- polar coordinates deriving - REMEMBER for exam
- error: $r\dot{r} = \dots = ar^4$
- For exam: $\dot{\theta} = \frac{x \dot{y} - \dot{x} y}{r^2}$
- eigenvectors != nullclines !!
- energy diminishes when using first derivative (second one is only inertial)
- trick to remember for exam: multiply by $\dot{x}$
- oscillator