The force of viscosity acting on a smooth sphere in stream line motion can be expressed with Stokes' formula:
F = 6 π η r v (1)
F = force (N)
η = viscosity of fluid
r = radius of sphere (m)
v= relative velocity between fluid and sphere (m/s)
The study of fluids - liquids and gases. Involving velocity, pressure, density and temperature as functions of space and time.