When an aircraft is flying, let V₁ be the speed of air just below the wings and V₂ be the speed of air just above the wing. Then 

Applying Bernoulli's equation between points 1 and 2, we can write, ${\mathrm{p}}_1+\frac{1}{2}{\mathrm{\rho v}}_1^2={\mathrm{p}}_2+\frac{1}{2}{\mathrm{\rho v}}_2^2$

$\Rightarrow {\mathrm{p}}_1-{\mathrm{p}}_2=\frac{1}{2}\mathrm{\rho }\left({\mathrm{v}}_2^2-{\mathrm{v}}_1^2\right)$

If A be the area of each wing, then total lift on the wings, $\mathrm{L}=2\mathrm{A}\times \left({\mathrm{p}}_1-{\mathrm{p}}_2\right)=\mathrm{A\rho }\left({\mathrm{v}}_2^2-{\mathrm{v}}_1^2\right)$

Air craft can fly only when $\mathrm{L}>0\mathrm{i}.\mathrm{e}.{\mathrm{V}}_2>{\mathrm{V}}_1$