PHYSICS FORM 4

INERTIA

OBJECTIVES• To know the exactly definition of

inertia.• To analyze the relationship between

inertia and mass.• To understand the effects of inertia

in daily life experience.

MENU• Definition of inertia• Relationship between mass inertia and m

ass.• Effect of inertia in our daily life• Quiz • Reference

When the cardboard covering the glass is pulled out quickly, what will

happens to the coin?

ANSWER

When the cardboard covering the glass is pulled out quickly, the coin resting on the cardboard drops into

the glass

What will happen to the rest of the coins when one of the coin is moved out

quickly?

ANSWER

The inertia of the coins maintains it in its original

position (at rest) even when one of the coin is

moved out quickly

INERTIA

Inertia is the property of matter that cause it to resist any change in its motion or state of rest

resistmenentang/ melawan

How could this HAPPENs ???

If an object is moving….

Initially :The car & driver are moving togethersuddenly : car → stops suddenly driver → continue moving forward The inertia of the driver resists the change in

its motion-thus he was thrown forward

It tends to stay in that position unless some force puts that object into motion

If an object is at rest…

Inertia is not physical quantity and thus it does not have units

The property of inertia is found from the Newton’s first law of motion

Newton’s First Law of Motion

"An object at rest tends to stay at rest and an object in motion the same speed and in the same direction tends to stay in motion with unless acted upon by an unbalanced force"

1st actv

The coin is in the state of rest When the cardboard is pulled quickly,

the cardboard moving together with the hand

But the inertia of the coin cause it to remain at rest and thus it falls into the cup

The inertia of the coin resists the change in its motion

The tendency of an object to remain at rest or, if moving, to continue its uniform motion in a straight line.

WHAT IS INERTIA

2nd actvThe bus & passengers are moving together

when the bus stops suddenly, the inertia of each passenger maintain its motion which is moving forward.

That’s why the passengers were thrown forward

The inertia of the passengers resists the change in its motion

RELATIONSHIP BETWEEN INERTIA

AND MASS

Mass can influence the

effects of inertia.

An object with a larger mass has a

larger inertia.

mass inertia

EXPERIMENT OF INERTIA

Inference : The Period of oscillation depends on the mass of plasticine.

Hypothesis : the greater the mass of plasticine,the longer the period of oscillation

Aim : To investigate the relationship between the Period of oscillation and the mass of plasticine

Variable :-manipulated : Mass of plasticine-responding : Period of oscillation-constant : Angle of displacement/ length of saw blade

Experiment of Inertia

2. Plasticine of mass of 10 g was weighed using electronic balance

1. The apparatus was set up as shown in the diagram

3. The plasticine was fixed to the free end of saw blade.

4. The plasticine was displaced horizontally and released to make it oscillates.

METHOD OF CONTROLLING THE MANIPULATED VARIABLE

Experiment of Inertia

6.Step 5 was repeated and the average time for the same mass of plasticine was calculated.

5. The time taken for 10 complete oscillations was measured using stopwatch and recorded.

REPEATING THE EXPERIMENT

7. The experiment was repeated for mass of plasticine of 40 g, 60 g, 80 g and 100 g.

METHOD OF CONTROLLING THE RESPONDING VARIABLE

Table for recording dataMass of plasticine m (g)

Time taken for 10 complete swings, t (s)

Period of oscillation, T = t1+t2 ÷ 10 (s) 2

T2 / s2

t1 t2 t1 + t2

2

1020304050

Then plot graph of T2 against m.

T2 / s2

m / g

Graph of T2 against m

CONCLUSION :From the graph, T2 is directly proportional to m. The hypothesis is accepted.

T2 / s2

m / g

Graph of T2 against m

CONCLUSION :From the graph, T2 is increase linearly with m. The hypothesis is accepted.

Interpreting data• Find the value of T when m = 45 g

T2 / s2

m / g45

0.33

*** intrapolationIf m = 45 g then T2 = 0.33 s2

YOU WANT TO KNOW THE

EXPLANATION ABOUT THIS???

CLICK ON THE VIDEO

If the motorcycle were to abruptly stop, then the rider in motion would continue in motion. The rider would likely be propelled from the motorcycle and be hurled into the air. Once

they leave the motorcycle, the rider becomes a projectile and continues in projectile-like

motion. It is because of inertia.

Applications of inertiaSome examples of using inertia in our daily life are :

1. To tighten the loose head of a hammer • To tighten the loose head of a hammer, knock one end of

the handle held vertically, on a hard surface. • The hammer head will continue on its downward motion• when the handle has been stopped, the top end of the

handle is slotted deeper into the hammer head.

2. Drying off the wet fur of cats and dogs.• Cats and dogs dry their wet fur by shaking their body

vigorously. • Water droplets on the fur tend to continue in motion when the

body has stopped shaking. • water droplets will be separated from the fur and fall away

3. To dislodge chili sauce from the bottle • Chili sauce in a bottle is poured out by a quick downward

movement of the bottle followed by a sudden stop. • The sauce in the bottle moves with the bottle during the

downward movement. • When bottle is stopped, the inertia of the sauce causes it to

continue on its downward movement and thus the sauce is forced out of the bottle.

4. Passengers are thrown forward when a bus moving bus stops suddenly

5. Passengers are hurled backward when a stationary bus move suddenly.

When a student is riding a bicycle and runs over a

stone, he is thrown forward. Why does this happen?

ANSWER

THE INERTIA OF THE STUDENT MAINTAINS HIS

FORWARD MOTION SO THAT HE IS THROWN FORWARD WHEN HIS

BICYCLE IS MOMENTARILY STOPPED BY THE STONE

References • FOCUS SUPER HOT SPM PHYSICS- S.L

Chang, Koay Kheng Chuan, Yew Kok Leh. Penerbitan Pelangi Sdn. Bhd.