∂ v → ∂ t + ( v → ⋅ ∇ ) v → = − 1 ρ ∇ P − ∇ Φ {\displaystyle {\frac {\partial {\vec {v}}}{\partial t}}+({\vec {v}}\cdot \nabla ){\vec {v}}=-{\frac {1}{\rho }}\nabla P-\nabla \Phi }