Lesson 2 - Principles of Fluid Mechanics 1
This lesson considers the unique property of viscosity of fluids (gases and liquids) which allows them to flow. It explores the classification of fluid viscosity behaviour by so-called Newtonian and non-Newtonian fluids. It will also examine the nature of static fluids, which will include the concept of pressure and head. The lesson finishes with a discussion on the different types of instrumentation for measuring pressure.
Definition of Fluids
When we think of an example of a fluid, the most common thought is probably a liquid. But gases are also classified as fluids, and the reason for this lies in the origin of the word ‘fluid’. Like most scientific words, it comes from the Latin word, fluidus, which means ‘to flow’.
We know that gases can be made to flow, for example, down a pipe, as can liquids. It is the ability of a substance to flow, which defines it as a fluid. Turn your thoughts to that of a solid, for a moment. A solid cannot be made to flow by gravity even if we apply a force such as giving it a push. It can resist gravity and our push. That is the reason why solids are not considered fluids.
Gases and liquids are both considered fluids.
We shall consider the ability of a fluid to flow in a little more scientific detail, by considering viscosity and Newton’s law of viscosity.