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An important field of study in engineering is fluid mechanics. Many of the basic principles of fluid mechanics were developed in parallel with those of solid mechanics, and its historical roots can be traced to such great scientists and mathematicians as Archimedes (287–212 B.C.), Leonardo da Vinci (1425–1519), Isaac Newton (1642–1727), Evangelista Torricelli (1608–1647), Blaise Pascal (1623–1662), Leonhard Euler (1707–1783), Osborne Reynolds (1842–1912) and Ernst Mach (1838–1916). Fluid mechanics is the study of fluids at rest and in motion. As a subdiscipline of engineering mechanics, fluid mechanics is broadly divided into two categories, fluid statics and fluid dynamics. As the term implies, fluid statics is the branch of fluid mechanics that deals with the behavior of fluids at rest. Fluid dynamics is the branch of fluid mechanics that deals with the behavior of fluids in motion. In fluid statics, the fluid is at rest with respect to a frame of reference. This means that the fluid does not move with respect to a body or surface with which the fluid is in physical contact. In fluid dynamics, the fluid moves with respect to a body or surface, common examples being the flow of a fluid within a pipe or channel or around an immersed object such as a submarine or aircraft.

There are two primary physical states of matter—solid and fluid, the fluid state being subdivided into the liquid and gas states. A fourth state, referred to as the plasma state, refers to atoms and molecules that are ionized (electrically charged). Plasmas are categorized as special types of fluids that respond to electromagnetic fields. The analysis of plasmas is complex and will not be considered in this book. A fundamental question to be answered is “What is the difference between a solid and a fluid?” Casual observations tell us that solids are “hard” whereas fluids are “soft”. Solids have a distinct size and shape and retain their basic dimensions even when large forces are applied to them. Fluids, however, do not really have a distinct size or shape unless they are confined in some manner by solid boundaries. When placed in a container, a fluid spreads throughout the container, taking on the shape of the container. This phenomena occurs to one degree or another for liquids and gases. This behavior may be explained by examining the atomic and molecular structure of matter. In solids, the spacing of atoms or molecules is small, and there are large cohesive forces between these particles that enable solids to maintain their shape and size. In fluids, the atomic or molecular spacing is larger, and the cohesive forces are smaller thereby permitting fluids more freedom of movement. At room temperature and atmospheric pressure, the average intermolecular spacing is approximately 10¹⁰ m for liquids and 10⁹ m for gases. The vast differences in cohesive forces in solids, liquids, and gases account for the rigidity of solids, the ability of liquids to fill containers from the bottom up, and the ability of gases to completely fill containers in which they are placed.

Although the differences between solids and fluids can be explained in terms of atomic or molecular structure, a more useful engineering explanation involves the response of solids and fluids to the application of external forces. Specifically, a fluid may be defined as a substance that deforms continuously when acted upon by a shear stress of any magnitude. Stress is a force that is applied over a specified area. A shear stress is produced when a force acts tangentially on a surface. When a solid material, such as metal, plastic, or wood, is subjected to a shear stress, the material deforms a small amount and maintains a deformed shape while the shear stress is applied. If the shear stress is not too great, the material even returns to its original shape when the force producing the stress is removed. When a fluid is subjected to a shear stress, however, the fluid continues to deform. Unlike a solid, a fluid cannot sustain a shear stress, so it continuously deforms; i.e., the fluid flows in response to the shear stress. Some substances, such as tar, toothpaste, putty, and other gunky and gooey materials, exhibit behavior that lies somewhere between solids and fluids. These types of substances will flow if the shear stress is high enough, but the analysis of these substances can be complex. We will therefore restrict our attention to common fluids such as water, oil, and air.

In most colleges and universities, one or more courses in fluid mechanics is required of mechanical, civil, and chemical engineering majors. Depending on the specific curricular policies of your school or department, other majors may also be required to take a course in fluid mechanics. Fluid mechanics is typically offered as part of a “thermofluid” sequence consisting of thermodynamics, fluid mechanics, and heat transfer because these three disciplines are closely related to one another. Courses in statics, strength of materials, electrical circuits, and other analytically-oriented courses round out the engineering science curriculum.

