Introduction

In this modern age, the word ‘science’ has got different meanings for different people. An ordinary man takes it as ‘something’ beyond his understanding, whereas others may take it as ‘mysteries of research’ which are understood only by a few persons working amidst complicated apparatus in a laboratory. A non-scientist feels that it is a ‘subject’ whose endeavour is aimed to improve the man’s life on the earth. A business executive has the idea that it is ‘something’ which solves our day to day manufacturing and quality control problems, so that the nation’s

economic prosperity keeps on improving. In fact, ‘science’ may be defined as the growth of ideas through observation and experimentation. In this sense, the subject of science does not, necessarily, has to contribute something to the welfare of the human life, although the man has received many benefits from the scientific investigations.

APPLIED SCIENCE

Strictly speaking, the world of science is so vast that the present day scientists and technologists have to group the various spheres of scientific activities according to some common

characteristics to facilitate their training and research programmes. All these branches of science, still have the common principle of employing observation and experimentation. The branch of science, which co-ordinates the research work, for practical utility and services of the mankind, is known as Applied Science.

ENGINEERING MECHANICS

The subject of Engineering Mechanics is that branch of Applied Science, which deals with the laws and principles of Mechanics, alongwith their applications to engineering problems. As a matter of fact, knowledge of Engineering Mechanics is very essential for an engineer in planning, designing and construction of his various types of structures and machines. In order to take up his job more  skilfully, an engineer must persue the study of Engineering Mechanics in a most systematic and scientific manner.

BEGINNING AND DEVELOPMENT OF ENGINEERING MECHANICS

It will be interesting to know, as to how the early man had been curious to know about the different processes going on the earth. In fact, he used to content himself, by holding gods responsible for all the processes. For a long time, the man had been trying to improve his ways of working. The first step, in this direction, was the discovery of a circular wheel, which led to the use of animal driven carts. The study of ancient civilization of Babylonians, Egyptians, Greeks and Roman reveal the use of water wheels and wind mills even during the pre-historic days.

384–322 BC). He used this word for the problems of lever and the concept of centre of gravity. At that time, it included a few ideas, which were odd, unsystematic and based mostly on observations containing incomplete information. The first mathematical concept of this subject was developed by Archimedes (287–212 BC). The story, for the discovery of First Law of Hydrostatics, is very popular even today in the history of the development of Engineering Mechanics. In the normal course, Hieron king of Syracuse got a golden crown made for his use. He suspected that the crown has been made with an adultrated gold. The king liked the design of the crown so much that he did not want it to be melted,in order to check its purity. It is said that the king announced a huge reward for a person, who can check the purity of the crown gold without melting it. The legend goes that Archimedes, a pure mathematician,

one day sitting in his bath room tub realised that if a body is immersed in water, its apparent weight is reduced. He thought that the apparent loss of weight of the immersed body is equal

to the weight of the liquid displaced. It is believed that without further thought, Archimedes jumeped out of the bath tub and ran naked down the street shouting ‘Eureka, eureka !’ i.e. I have found it, I have found it !’

The subject did not receive any concrete contribution for nearly 1600 years. In 1325, Jean Buridan of Paris University proposed an idea that a body in motion possessed a certain impetus

i.e. motion. In the period 1325–1350, a group of scientists led by the Thomas Bradwardene of Oxford University did lot of work on plane motion of bodies. Leonarodo Da Vinci (1452–1519),

a great engineer and painter, gave many ideas in the study of mechanism, friction and motion of bodies on inclined planes. Galileo (1564–1642) established the theory of projectiles and gave a

rudimentary idea of inertia. Huyghens (1629–1695) developed the analysis of motion of a pendulum. As a matter of fact, scientific history of Engineering Mechanics starts with Sir Issac Newton (1643–1727). He introduced the concept of force and mass, and gave Laws of Motion in 1686. James Watt introduced the term horse power for comparing performance of his engines. John Bernoulli (1667–1748) enunciated the priciple of virtual work. In eighteenth century, the subject of Mechanics was termed as Newtonian Mechanics. A further development of the subject led to a controversy between those scientists who felt that the proper measure of force should be change in kinetic energy produced by it and those who preferred the change in momentum. In the nineteenth century, many scientists worked tirelessly and gave a no. of priciples, which enriched the scientific history of the subject.

In the early twentieth century, a new technique of research was pumped in all activities of science. It was based on the fact that progress in one branch of science, enriched most of the bordering branches of the same science or other sciences. Similarly with the passage of time, the concept of Engineering Mechanics aided by Mathematics and other physical sciences, started contributing and development of this subject gained new momentum in the second half of this century. Today, knowledge of Engineering Mechanics, coupled with the knowledge of other specialised subjects e.g. Calculus, Vector Algebra, Strength of Materials, Theory of Machines etc. has touched its present height. The knowledge of this subject is very essential for an engineer to enable him in designing his all types of structures and machines.

DIVISIONS OF ENGINEERING MECHANICS

The subject of Engineering Mechanics may be divided into the following two main groups:

1.      Statics, and

2.      Dynamics.

STATICS

It is that branch of Engineering Mechanics, which deals with the forces and their effects, while acting upon the bodies at rest.

DYNAMICS

It is that branch of Engineering Mechanics, which deals with the forces and their effects, while acting upon the bodies in motion. The subject of Dynamics may be further sub-divided into the

following two branches :

Kinetics, and 2. Kinematics.

KINETICS

It is the branch of Dynamics, which deals with the bodies in motion due to the application

of forces.

KINEMATICS

It is that branch of Dynamics, which deals with the bodies in motion, without any reference

to the forces which are responsible for the motion.

FUNDAMENTAL UNITS

The measurement of physical quantities is one of the most important operations in engineering.

Every quantity is measured in terms of some arbitrary, but internationally accepted units, called

fundamental units.

All the physical quantities, met with in Engineering Mechanics, are expressed in terms of three

fundamental quantities, i.e.

1.      length, 2. mass and 3. time.

DERIVED UNITS

Sometimes, the units are also expressed in other units (which are derived from fundamental

units) known as derived units e.g. units of area, velocity, acceleration, pressure etc.

SYSTEMS OF UNITS

There are only four systems of units, which are commonly used and universally recognised.

These are known as :

1. C.G.S. units, 2. F.P.S. units, 3. M.K.S. units and 4. S.I. units.

In this book, we shall use only the S.I. system of units, as the future courses of studies are

conduced in this system of units only.

S.I. UNITS (INTERNATIONAL SYSTEM OF UNITS)

The eleventh General Conference* of Weights and Measures has recommended a unified

and systematically constituted system of fundamental and derived units for international use. This

system of units is now being used in many countries.

In India, the Standards of Weights and Measures Act of 1956 (vide which we switched over to

M.K.S. units) has been revised to recognise all the S.I. units in industry and commerce.

In this system of units, the †fundamental units are metre (m), kilogram (kg) and second (s)

respectively. But there is a slight variation in their derived units. The following derived units will be

used in this book :