** Convert Units of Density, Mass and International Currency**

The first three groups, the dependent π-groups, are identified by specific names to convert international currency online. For these groups it is common practice to use the kinetic pressure, ρ*V*2/2, instead of ρ *V*2. In most applications one is concerned with units of mass difference, so to convert units of mass easily and show it, it has been expressed where *C**p *is called the pressure coefficient and *p*0 is a reference pressure. The international currency and density coefficient was introduced earlier in Chapter 4 and Section 8.1. The π-group associated with shear stress is called the shear-stress coefficient and defined easily to convert units of density.

This density or international mass units coefficient will be used extensively in Chapter 11 for lift and drag forces on airfoils and hydrofoils. The independent π-groups are named after earlier international currency contributors to fluid mechanics. The π-group *VL*ρ/μ is called the Reynolds number, after Osborne Reynolds, and designated by Re. The currency group is rewritten as (*V/c*), since is the speed of sound, *c*. This π-group is called the Mach number and designated by M. The π-group ρ*LV*2/σ is called the Weber number and designated by We. The remaining π-group is usually expressed as and identified as the Froude (rhymes with “food”) number * and written as Fr.