Hydraulics and Fluid Mechanics - Fluid Properties

There are three states of matter which are recognised e.g. solid, liquid, gas. Solid can resist deformation but liquid and gas can not., so they flow under the action of force.
A Fluid is defined as a substance which deforms continuously, or flows, when subjected to shearing forces. Both liquid and gas come under the category of fluid.
Shear stresses are developed when the particles of fluid move with respect to one another. In real world shear forces are present when we consider flow past solid boundaries; aeroplanes, cars, pipe walls, river channels etc.
Some basic definitions are important to understand
1. Specific gravity or relative density is defined as the ratio of the density of a substance to the density of some standard substance at a specified temperature (usually water at 4 °C, and atmospheric pressure having a density of 1000 kg/m3). Specific gravity is a dimensionles quantity.
2. Specific weight is the weight of a unit volume of a substance. Specific weight=specific gravity X acceleration due to gravity.

3. Viscosity is a property that represents the internal resistance of a fluid to motion or the ‘fluidity’. Viscosity is due to the cohesive forces between the molecules.  Viscosity is measured in two forms; Dynamic (or absolute)  and Kinematic.
All fluids are viscous in nature. "Newtonian Fluids" obey the linear relationship given by Newton's law of viscosity. which states that shear stress is directly proprtional to velocity gradient.
4. Surface Tension is a property of fluid that is caused by cohesion of similar molecules. It can also be termed as the contractive tendency of the surface of a fluid that allows it to resist an external force. It is because of surface tension that some objects denser than water can float on the surface of water.
In a fluid mass, each molecule is pulled equally in every direction by neighboring molecules, resulting in a net force of zero. The molecules at the surface do not have other molecules on all sides of them and therefore are pulled inwards. This phenomena develops some internal pressure and forces the liquid surfaces to contract to the minimum area.Surface tension has the dimension of force per unit length, or of energy per unit area.
Surface tension  can be defined as the energy required to stretch a unit change of a surface area. Surface tension decreases with increase in temperature.
5. Fluid Pressure is defiend as "the normal force per unit area exerted on an imaginary or real plane surface in a fluid "
Pressure is measured in Pascal (Pa) which is equal to Newton per sq m. or psi (pound per sq inch)

Do you know what is Bernoulli equation and
Continuity equation

Hoover dam is an arch-gravity dam constructed on Colorado river in USA. Hoover dam

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