Introduction to Engineering Mechanics
Berke Gür
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Chapter Objectives
• The aim of this chapter is to provide a general introduction to
engineering mechanics
• Fundamental mechanics concepts, quantities, terminology, and
idealizations are introduced
• A historical and philosophical outline of mechanics is introduced
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Engineering Mechanics
• Mechanics is the branch of natural sciences that studies the effect of
forces on objects
• Engineering mechanics is the study of the principles of mechanics (from
an engineering perspective) and its applications to engineering
problems
• On the simplest level, engineering mechanics can be divided into 3 main
groups
– Statics: The study of the external effects of forces on systems that are not
moving
– Dynamics: The study of the external effects of forces on systems that are
undergoing motion
– Mechanics of Materials: The study of the internal effects of forces on (static or
dynamic) systems
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Engineering Mechanics
• In the MCH curriculum, engineering mechanics is covered in two
courses:
– MCH2008 Engineering Mechanics (3rd semester)
– MCH2018 Mechanics of Materials (4th semester)
• MCH2008 is a (unofficial) prerequisite to MCH2018
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Fundamental Concepts
• Space: The geometric volume occupied by bodies and mathematically
defined using a coordinate system
• Inertia: Resistance of a body to motion
• Mass: The resistance of a body to translational motion
• Force: Action of one body on another
Is a vector defined by a magnitude, direction, & point of application
Forces can be contact or body, concentrated or distributed
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Fundamental Concepts
• Scalar Quantities: A quantity defined only by a magnitude (e.g., time,
volume, density, speed, energy, mass)
• Vector Quantities: A quantity defined by magnitude and direction (e.g.,
displacement, velocity, acceleration, force, moment, momentum)
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Fundamental Concepts
• Vectors can be:
– Free Vectors: Action not associated with a line (e.g., displacement vector of a
rigid body is valid through any point on the body)
– Sliding Vectors: Action associated with a unique line of action but not a point of
application (e.g., force applied to a rigid body, considering only external effects)
– Fixed Vectors: Action is confined to a unique line and a point of application (e.g.,
force applied to a rigid body, considering internal effects)
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Fundamental Concepts
• Particle (or point mass) – a body with a mass but negligable dimensions
• Rigid Body – a body where the distance between any two points on the
body is always fixed
A rigid body is also said to be non-deformable
All real objects are deformable
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Fundamental Concepts
• System:
“a regularly interacting or interdependent group of items forming a unified
whole...”
• A car suspension system is a typical mechanical system that is analyzed
using principles of mechanics
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Newton’s Laws
• Law I:
A particle remains at rest or continues to move with
uniform velocity (along a straight line with constant
speed) if there is no unbalanced force acting on it
• Law II:
The acceleration of the particle is proportional to the
vector sum of the forces acting on it & is in the
direction of this vector sum
F ma
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Newton’s Laws
• Law III: (Action-Reaction)
The forces of action and reaction between interacting bodies are equal in
magnitude, opposite in direction and collinear (lie along the same line)
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Newton’s Laws
• An additional law attributed to Newton is the law of gravitation which
defines the mutual attraction force F between two masses
m1m2
F G 2
r
where G is the constant of gravitation (6.673×10−11 m3/(kg·s2)), m1 & m2
are the masses of the two bodies, and r is the distance between them
• The gravitational attraction force is along the line joining the centers of
the two masses
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Newton’s Laws
• We take the weight of an object as the gravitational attraction force
between Earth and the object
W mg
where g is the gravitational acceleration (9.81 m/s2)
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Example: Mass-Weight
• Determine the weight of a car which has a mass of 1400 kg
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Example: Mass-Weight
• Using Newton’s law of gravitational attraction, determine the weight of
a 70 kg man on Earth (note that the mass and radius of the Earth are
m = 5.976×1024 kg, r = 6371 km)
• Compare your result with that calculated from W = mg
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Units
• We will be using the SI units in this course
• Units are generally overlooked by most students, however, they may
serve as an instrument for checking your work
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Next Lecture
• Lecture topics
– Force Systems
• Questions?
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