Sec. 1.1-1.92What’s the Point?• Context– Fluids have many characteristics that make them different from solids. That’s why we are in this class.• Motivation– We are unfamiliar with many important characteristics of fluids. •Learning objective– Demonstrate knowledge of the properties of fluids through the mastery of definitions and discussions of their effects
Sec. 1.1-1.931.1 What is a fluid?•Definition: Stress – force per unit area–Normal stress acts perpendicular to a face–Shear stress acts parallel to a face•From our perspective, there are two states of matter –A fluidis a substance that deforms continuously (flows) under the application of a shear stress, no matter how small•A fluid at rest must have zero shear stress (hydrostatic). Only a normal stress σ=-p–A soliddoes not deform continuously (flow) for an arbitrarily small shear stress•Two classes of fluids–A liquidhas closely packed molecules with strong cohesive forces (retains volume and forms a free surface)–A gashas has widely spaced molecules with weak cohesive forces (no definite volume)
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