What is the significance of the T - V Lagrangian of a system?

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Discussion Overview

The discussion revolves around the significance of the T - V Lagrangian in various contexts, including its implications for physical systems, factory production, and the choice of motion. Participants explore the meaning of the integral of T - V, referred to as action, and its relevance in different scenarios, such as energy conservation and trajectory determination.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants propose that the quantity $$\int_x T - V$$ signifies action, which is important because the actual trajectory minimizes this action.
  • Others argue that the integral $$\int_x T - V$$ can be interpreted in the context of a factory's budget, questioning whether factory production follows a Lagrangian principle.
  • A participant suggests that the quantity $$\int_s T - V$$ over all possible paths may have significance, though its meaning is not clearly defined.
  • One participant emphasizes that the action is a functional of possible trajectories and is not an observable in a traditional sense.
  • Another viewpoint highlights that the action principle leads to the Euler-Lagrange equations, which describe the motion of particles and can be generalized to different coordinate systems.
  • There is a discussion about the relationship between energy conservation and the time derivative of kinetic and potential energy, with some participants exploring the implications of this relationship in the context of the Lagrangian formulation.

Areas of Agreement / Disagreement

Participants express a range of views on the significance of the T - V Lagrangian, with some agreeing on its role in determining trajectories while others raise questions about its applicability in different contexts. The discussion remains unresolved regarding the broader implications of the integral of T - V in various scenarios.

Contextual Notes

Some claims depend on specific interpretations of energy conservation and the definitions of kinetic and potential energy. The discussion includes varying assumptions about the applicability of the Lagrangian framework in different physical and theoretical contexts.

  • #31
PS in this case, you can see that we have a common average velocity between all potential paths. And, any attempt to vary the velocity produces a greater increase in the action when ##v > \frac X T## than the reduction when ##v < \frac X T##. In other words, the ##v^2## term ensures that uniform velocity minimises the integral. Although, it's a bit more effort to prove that formally.
 

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