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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.