Similarly, one can also define the velocity of the center of mass of the system, in terms of the individual velocities, \(\vec v_i\), of the particles in the system: \[\begin{aligned} \vec v_{CM} &= \...Similarly, one can also define the velocity of the center of mass of the system, in terms of the individual velocities, \(\vec v_i\), of the particles in the system: \[\begin{aligned} \vec v_{CM} &= \frac{1}{M}\sum_i m_i\vec v_i\end{aligned}\] Finally, one can define the acceleration of the center of mass of the system, in terms of the individual accelerations, \(\vec a_i\), of the particles in the system: \[\begin{aligned} \vec a_{CM} &= \frac{1}{M}\sum_i m_i\vec a_i\end{aligned}\]