17MECH01P
BUE Faculty of Engineering - Prep Year
AY 2017-2018
Mechanics -
“What we know is a drop, what we don't know is an ocean.”
Sir
Isaac Newton
Mechanics – Introduction
Disclaimer Notice
The material (text and designs) of the Lectures are created by Prof. Talat Fawzy Refai.
Most of the assigned tutorial problems are taken from the official text book.
Most of the Images and logos are taken from the internet (Google Images).
The official text book is Vector Mechanics for Engineers (Beer, Johnston and Mazurka) 11th edition.
Lectures are presented using POWER POINT (OFFICE 2010)
Module Leader: Professor Talat Fawzy Refai
Office Room: 315A
email: talat.refai@bue.edu.eg
Module Title: Mechanics
Module Code: 17MECH01P
Mechanics -
“This most beautiful system of the sun, planets and comets,
could only proceed from the counsel and dominion of an
intelligent and powerful Being.”
Sir
Isaac– Introduction
Newton,
Mechanics
The Science of Mechanics
Motion- is the basis for
“Truth is ever to be found in the simplicity, and not in the multiplicity and confusion of things.”
Sir Isaac Newton
Mechanics – Introduction
Particle Mechanics - Module
Particles and Bodies
Mechanics Time Table (Lectures and Tutorials)
Newton’s Laws of Motion
Force Vectors
The Touch of Mechanics
Mechanics – Introduction
The SI system of units was formally adopted in October 1960 by the
International Organization For Standardization (ISO). Ever since, the SI system
of units have gained grounds and worldwide recognition. The SI units has
proven to be the best system of units for engineers.
SI Base Units
Length (m) : meter
The meter is the SI unit of length and is defined as the length equal to
1,650,763.73 wave length of the orange line in the spectrum of an
internationally specified krypton lamp.
Mechanics -
Mass (kg) : kilogram
The kilogram is the SI unit of mass and is defined as the mass of a platinumiridium cylinder kept at Sévre in France.
Time (s) : second
The second is the SI unit of time and is defined as the interval occupied by
9,192,631,770 cycles of radiation corresponding to the transition of the
caesium-133 atom.
Derived Units
Force: Newton (N)= kg.m/s2
Work/Energy : Joule ( J)= N.m
“I often say that when you measure what you are
speaking about, and express it in numbers, you
know something about it. But when you cannot
express it in numbers your knowledge is a meager
and unsatisfactory kind. It may be the beginning
of knowledge, but you have scarcely, in your
thoughts, advanced to the age of science, whatever the
matter may be”.
Lord Kelvin ( William Thomson)
(26 June
1824 – 17 December
1907
Mechanics
– Introduction
Derived Quantities
Basic Quantities
Length L : L (m)
velocity multiplied by mass
Momentum (kg-m/s)
velocity square multiplied by half the mass
Energy ( N-m=J)
Length divided by time t(s) leads to
Velocity : v=L/t (m/s)
velocity divided by time t(s) leads to
Force multiplied by time
Impulse (kg-m/s)
Mechanics -
Force multiplied by length
Work ( N-m=J)
Acceleration : a=v/t (m/s2)
Interrelations
Acceleration multiplied by mass m(kg) leads to
Impulse (kg-m/s)
Momentum (kg-m/s)
Work ( N-m=J)
Energy ( N-m=J)
The Force F=ma (N)
Mechanics – Introduction
Mechanics of Particles (Module Contents)
Dynamics: Objects in motion
Statics: objects at rest
Kinematics – Geometry of Motion
Forces
Forces in 2D and Particle equilibrium -Scalar
Displacement – Velocity - Acceleration
Forces in 3D and Particle equilibrium -Vectors
Rectilinear Motion
Moments and Couples
Force-Couples Resultants
1st class test 20%
Curvilinear Motion : Cartesian Coordinates
Mechanics -
Curvilinear Motion: Intrinsic/Polar Coordinates
Dynamics: Objects in motion
2st class test 20%
Kinetics – Newton’s Law of Motion - F=ma
Force-Acceleration Method
Work-Energy Method
Impulse-Momentum Method
Unseen Exam
Mechanics – Introduction
Example (Bodies)
Particles and Bodies
When we need to study
The effect of forces on the different parts of the car
The motion of the different parts relative to each other
Mechanics -
Dimensions must be included
Mechanics – Introduction
Example - Particle
When we need to study
The location, displacement, distance, velocity
Dimensions are irrelevant
Bodies and Particles
Mechanics -
The body is treated as a particle,
forces are concurrent
Mechanics – Introduction
the earth is treated as a Dimensional object
(a body)
Mechanics -
Mechanics – Introduction
Example : The earth as a particle
Mechanics -
When the object’s dimensions are irrelevant to its motion, we treat the object as a particle (point in space)
The Earth moves at about 100,000 km/h around the Sun (which is 1000 times faster than the speeds we go
at on a highway!)
Mechanics – Introduction
Lectures
Date
Lecture Topics
1
06/2/16
Introduction
2
13/2
Particle Equilibrium 2D
3
20/2
Particle Equilibrium 3D
4
27/2
Moments and Couples
5
05/3
Force-Couple Res
6
12/3
Kinematics-1
7
19/3
Kinematics-2
8
26/3
Kinematics-3
9
02/4
Kinetics-1
10
09/4
Kinetics-2
11
16/4
Kinetics-3
12
23/4
13
03/5
Tutorials
Sat
Sun
Sat
C
D
D1
Sun
Mechanics Midterm
Mon
Tue
C3 & C4
C1 & D4
Wed
Thu
Note
D2, D3, C2
Test-1
Test-2
revision
Midterm break: 30/4-6/5
Revision week: 7/5-11/5
Exams 14/5
Mechanics – Introduction
Mechanics -
Module specifications include information about how a module is taught
and assessed and the intended learning outcomes for the student.
Mechanics – Introduction
Module Title
Level
Module Code
Credit Value
Student Study Hours
Mechanics
“P”
17MECH01P
10
Contact hours: 48
Student managed learning hours:
Type of session
Typical Student Effort
Typical number in the semester/s
Lecture
Tutorial
Private study
Pre-requisite learning
Co-requisites
Excluded combinations
Module co-ordinator
Faculty/Department
Short Description
Aims
Employability
52
12
12
Non
Typical hours per
week
2
2
Total
hours
24
24
52
Mechanics -
Prof. Talat Fawzy Refai
Mechanical Engineering Department, Faculty of Engineering
This module is to provide principles, ideas, and skills of the mechanics of particles
The aims of this module are understanding the basics of statics and dynamics of particles. The
module constructs a relation among mechanics and everyday life problems and tasks. A wide
range of real world problems are presented in order to show the role of statics and dynamics in
analysing and designing such applications
Students will gain a wide range of employability skills and experience, including communication and
analytical skills, team working skills, and time-management skills.
Mechanics – Introduction
Knowledge and Understanding
On completion of this module students should be able to:
1.
Recognize, distinguish and describe basics of particle statics
2.
Recognize, distinguish and describe basics of particle kinematics and kinetics
Intellectual Skills:
On completion of this module students should be able to/demonstrate ability in:
Learning Outcomes
3. Draw free body diagrams to identify and analyze the equilibrium status of mechanical systems.
4. Select the proper (Force-Acceleration, Work-Energy, or Impulse-Momentum) method for solving kinetics problem.
5. Set up, analyze, and solve the different forms of the equations of motion.
Practical Skills:
On completion of this module students should be able to/demonstrate ability in:
6. Analyse simple structures under a system of forces in two and three dimensions;
7. Analyse simple dynamical systems in two dimensions using different coordinate systems.
Mechanics Transferable Skills:
On completion of this module students should be able to/demonstrate ability in:
8.
Solve mechanics problems using more than one approach.
Employability
Teaching and learning pattern
Students will gain a wide range of employability skills and experience, including communication and analytical skills, team
working skills, and time-management skills.
Total student effort for the module: 100 hours on average.
The BUE attendance policy applies, refer to current GAR and Student Handbook for further details.
Teaching & Learning:
1.
12, 2h lectures. This method informs learning outcomes 1, 2.
2.
12, 2h tutorials. This method informs learning outcomes 3, 4, 5, 6.7
Mechanics – Introduction
Part I: Statics

