Fluid Mechanics

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Introduction to Fluid Mechanics



.Fluid Mechanics is concerned with the behavior of fluids at rest and in motion

.Distinction between solids and fluids:
-According to our experience: A solid is “hard” and not easily deformed. A fluid is “soft” and deforms easily.
-Fluid is a substance that alters its shape in response to any force however small, that tends to flow or to conform to the outline of its container, and that includes gases and liquids and mixtures of solids and liquids capable of flow.
-A fluid is defined as a substance that deforms continuously when acted on by a shearing stress of any magnitude.



Dimensions and Units


In fluid mechanics we must describe various fluid characteristics in terms of certain basic quantities such as length, time and mass
A dimension is the measure by which a physical variable is expressed qualitatively, i.e. length is a dimension associated with distance, width, height, displacement.
Basic dimensions: Length, L
(or primary quantities) Time, T
Mass, M
Temperature, Q
We can derive any secondary quantity from the primary quantities i.e. Force = (mass) x (acceleration) : F = M L T-2

A unit is a particular way of attaching a number to the qualitative dimension: Systems of units can vary from country to country, but dimensions do not


Dimensional Homogeneity


.All theoretically derived equations are dimensionally homogeneous: dimensions of the left side of the equation must be the same as those on the right side.
Some empirical formulas used in engineering practice are not dimensionally homogeneous

.All equations must use consistent units: each term must have the same units. Answers will be incorrect if the units in the equation are not consistent. Always chose the system of units prior to solving the problem