Solucionario De Mecanica De Materiales De Gere

Chapter 1 Introduction and Basic Concepts

Chapter 1 INTRODUCTION AND BASIC CONCEPTS
Fluid Mechanics and Classification of Fluid Flow 1-1C The flow of an unbounded fluid over a surface such as a plate, a wire, or a pipe is external flow. The flow in a pipe or duct is internal flow if the fluid is completely bounded by solid surfaces. The flow of liquids in a pipe is called open-channel flow ifthe pipe is partially filled with the liquid and there is a free surface, such as the flow of water in rivers and irrigation ditches. 1-2C A fluid flow during which the density of the fluid remains nearly constant is called incompressible flow. A fluid whose density is practically independent of pressure (such as a liquid) is called an incompressible fluid. The flow of compressible fluid (such asair) is not necessarily compressible since the density of a compressible fluid may still remain constant during flow. 1-3C A fluid in direct contact with a solid surface sticks to the surface and there is no slip. This is known as the no-slip condition, and it is due to the viscosity of the fluid. 1-4C In forced flow, the fluid is forced to flow over a surface or in a tube by external means suchas a pump or a fan. In natural flow, any fluid motion is caused by natural means such as the buoyancy effect that manifests itself as the rise of the warmer fluid and the fall of the cooler fluid. The flow caused by winds is natural flow for the earth, but it is forced flow for bodies subjected to the winds since for the body it makes no difference whether the air motion is caused by a fan or bythe winds. 1-5C When a fluid stream encounters a solid surface, the fluid velocity assumes a value of zero at the surface. The velocity then varies from zero at the surface to the freestream value sufficiently far from the surface. The region of flow in which the velocity gradients are significant is called the boundary layer. The development of a boundary layer is caused by the no-slip condition.1-6C Classical approach is based on experimental observations whereas statistical approacg is based on the average behavior of large groups of particles. 1-7C A process is said to be steady-flow if it involves no changes with time anywhere within the system or at the system boundaries. 1-8C Stress is defined as force per unit area, and is determined by dividing the force by the area upon which itacts. The normal component of a force acting on a surface per unit area is called the normal stress, and the tangential component of a force acting on a surface per unit area is called shear stress. In a fluid, the normal stress is called pressure. 1-9C A system is defined as a quantity of matter or a region in space chosen for study. The mass or region outside the system is called thesurroundings. The real or imaginary surface that separates the system from its surroundings is called the boundary. 1-10C Systems may be considered to be closed or open, depending on whether a fixed mass or a volume in space is chosen for study. A closed system (also known as a control mass) consists of a fixed amount of mass, and no mass can cross its boundary. An open system, or a control volume, is aproperly selected region in space.

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Chapter 1 Introduction and Basic Concepts Mass, Force, and Units 1-11C Pound-mass lbm is the mass unit in English system whereaspound-force lbf is the force unit. One pound-force is the force required to accelerate a mass of 32.174 lbm by 1 ft/s2. In other words, the weight of a 1-lbm mass at sea level is 1 lbf. 1-12C Kg is the mass unit in the SI system whereas kg-force is a force unit. 1-kg-force is the force required to accelerate a 1-kg mass by 9.807 m/s2. In other words, the weight of 1-kg mass at sea level is 1...