Under creeping fluid flow conditions at Reynolds numbers much less than unity, the coefficient of friction 𝑁 f varies linearly in proportion to 𝑁 Re . In the context of Newtonian forces, these two dimensionless quantities are broadly defined as 𝑁 f = 𝐹 (𝐴𝜌𝑢 ̅ 2 ) ⁄ and 𝑁 Re = 𝑢 ̅𝐿 𝜄 fluid , ⁄ where F is the frictional force under consideration [kg 1 m 1 s -2 ], ρ is mass density [kg 1 m -3 ], 𝑢 ̅ is mean speed [m/s], A is the representative area [m 2 ], and L is the length scale [m] corresponding to the macroscopic velocity gradient of interest.