Fluid Mechanics-Some Characteristics of Fluids

Fluid mechanics is that discipline within the broad field of applied mechanics concerned with
the behavior of liquids and gases at rest or in motion. This field of mechanics obviously
encompasses a vast array of problems that may vary from the study of blood flow in the
capillaries 1which are only a few microns in diameter2 to the flow of crude oil across Alaska
through an 800-mile-long, 4-ft-diameter pipe. Fluid mechanics principles are needed to explain
why airplanes are made streamlined with smooth surfaces for the most efficient flight,
whereas golf balls are made with rough surfaces 1dimpled2 to increase their efficiency. Numerous
interesting questions can be answered by using relatively simple fluid mechanics
ideas. For example:
 How can a rocket generate thrust without having any air to push against in outer space?
 Why can’t you hear a supersonic airplane until it has gone past you?
 How can a river flow downstream with a significant velocity even though the slope of
the surface is so small that it could not be detected with an ordinary level?
 How can information obtained from model airplanes be used to design the real thing?
 Why does a stream of water from a faucet sometimes appear to have a smooth surface,
but sometimes a rough surface?
 How much greater gas mileage can be obtained by improved aerodynamic design of
cars and trucks?
The list of applications and questions goes on and on—but you get the point; fluid mechanics
is a very important, practical subject. It is very likely that during your career as an engineer
you will be involved in the analysis and design of systems that require a good understanding
of fluid mechanics. It is hoped that this introductory text will provide a sound foundation of
the fundamental aspects of fluid mechanics.