For instance consider fluid dynamics as it relates to hemodynamics (it is fluid, degrees
of viscosity). For
an anology there
is water flow down a channel (river) and
the banks
of the river have different sized barriers. The river flows with a given velocity (movement) and it will have a different sectional flow patterns and velocity based tortuousity,etc. Add volume and pressure at the mouth of the river and because of tortuosity, shear stress, velocity, etc.