Engineering Mechanics

1. ENGINEERING MECHANICS
Lecture No. 1
Asad Ali
MS Industrial Engineering
BS Mechanical Engineering
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2. 2
LECTURE NO. 1
Introduction
Force
Law of Forces
System of Forces
Lami’s Theorem
Moment of Force
Couple

3. INTRODUCTION
Mechanics
The branch of physical science that deals with the state of rest or the state of motion is
termed as Mechanics.
Engineering Mechanics
The Engineering Mechanics is the branch of Engineering science which deals with the
principles of mechanics along with their engineering problems. Engineering Mechanics is
divided into two main groups.
Statics
Dynamics 3

4. INTRODUCTION
Statics
The branch of Engineering Mechanics which deals with the forces and their effects while
acting upon the bodies at rest.
Dynamics
The branch of Engineering Mechanics which deals with the forces and their effects while
acting upon the bodies in motion. Dynamics is further divided into two groups.
Kinetics
Kinematics
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5. INTRODUCTION
Kinetics
The branch of Dynamics which deals with the bodies in motion due to the application of
forces.
Kinematics
The branch of Dynamics which deals with the bodies in motion without considering the
forces which are responsible for motion.
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6. INTRODUCTION
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Engineering
Mechanics
Dynamics
Kinetics
Kinematics
Statics

7. FORCE
Force
It may be defined as an agent which produces or tends to produce, destroy or tends to
destroy the motion of a body. A force while acting on a body may
a. Change the motion of body
b. Retard the motion of body
c. Give rise to the internal tresses of the body
In order to find the effect of force on body, we must know the nature, magnitude and
line of action of force.
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8. FORCE
In MKS system magnitude of force expressed in Kilogram force (kgf)
In SI system magnitude of force expressed in newton (N)
1kgf = 9.81N
Resultant Force
It is the single force which produces the same effect as produced by all the given forces
acting on the body
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9. LAW OF FORCES
The resultant force may be determined by the following three laws of forces.
Parallelogram law of forces
Triangle law of forces
Polygon law of forces
Parallelogram law of forces
It states if two forces acting simultaneously on a particle be represented in magnitude and
direction by the two adjacent sides of a parallelogram then their resultant is represented in
magnitude and direction by the diagonal of the parallelogram drawn from the same point. 9

10. LAW OF FORCES
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Parallelogram law of forces
Where α is the resultant angle make with force P

11. LAW OF FORCES
Triangle law of forces
If two forces acting at a point are represented in magnitude and direction by the two
adjacent sides of a triangle taken in order, then the closing side of the triangle taken in the
reversed order represents the resultant of the forces in magnitude and direction.
Polygon law of forces
If a number of forces acting simultaneously on a particle be represented in magnitude and
direction by the sides of a polygon taken in order, their resultant may be represented in
magnitude and direction by the closing side of the polygon taken in opposite order.
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12. LAW OF FORCES
Polygon law of forces
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Where A, B, C and D are the
forces
and R = Resultant force
Blue arrow show anticlockwise of
forces
Red arrow show clockwise of
resultant which show reverse order

13. SYSTEM OF FORCES
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System of Forces
When two or more than two forces act on a body, they are said to form a system of forces.
Following are the various system of forces
Coplanar forces
Concurrent forces
Coplanar concurrent forces
Coplanar non-concurrent forces
Non-coplanar concurrent forces
Non-coplanar non-concurrent forces

14. SYSTEM OF FORCES
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Coplanar forces
Forces whose line of action lie on the same plane, are known as coplanar forces.
Concurrent forces
The forces which meet at one point, are known as concurrent forces.
Coplanar concurrent forces
Forces which meet at one point and lines of action also lie on the same plane are known as
coplanar concurrent forces.
Coplanar non-concurrent forces
The forces whose line of action lie on the same plane but they do not meet at one point are
known as coplanar non-concurrent forces.

15. SYSTEM OF FORCES
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Non-coplanar concurrent forces
Forces whose line of action do not lie on the same plane, but they meet at one point.
Non-coplanar non-concurrent forces
Forces whose line of action do not lie on the same plane & they do not meet at any point.

16. LAMI’S THEOREM
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Lami’s Theorem
Lami's theorem states that if three forces acting at a point are in equilibrium, each force is
proportional to the sine of the angle between the other two forces.

17. MOMENT OF FORCE
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Moment of Force
The turning effect of a force is known as the moment. It is the product of the force multiplied
by the perpendicular distance from the line of action of the force to the pivot or point where
the object will turn and the unit of moment is Nm.

18. COUPLE
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Couple
The two equal and opposite forces, whose line of action are different form a couple. The
perpendicular distance between the line of action of two equal and opposite forces is known
as arm of couple.

19. THANK YOU
I See Humans But No Humanity
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