definition, classification and units used in engineering mechanics classification of mechanics units used in machanics

1. University of Engineering &Technology Peshawar
CE-117: Engineering Mechanics
MODULE 1:
Introduction to Engineering Mechanics
(some of Fundamental concepts)
Prof. Dr. Mohammad Javed
mjaved@uetpeshawar.edu.pk
1

2. COURSE OBJECTIVE
This course aims at enabling the Civil engineering students to
analyze various systems of forces and thereby be able to
calculate the magnitude of these forces on various systems in
statics and dynamics.

3. By the end of semester, students should be able to:
CLO1. Handle problems related to Moment, Couple, Centroid, Moment of
inertia and Product of inertia for planar systems (C3).
CLO2. Determine Resultant of Planar force systems (C3)
CLO3. Analyze Statically determinate Planar force systems to calculate
reactions, internal, force and displacements (C4)
COURSE LEARNING OUT COMES (CLOs)

4. Week Hrs TOPIC CLOs
addressed
Quiz/
Assignment
1 2
Concepts of measurement of mass, force, time and space.
Force Classification. Principle of Transmissibility. System of
units.
1-2
1-2 1+1 Vector and scalar quantities. Type of vectors. Vector
Operations. Laws of Parallelogram and Polygon of vectors
addition.
1-2
2 2 Resultant of two, coplanar concurrent forces by
Parallelogram law. Resolution of a force into rectangular and
non-rectangular components. Resultant of two and more
than two, coplanar concurrent force system by summing
rectangular components.
2,3
3 3 Position Vector, Moment (vector and various scalar
methods). Varignon’s theorem. 2,3
4 1 Couple. Resolution of force into a force-couple system. 1-2
4 2 Replacing a force-couple system with i) Equivalent force –
couple system ii) Single force. 2,3
COURSE OUTLINES

5. COURSE OUTLINES
5 1.5 Resultant of Coplanar Parallel force (point and
distributed) system 2,3
5 1.5 Resultant of Coplanar non parallel, non-
concurrent force system. 2,3
6 3 Free Body Diagram development
1,3,4
7 1+1 Triangle and Polygon laws of forces. Lami’s
theorem. Equilibrium analysis of coplanar
concurrent force systems
1,4
7 1 Equilibrium analysis of coplanar parallel force
systems. 4
8 1.5 Equilibrium analysis of coplanar non parallel, non-
concurrent force systems. 4
8 1.5 Two force and three force bodies concept for
equilibrium analysis
1,3
9 Mid Term Exam

6. COURSE OUTLINES
10 3 Type of structures. Constraints and Statically
determinacy. Equilibrium analysis of Multi forces pin
jointed frames.
1,3,4
11 3 Determination of internal forces in statically
determinate Trusses by method of joints and method
of sections
4
12 3 Determination of internal forces in statically
determinate beams
4
13 3 Dry Friction. Analysis for Impending sliding and over
turning 1,4
H.A. 11 &

7. COURSE OUTLINES
14 2 Centroid of simples areas (by integration)
Centroid of composite areas
2
14-15 1+3 Moment of inertia of simple areas (by
integration) and composite areas. 2
16 1.5 Product of inertia of simple areas (by
integration)and composite areas.
2
16 1.5 Fundamental of dynamics for explaining
work and energy
1-3
17 3 Work. Energy. Work- Energy Principle.
Conservative and non-conservative forces.
Conservation of Mechanical Energies.
1-4
18 Final Term examination

8. Text Books:
Engineering Mechanics by J.L. Meriam and L.G. Craige, McGraw Hill.
Reference Books:
1. Engineering Mechanics by R.C. Hibbler, Prentice-Hall.
2. Engineering Mechanics by F.L.Singer, Harper and Row
RECOMMENDED BOOKS

9. Marks Distribution
• Sessional marks 30%
• Mid term 20%
• Final term (from full course) 50%
Sessional Marks Distribution:
• Quizzes: 50% of sessional marks (Total 3 quizzes. Each quiz will
be taken after 1 week of completing the topic as mentioned in course out lines.
First 15 minutes of relevant class will be dedicated for conducting Quiz.
• Assignments: 50% of sessional marks
9

