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2.3
UNDERSTANDIN
G INERTIA
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Play : DODO
Watch the motion carefully.
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Everyday life experiencesEveryday life experiences
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You lurch forwardwhen the car stopssuddenly.
You lurch backwardswhen the car starts tomove suddenly.
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you kick a rock.You lurch forward
Rock
Banana
skin
you steps on banana skin .You lurch backwards
You are running and accidentally .......
Your feet is brought toa stop, but the inertiaof your body tends tocontinue moving
forward.
Your feet are carriedforward with a highervelocity but the inertiaof your body keeps you
in the initial velocity.
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The examples show that our body
has an inbuilt resistance to anychange in its state of rest or
motion.
This reluctance to change is called
inertia
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Carry out Hands-on activity 2.5
(practical book pg 15)
to gain an idea of inertia
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The concept ofinertia was explained by Sir
Isaac Newton in the first law of motion.
Newtons first law of motion
states that
The inertia of an object is the
tendency of the object to remain at
rest or, if moving, to continue itsuniform motion in a straight line.
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Situations involving inertiaSituations involving inertia
A body at rest tends toA body at rest tends to
stay at reststay at rest
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When the cardboard is flicked, the
coin remains in the initial position
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When the stack of coins is flicked
by a ruler, the bottom coin is
knocked off . Others remain at rest.
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When the tablecloth is pulled swiftly
and horizontally, all the tableware
remains on top of the table.
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Situations involving inertiaSituations involving inertia
A body in motion tends toA body in motion tends to
stay in motionstay in motion
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When the umbrella has stopped
spinning, droplets of water are
spun off .
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cant stopimmediately
The car has stopped but the man
in the car is still moving forward.
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Relationship betweenRelationship between
mass and inertiamass and inertia
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Hard to get moving easy to get moving
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Hard to get moving easy to get moving
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Hard to get movingeasy to get moving
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Hard to get the moving tanker to stop.
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The fat boy is more difficult to stop.
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It is difficult to stop the bowling ball
from rolling.
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Do not stand in the way of a moving
truck. It is very difficult for it to stop.
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An object with a larger mass isdifficult to get started from rest.
Once moving, an object with a larger
mass is difficult to stop its motion.
An object with a largermass has a larger inertia
CONCLUSION
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Carry out Hands-on activity 2.6
(adapted from practicalbook pg 20)
to find out the relationship
between inertia and mass
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Discussion HandDiscussion Hand--on activity 2.6on activity 2.6
1. The quantity used to representinertia is the period of oscillation.
2. When the mass increases, theinertia increases.
3. Objects with a large mass have alarge inertia. It is difficult to set anobject of large mass in motion or to
stop it.
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The positive effectThe positive effect
of inertiaof inertia
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Chili sauce in
the bottle can be
poured out by a
quick downward
movement
followed by asudden stop
Inertia of the
sauce caused itto continue its
downward
mov
ement.
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The head of the
hammer is secured
tightly to its handle
by knocking the
bottom of the
handle againsthard surface.
The head of the
hammer has a biginertia .It continues
the downward
mov
ement.
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The oil
drilling
platformfloating in
the sea.
The platform is very massive and has a very
big inertia so that it can stand in the same
place perpetually.
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The child
chased byan elephant
ran in a
zigzag path.
Elephant has a large mass
and hence has a largeinertia. It is very difficult for
it to change the direction
of motion.
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The negative effectThe negative effect
of inertiaof inertia
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Passengers
of the car
might becrash into
parts of the
car or thrown
out from acar during an
accident.
To reduce the risk,
(i) wear seat belts
(ii) air bag system
(iii) Headrest to
prevent whiplash
injuries to the neck.
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Item such as furniture and larger electrical
appliances may(i) fall off the lorry when the lorry starts to
move.
(ii) thrown forward when the lorry brakes
suddenly.
To reduce the
risk,
all theseitems must be
securely
fasten to the
lorry.
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Great
impact
from themovement
of the liquid
forward
when thelorry stops
suddenly.To reduce the risk, a lorry tankers
(i) has a strong iron structure
between the drivers cabinand the load
(ii) divide internally into
compartments.