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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)