introduction to engineering mechanics;

vector analysis;

forces on particles;

equilibrium of particles;

forces and moments;
Part II: Planar Dynamics of Rigid Bodies
Indicative content





kinematics of particles;(rectilinear and curvilinear motion)
kinetics of particles;
Force-Acceleration methods;
Work and Energy methods;
Impulse and Momentum methods.
Assessment
Elements &
weightings
Mechanics -
Methods of
Feedback
Assessment Type
One in-class
assessment
Unseen final
exam
Weight %
ILOs
Semester for
Exam/
Assessed
Exam
Written Coursework Length
40%
2,4 and 6
1 and 2
60 minutes
60%
1-7
1 and 2
120 minutes
Mechanics – Introduction
Newton’s Laws of Motion
Mechanics -
“I do not know what I may appear to the world, but
to myself I seem to have been only like a boy
playing on the sea-shore, and diverting myself in
now and then finding a smoother pebble or a
prettier shell than ordinary, whilst the great ocean
of truth lay all undiscovered before me.”
Mechanics
– Introduction
Sir Isaac
Newton
Newton’s 1st Law
If the resultant force acting on an object is zero, then it will remain at rest or in
uniform motion in a straight line unless acted upon by an external force
Newton’s 2nd Law
The acceleration of an object as produced by a net force is directly proportional to the
magnitude of the net force, in the same direction as the net force, and inversely
proportional to the massMechanics
of the object.
F
dp d  mv   dm v  m dv  dm v  ma

