Fluids OR Liquid Substance
Liquids are those substances that have the ability to flow at normal temperature and they do not keep their fixed shape but take the shape of the vessel in which they are kept.
Or
A liquid is a substance that, at room temperature, has sufficient capacity to hold the shape of the container into which it is poured.
The continuous deformation of a fluid by a small amount of shear force (deformation) until this force is removed.
All liquids, gases, and vapors are called liquids.
classification of liquids
Liquids can be classified on the following basis.
On the basis of compressibility or ease or difficulty in compressing, all liquids are of the following two types-
1. Liquid
2. Gases and vapors
1. Liquids - These are also called incompressible liquids from the practical point of view. These are liquids that cannot be easily compressed and are less affected by temperature changes. The shape of liquids changes infinitely when a slight external pressure is applied, but the volume remains constant. There is negligible change in the density of liquids due to pressure, whereas this change is substantial in gases and vapors.
2. Gases and vapors - These are also called compressible liquids. These are liquids that can be easily compressed and temperature changes have a great effect on them. They spread over the entire space of the container to be kept.
The following two types of fluids are given on theoretical and practical basis-
1. Ideal Liquid
2. Workable liquids.
1. Ideal substances - These are also called perfect substances. Ideal fluids are those which exert a pressure force perpendicular to the surface at every point in contact with the surface.
Ideal liquid cannot be compressed and has surface tension and does not have the properties of viscosity. In fact, no liquid is an ideal liquid, but from an experimental point of view, liquids for which the value of viscosity is very low, such as air and water, etc., are considered ideal liquids.
2. Practical matter - This is also called real matter. Practical fluids are those which offer some resistance to the displacement of any of their particles. They can be pressed and also have the properties of surface tension and viscosity.