L(\vec{r'}, \dot{\vec{r'}}, t)=L(\vec{r}, \dot{\vec{r}}, t)+\delta\theta\frac{\partial L}{\partial \vec{r}}\vec{u}\times\vec{r}+\delta\theta\frac{\partial L}{\partial \dot{\vec{r}}}\vec{u}\times\dot{\vec{r}}+...