10. Assignment & Exam policy
• Assignment policy:
The assignments are due 01 week after they are assigned, and should
be done in a neat and orderly fashion.
• Late submission will not be accepted.
• Examination policy:
Failure to take the mid-term examination or the final examination will
result in a failing grade for the course.
10

11. Lecture’s Objectives
• To define and discuss various branches of Mechanics
• To discuss some of fundamental concepts used in Engineering Mechanics
• To discuss system of units used in Engineering

12. Introduction to Mechanics
• Mechanics is the branch of Science which deals with the effect of forces
on bodies.
• Figure 1:What is the effect of 2kg mass (Force ?)
on attached cables (Body) ?
• Figure 2:What is the effect of 800 N reaction
(Force ?) on Tendon (Body ?)
Figure 1
Figure 2 12

13. Introduction to Mechanics
• Figure 3:What is the effect of Force ‘F’
on rod (Body) of length ‘L’?
Figure 3
13

14. CLASSIFICATION OF MECHANICS
Mechanics
Rigid
bodies
Fluids
Deformable
bodies
Engineering Mechanics
Statics Dynamics
Kinematics Kinetics
(Engineering
Mechanics)
(Solid Mechanics)
(Fluid Mechanics)

15. RIGID BODY MECHANICS
Rigid body:
Anybody which doesn’t undergo deformation (change in length or
change in area or change in shape) under the action of forces is said
to be rigid body
Deformable body Rigid body
Rigid body (Engineering Mechanics ) Deformable body (Mechanics of Solid)

16. Consider the given figure. The calculation of the tension in the cable which
supports the boom of a mobile crane under load is essentially unaffected by
the small internal deformations in the structural members of the boom.
16
RIGID BODY MECHANICS
For the purpose of determining the
external forces which act on the boom, we may
treat it as a rigid body.
Actually solid bodies are never rigid; they deform
under the action of applied forces.
In many cases this deformation is negligible
compared to the size of the body and the body is
assumed to be rigid

17. • Deformable Body: Bodies in which
appreciable deformation is produced under
application of load.
• Deformable Body Mechanics
Deformable body mechanics (Mechanics of
solids course) deals with how forces are
distributed inside bodies, and with the
deformations caused by these internal force
distributions. These internal force produce
"stresses" in the body, which could ultimately
result in the failure of the material itself.
17
DEFORMABLE BODY MECHANICS

18. The Mechanics of fluids is the branch of mechanics that deals with liquids or
gases.
 Fluids are commonly used in engineering applications. They can be
classified as incompressible, or compressible.
 While all real fluids are compressible to some degree, most liquids can be
analyzed as incompressible in many engineering applications.
 Applications of fluid mechanics abound, from hydraulics and general flow
in pipes to air flow in ducts to advanced applications in turbines and
aerospace.
 The study of the mechanics of fluids will be studied in courses called Fluid
Mechanics, Hydraulics and other relevant subjects.
18
FLUID MECHANICS

19. • Statics: It is that branch of Engineering Mechanics, which deals with the forces and
their effects, while acting upon the bodies at rest or or moving with constant velocity
(acceleration = 0 ?).
• 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, and 2.
Kinematics.
• Kinematics: Kinematics is the branch of mechanics which deals with motion
parameters without considering the forces responsible for motion.
• Kinetics: Kinetics is the branch of mechanics which deals with motion parameters as
well as forces responsible for motion.
CLASSIFICATION OF RIGID BODY MECHANICS
S= vit +1/2 at2
Fi= ma

20. Applications of Statics
20

21. 1. Mechanics of solids I &II (2nd & 3rd semester)
2. Fluid Mechanics I &II (3rd & 4th semester)
3. Hydraulics Engineering (5th semester)
4. Irrigation Engg and Water Management (8th semester)
5. Structural Analysis I &II (4th & 5th semester)
6. Reinforced concrete design I & II (6th & 7th semester)
7. Steel Structures (8th semester)
8. Geotechnical Engineering I &II (4th & 5th semester)
9. Foundation Engineering (6th semester)
10. Introduction to Structural Dynamics and Earthquake Engineering
(8th semester)
Civil Engineering courses requiring knowledge of
Engineering Mechanics as pre-requisite

