# Conservation of momentum $\vec{L}$ and $\tau$ equations. [closed]

• My book says for reference point $A$, $$\frac{d L_A}{dt}=\frac{d}{dt}(I_{cm}\omega+\vec{r_{cm}} \times M\vec{v}) \neq I_A \frac{d\omega}{dt}$$ so torque equation can be applied to a rigid body in a general motion only and only about an axis through CM (center of mass). What does this mean?