Equation of motion from Hamiltonian

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Homework Help Overview

The discussion revolves around deriving equations of motion from a given Hamiltonian for a system of identical particles. The Hamiltonian includes kinetic and potential energy terms, and participants are exploring the application of Hamilton's equations of motion.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • The original poster attempts to apply Hamilton's equations to derive motion equations but questions the correctness of their approach. Some participants raise concerns about dimensional consistency in the equations presented.

Discussion Status

The discussion is ongoing, with participants providing guidance on checking dimensions and consistency in the equations. There is an active exploration of the implications of the original poster's statements, particularly regarding the partial derivatives.

Contextual Notes

Participants are focusing on the dimensional analysis of the equations and the definitions provided in the homework statement. There may be assumptions about the nature of the particles and the form of the Hamiltonian that are under scrutiny.

LagrangeEuler
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Homework Statement


H=\sum^N_{i=1}(\frac{p_i^2}{2m}+\frac{1}{2}(x_{i+1}-x_i)^2+(1-\cos(2\pi x_i))

Homework Equations


Hamilton equation of motion I suppose
##\dot{q}=\frac{\partial H}{\partial p}##
##\dot{p}=-\frac{\partial H}{\partial q}##[/B]

The Attempt at a Solution


If particles are identical then
##\dot{p}=m \dot{x}##
So if I understand well I will get from here system of equations
##\dot{p_1}=-\frac{\partial H}{\partial x_1}##
If I take for example m=1, then
##\dot{x_1}=-\frac{\partial H}{\partial x_1}##
Is this correct?
 
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no. Check the dimensions.
 
Ok. Can I get some help?
 
Yes: write down the dimensions and check,
 
In particular I think BvU is trying to draw your attention to the partial derivatives you wrote in your last statements. Check those dimensions to see if they are consistent with the definitions you wrote in the relevant equations section.
 

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