ENGINEERING

MECHANICS
 Module 1

• Introduction to Engineering Mechanics-statics-

basic principles of statics-Parallelogram law,
equilibrium law, principles of superposition and
transmissibility, law of action and
reaction(review) free body diagrams.
• Concurrent coplanar forces-composition and
resolution of forces-resultant and equilibrium
equations – methods of projections – methods of
moments – Varignon’s Theorem of moments
• MECHANICS
• Mechanics can be defined as the branch of
physics concerned with the state of rest or
motion of bodies that subjected to the action
of forces.
 RIGID BODY
• A rigid body may be defined as a body in which
the relative positions of any two particles do not
change under the action of forces means the
distance between two points/particles remain
same before and after applying external forces.
• OR
• A body which does not deform under the
influence of forces is known as a rigid body.
• Physical bodies deform slightly under the action
of loads. If the deformation is negligible
compared to its size, the body is termed as rigid.
In Rigid Body mechanics, we assume bodies to be
rigid bodies
• The subject of Engineering Mechanics may be
divided into the following two main groups:
• 1. Statics, and 2. Dynamics.
• 1. STATICS
• It is that branch of Engineering Mechanics,
which deals with the forces and their effects,
while acting upon the bodies at rest.
• 2. 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 :
• 1. KINETICS
• It is the branch of Dynamics, which deals with
the bodies in motion due to the application of
forces.
• 2. 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
 Force
• Force may be defined as any action that tends to
change the state of rest or motion of a body to
which it is applied.
• The three quantities required to completely
define force are called its specification or
characteristics.
• 1. Magnitude
• 2. Point of application
• 3. Direction of application/Line of action
Force is a vector quantity and its unit is
Newton (N)
 SYSTEM OF FORCES
• When two or more forces act on a body, they
are called to form a system of forces. :
• 1. Coplanar forces. The forces, whose lines of
action lie on the same plane, are known as
• coplanar forces.
• 2. Collinear forces. The forces, whose lines of
action lie on the same line, are known as
collinear forces.

• 3. Concurrent forces. The forces, which meet

at one point, are known as concurrent forces.
The concurrent forces may or may not be
collinear.
• 4. Coplanar concurrent forces. The forces, which meet
at one point and their lines of action also lie on the
same plane, are known as coplanar concurrent forces.
• 5. Coplanar non-concurrent forces. The forces, which
do not meet at one point, but their lines of action lie
on the same plane, are known as coplanar non-
concurrent forces.
• 6. Non-coplanar concurrent forces. The forces, which
meet at one point, but their lines of action do not lie
on the same plane, are known as non-coplanar
concurrent forces.
• 7. Non-coplanar non-concurrent forces. The forces,
which do not meet at one point and their lines of
action do not lie on the same plane, are called non-
coplanar non-concurrent forces.
 Parallel Force Systems:
• Forces whose line of action are parallel to
each other are called parallel force system.
They are of 2 types
• Like Parallel Forces

• Unlike Parallel Forces

 Law of Transmissibility of Force
• Principle of transmissibility states that a force may
be applied at any point on a rigid body along
itsgiven line of action without altering the effects of
the force on which it acts.
• For example, the force F acts on a rigid body at point
A. According to the principle of transmissibility of
forces, this force has the same effect on the body as
a force F applied at point B along its line of action
• RESULTANT FORCE
• If a number of forces, P, Q, R ... etc. are acting
simultaneously on a particle, then it is possible to
find out a single force which could replace them
i.e., which would produce the same effect as
produced by all the given forces.
• This single force is called resultant force and the
given forces R ... etc. are called component
forces.
• COMPOSITION OF FORCES
• The process of finding out the resultant force, of
a number of given forces, is called composition of
forces or compounding of forces.
• The resultant force, of a given system of
forces, may be found out analytically by the
following methods :
• 1. Parallelogram law of forces. 2. Method of
resolution
 Parallelogram Law of Forces
• If two forces acting at a point be represented
in magnitude and direction by the two
adjacent sides of a parallelogram, then their
resultant is represented in magnitude and
direction by lite diagonal of the
parallelogram passing through that point
• Two forces of 100 N and 150 N are acting
simultaneously at a point. What is the
resultant of these two forces, if the angle
between them is 45°?
 Assignment Question 1
• Two forces act at an angle of 120°. The bigger
force is of 40 N and the resultant is
perpendicular to the smaller one. Find the
smaller force.
 Resolution Of Forces
• The process of splitting up the given force into
a number of components, without changing
its
• effect on the body is called resolution of a
forceForces can be resolved in any 2
directions. However, it is convenient to resolve
them into the two orthogonal components
(mutually perpendicular directions)
Resolution of Force in Rectangular
Coordinates
 Law of action and reaction-
• Any pressure on a support causes an equal
and opposite pressure from the support so
that action and reaction are two equal and
opposite forces (Newton’s third law)