What is the difference between relative and absolute motion?

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Discussion Overview

The discussion centers on the concepts of relative and absolute motion, exploring definitions, examples, and the implications of these terms within different frameworks of physics, including classical mechanics, general relativity, and quantum mechanics.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants propose that position and velocity are relative to a frame of reference, while acceleration and forces can be considered absolute, barring general relativity considerations.
  • Questions arise about whether the Earth's rotation is relative or absolute, with suggestions that it can be expressed relative to something but also quantified in absolute terms.
  • One participant seeks clarity on defining relative and absolute motion, suggesting that relative requires a frame of reference, while absolute does not.
  • Another participant mentions that the definitions should apply to bodies not approaching the speed of light.
  • Concerns are raised about the universality of these definitions across different theories, specifically questioning their acceptance in quantum mechanics and general relativity.
  • Disagreement emerges regarding the quantification of absolute rotation, with some asserting it is possible while others contest this claim.
  • A later reply expresses frustration over the lack of resolution, suggesting that the discussion is circular and unresolved.

Areas of Agreement / Disagreement

Participants do not reach consensus on the definitions of relative and absolute motion, particularly regarding the quantification of absolute rotation and the applicability of these concepts across different physical theories. Disagreements persist, with some participants asserting that absolute values can be quantified while others contest this view.

Contextual Notes

Limitations include the ambiguity in definitions and the potential dependence on the context of classical mechanics versus modern physics theories. The discussion reflects varying interpretations and lacks a unified understanding of the terms involved.

Shahin.Omar
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Hello!

Can someone explain to me what is relative, and what is non-relative or absolute?
As I understand linear motion at constant velocity is called relative.
Can you give more such examles for me to understand why something is called relative?

Cheers!
 
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Position and velocity are relative to some frame of reference. Acceleration and related forces can be considered to be absolute if not considering general relativity issues.

Getting back to position and velocity, say you're standing at some spot on the earth. The Earth is rotating, so except at the poles, it's surface is moving (with respect to it's own axis), the Earth is orbiting the sun, the sun is orbiting the center of our galaxy, and our galaxy is moving with respect to others.
 
Jeff Reid said:
Position and velocity are relative to some frame of reference. Acceleration and related forces can be considered to be absolute if not considering general relativity issues.

Please can you exlain it a little bit more, and what is accepted in physics today?

Is rotation of Earth on its axis relative?

And can I define 'relative' as an event/attribute that requires a frame of reference for it to be detected?

:)
 
Last edited:
Shahin.Omar said:
Is rotation of Earth on its axis relative?
You can express rotation relative to something. But you can also quantify rotation's absolute value, which doesn't work for linear motion at constant velocity.
 
A.T. said:
But you can also quantify rotation's absolute value, which doesn't work for linear motion at constant velocity.

Whats rotation's absolute value, how do I quantify it?
Can you help me define relative and absolute so I can tell what is relative and what is not?
 
Just to add, the definitions required is for bodies *not* approaching the speed of light.
 
Last edited:
Shahin.Omar said:
Whats rotation's absolute value, how do I quantify it?
You can measure the inertial forces and calculate the rate of rotation from it.
Shahin.Omar said:
Can you help me define relative and absolute so I can tell what is relative and what is not?
Relative means it was compared to some arbitrary reference. Absolute means no arbitrary reference was used.
 
A.T. said:
Relative means it was compared to some arbitrary reference. Absolute means no arbitrary reference was used.

Can you also tell me the exact extent to which the above definitions are correct (apart from the term I used)?
 
Shahin.Omar said:
Can you also tell me the exact extent to which the above definitions are correct
Can you ask a physically relevant question?
 
  • #10
A.T. said:
Can you ask a physically relevant question?

Sorry for any ambiguity!

What I wanted to know is if the definitions you gave are universally accepted by all theories (like Quantum Mechanics and General Relativity) or they are only correct from Classical Mechanics point of view?

If it is only accepted in classical mechanics, can you tell me what is the accepted definition in GR or QM?

Hope this clarifies any doubts.

:)
 
  • #11
:smile:
 
  • #12
A.T. said:
You can express rotation relative to something. But you can also quantify rotation's absolute value, which doesn't work for linear motion at constant velocity.

I have not had a final reply to this thread, I did not form my question correctly in the beginning, not that it was easy, sometimes you don't know how to put it?

I would like to close this thread with final conclusion; while we can quantify what is relative we cannot quantify what is absolute, if we could quantify what is absolute there would no difference between relative and absolute.

A.T. was wrong in saying, "But you can also quantify rotation's absolute value."

Cheers guys!
 
  • #13
The only one who is wrong here is you, Shahin.
 
  • #14
D H said:
The only one who is wrong here is you, Shahin.

No problem, except you cannot prove it. Be happyy!

Cheers!
 
Last edited:
  • #15
Shahin.Omar said:
A.T. was wrong in saying, "But you can also quantify rotation's absolute value."

That's not true. You can. Repeating that you can't doesn't make it less true.

This thread is demonstrating rotation - it's going around in circles.
 
Last edited:

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