Fluid
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Concept of Fluid
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Density
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Pressure: Pressure in a Fluid. Pascal´s principle
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Buoyancy. Archimede´s Principle.
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Forces on submerged surfaces
Fluids in motion
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Continuity equation.
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Bernoulli´s Equation
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Viscous Flow. Viscosity. Poiseuille´s Law. Skin drag
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turbulent flow.
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Fluids in Motion . Description of the Fluid Flow
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A fluid flow may be described in two different ways: the Lagrangian approach (named after the
French mathematician Joseph Louis, and the Eulerian approach (named after LeonhardEuler, a
famous Swiss mathematician). In the Lagrangian approach, one particle is chosen and is
followed as it moves through space with time. The line traced out by that one particle is called a
particle pathline.
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A Eulerian approach is used to obtain a clearer idea of the flow at one particular instant. The
entire flow field is easily visualized. The lines comprising this flow field are called streamlines. A
streamline is a line drawn through a fluid in such a manner that it has the direction of the fluid
velocity at every point.
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Thus, a pathline refers to the trace of a single particle in time and space, whereas a streamline
presents the line of motion of many particles at a fixed time. Both coincide in a steady flow.