The controlling force curves $\text{P, Q,}$ and $\text{R}$ for a spring controlled governor are shown in the figure, where $r_{1}$ and $r_{2}$ are any two radii of rotation.

The characteristics shown by the curves are

1. $\text{P}$ – Unstable; $\text{Q}$ – Stable; $\text{R}$ – Isochronous
2. $\text{P}$ – Unstable; $\text{Q}$ – Isochronous; $\text{R}$ – Stable
3. $\text{P}$ – Stable; $\text{Q}$ – Isochronous; $\text{R}$ – Unstable
4. $\text{P}$ – Stable; $\text{Q}$ – Unstable; $\text{R}$ – Isochronous