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## Main Question or Discussion Point

Hello! My fluid dynamics book doesn't bother explaining this properly, so can somebody please give a short, intuitive (if possible...) explanation to the following 3 formulas concerning lift and drag? And are they only valid for circular, rotating cylinders (magnus effect)?

[tex] L = C_L \cdot \frac{1}{2} \rho U^2 \cdot A[/tex]

[tex] D = C_D \cdot \frac{1}{2} \rho U^2 \cdot A[/tex]

[tex] C_L = \pi a \omega / U_{\infty}[/tex]

I believe my book used Kutta-Zhukovsky's theorem,

[tex] L = \Gamma \cdot \rho U_{\infty} [/tex]

to get the first. The second one I am very confused about, because according to inviscid theory drag is non-existant.

[tex] L = C_L \cdot \frac{1}{2} \rho U^2 \cdot A[/tex]

[tex] D = C_D \cdot \frac{1}{2} \rho U^2 \cdot A[/tex]

[tex] C_L = \pi a \omega / U_{\infty}[/tex]

I believe my book used Kutta-Zhukovsky's theorem,

[tex] L = \Gamma \cdot \rho U_{\infty} [/tex]

to get the first. The second one I am very confused about, because according to inviscid theory drag is non-existant.

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