Download - Physics (Ashutosh 9th D)
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Force & Laws of MotionForce & Laws of Motion
AshutoshAshutosh
99thth DD
RollRoll--No:No:--66
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What is Force?
A push or pull acting on the body is
known as force
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Two types of forceTwo types of force
Balanced Force
Unbalanced Force
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Balanced ForceBalanced Force
When two forces of equal magnitude
When two forces of equal magnitudebut acting in opposite directions on anbut acting in opposite directions on an
object simultaneously,then the objectobject simultaneously,then the object
continues in its state of rest or ofcontinues in its state of rest or of
uniform motion in a straight line.suchuniform motion in a straight line.suchforces acting on the object are knownforces acting on the object are known
asas Balanced Force.Balanced Force.
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Unbalanced ForceUnbalanced Force
When two forces of unequal magnitudesWhen two forces of unequal magnitudesact in opposite directions on an objectact in opposite directions on an object
simultaneously,then the object in thesimultaneously,then the object in the
direction of large force.T
hese forcesdirection of large force.T
hese forcesacting on the object are known asacting on the object are known as
Unbalanced Force.Unbalanced Force.
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Laws of motion
There are three laws of motion:-
1.First law of motion2.Second law of motion
3.Third law of motion
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First law of motion
According to this law everybody
continues in its state of rest or uniform
motion in a straight line unlesscompelled by some external force
(i.e.unbalanced force) to change that
state.
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Second law of motion
According to this law,the change in
momentum of a body per unit time is
directly proportional to the unbalanced
force acting on the body and the
change in momentum takes place in the
direction of unbalanced force on the
body.
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Third law of motionThird law of motion
Action and reaction are equal and
opposite.
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Inertia
The tendency of a body to oppose or resist
any change in its state of rest or uniform
motion is called inertia of the body .
There are three types ofInertia:-
1.Inertia of Rest
2. Inertia of Motion
3. Inertia of Direction
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Inertia of Rest
The tendency of a body to oppose any change in itsstate of rest is known as inertia of rest.
Example:-When a tree is viourously shakensome ofthe leaves fall from the trees.
When a tree is vigorously shaken,the branches ofthe tree come in Motion but the leaves tend to
continue in their state of rest due to inerria of rest.Asaresult of this leaves get separated from thebranches of the tree and hence fall down
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Inertia of Motion
The tendency of a body to oppose any change in its
state of uniform motion is known as inertia of
Motion.
Example:-The passengers fall forward when a fast
moving bus stops suddenly.
This is because,the lower part of the bodies of thepassengers come to rest as soon as the bus
stops.But the upper part of their bodies continue to
move forward due to inertia of motion.
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Inertia of Direction
The tendency of a body to oppose any change in its
direction of motion is known as inertia of direction.
Example:-When a fast moving bus negotiate a curveon the road, passengaers fall towards the centre of
the curved road.
This is due to the tendency of the passengers to
continue to move in a straight line.
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Momentum
Momentum is nothing but product of
mass and velocity.
Momentum of fast running man is
more than that of running slow.