FLUID MECHANICS

Fundamental Concepts:

·         Mechanics : Deals with action of forces on bodies at rest or in motion.

·         State of rest and Motion: They are relative and depend on the frame of reference.  If the position with reference to frame of reference is fixed with time, then the body is said to be in a state of rest.  Otherwise, it is said to be in a state of motion.

·         Scalar and heater quantities: Quantities which require only magnitude to represent them are called scalar quantities.  Quantities which acquire magnitudes and direction to represent them are called vector quantities.

Eg: Mass, time internal, Distance traveled à Scalars

            Weight, Displacement, Velocity à Vectors

·         Velocity and Speed: Rate of displacement is called velocity and Rate and distance traveled is called Speed.

Unit: m/s

·         Acceleration: Rate of change of velocity is called acceleration. Negative acceleration is called retardation.

·         Momentum: The capacity of a body to impart motion to other bodies is called momentum.

The momentum of a moving body is measured by the product of mass and velocity the moving body

Momentum = Mass x Velocity

Unit: Kg m/s

·       Newton’s first law of motion: Every body continues to be in its state of rest or uniform motion unless compelled by an external agency.

·       Inertia: It is the inherent property the body to retain its state of rest or uniform motion.

·       Force: It is an external agency which overcomes or tends to overcome the inertia of a body.

·       Newton’s second law of motion: The rate of change of momentum of a body is directly proportional to the magnitudes of the applied force and takes place in the direction of the applied force.

·       Matter: Anything which possess mass and requires space to occupy is called matter.

·       States of matter:

Matter can exist in the following states

¨      Solid state.

¨      Fluid state.

¨      Solid state: In case of solids intermolecular force is very large and hence molecules are not free to move. Solids exhibit definite shape and volume. Solids undergo certain amount of deformation and then attain state of equilibrium when subjected to tensile, compressive and shear forces.

¨      Fluid State: Liquids and gases together are called fluids. Incase of liquids Intermolecular force is comparatively small. Therefore liquids exhibit definite volume. But they assume the shape of the container

            Liquids offer very little resistance against tensile force.  Liquids offer maximum resistance against compressive forces. Therefore, liquids are also called incompressible fluids. Liquids undergo continuous or prolonged angular deformation or shear strain when subjected to tangential force or shear force. This property of the liquid is called flow of liquid. Any substance which exhibits the property of flow is called fluid. Therefore liquids are considered as fluids.

            In case of gases intermolecular force is very small. Therefore the molecules are free to move along any direction. Therefore gases will occupy or assume the shape as well as the volume of the container.

            Gases offer little resistance against compressive forces. Therefore gases are called compressible fluids. When subjected to shear force gases undergo continuous or prolonged angular deformation or shear strain. This property of gas is called flow of gases. Any substance which exhibits the property of flow is called fluid. Therefore gases are considered as fluids. 

Thermodynamics

Thermodynamics deals with heat inter-action and work inter-action with the substances called systems. Work and heat are forms of energy. Transfer of heat or work to a substance brings about certain changes in the substance and whatever change happens is called a process. Thermo means heat. Since work is also a form of energy, thermo is taken to mean heat and work. Dynamics refers to the changes that occur as a result of heat or work transfer.

Biological systems are capable doing work. For example, micro-organism is capable swimming in the body fluid of its host. It needs to do the work. Where does energy for doing this work come from? It is the metabolic activity that converts some form of energy (Nutrition that it takes form host is a form of chemical energy) into work. It is important then to understand how this happens so that we can exploit this to our engineering benefit.

In thermodynamics we have work transfer, heat transfer and then we have a system for interaction which undergoes a process.