Exploring the Investigative World of Science Class 8 (Curiosity)

This chapter opens our science journey for the year — it reminds us what the scientific method is, shows how science reaches far beyond the textbook into everyday life, previews the topics we will study, and teaches us how to ask questions and find answers like a real scientist.
Understanding the Name of the Chapter
Exploring
Looking closely to discover and understand new things.
Investigative
Asking questions and finding answers through observation and experiment.
World of Science
Everything around us that science helps us understand, from the tiny to the vast.
Topics We Will Study in This Chapter
1
Science and the Scientific Method
2
Science — Beyond the Textbook
3
Science Through Exploration
4
Think Like a Scientist

The Scientific Method
Science has three core aspects
First we make an observation
Then we do experimentation
Last we draw conclusions
This step-by-step way is the scientific method
Example 1 — A scientist at work
observes something curious
tests it through experiments
draws a conclusion from results
Example 2 — Science in daily life
toothpaste, soap and shampoo
clothes and food we use
all are gifts of science
Important Points
The three core aspects of science are observation, experimentation and drawing conclusions.
Science is about being curious about the world and how it behaves.
Science is present all around us, from the microscopic to the macroscopic world.
Definition — Scientific Method
The scientific method means a step-by-step way to explore and understand the world, just like scientists do, through observation, experimentation and drawing conclusions.

Science as a Journey of Discovery
Science is more than theories and laws
It is a journey of discovery
We explore by asking questions
Then we find the answers
It helps us understand how things work
Example 1 — Everyday wonders
why oil floats on water
why we fall on slippery surfaces
why a thrown object comes down
Example 2 — Boiling water to steam engine
steam occupies a larger volume
this creates pressure
the idea led to the steam engine
Important Points
The steam engine was first built by Thomas Newcomen and improved by James Watt.
Thomas Edison invented the incandescent lamp, built on the earlier arc lamp idea.
Vaccines, life-saving drugs, telephone, internet, aeroplane and satellite are great gifts of science.
Definition — Science
Science means a journey of discovery that helps us explore the world by asking questions and finding answers.
Q 1
Objective Type Questions Q1(e) - Page 13 Lakhmir Singh
Question
Name the following: A form of energy used to see objects around us.
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Light
Explanation
Light is a form of energy; without it we could not see objects around us.
Q 2
Objective Type Questions Q2(a) - Page 13 Lakhmir Singh
Question
Fill in the blank: Oil ________ on water.
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floats
Explanation
Oil is lighter than water, so it floats on its surface.
Q 3
Objective Type Questions Q2(b) - Page 13 Lakhmir Singh
Question
Fill in the blank: ________ helps us to discover things in the universe and how things work.
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Science
Explanation
Science helps us understand the universe and how things work.
Q 4
Objective Type Questions Q2(c) - Page 13 Lakhmir Singh
Question
Fill in the blank: ________ discovered incandescent lamp.
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Thomas Edison
Explanation
Edison invented the incandescent lamp, building on earlier arc lamp ideas.
Q 5
Objective Type Questions Q2(e) - Page 13 Lakhmir Singh
Question
Fill in the blank: ________ has helped in the eradication of many diseases.
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Vaccine (vaccination)
Explanation
The discovery of vaccines helped eradicate deadly diseases like polio and smallpox.

