1. Fluids Mechanics and Fluid Properties 1.1 （1。）.pdfVIP

1. Fluids Mechanics and Fluid Properties What is fluid mechanics? As its name suggests it is the branch of applied mechanics concerned with the statics and dynamics of fluids - both liquids and gases. The analysis of the behaviour of fluids is based on the fundamental laws of mechanics which relate continuity of mass and energy with force and momentum together with the familiar solid mechanics properties. 1.1 Obj ectives of this section • Define the nature of a fluid. • Show where fluid mechanics concepts are common with those of solid mechanics and indicate some fundamental areas of difference. • Introduce viscosity and show what are Newtonian and non-Newtonian fluids • Define the appropriate physical properties and show how these allow differentiation between solids and fluids as well as between liquids and gases. 1.2 Fluids There are two aspects of fluid mechanics which make it different to solid mechanics: 1. The nature of a fluid is much different to that of a solid 2. In fluids we usually deal with continuous streams of fluid without a beginning or end. In solids we only consider individual elements. We normally recognise three states of matter: solid; liquid and gas. However, liquid and gas are both fluids: in contrast to solids they lack the ability to resist deformation. Because a fluid cannot resist the deformation force, it moves, itf lows under the action of the force. Its shape will change continuously as long as the force is applied. A solid can resist a deformation force while at rest, this force may cause some displacement but the solid does not continue to move indefinitely. The deformation is caused by shearing forces which act tangentially to a surface. Referring to the figure below, we see the force F acting tangentially on a rectangular (solid lined) element ABDC. This is a shearing force and produces the (dashed li