Non-Inertial Frame: Key Clues & Examples

Click For Summary

Discussion Overview

The discussion centers around the concept of non-inertial frames of reference, exploring when and how to identify them, as well as the implications of their use in physics. Participants provide examples and clarify distinctions between inertial and non-inertial frames, touching on both Newtonian and General Relativistic perspectives.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants propose that a non-inertial frame is one that is accelerating with respect to another frame, using the Earth as an example due to its rotation and orbit.
  • Others argue that the presence of fictitious forces, such as the Coriolis and centrifugal forces, indicates one is in a non-inertial frame, as experienced on Earth or in a turning car.
  • A participant suggests that all reference frames could be considered non-inertial, prompting a challenge regarding the definition of inertial frames in relation to fixed stars.
  • Another participant clarifies that in Newtonian physics, acceleration is absolute, and thus one cannot claim a frame is inertial based solely on perspective.
  • There is a discussion about the distinction between proper acceleration and coordinate acceleration, with some emphasizing that proper acceleration is what an accelerometer would measure.
  • Participants discuss the implications of fictitious forces in determining whether a frame is non-inertial, with a focus on the differences between perspectives of observers in different frames.

Areas of Agreement / Disagreement

Participants express differing views on the definitions and implications of non-inertial frames, with no consensus reached on whether all frames can be considered non-inertial or the nature of fictitious forces. The discussion remains unresolved regarding the interpretation of acceleration and its relation to inertial frames.

Contextual Notes

There are limitations in the assumptions made about the definitions of inertial and non-inertial frames, as well as the dependence on perspectives and interpretations of acceleration. The discussion does not resolve these complexities.

mikengan
Messages
4
Reaction score
0
I confuse when should I use non-inertial frame...
is there any keyword or key clues that remind you of using non-inertial frame of reference?

can anyone help explain this with an example?
 
Physics news on Phys.org
A non-inertial frame is a frame of reference which is accelerating with respect to another frame of reference.

For example, for people standing on the Earth we are in a non-inertial frame of reference, because the Earth is rotating with respect to the "fixed" stars, and simultaneously moving in a curved orbit around the sun.

If you want a deeper understanding than that, you'll probably have to read up on some general relativity.
 
It depends a bit on how you're looking at this problem. Physically, we can tell we are in a non-inertial frame by the appearance of fictitious forces in our frame. For example, here on Earth, we experience the coriolis force and the centrifugal force (for the Earth, it's hard to notice since it's angular velocity is so low). When your car is turning, you feel a centrifugal force even though nothing is pushing on you. This tells you that you're in a non-inertial reference frame.

The difference between a Newtonian non-inertial frame and a General Relativistic non-inertial frame would be which forces we call "fictitious forces". Specifically GR does not treat the gravitational force as a real force, it is more like a "fictitious force".
 
dipole said:
A non-inertial frame is a frame of reference which is accelerating with respect to another frame of reference.
That would make all reference frames non-inertial.
 
No it wouldn't. Explain how you arrive at that conclusion. The point is, in Newtonian physics (which I assume is the scope the OP is working in) velocities are relative, but acceleration is absolute - it is not correct to say that if I am accelerating on a train and see a person standing at the train station, that from my point of view, that person is in a non-inertial frame of reference and my frame is inertial, because there are no measurable ficticious forces acting on that person, but there are on me. All frames which are inertial with respect to the "fixed stars" are interial relative to each other, and any frame which is non-inertal with respect to the fixed stars is non-inertial to all others.
 
I think what A.T. meant is you should've said:
"A non-inertial frame is a frame of reference which is accelerating with respect to an intertial frame of reference"

(Because inertial reference frames are accelerating with respect to non-inertial reference frames, right?)
 
dipole said:
velocities are relative, but acceleration is absolute
Proper acceleration is absolute. But you were taking about coordinate acceleration relative to something:
dipole said:
A non-inertial frame is a frame of reference which is accelerating with respect to another frame of reference.

dipole said:
if I am accelerating on a train
I guess you mean proper acceleration that an accelerometer on the train would measure?

dipole said:
and see a person standing at the train station, that from my point of view, that person is in a non-inertial frame of reference and my frame is inertial,
No. Whether a frame is inertial or not is not a matter of perspective. Proper acceleration is absolute.

dipole said:
because there are no measurable ficticious forces acting on that person, but there are on me.
If there are fictitious forces in the frame of the train, then we know that the train-frame is non-inertial. So the train passenger cannot say "from my point of view, my frame is inertial", as you did above.
 

Similar threads

High School Inertial vs non inertial frames
  • · Replies 3 ·
Replies
3
Views
2K
Undergrad Inertia/Non-inertial frame - isotropy
  • · Replies 22 ·
Replies
22
Views
2K
Undergrad Is calling fictitious forces "not real" just about terminology?
  • · Replies 114 ·
4
Replies
114
Views
7K
Undergrad Reference frames in terms of homogenity/isotropy
  • · Replies 18 ·
Replies
18
Views
2K
High School What are non-inertial frames of reference?
  • · Replies 15 ·
Replies
15
Views
3K
Undergrad Using reference frames for derivation of Lagrangian
  • · Replies 25 ·
Replies
25
Views
3K
Undergrad Which inertial frame is used when resolving toward the centre
  • · Replies 15 ·
Replies
15
Views
2K
Graduate Is this point of contact an inertial frame?
  • · Replies 2 ·
Replies
2
Views
2K
Graduate Position formula in a non-inertial frame
  • · Replies 7 ·
Replies
7
Views
2K
Undergrad Are Newton's Laws just definitions?
  • · Replies 11 ·
Replies
11
Views
2K