On a cylinder, the force due to rotation is known as Kutta–Joukowski lift. It can be analysed in terms of the vortex produced by rotation. The lift on the cylinder per unit length, L ′ ′ , is the product of the freestream velocity, v ∞ ∞ (in m/s), the freestream density of the fluid, ρ ρ ∞ ∞ (in kg/m), and circulation of fluid established by the rotation, Γ Γ , due to viscous effects: