积分形式的动量方程及动量矩方程为$\frac{\partial}{\partial t}\int_\tau\rho\boldsymbol{v}\,d\tau+\oint_S \rho\boldsymbol{v}_n\boldsymbol{v}\,dS=\int_\tau\rho\boldsymbol{F}\,d\tau+\oint_S \boldsymbol{P}_n\,dS$，$\frac{\partial}{\partial t}\int_\tau \boldsymbol{r}\times\rho\boldsymbol{v}\,d\tau+\oint_S \rho\boldsymbol{v}_n(\boldsymbol{r}\times\boldsymbol{v})\,dS=\int_\tau\boldsymbol{r}\times\rho\boldsymbol{F}\,d\tau+\oint_S\boldsymbol{r}\times\boldsymbol{P}_n\,dS$。阻碍人们顺利应用的主要是非定常运动时的体积分 $\int_\tau\frac{\partial(\rho\boldsymbol{v})}{\partial t}\,d\tau$。

出处：206