At a sudden contraction in a pipe the diameter changes fromd1tod2. the pressure drop,δp, which develops across the contraction is a function ofd1andd2, as well as the velocity, v, in the larger pipe, and the fluid density, rho, and viscosity,μ. used1,v, andμas repeating variables to determine a suitable set of dimensionless parameters. why would it be incorrect to include the velocity in the smaller pipe as an additional variable?