Strange Hamilton Jacobi equation

AI Thread Summary
The discussion centers on the Hamilton-Jacobi equation and its compatibility with a modified equation involving the action S, the Laplacian operator L, and a potential V. It establishes that the equation can be equated to zero, leading to a form that aligns with the Hamilton-Jacobi framework when the Hamiltonian is defined appropriately. The relationship between the action and the Hamiltonian is highlighted, showing that the potential W is non-conservative and represents virtual work. This raises questions about the interpretation of W in the context of the Hamilton-Jacobi equation. Overall, the conversation delves into the nuances of applying the Hamilton-Jacobi formalism to a particle under a specific potential.
eljose
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let be (dS/dt)+(gra(S))^2/2m+(LS)+V(x) where L is the Laplacian Operator and V is the potential...could it be considered as the Hamiltan Jacobi equation for a particle under a potential Vtotal=V(x)+(LS) where S is the action
 
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eljose said:
let be (dS/dt)+(gra(S))^2/2m+(LS)+V(x) where L is the Laplacian Operator and V is the potential...could it be considered as the Hamiltan Jacobi equation for a particle under a potential Vtotal=V(x)+(LS) where S is the action

I assume you mean to equate to 0, i.e.:

\frac{\partial S}{\partial t}\right)+\frac{(\vec\nabla S)^2}{2m}+\vec\nabla S+V(q)=0

If we compare it to the Hamillton-Jacobi equation for the generating function S (a concept more general than the "action")

H\left(q,\frac{\partial S}{\partial q},t\right)+\frac{\partial S}{\partial t}=0

we find they are compatible provided we let

H\left(q,\frac{\partial S}{\partial q},t\right)=\frac{(\vec\nabla S)^2}{2m}+\vec\nabla S+V(q)

Since p_i=\frac{\partial S}{\partial q_i}, we can rewrite it as

H\left(q_i,p_i,t\right)=\frac{(\sum_i p_i)^2}{2m}+\vec\nabla S+V(q)

or

H=T+W

where

W=\sum_i p_i+V(q_i).

Here we see that W=f(p_i,q_i), in other words the "potential" W is not conservative and the meaning of W is that of "virtual work". Is that the source of your doubts?
 
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