CHAPTER 1

INTRODUCTION TO MECHANICS

BKF 1313 ENGINEERING MECHANICS

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.

BRANCHES OF MECHANICS

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

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 lawTwo force acting on a particle may be replaced by a single force, called their resultant

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.

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.

• 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.

• 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 Second Law: A particle will have an acceleration proportional to a nonzero resultant applied force.

amF

Newton’s Law of Gravitation: Two particles are attracted with equal and opposite forces,

F-F

r m

M

NEWTON’S THREE FUNDAMENTAL LAWS

2r

MmGF

Constant of gravitation

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/s2 F= kg ∙ m/s2

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

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., cm2 = cm • cm

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).

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.

EXERCISES

1. The subject of mechanics deals with what happens to a body when ______ is / are applied to it.

A) magnetic field B) heat C) forces

D) neutrons E) lasers

2. ________________ still remains the basis of most of today’s engineering sciences.

A) Newtonian Mechanics B) Relativistic Mechanics

C) Euclidean Mechanics C) Greek Mechanics

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

END OF THE LECTURE

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