Introduction to engineering mechanics.ppt

basic concepts to engineering mechanics

1. CHAPTER 1
INTRODUCTION TO
MECHANICS

2. WHAT IS MECHANICS??
Mechanics is the science which describes and predicts the
conditions of rest or motion of bodies under the action of forces.
Mechanics is an applied science since it deals with the study of
physical phenomenon.
Mechanics is the foundation of most engineering sciences and
is a crucial requirement to their study.

3. BRANCHES OF MECHANICS

4. Engineering Mechanics
Rigid-body Mechanics
Statics: deals with equilibrium of bodies under action of forces
(bodies may be either at rest or move with a constant velocity).

5. Engineering
Mechanics
Rigid-body Mechanics
•Dynamics: deals with motion of bodies (accelerated motion)

6. What may happen if static's is not applied properly?

7. FUNDAMENTAL CONCEPTS & PRINCIPLES
•Space - associated with the notion of the position of a point P given in terms
of three coordinates measured from a reference point or origin.
•Time - definition of an event requires specification of the time at
which it occurred.
•Mass - used to characterize and compare bodies, e.g., response to
earth’s gravitational attraction and resistance to changes in translational
motion.
•Force - represents the action of one body on another. A force is
characterized by its point of application, magnitude, and direction, i.e.,
a force is a vector quantity.
The basic concept used in mechanics are space, time, mass and force
Mathematical expressions possessing magnitude and
direction, which add according to the parallelogram law
Parallelogram law
Two force acting on a particle may be replaced
by a single force, called their resultant

8. In Newtonian Mechanics, space, time, and mass are absolute concepts,
independent of each other. Force, however, is not independent of the other
three. The force acting on a body is related to the mass of the body and the
variation of its velocity with time, F=ma.
Force can also occur between bodies that are physically separated (Ex:
gravitational, electrical, and magnetic forces)
Principle of Transmissibility – conditions of equilibrium or of motion of
rigid body will remain unchanged if a force acting at a given point of the
rigid body is replaced by a force of the same magnitude and same direction,
but acting at a different point.

9. REMEMBER
Mass is a property of matter that does not change from one location to
another.
Weight refers to the gravitational attraction of the earth on a body or
quantity of mass. Its magnitude depends upon the elevation at which the
mass is located
Weight of a body is the gravitational force acting on it.

10. •Newton’s First Law: If the resultant force on a particle is zero, the particle
will remain at rest or continue to move in a straight line with constant speed.
•A particle originally at rest, or moving in a straight line with constant velocity,
tends to remain in this state provided the particle is not subjected to an
unbalanced force.
•First law contains the principle of the equilibrium of forces
•main topic of concern in Statics
NEWTON’S THREE FUNDAMENTAL LAWS

11. •Newton’s Second Law: A particle will have an acceleration proportional to a
nonzero resultant applied force.
amF


NEWTON’S THREE FUNDAMENTAL LAWS
A particle of mass “m” 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.
Second Law forms the basis for most of the analysis in Dynamics

12. •Newton’s Third Law: The forces of action and reaction between two particles
have the same magnitude and line of action with opposite sense.
NEWTON’S THREE FUNDAMENTAL LAWS
Third law is basic to our understanding of Force
Forces always occur in pairs of equal and opposite forces.

13. NEWTON’S LAW OF GRAVITATIONAL ATTRACTION
F = mutual force of attraction between two particles
G = universal constant of gravitation
Experiments ?????? G = 6.673x10
-11
m
3
/(kg.s
2
)
Rotation of Earth is not taken into account
m
1, m
2 = masses of two particles
r = distance between two particles
Weight of a body (gravitational force acting on a body) is required to be
computed in Statics as well as Dynamics.
This law governs the gravitational attraction between any two particles.
F  G
m
1m
2
r
2

14. SYSTEMS OF UNITS
Length, mass and time are the fundamental dimensions while
force is the derived dimension
A magnitudes assigned to the dimensions are called units
F = m * a
•Force units can be formed by combination of primary units
•example: m= x kg ; a= y m/s
2
 F= kg ∙ m/s
2

Conversion factors were used in order to convert the units from
one system to another system

15. RULES FOR USING SI SYMBOLS
No Plurals (e.g., m = 5 kg not kgs )
Separate Units with a • (e.g., meter second = m • s )
Most symbols are in lowercase (some exception are N, Pa)
Exponential powers apply to units , e.g., cm
2
= cm • cm

16. NUMERICAL CALCULATIONS
Must have dimensional “homogeneity.” Dimensions have to be
the same on both sides of the equal sign, (e.g. distance = speed 
time.)
Be consistent when rounding off.
•≥ 5, round up (3528  3530)
•< 5, round down (0.03521  0.0352)
Use an appropriate number of significant figures (3 for answer, at
least 4 for intermediate calculations).

17. PROBLEM SOLVING STRATEGY: IPE
1. Interpret Read carefully and determine what is given and what is
to be found/delivered. Ask, if not clear. If necessary,
make assumptions and indicate them.
2. Plan Think about major steps (or a road map) that you will take to
solve a given problem. Think of alternative/creative
solutions and choose the best one.
3. Execute Carry out your steps. Use appropriate diagrams and
equations. Estimate your answers. Avoid simple
calculation mistakes. Reflect on / revise your work.

18. SCALARS AND VECTORS
Scalars: only magnitude is associated.
•Ex: time, volume, density, speed, energy, mass
Vectors: possess direction as well as magnitude, and must obey
the parallelogram law of addition (and the triangle law).
•Ex: displacement, velocity, acceleration, force, moment,
momentum
•Equivalent Vector: V = V
1 + V
2 (Vector Sum)
Speed is the magnitude of velocity.

19. http://phet.colorado.edu/sims/vector-ad
dition/vector-addition_en.html

20. EXERCISES
2. In three step IPE approach to problem solving, what does P stand
for
A) Position B) Plan C) Problem
D) Practical E) Possible
1. For a static’s problem your calculations show the final answer as
12345.6 N. What will you write as your final answer?
A) 12345.6 N B) 12.3456 kN C) 12 kN
D) 12.3 kN E) 123 kN

21. END OF THE LECTURE
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