User:!jim/Sandbox

Failed to parse (unknown function "\em"): {\displaystyle \frac{DN_{sys}}{Dt} = \int_{c.v.}^{} \frac{\partial}{\partial t} (\rho \eta) dV + \int_{c.s.}^{} \rho \eta \overrightarrow{V_b}\cdot \widehat{n} dA+\int_{c.s.}^{} \rho \eta \em{\overrightarrow{V_r}}\cdot \widehat{n} dA}