Energy in different references

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Discussion Overview

The discussion revolves around the concept of energy as perceived from different reference frames, particularly in the context of special relativity and Newtonian mechanics. Participants explore the implications of kinetic energy in rotating and stationary frames, questioning the existence and utility of this energy in practical applications.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • hisham.i questions whether the kinetic energy of a body in circular motion, as viewed from a stationary reference frame, truly exists.
  • Some participants assert that using a rotating reference frame is not permissible in special relativity, emphasizing the need for uniform, non-rotational frames.
  • Others argue that any coordinate system can be used as long as it is not labeled as an inertial frame, suggesting that the issue of kinetic energy is also relevant in Newtonian mechanics.
  • hisham.i further inquires about the practical application of this kinetic energy, specifically whether it can be harnessed to generate electricity.
  • One participant claims that everything with rest mass or relativistic mass possesses energy, implying a broader perspective on energy existence.

Areas of Agreement / Disagreement

Participants express differing views on the validity of using rotating reference frames in special relativity, with some asserting it is not allowed while others maintain that it is permissible under certain conditions. The discussion remains unresolved regarding the practical implications of kinetic energy in different frames.

Contextual Notes

There are limitations in the discussion regarding the definitions of inertial and non-inertial frames, as well as the assumptions made about the applicability of energy concepts across different physical theories.

hisham.i
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I was thinking in special relativity and how does the energy look from one reference to another,
if i consider a body making a circular motion in reference R1, with an angular velocity w1,and a stationary body in reference R2, R1 see that the body in R2 is rotating with an angular velocity |w1|, so the body in reference R2has a kinetic energy 1/2(I*W1^2) from reference R2point of view.
But the idea which is puzzling me is: Is this kinetic energy really exist?!
 
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Hi hisham.i! :smile:

Are you using the rotating body in R1 as a reference frame?

You can't do that in special relativity …

all frames must have uniform velocity and be non-rotational. :wink:
 
Tiny-tim, that's not correct. You can use any coordinate system you want as long as you don't call it an inertial frame.

hisham.i, your question doesn't have anything to do with relativity. You have the same issue in Newtonian mechanics. The answer is yes, the kinetic energy is different in different coordinate systems.
 
Hi Fredrik! :smile:
Fredrik said:
Tiny-tim, that's not correct. You can use any coordinate system you want as long as you don't call it an inertial frame.

Yes, I agree, but I meant frames "in special relativity", by which I took hisham.i to mean frames related by the Lorentz transformation.
 
Fredrik said:
hisham.i, your question doesn't have anything to do with relativity. You have the same issue in Newtonian mechanics. The answer is yes, the kinetic energy is different in different coordinate systems.
Yes you are right..
but the point is can i really use this energy in the other reference i mean can i generate electricity from this rotation?
 
yes, everything has energy so far it once had a rest mass..or relativistic mass
 

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