Answer:
Factors that influence flow :
Flow patterns in a fluid (gas or liquid) depend on three factors: the characteristics of the fluid, the speed of flow, and the shape of the solid surface. Three characteristics of the fluid are of special importance: viscosity, density, and compressibility. Viscosity is the amount of internal friction or resistance to flow. Water, for instance, is less viscous than honey, which explains why water flows more easily than does honey.
All gases are compressible, whereas liquids are practically incompressible; that is, they cannot be squeezed into smaller volumes. Flow patterns in compressible fluids are more complicated and difficult to study than those in incompressible ones. Fortunately for automobile designers, at speeds less than about 220 miles (350 kilometers) per hour, air can be treated as incompressible for all practical purposes. Also, for incompressible fluids, the effects of temperature changes can be neglected.