Derivation of relativistic momentum

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Discussion Overview

The discussion revolves around the derivation of the relativistic momentum equation p = ymv and the associated kinetic energy formula, specifically seeking a one-dimensional derivation without the use of 4-vectors or two-dimensional collisions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Homework-related

Main Points Raised

  • One participant asks if the equation p = ymv can be derived in one dimension without using 4-vectors or 2-dimensional collisions, expressing difficulty with the mathematics in a referenced paper.
  • Another participant suggests that it is possible to derive the equation, noting that p=mv is not conserved in all reference frames, and provides a link to a resource on special relativity dynamics.
  • A third participant agrees with the possibility of the derivation, stating that the referenced paper appears valid, and asks for clarification on specific parts of the paper that are confusing.
  • One participant expresses confusion about the mathematical processes in specific equations (3.6 and 3.7) from the paper.
  • A different participant mentions that Louis De Broglie used Hamilton-Jacobi mathematics for similar derivations, suggesting further derivations of the relativistic energy equation are possible.
  • Another participant attempts to clarify the confusion regarding the mathematical processes, explaining the concept of a Taylor series as a method for approximating functions.

Areas of Agreement / Disagreement

Participants express varying levels of understanding and agreement on the feasibility of deriving the equation in question. There is no consensus on the specific mathematical processes involved, as some participants seek clarification while others reference different methods or approaches.

Contextual Notes

Participants highlight limitations in understanding specific mathematical steps and the dependence on the clarity of the referenced paper. The discussion reflects a range of familiarity with the underlying mathematics and concepts.

albertrichardf
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Hi all,
Is it possible to derive the equation p = ymv, and hence based on this, kinetic energy formula, without referring to 4-vectors or 2-dimensional collisions, that is derive it in one dimension?
I tried this website/pdf but the mathematics is beyond my understanding. So could some one either explain the pdf, or derive the equation themselves?
Thanks.
Here is the link:
http://arxiv.org/pdf/physics/0402024.pdf
 
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Is it possible to derive the equation p = ymv, and hence based on this, kinetic energy formula, without referring to 4-vectors or 2-dimensional collisions, that is derive it in one dimension?
... yes - sort of.

You start by showing that p=mv is not conserved in all reference frames.
http://en.wikibooks.org/wiki/Special_Relativity:_Dynamics

Note: in 1D, the 4-vector just has a zero in each of the unused positions.
 
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Albertrichardf said:
Is it possible to derive the equation p = ymv, and hence based on this, kinetic energy formula, without referring to 4-vectors or 2-dimensional collisions, that is derive it in one dimension?

Since the derivation in the paper you linked to looks valid, I would say yes. :wink:

Albertrichardf said:
I tried this website/pdf but the mathematics is beyond my understanding. So could some one either explain the pdf, or derive the equation themselves?

Can you be a bit more specific about what in the pdf you are unable to understand?
 
i don't get the mathematical processes from equation 3.6 and 3.7.
 
Hi Albertrichardf,

In addition to the paper you referred to, Louis De Broglie derived that (and other formulas expressed in 3-vectors) using Hamilton-Jacobi mathematics. It's possible to go still further and derive the relativistic energy equation and all of its variations.
 
Albertrichardf said:
i don't get the mathematical processes from equation 3.6 and 3.7.

It's just a taylor series.

Basically the idea is that you can approximate a function near a point by a straight line

If you have f(x) and you want to approximate it near some value "a", the first 2 terms of the series are

f(a) + (df/dx)*(x-a)

see http://en.wikipedia.org/wiki/Taylor_series
 
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