Is the lagrangian always K.E-PE?

[quantumfireball]

Is the lagrangian always K.E-PE?
I don't think so?
so WHAT REALLY is the physical significance of the lagrangian?
Superficially it appears to be KE-PE,but the lagrangian for a charged particle in a vector potential is 1/2MV.V +qV.A-qW.
where V=velocity
A=vector potential
W=Scalar potential.
If the hamiltonion for the above lagrangian is calculated it turns out to be 1/2MV.V+qW.
So what does the term eV.A represent?
It appears to be the interaction energy.
But why does it dissapaer in the hamiltonion.

 

[Almsco]

The term qV.A represents the interaction energy between the particle and the vector potential, which is also known as the Lorentz force. It disappears in the Hamiltonian because it is a conservative force and its work done is zero. Therefore, it does not contribute to the energy of the system.