dt
dt
dt
dt
dt
Newton’s 3rd Law
For every action, there is an equal and opposite reaction
F
F
Mechanics – Introduction
The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net
force, in the same direction as the net force, and inversely proportional to the mass of the object.
F  ma  m
dv
dt
1- When a non zero net (resultant) force acts on an object an acceleration is created.
2- The direction (Orientation and sense) of the Mechanics
acceleration
is the same as that of the resultant force F.
-
a
F
F
a
a
F
a
F
a
F
F
F
F
a
a
a
Mechanics – Introduction
Acceleration and Velocity
Acceleration is a vector quantity that is defined as the rate at which an object changes its velocity
(magnitude (speed) and direction), i.e.
a=
dv
dt
curved line
1- the velocity is tangent to the path of motion.
an
a
v
at
Mechanics -
straight line
v
a=a t
2- Acceleration and deceleration
at
v
Acceleration
at
v
Acceleration
at
v
deceleration
at
v
deceleration
Mechanics – Introduction
Newton’s 1st Law
If the resultant force acting on an object is zero, then it will remain at rest or in uniform motion in a
straight line unless acted upon by an external force
dv
F  0  ma  m
dt
dv
m
0
dt
v  constant
v0
straight line
v=constant
v
Mechanics F=0
object at rest
F
F
It will remain in motion with a
constant velocity (same magnitude
and same direction)
v
v
Conclusion
Thus the role of the force is to change the state of motion of the object on which it acts and not to sustain motion
*Inertia
The tendency of an object at rest to remain at rest or of a body in straight line motion to stay in motion in a straight line
unless acted on by an outside force. One of the biggest unsolved mysteries in physics was the concept of mass. Why does
anything have mass at all, or inertia? Why does the amount of physical “stuff” in an object define how easy it is to get
moving, or how hard it is to make it stop?
Mechanics – Introduction
Newton’s 3rd Law
Action Reaction Law
F
F
For every action, there is an equal and opposite reaction
Mechanics -
From the law we conclude that
1- forces are created in pairs
2- the two forces are equal in magnitude
3- the two forces are collinear
4- the two forces are of opposite senses
Mechanics – Introduction
Sir according to Newton's third law, if we pull on the cart ,
Sir haven’t
heard
about
Yes ofyou
course
now
lets Newton’s 3rd law?
move
it will pull back on lets
me with
anwe
equal force in opposite
movehave
and not
waste time
no time
direction and in turn
these
two forces will cancel each
to be
waste
other. Thus I will not
able to move.
WHY?
Sir I will not move
Mechanics -
Oh no mechanics again
The man stepped down and whispered in the ears of the donkey with some words after which it
started to move. What are these words?
Mechanics – Introduction
Mechanics -
“How came the bodies of animals to be contrived with so much art, and for what ends were their several parts?
Was the eye contrived without skill in Opticks, and the ear without knowledge of sounds?...and these things being rightly dispatch’d, does
it not appear from phaenomena that there is a Being incorporeal, living, intelligent...?”
Mechanics – Introduction
Sir Isaac Newton
Mechanics -
The Millau Viaduct cable bridge : spans the valley of the river Tarn near Millau in southern
France
Mechanics – Introduction
The Millau Viaduct cable bridge : spans the valley of the river Tarn near Millau in southern
France
Mechanics -
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Mechanics -
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Mechanics -
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Mechanics -
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Mechanics -
Mechanics – Introduction
Mechanics -
1 light years = 9.46 × 1012 kilometers
Three billion miles= 3X1.6x109 = 4.8x109 billion kilometers nearly 5x10-4 light year
Thus with the speed of the New horizon (59000 km/h) it will cover one light year in nearly
20000=2x104 earthly years !!!!!!!!
Mechanics – Introduction
The Andromeda Galaxy is a lot bigger than the Milky Way. It contains around a trillion stars, compared with the Milky Way's
estimated 200 billion to 400 billion stars. It also measures around 220,000 light-years in diameter, compared with the Milky
Way's 100,000 light-years.
Mechanics -
Andromeda Galaxy
Milky way Galaxy
Solar system
1 light years =9.4605284 × 1012 kilometers
Mechanics – Introduction
Mechanics -
Mechanics – Introduction
UK/Egyptian Grades and Marks
Pass
Fail
0
50
65
54
Egyptian %
UK %
44
60
47
Very
Good
Good
54
72
57
79 82
Mechanics -
60
95.6
85
75
69
Excellent
64
67
90 95
70
74
77
40
F
0
D- D D+ C- C C+ B- B B+ A- A A+
1.3 1.6 1.8 2.0 2.3 2.5 2.7 3.1 3.5 3.7 3.9 4.0
A person can fail many times , but he isn’t a
failure until he begins to blame somebody else.
John Burroughs
American Author
100
97.8
96.5 97.1
98.7 99.3
Marks
0
50
Grade
80
84
87
90
94
97
100
Grade
GPA
GPA : Grade Point Average
Mechanics – Introduction