Relativistic angular momentum and cyclic coordinates

Click For Summary

Discussion Overview

The discussion revolves around the relativistic Lagrangian for a particle in a central potential, specifically focusing on the calculation of angular momentum and the application of the Lagrangian formalism in a relativistic context.

Discussion Character

  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant expresses confusion regarding the calculation of angular momentum from their relativistic Lagrangian, questioning whether the derivative with respect to angular velocity should yield conserved angular momentum.
  • Another participant provides an alternative form of the Lagrangian and calculates the partial derivative with respect to angular velocity, suggesting that the expected result is indeed obtained.
  • A later reply indicates that the initial confusion was resolved, and the participant achieved the correct result upon re-evaluation.

Areas of Agreement / Disagreement

The discussion reflects an initial uncertainty from one participant, but later responses indicate that the calculations can yield correct results, suggesting a resolution for that individual. However, no consensus is reached on the broader implications or interpretations of the results.

Contextual Notes

The discussion does not clarify the assumptions made in the calculations or the specific conditions under which the results hold. There is also no exploration of potential limitations in the application of the relativistic Lagrangian.

maverick_starstrider
Messages
1,118
Reaction score
7
I'm getting myself confused here. If my relativistic Lagrangian for a particle in a central potentai is

[tex]L = \frac{-m_0 c^2}{\gamma} - V(r)[/tex]

should

[tex]\frac{d L}{d \dot{\theta}}[/tex]

not give me the angular momentum (which is conserved)? Instead I get

[tex]\frac{d L}{d \dot{\theta}} = -4 m v r^2 \dot{\theta}\gamma[/tex]
 
Physics news on Phys.org
Anyone?
 
[tex]L = - {m_0}{c^2}\sqrt {1 - \frac{{{{\dot r}^2} + {r^2}{{\dot \theta }^2}}}{{{c^2}}}} - V\left( r \right)[/tex]

so

[tex]\frac{{\partial L}}{{\partial \dot \theta }} = \gamma {m_0}{r^2}\dot \theta[/tex]

What's the problem?
 
Absolutely nothing apparently. I just did it again this morning and got the right answer. Sorry for the time waste.
 

Similar threads

  • · Replies 15 ·
Replies
15
Views
1K
  • · Replies 3 ·
Replies
3
Views
1K
  • · Replies 8 ·
Replies
8
Views
2K
  • · Replies 3 ·
Replies
3
Views
1K
  • · Replies 0 ·
Replies
0
Views
1K
  • · Replies 1 ·
Replies
1
Views
1K
  • · Replies 1 ·
Replies
1
Views
1K
  • · Replies 0 ·
Replies
0
Views
2K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 1 ·
Replies
1
Views
558