation to inerital frame

Although traditionally analysis in non-inertial frames was carried out by first mapping everything into an inertial frame, making the use of fictitious forces unnecessary, that approach is not so common today. In the context of defining a noninertial frame, the emphasis is not upon how a calculation might proceed by avoiding use of a non-inertial frame. Rather, the definition of a noninertial frame must identify what is unique about such frames, and that is the need for fictitious forces. That by no means suggests that a mapping into an inertial frame cannot be done if that is expedient.

I have rewritten the Intro to make the option of mapping to an inertial frame a clear alternative. Brews ohare (talk) 14:01, 8 October 2008 (UTC)

Merger proposal

Against merger

I find the article Noninertial reference frames should be deleted. It is a limited and incoherent view of the topic and adds nothing to Non-inertial reference frame.

My vote is against this merging. Brews ohare Brews ohare (talk) 21:46, 24 December 2008 (UTC)

I have redirected Noninertial reference frames to Non-inertial reference frame. Brews ohare (talk) 19:29, 18 January 2009 (UTC)

Clean up

A clean-up template has been inserted in this article, with no guidance as to the issues requiring clean-up. I have replaced the Quotations with cquotes because, in my experience, Quotations raise the hackles of some, simply because of dislike of the formatting. I also broke the article into sub-sections, for clarity. I am removing the template in lieu of any guidance as to what is desired here. Brews ohare (talk) 21:54, 24 December 2008 (UTC)

Merger proposal (Accelerated reference frame)

These articles: Accelerated reference frame and Non-inertial reference frame should be merge. Or perhaps someone could explain why there are two articles about the same topic. Am I missing something? sanpaz (talk) 17:46, 26 May 2010 (UTC)

Merge preferably as Non-inertial reference frame - I don't think you're missing anything! Djr32 (talk) 22:25, 1 June 2010 (UTC)

Done. "Accelerated reference frame" was mostly a direct copy of Fictitious forces. --RockMagnetist (talk) 17:28, 15 October 2010 (UTC)

Detection of a non-inertial frame: need for fictitious forces

There seems to be an issue in the article that comes to a head in the above section. The examples given there refer to frames in which there is no need for acceleration to achieve the problematic results cited.

An object dropped to the Earth's surface will accelerate, due to the gravitational forces the Earth exerts on it. However, the same "curvature" of trajectory can be seen in the trajectory of a bullet fired in space at an object that is moving in relation to the shooter ie in frames in which there is no acceleration present. There seems to be no need of acceleration to require the use of fictional forces to "explain"/calculate the motion observed. The trajectory is curved from the point of view of the inertial frame of that which is being shot at, but it is straight from the point of view of the inertial frame of the shooter. There seems to me to be a need here only for recognition of the two inertial frames involved rather than for the introduction of the non-inertial frame.

What am I missing?

--LookingGlass (talk) 13:45, 28 November 2012 (UTC)

I think what you're missing is that in the bullet situation, the bullet's trajectory is not curved, but straight, even though the two observers disagree about the direction of that straight path.

--Gafter (talk) 22:19, 30 January 2016 (UTC)

Acceleration is not relative

This Wikipedia page opens with:

"A non-inertial reference frame is a frame of reference that undergoes acceleration with respect to an inertial frame."

Whilst speed and motion are relative, acceleration is not. Acceleration is experienced solo. So the opening line makes no sense at all. LeeMcLoughlinScientist (talk) 22:50, 7 October 2022 (UTC)