Is the formula $\vec{F} = m\vec{a}$ valid in all circumstances? Why?

(N/A) No,the formula $\vec{F} = m\vec{a}$ is not valid in all circumstances.
Newton's Second Law is fundamentally defined as $\vec{F} = \frac{d\vec{p}}{dt}$,where $\vec{p} = m\vec{v}$ is the linear momentum.
Expanding this,we get $\vec{F} = \frac{d(m\vec{v})}{dt} = m\frac{d\vec{v}}{dt} + \vec{v}\frac{dm}{dt}$.
If the mass $m$ is constant,then $\frac{dm}{dt} = 0$,which simplifies the equation to $\vec{F} = m\vec{a}$.
However,in cases where mass changes (e.g.,rocket propulsion) or at relativistic speeds where mass depends on velocity,the formula $\vec{F} = m\vec{a}$ does not hold.