Engineers use principles of fluid mechanics to analyze and design a wide variety of devices and systems. Consider the plumbing fixtures in your home. The sink, bathtub or shower, toilet, dishwasher, and washing machine are supplied water by a system of pipes, pumps, and valves. When you turn on a faucet, the rate at which the water flows is determined by principles of fluid mechanics. The analysis and design of virtually every type of transportation system involves the use of fluid mechanics. Aircraft, surface ships, submarines, rockets, and automobiles require the application of fluid mechanics in their design. Mechanical engineers use fluid mechanics to design heating and air-conditioning systems, turbines, internal combustion engines, pumps, and air compressors. Aeronautical engineers use fluid mechanics to design aircraft, spacecraft, and missiles. Chemical engineers use fluid mechanics to design chemical processing equipment such as heat exchangers and cooling towers. Civil engineers use fluid mechanics to design water treatment plants, flood control systems, irrigation channels, and dams. Principles of fluid mechanics are even important in the design of ground-based structures. The collapse of the Tacoma Narrows Bridge in 1940 could have been prevented had the designers paid attention to the possible effects of wind forces on suspension bridges. Principles of fluid mechanics are necessary for understanding winds and ocean currents. A proper understanding of fluid mechanics is also needed for studying blood flow in the human circulatory system. The list of fluid mechanics applications is long indeed. Figure 1, Figure 2 and Figure 3 show some engineering systems that involved the use of fluid mechanics in their design.

Professional Success: Choosing an Engineering Major

Perhaps the biggest question facing the new engineering student (besides: “How much money will I make after I graduate?” ) is: “In which field of engineering should I major?” Engineering is a broad area, so the beginning student has numerous options. The new engineering student should be aware of a few facts. First, all engineering majors have the potential for preparing the student for a satisfying and rewarding engineering career. As a profession, engineering has historically enjoyed a fairly stable and well-paid market. There have been fluctuations in the engineering market in recent decades, but the demand for engineers in all the major disciplines is high, and the future looks bright for engineers. Second, all engineering majors are academically challenging, but some engineering majors are more challenging than others. Study the differences between the various engineering programs. Compare the course requirements of each program by examining the course listings in your college or university catalog. Ask department chairs to discuss the similarities and differences between their engineering programs and the programs in other departments. (Just keep in mind that professors, like everyone else, are biased and will probably tell you that their engineering discipline is the best.) Talk with people who are practicing engineers in the various disciplines, and ask them about their educational experiences. Learn all you can from as many sources as you can about the various engineering disciplines. Third, and this is the most important point, try to answer the question: “What kind of engineering will be the most gratifying for me?” It makes little sense to devote four or more years of intense study of X engineering just because it happens to be the highest paid discipline, just because your uncle Vinny is an X engineer, just because X engineering is the easiest program at your school, or just because someone tells you that they are an X engineer, so you should be one too.

probably tell you that their engineering discipline is the best.) Talk with people who are practicing engineers in the various disciplines, and ask them about their educational experiences. Learn all you can from as many sources as you can about the various engineering disciplines. Third, and this is the most important point, try to answer the question: “What kind of engineering will be the most gratifying for me?” It makes little sense to devote four or more years of intense study of X engineering just because it happens to be the highest paid discipline, just because your uncle Vinny is an X engineer, just because X engineering is the easiest program at your school, or just because someone tells you that they are an X engineer, so you should be one too.

Engineering disciplines may be broadly categorized as either mainstream or narrowly focused. Mainstream disciplines are the broad-based, traditional disciplines that have been in existence for decades (or even centuries) and in which degrees are offered by most of the larger colleges and universities. Many colleges and universities do not offer engineering degrees in some of the narrowly focused disciplines. Chemical, civil, computer, electrical, and mechanical engineering are considered the core mainstream disciplines. These mainstream disciplines are broad in subject content and represent the majority of practicing engineers. Narrowly focused disciplines concentrate on a narrow engineering subject by combining specific components from the mainstream disciplines. For example, biomedical engineering may combine portions of electrical and mechanical engineering plus components from biology. Construction engineering may combine elements from civil engineering and business or construction trades. Other narrowly focused disciplines include materials, aeronautical and aerospace, environmental, nuclear, ceramic, geological, manufacturing, automotive, metallurgical, corrosion, ocean, and cost and safety engineering.

Should you major in a mainstream area or a narrowly focused area? The safest thing to do, especially if you are uncertain about which discipline to study, is to major in one of the mainstream disciplines. By majoring in a mainstream area, you will graduate with a general engineering education that will make you marketable in a broad engineering industry. On the other hand, majoring in a narrowly focused discipline may lead you into an extremely satisfying career, particularly if your area of expertise, narrow as it may be, is in high demand. Perhaps your decision will be largely governed by geographical issues. The narrowly focused majors may not be offered at the school you wish to attend. These are important issues to consider when selecting an engineering major.

Introduction

Objectives

Professional Success: Choosing an Engineering Major