What is the difference between energy and relativistic mass?

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Discussion Overview

The discussion centers on the distinction between energy and relativistic mass, exploring theoretical implications and interpretations within the context of special relativity. Participants examine the relevance of the equation E = mc² and the concept of invariant mass versus relativistic mass.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants argue that energy and relativistic mass are not the same, despite being related by the equation E = mc².
  • Others suggest that the term "relativistic mass" is outdated and that modern physics relies on the concept of invariant mass.
  • A participant points out that E = mc² applies to an object at rest, while the energy of a moving object is described by a different equation involving relativistic momentum.
  • There is a discussion about the interpretation of mass in different frames of reference, with some asserting that mass should remain invariant across Lorentz frames.
  • Some participants express confusion about the measurement of rest mass and energy, questioning the methods used to determine these quantities.
  • One participant provides an example illustrating how energy changes as velocity approaches the speed of light, referencing the Lorentz factor.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether relativistic mass is an outdated concept or if it still holds relevance in certain contexts. There are competing views on the definitions and implications of mass and energy in relativistic physics.

Contextual Notes

Limitations in the discussion include varying interpretations of mass, the dependence on specific definitions, and unresolved questions regarding measurement techniques for energy and mass.

  • #31
Meir Achuz said:
In the modern interpretation, m is the "invariant mass" of an object, and the equation E=mc^2 holds only in the rest system.



is the rest system to viewer?
 
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  • #32
dreamfly said:
is the rest system to viewer?

I'm pretty sure Meir meant "the rest system of the object in question."

In the usual modern terminology the energy of an object is

E = \frac {mc^2}{\sqrt {1 - u^2 / c^2}}

where u is the speed of the object in whatever reference frame you're working in, and m is the invariant mass, which is often called the "rest mass". This reduces to E = mc^2 when u = 0, i.e. when the object is at rest.
 
  • #33
jtbell said:
I'm pretty sure Meir meant "the rest system of the object in question."

In the usual modern terminology the energy of an object is

E = \frac {mc^2}{\sqrt {1 - u^2 / c^2}}

where u is the speed of the object in whatever reference frame you're working in, and m is the invariant mass, which is often called the "rest mass". This reduces to E = mc^2 when u = 0, i.e. when the object is at rest.



Thank you!
 

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