Engg Mech Notes1rev1

8/13/2019 Engg Mech Notes1rev1

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Freddie E. Bien, MSCE, M.ASEP

Structural Engineer

Asst. Professor, College of Engineering

ATENEO DE NAGA UNIVERSITY

LEARNING OBJECTIVES:

1. To Define engineering mechanics

. .

3. To state the Newtons Law of motion

4. To review conversion of units.


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The Flemish mathematician first

to demonstrate resolution of

forces, there by establishing the

foundation of modern statics


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Before we define engineering

mechanics , let us consider thesimilarities and differences of

physics and engineering

PHYSICS- Science that relates properties of matter and

energy, excluding b iological and chemical effects

- It includes, mechanics, thermodynamics,

e ec r c y an magne sm an nuc ear p ys cs.

ENGINEERING

- Is the application of the mathematical and

physical sciences(physics, chemistry, and

biology) to the design and manufacture of items

.ENGINEERING DESIGN

- The process of devising a system, component

or process to meet desired needs. (according toAcceditation Board for Engineer ing and Technology (ABET))


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MECHANICS

- A branch of physics that consider the action of

forces on bodies or f luids that are at rest (statics)or in motion (dynamics)

WHAT IS ENGINEEERING MECHANICS?

- A branch of engineering that applies the

principles of mechanics to mechanical design

which take into account the effect of forces.

Engineering Approach to Problem Solving1. Draw an appropriate figure on which all dimensions

are shown.

2. Write down what is given and the quantities to be

found.

3. Write down all formulas.

4. Make sure that your solution is arrange which can be

followed by your self and another person.

5. Study the sample problems the will aid the students

in making adequate arrangements.

. wou e e p u o emp oy era quan es odenote numerical values.

7. In completing the problems, it is necessary to to

finally replace these literal.

8. Used of calculators


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[R.C. Hibbeler]

[R.C. Hibbeler]


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Problem Analysis is divided into the four

parts

.

2. REQUIRED

3. SOLUTION

4. VALIDATE

Does my answer make sense?

Is your answer reasonable?

NEWTONS LAW OF MOTION

1. If a particle is at rest(or moving with constant

velocity in a straight line), it will remain at rest

(or continue to move with constant velocity in a

straight line) unless acted upon by a force.

2. A particle acted upon by a force will accelerate

in a direction of the force. The magnitude of

the acceleration is proportional to the mass of

the particle. F = ma

. ,opposite reaction; that is the forces of

interaction between two particles are equal in

magnitude and oppositely directed along the

same line of action


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From 2nd Newtons Law of Motion

F = m a F = Force, Nm = mass in kga = acceleration, m/s2

1 N = 1 kg.m/s2

For gravitational system [FLT]

FTm

2

=

2T

mLF=


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Weight, W = mg

SI: g = 9.81 m/s2

,

U.S Customary Units:

g = 32.2 ft/s2

mass mslu

Weight, W = mg


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[R.C. Hibbeler]

[ R.C. Hibbeler]

Problem 1

Convert the quantities 350 lb.s to N.s and KN.s

Convert the quantities 50 slug/ft3 to kg/m3

to g/m3

to Mg/m3


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Problem set #1

Problem 1.1 to 1.5, 1.8 page 9 of textbook

LEARNING OBJECTIVES:

1. To review metric conversion of units.

.


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Law of Gravitation

States that the two particles are attracted to

each other by a forces of magnitude F that act

along the line connecting the particle where

2R

mmGF BA=

Where:

G= 6.67x10-11 m3/(kg.s2)

mA = mass of earth, Me kg

mB = mass of body, m kg

R = mean radius of earth R mF = weight of the body, N

Comparing

2

e

e

RmMGW= and W = mg

It follows that2

e

e

R

MGg=

Problem 3 [1.6/9]In a certain application, the acceleration a and the

position coordinate x of a particle are related bygkx

a=

Where g is the gravitational acceleration, k is constant

and W is the weight of the particle. Show that this

equation is dimensionally consistent if the dimension of

k is [MT-2]

W

=

2][

T

Lg

== Wxkg

Wa ]][][[ =

[ ]Lx =][

[ ]2== MLTmgW

Where:


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Problem 4 [1.15/10]

Two 10 kg spheres are placed 500mm apart. Expressthe gravitational attraction acting on one of the spheres

as a percentage of its weight on earth.

Given:

mA = 10 kg G = 6.67x10-11 m3/(kg.s2)

mB = 10 kg

R = 0.5 m

2R

GF=

W = mg

Percentage of weight =(F/W)x100%

Problem 5 [1.20/10]

Find the elevation h (km) where the weight of the object is

one tenth its weight on the surface of the earth. Use mass

of earth, Me = 5.9742x1024 kg, radius of earth,

Re = 6378km, G = 6.67x10-11 m3/(kg.s2)

On earth: 2e

ee

R

mGMW =

At elevation h:

( )2hRmGM

We

e

+=

10

EWW=


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Problem set #2:

Problem 1.13, 1.18 and 1.21 page 10 of textbook

REFERENCES :Pytel, A. and Kiusalaas, J., Understand ing Engineering

Mechanics: Statics Published: Philippines: Cengage Learning Asia

Pte. Ltd, c2010

Hibbeler, R. C. Engineering Mechanics: Combined Statics and

dynamics. Published: Singapore: Pearson, c2010

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