22. Definitions
Space: It is the geometric region occupied by bodies whose positions are
described by linear and angular measurements relative to a coordinate
system. For three-dimensional problems, three independent coordinates are
needed. For two-dimensional problems, only two coordinates are required.
Time: It is conceived as a succession of events. Although the principles of
statics are time independent, this quantity plays an important role in the study of
dynamics.
Two dimensional rectangular Coordinate system Three dimensional Coordinate system
22

23. Definitions
Mass : The quantity of the matter possessed by a body is called mass.
 The mass of a body will not change unless the body is damaged and part of it
is physically separated.
 When a body is taken out in a space craft, the mass will not change but its
weight may change due to change in gravitational force. Even the body may
become weightless when gravitational force vanishes but the mass remain
the same.
23

24. Definitions
Particle: A particle is an object whose mass is concentrated at a
point. For this reason, a particle is also called a point mass, and it is said
to have zero volume
24
Size of earth is insignificant compared to the
size of its orbit. Earth can be modelled as a
particle when studying its orbital motion
Body: A body has mass and occupies a volume of space

25. 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 action of a force is completely characterized
by
1. its magnitude,
2. direction of its action, and
3. Its point of application.
25

26. Newton’s Three Laws of Motion
• Engineering mechanics is formulated on the basis of Newton’s three laws of
motion, the validity of which is based on experimental observation. These
laws apply to the motion of a particle as measured from a nonaccelerating
reference frame.
• First Law: Every body continues in its state of rest or of uniform
motion unless or until some external force acts on it.
• A football will remain at rest
unless acted upon by unbalanced force
26

27. Newton’s Three Laws of Motion
• Second Law: A particle acted upon by an unbalanced force F
experiences an acceleration a that has the same direction as the force
and a magnitude that is directly proportional to the force.
• If F is applied to a particle of mass m , this law may be expressed
mathematically as F = ma
27

28. Newton’s Three Laws of Motion
Third Law: The forces of action and reaction between bodies in contact
are equal in magnitude, opposite in direction and collinear (same line
of action).
28
Examples of Newton third law of motion

29. Classification of Force
Force
Body Force
For the application of such
forces contact between the
surfaces is not essential. e.g.,
gravitational force, magnetic
force etc.
Surface Force
For the application of this type of
force contact between the
surfaces is necessary i.e. friction
force, Reaction force of the roller
and hinge support
29

30. 30
Classification of Force

31. Force
Concentrated
Force
Distributed
Force
31
Classification of Force

32. 32
1. Concentrated force concentrated
forces exerted at point or location
2. Distributed force
A force applied along a length or over
an area. The distribution can be uniform
or non-uniform.
Concentrated forces, P1, P 2
What are other concentrated forces ?
Distributed forces
Classification of Force

33. Load is a term frequently used in engineering to mean the
force exerted on a surface or body.
33
Structural loads

34. Dead Loads: Vertical loads that are fixed in position and are
produced by the weight of the elements of the structure or
the whole structure with all its permanent components.
Examples are: own weight of structural member and super
imposed loads (e.g. walls and flooring cover)
34
Type of Structural loads

35. Live Loads: consist mainly of
occupancy loads (e.g. people
and furniture) in buildings and
traffic loads on bridges.
They may be either fully or
partially in place or not present
at all, and may also change in
location.
35
Type of Structural loads

36. Wind Loads: are the positive or
negative pressures exerted on a
building when it obstructs the flow
of moving air.
Wind loads generally act perpendicular
the surface of the structure.
Value of load varies depending on the
geographic location of the building
and its height.
36
Type of Structural loads

37. Seismic Loads: are the inertial forces that act on the structure
due to earthquake-induced ground motions.
37
Type of Structural loads
Ground acceleration, a
Inertial force
=ma

38. Snow Loads: the amount of snow load on a roof structure is
dependent on a variety of factors:
• Roof geometry,
• Size of the structure,
• Insulation of the structure,
• Wind frequency,
• Snow duration,
• Geographical location of the structure.
38
Type of Structural loads

39. Lateral Soil and Hydro-static Loads:
39
Type of Structural loads

40. Thermal and Settlement Loads:
40
Type of Structural loads
Thermal Loads Settlement Loads

41. External and Internal Effects of a force
External force
For the bracket of Fig. 2/1 the effects of P external
to the bracket are the reactive forces (not shown)
exerted on the bracket by the foundation and
bolts because of the action of P.
 Forces external to a body can be either applied
forces or reactive forces.
41
Applied force
What are the other external effects ?

