Derivation in classical mechanics

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Discussion Overview

The discussion revolves around the derivation of differential identities in classical mechanics, specifically concerning the relationships between action, Hamiltonian, Lagrangian, kinetic energy, and potential energy. Participants explore whether additional identities exist and their significance in solving equations of motion.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant questions the completeness of the differential identities related to action, Hamiltonian, Lagrangian, kinetic energy, and potential energy, suggesting that there may be more identities that make sense.
  • Another participant asserts that once the Hamiltonian or Lagrangian is established, the other quantities can be derived, but questions the necessity of doing so for solving equations of motion.
  • A request for examples is made to illustrate how to derive the additional quantities mentioned.
  • A later reply emphasizes the expectation for participants to engage in their own work rather than expecting comprehensive examples or explanations from others.

Areas of Agreement / Disagreement

Participants express differing views on the necessity and completeness of the differential identities in classical mechanics. There is no consensus on whether additional identities are needed or how they should be derived.

Contextual Notes

Some participants indicate that the discussion may be limited by the expectation of providing extensive examples or explanations, which may not be feasible within the forum's context.

Jhenrique
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I'm studying classical mechanics and I'm stumbling in the quantity of differential identities.

Being S the action, H the hamiltonian, L the lagrangian, T the kinetic energy and V the potential energy, following the relationships:

attachment.php?attachmentid=70623&stc=1&d=1402838216.png


But, the big question is: that's all? Or has exist more?

Seems be missing
$$\frac{\partial S}{\partial q'} \;\;\; \frac{\partial S}{\partial p} \;\;\; \frac{\partial S}{\partial p'} \;\;\; \frac{\partial S}{\partial q'} \;\;\; \frac{\partial L}{\partial p} \;\;\; \frac{\partial L}{\partial p'} \;\;\; \frac{\partial H}{\partial p'} \;\;\; \frac{\partial H}{\partial q'} \;\;\; \frac{\partial V}{\partial q'} \;\;\; \frac{\partial V}{\partial p} \;\;\; \frac{\partial V}{\partial p'} \;\;\; \frac{\partial T}{\partial q} \;\;\; \frac{\partial T}{\partial p} \;\;\; \frac{\partial T}{\partial p'}$$
These relation exist? Make sense? If yes, how will be the identities?
 

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Once you write down the Hamiltonian or the Lagrangian then you certainly can write down all of the rest of those quantities, but there is no point it doing so. You can already solve the equations of motion without them.
 
DaleSpam said:
Once you write down the Hamiltonian or the Lagrangian then you certainly can write down all of the rest of those quantities

How? Give me examples...
 
First, it's please give me examples. We are not your servants, to be ordered around.

Second, you're essentially asking us to write down a textbook for you. I'm afraid that's beyond what one can reasonably expect PF to do. You are going to have to do some work on your own.

This looks like a good time to close this thread.
 

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