1. The problem statement, all variables and given/known data why we cant form the pi group by using repeating variable of (μ, ρ , v) or (D, v , μ ) ? http://www-mdp.eng.cam.ac.uk/web/li...mal_dvd_only/aero/fprops/dimension/node9.html http://www.efm.leeds.ac.uk/CIVE/CIVE1400/Section5/dimensional_analysis.htm 2. Relevant equations 3. The attempt at a solution according to the principle , when we choose the repeating variable , it cant form the dimensionless group , right ? for (μ, ρ , v) , i have (M/LT)(M/(L^3))(L/T) , i got (M^2)(L^-3)(T^-2) for (D, v , μ ) , i have (L)(L/T)(M/LT) , i got ML(T^-2) , both group are not dimensionless, why is it a must to form group by using (D, ρ , v) ??