c 1 Basic Concepts on Statics111

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JJ205

ENGINEERINGMECHANICS

COURSE LEARNING OUTCOMES :

Upon completion of this course, students should be able to:

CLO 1. apply the principles of statics and dynamics to solve

engineering problems (C3)CLO 2. sketch related diagram to be used in problem solving(C3)

CLO 3. study the theory of engineering mechanics to solverelated engineering problems in group (A3)


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BASIC CONCEPTS ON

STATICS CLO 1. apply the principles of statics

and dynamics to solve engineering

problems (C3)

CLO 3. study the theory of

engineering mechanics to solverelated engineering problems in group(A3)


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INTODUCTION (CLO 1)

MECHANICS - Body of Knowledge whichDeals with the Study and Prediction of theState of Rest or Motion of Particles and Bodiesunder the action of Forces.

STATICS - Statics Deals With the Equilibriumof Bodies, That Is Those That Are Either at

Rest or Move With a Constant Velocity.

DYNAMICS - Dynamics Is Concerned Withthe Accelerated Motion of Bodies


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MASS

The quantity of the matter possessed by a body iscalled 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, themass 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.


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Continue

TIME Time is conceived as a successionof events. Although the principles of statics

are time independent, this quantity doesplay an important role in the study ofdynamics.

LENGTH Length is needed to locate theposition of a point in space and therebydescribe the size of a physical system.Once a standard unit of length is defined,one can then quantitatively definedistances and geometric properties of abody as multiples of the unit length.


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Concentrated force

Represents the effect of a loading which

is assumed to act at a point on a body.

We can represent a load by aconcentrated force, provided the area

over which the load is applied is very

small compared to the overall size of the

body.

Example: contact force between a wheel

and the ground.


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SCALARS AND VECTORS (CLO 1)

SCALARS A quantity characterizedby a positive or negative number is

called scalar. For example; mass,

volume and length. VECTOR A vector is quantity that

has both a magnitude and the

direction. For example; weight, forceand moment.


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VECTORS (CLO 1)

FREE VECTORS One whose action isnot confined to or associated with aunique line in space. For example, if abody moves without rotation, then the

movement or displacement of any pointin the body maybe taken as a vector, andthis vector will be describe equally wellthe direction and magnitude of thedisplacement of every point in the body.Hence , we may represent thedisplacement of such a body by a freevector.


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VECTORS

SLIDING VECTORS Is one forwhich a unique line in space must be

maintained along which the quantity

acts. When we deal with the externalaction of a force on a rigid body, the

force may be applied at any point

along its line of action withoutchanging its effect on the body as a

whole and hence may be considered a

sliding vector.


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VECTORS

FIXED VECTORS is one for which aunique point of application is specified,and therefore the vector occupies aparticular position in space. The action of

a force on a deformable or non rigidbody must be specified by a fixed vectorat the point of application of the force. Inthis problem the forces and deformationsinternal to the body will be dependent onthe point of application of the force, aswell as its magnitude and line of action.


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NEWTONS LAWS OF MOTION

(CLO 1)

FIRST LAW A particle originally at rest, or moving in astraight line with constant velocity, will remain in thisstate provided the particle is not subjected to anunbalanced force.

SECOND LAW A particle acted upon by anunbalanced force F experiences an acceleration athat has the same direction as the force and amagnitude that is directly proportional to the force. If Fis applied to a particle of mass m, this law maybe

expressed mathematically as ; F = ma.

THIRD LAW The mutual forces of action and reactionbetween two particles are equal, opposite, andcollinear.


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SI SYSTEM AND UNIT (CLO 3)

Mechanics deals with fourfundamental quantities; length, mass,

force, and time.

QUANTITY DIMENSIONALSYMBOL

SI UNITS

UNIT SYMBOL

MASS M Kilogram kg

LENGTH L Meter m

TIME T second s

FORCE F newton N

* The unit of force, called a newton (N), is derived from F=ma.

1 newton is equal to a force required to give 1 kg of mass an acceleration of 1 m/s2.

(N = kg. m/s2)


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PREFIXES (CLO 3)

When a numerical quantity is eithervery large or very small, the units used

to define its size maybe modified by

using prefix. For example;Exponential

form

prefix SI symbol

1 000000000 109 giga G

1000 103 kilo k

0.001 10-3 mili m

0.000001 10-6 micro

0.000000001 10-9 nano n


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Example (CLO 3) :

Evaluate each of the following andexpress with SI units having an

appropriate prefix:

a) (50 mN)(6 GN)b) (400 mm)(0.6 MN)2

c) 45 MN3/900 Gg


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Continue

First, convert each number to base units,perform the indicated operations, then,

choose an appropriate prefix.

a)

Note carefully the convention kN2 = (kN)2 = 106 N2


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b)

We can also write:

Continue


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Continue


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Exercises:

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c 1 Basic Concepts on Statics111