Example Drag Force on a Sphere

Take the product of one of the remaining variables (F the dependent variable) to a known power (1) and recurring variables to unknown powers  

Equating the powers of each dimension in turn and solving simultaneously for the unknown powers  

CD is known at the drag coefficient. Drag coefficients are normally expressed in the form Cd = (F j A) ji puff), where A is the projected or cross-sectional area of the particle in the direction of flow. Hence the particular form shown in Equation (9). Re is the particle Reynolds number, Re = (pit, dip). and is the reciprocal of the second dimensionless group found above. 

The Reynolds number characterises the type of flow (see Chapter 3, Concepts of Fluid Flow , for more information). 

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