Friday, July 24, 2015

On Second Thought... Potential Density

From the post " \(PE\) Ain't Physical Education" dated 22 Jul 2015,

\(L=-\cfrac { 1 }{ 2 } \psi _{ c }\cfrac { \psi _{ c }+u }{ u } { e^{ u }\left( { e^{ 2u }-1 } \right) ^{ 1/2 } }-\psi _{ n }\)

\(\cfrac{d}{dt}\left\{\cfrac{\partial\,L}{\partial\dot{x}}\right\}=\cfrac{d}{dt}\left\{\cfrac{1}{2}m2v\right\}=ma\)

since,

\(v^2=-\cfrac { 1 }{ m }  \psi _{ c } \cfrac { \psi _{ c }+u   }{ u }{ e^{ u }\left( { e^{ 2u }-1 } \right) ^{ 1/2 } }\)

And

\(\cfrac{\partial\,L}{\partial x}=-\cfrac{\partial\,\psi_n}{\partial x}=F_{\rho}\)

And we have,

\(F_{\rho}=ma\)

Wrong!  This is not Newton's Law Of Motion.  Which means \(\psi_n\) is not potential but potential density.  In which case,

\(\cfrac{\partial\,L}{\partial x}=-\cfrac{\partial}{\partial x}\left\{\int_V\psi dV\right\}=\int_V{-\cfrac{\partial\,\psi}{\partial x}}dV=\int_V{F_{\rho}}dV=F\)

where \(F\) is the total force on the point particle and is in the direction of lesser \(\psi\) for a positive particle.

And we have,

\(F=ma\)

But, more importantly, should

\(\psi_n\)  be  \(\psi_n-\psi(x)\)

instead?  In which case,

\(F=F_n-F(x)\)

where the resultant force \(F\) on the particle is \(F_n-F(x)\) in the direction of lesser \(\psi\) for a positive particle and reversed for a negative particle.  \(F(x)\) being due to the containing particle.

Good  Morning.