Introduction_ppt [Uyumluluk Modu]

8/18/2019 Introduction_ppt [Uyumluluk Modu]

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IntroductionIntroduction toto DynamicsDynamics


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Dynamics is that branch of mechanics

which deals with the motion of bodies

under the action of forces. Dynamicshas two distinct parts: kinematics and

kinetics. Kinematics is the stud of

motion without reference to the forceswhich cause motion. Kinetics relates the

action of forces on bodies to their

resulting motions.


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When machines and structures started to

operate with high speeds it became necessary

to make calculations based on the principles

of dynamics rather than on the principles of

.


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The rapid technological developments of the

present day require increasing application of the

principles of mechanics. These principles arebasic to the analysis and design of moving

loads, robotic devices, automatic controlsystems, rockets and machinery of all types.


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BASIC CONCEPTS

The basic concepts in mechanics are

space, time, mass and force. Amongthese, space, time, mass are absolute

quantities, which mean that they are

independent of each other and cannot beexpressed in terms of other quantities or in

simpler terms. Force, on the other hand, is

a derived quantity.


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Space (uzay) is the geometric region occupiedby bodies. Position in space is specified by linear

or angular measurements with respect to a

geometric reference system. In NewtonianMechanics the basic reference system is named

as the “ primary inertal system” (birincil mutlak

sistem) and it is a virtual system assumed asneither rotating or translating in space.


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For the examination of motion occurring on or

near Earth, it is suitable to use a reference

system attached to Earth as the primary inertial

system.


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Time (zaman) is a measure of the

succession of events and is considered an

absolute quantity in Newtonian mechanics.


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Mass (kütle) is the quantitative measure

of the inertia or resistance to change in

motion of a body. Mass can also beconsidered as the amount of matter within

.

absolute quantity, its weight can change

depending on the gravitational force

(W=mg).


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Force (kuvvet) is the action of one bodyon another. A force possesses both

,

vector quantity.


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A particle (parçacık veya maddesel nokta) is abody of negligible dimensions. Generally a particle

is thought to be an infinitesimally small element

which possesses all properties of a body. Butwhen the dimensions of a body are irrelevant to

the description of its motion or the action of forces

on it, a large body may also be treated as aparticle.


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A particle has mass but no shape and dimensions.

The body is considered to be concentrated at a

single point which usually will be its mass center. All the forces acting on the body will have to pass

from this point, i.e. the forces will be concurrent .


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Some examples to particles are shown here; a

ball, a block, even an airplane can be consideredas particles.


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A rigid body (rijit veya katı cisim) is a body

whose changes in shape are negligible comparedwith the overall dimensions of the body or with the

changes in position of the body as a whole. The

s ape an mens ons o a r g o y w rema nthe same under all conditions of loading and at all

times.


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Some examples of rigid bodies areshown here.


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Displacement (Yer Değiştirme) Time rate of

change of position coordinates. Displacement is

a vector quantity. Examination of displacementis carried out by means of a suitable coordinate

system. The selected coordinate system can

e er e an a so u e xe or a mov ngsystem.


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Trajectory / Path (Yörünge) It is a line or acurve obtained when all the points a body

occupies within a specific time period are joined.


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Kinetics (Kinetik) Observes motion by

considering the forces that cause the motion. In

this field, in addition to the quantities inkinematics, forces and / or moments, together

with mass also take part in relationships.


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NEWTON’S LAWS

Law I. (Equation of Equilibrium) A particle

remains at rest or continues to move with uniformvelocity (along a straight line with a constant

s eed if there is no unbalanced force actin on it.

0F =∑

r


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NEWTON’S LAWS

Law II. (Equation of Motion)The acceleration of

a particle is proportional to the resultant forceacting on it and is in the direction of this force.

amF r

r

=∑

) Newton (Ns

mkgmaF

2 =⋅==


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NEWTON’S LAWS

Law III. (Principle of Action and

Reaction) The forces of action and reactionbetween interacting bodies are equal in

collinear.


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GRAVITATION Newton’s law of gravitation, which governs

the mutual attraction between bodies, is stated as

G = a universial constant called the constant of gravitation

2

21

r

mmG F =

21mm

2

21

r

mmG F =

2

2121

r

mmG F F ==

2

3

2

22

21

2

skg

m

kgkgs

mmkg

kgkg

m N

mm

r FG

⋅=

⋅⋅

⋅⋅=

⋅

⋅=

⋅=

2r

2

31110673.6

skg

mG

⋅×=

−


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r

r

UNITS

The International System of metric units

(SI) is defined and used in this lecture.

r

r

Units

am= am=Mass m kg (kilogram)

Time t s (second)

Length L m (meter)

Force F N (Newton)

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