42. External and Internal Effects of a force
Internal force
The effects of P internal to the bracket are the
resulting internal forces and deformations
distributed throughout the material of the bracket.
 The relation between internal forces and
internal deformations depends on the material
properties of the body and is studied in strength
of material (also known as Mechanics of Solids or
Mechanics of materials)
42

43. 43
Type of Internal forces
Tension

44. Stress
Stress is a term used to express
the internal force or resistance,
offered by a particle to the
adjacent particle in a body under
the action of external loads.
• Stress is the internal resistance
per unit area.
44

45. 45
Torsional
Normal

46. 46
Classification of Force system

47. TYPES OF FORCES & FORCE SYSTEM
collinear forces concurrent forces
Parallel forces Non-concurrent & non-parallel forces
Classification of Coplanar Force system

48. Principle of Transmissibility
“A force may be applied at any point on its given line of action without
altering the resultant effects of the force external to the rigid body on which it
acts “
48
What are the external effects
on the given body ?

49. Units of Measurement
• In mechanics we use four fundamental quantities called
fundamental mechanical dimensions. These are length, mass,
force, and time.
• Although there are a number of different systems of units
major systems of units are
1. The International System of Units (SI units)
2. U.S. Customary Units
49

50. Units of Measurement
SI Units. The International System of units, abbreviated SI is a modern
version of the metric system which has received worldwide recognition.
• SI system defines length in meters (m), time in seconds (s),and mass in
kilograms (kg).
• The unit of force, called a newton (N), is derived from F = ma. Thus, 1
newton is equal to a force required to give 1 kilogram of mass an
acceleration of 1 m/s2 (N = kg .m/s2) .
50

51. Units of Measurement
• U.S. Customary. In the U.S. Customary system of units (FPS) length is
measured in feet (ft), time in seconds (s), and force in pounds (lb).
• The unit of mass, called a slug , is derived from F = ma . Hence,
• 1 slug is equal to the amount of matter accelerated at 1 ft/s2 when acted
upon by a force of 1 lb (slug = lb.s2/ft) .
51

52.  In U.S. units the pound is also used on occasion as a unit of mass.When
distinction between the two units is necessary, the force unit is frequently
written as lbf and the mass unit as lbm
 Also, in the U.S. units (some time also called FPS system of units), following
relations are used
 1 ft = 12 in. (inches), 1 yard (yd)= 3 ft, 1 mile (mi)= 1760 yd= 5280 ft ,
 1 kilo-pound (kip)= 1000 lb ; 1 ton = 2000 lb ; 1 tonne = 1000 kg*= 2205 lb
52
Units of Measurement
*In the MKS (meter, kilogram, second) gravitational system, which has been used for many years in non-English-
speaking countries, the kilogram, like the pound, has been used both as a unit of force and as a unit of mass.

53. Abbreviation for inch.
Note that in previous slide the abbreviation for inch is “in.”, which
contains a period. This is unusual, but is done because without the
period, the abbreviation would also be the same as a word in the
English language, and this might lead to confusion.
53

54. Common pitfall
Weight and mass are different.
It is unfortunately common for people, especially lay people,
to refer to weight using mass units. For example, when a
person says,“I weigh 70 kg.”, the person really means “My
mass is 70 kg”
54

55. Conversion of Units
• Following table provides a set of direct conversion factors between FPS
and SI units for the basic quantities.
55

56. Dimensions versus units.
Dimensions and units are different.
Dimensions are a measurable extent of some kind, while Units are
used to measure a dimension.
For example, length and time are both dimensions, and meter and
second, respectively, are units used to measure these dimensions
56

57. Common prefixes used in the SI unit systems.
57

58. Problems
• Example 1
58

59. Common pitfall
Omitting units in equations.
The most serious mistake made when performing unit
conversions (as well as when writing equations in general)
is to omit units in equations.
Although writing units in equations takes a few moments
longer, doing so will help avoid the errors that are sure to
result if you do not make this a practice
59

60. Problems
• Problem 2
60

61. Problems for practice
61
1.1
1. 2
1.3
Ans:24.6 m/s
Ans: 101 kPa
Ans:

62. Problems For Practice
62
1. 5
1.4
Ans:
Ans: 98.1 N, 4.9mN, 44.1 kN