- #1
Steven Wang
- 8
- 0
In Landau's Mechanics, if an inertial frame [itex]\textit{K}[/itex] is moving with an infinitesimal velocity [itex]\textbf{ε}[/itex] relative to another inertial frame [itex]\textit{K'}[/itex], then [itex]\textbf{v}'=\textbf{v}+\textbf{ε}[/itex]. Since the equations of motion must have the same form in every frame, the Lagrangian [itex]L(v^2)[/itex] must be converted by this transformation into a function [itex] L'[/itex] which differs from [itex]L(v^2)[/itex], if at all, only by the total time derivative of a function of co-ordinates and time. Then he gave the formula [itex]L'=L(v'^2)=L(v^2+2\textbf{v}\bullet\textbf{ε} + \textbf{ε}^2)[/itex].
So my question is what does the sentence 'the equations of motion must have the same form in every frame' mean? Whether [itex]L'(v'^2)=L(v'^2)[/itex] or [itex]L'(v'^2)=L(v^2)[/itex]? Why?
And what is the variable in the two Lagrangians,[itex]\textbf{v}[/itex] or [itex]\textbf{v}'[/itex]?
So my question is what does the sentence 'the equations of motion must have the same form in every frame' mean? Whether [itex]L'(v'^2)=L(v'^2)[/itex] or [itex]L'(v'^2)=L(v^2)[/itex]? Why?
And what is the variable in the two Lagrangians,[itex]\textbf{v}[/itex] or [itex]\textbf{v}'[/itex]?