The Invisible World and the Cell
Tiny living things are around us
They live in air, water and soil
We need a microscope to see them
These are called microorganisms
The cell is the basic unit of life
Example 1 — Useful and harmful microbes
Lactobacillus turns milk to curd
yeast helps make cakes
bread mould spoils bread
Example 2 — Building block of life
all living things are made of cells
a cell is the basic structural unit
and the functional unit of life
Important Points
Bacteria, fungi, virus and protozoa are some examples of microbes.
Some microorganisms are useful and some are harmful.
Science covers both the macroscopic and the microscopic world.
Definition — Microorganisms
Microorganisms means the tiny living things, found in air, water and soil, that we cannot see with the naked eye.
Electricity, Force and Pressure
Electricity has heating and magnetic effects
Heating effect lights bulbs and heaters
Magnetic effect runs motors and MRI
Force explains why objects move or stop
Pressure tells how force spreads over an area
Example 1 — Effects of electricity
heating effect boils water in a kettle
magnetic effect rings an electric bell
also powers a loudspeaker
Example 2 — Force in action
a ball stops rolling after a while
a thrown ball comes back down
force changes an object's shape
Important Points
The magnetic effect of current is used to create the magnetic field for MRI machines and to separate scrap metals.
Pressure helps explain atmospheric pressure, how wind blows and how cyclones form.
Knowledge of water pressure helps in designing dams.
Definition — Pressure
Pressure means how a force is distributed over an area.
Matter, Light and the Sky
Matter exists as solid, liquid and gas
It can be a pure substance or a mixture
Light is a form of energy to see things
Light reflects off mirrors and surfaces
Reflected light lets us see the Moon
Example 1 — Pure substance and mixture
air we breathe is a mixture
water we drink is a compound
iron sinks but a ship floats
Example 2 — Light and the sky
a magnifying glass makes things bigger
we see different parts of the Moon
this led to making calendars
Important Points
Most things around us are mixtures of pure substances like elements and compounds.
Aryabhata, a famous mathematician and astronomer, explained the occurrence of eclipses.
Aryabhata stated that the westward movement of the Sun and stars is due to the Earth's rotation on its axis.
Definition — Cell
A cell means the basic structural and functional unit of all living beings.
Q 1
Objective Type Questions Q1(a) - Page 13 Lakhmir Singh
Question
Name the following: It occupies a very large volume and on expansion produces pressure.
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Steam (gas)
Explanation
Steam occupies a larger volume and creates pressure on expansion, the idea behind the steam engine.
Q 2
Objective Type Questions Q1(b) - Page 13 Lakhmir Singh
Question
Name the following: The tiny creatures which are not visible to the naked eye.
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Microorganisms (microbes)
Explanation
Microorganisms are so small that we need a microscope to see them.
Q 3
Objective Type Questions Q1(c) - Page 13 Lakhmir Singh
Question
Name the following: The loudspeaker and doorbell work on this principle.
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Magnetic effect of electric current
Explanation
The magnetic effect of current is used in loudspeakers and electric doorbells.
Q 4
Objective Type Questions Q1(d) - Page 13 Lakhmir Singh
Question
Name the following: The different states of matter.
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Solid, liquid and gas
Explanation
Matter exists in three states — solid, liquid and gas.
Q 5
Objective Type Questions Q2(d) - Page 13 Lakhmir Singh
Question
Fill in the blank: A ________ is the basic structural and functional unit of life.
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cell
Explanation
All living things are made of cells, the basic unit of life.
Q 6
Objective Type Questions Q3(a) - Page 14 Lakhmir Singh
Question
State whether true or false: The fungus, bread mould curdles milk.
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False
Explanation
Bread mould spoils bread; milk is curdled into curd by Lactobacillus bacteria.
Q 7
Objective Type Questions Q3(b) - Page 14 Lakhmir Singh
Question
State whether true or false: Force helps to move or stop an object.
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True
Explanation
A force can move a stationary object and stop a moving one.
Q 8
Objective Type Questions Q3(c) - Page 14 Lakhmir Singh
Question
State whether true or false: We can see objects because they disperse light.
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False
Explanation
We see objects because they reflect light into our eyes, not because they disperse it.
Q 9
Objective Type Questions Q3(d) - Page 14 Lakhmir Singh
Question
State whether true or false: The Earth rotates on its own axis.
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True
Explanation
Aryabhata stated that the apparent westward movement of the Sun and stars is due to the Earth's rotation on its axis.
Q 10
Multiple Choice Questions Q1 - Page 14 Lakhmir Singh
Question
Which among the following states of matter occupy a greater volume?
(a) steam
(b) ice
(c) water
(d) snow
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(a) steam
Explanation
Steam is a gas, which occupies a much larger volume than ice, water or snow.
Q 11
Multiple Choice Questions Q2 - Page 14 Lakhmir Singh
Question
The organism Lactobacillus is a:
(a) virus
(b) protozoa
(c) bacteria
(d) fungi
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(c) bacteria
Explanation
Lactobacillus is a bacteria that helps convert milk into curd.
Q 12
Multiple Choice Questions Q3 - Page 14 Lakhmir Singh
Question
The heating effect of current is used to:
(a) ring a doorbell
(b) light bulbs
(c) run MRI machine
(d) power electric motor
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(b) light bulbs
Explanation
Light bulbs work on the heating effect; the others use the magnetic effect of current.
Q 13
Multiple Choice Questions Q4 - Page 14 Lakhmir Singh
Question
It sinks in water.
(a) iceberg
(b) ship
(c) brick
(d) piece of wood
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(c) brick
Explanation
A brick is heavier than the water it displaces, so it sinks; the others float.
Q 14
Multiple Choice Questions Q5 - Page 14 Lakhmir Singh
Question
The Indian astronomer who explained eclipses:
(a) Aryabhata
(b) Acharya Jagadish Chandra Bose
(c) Varahamihira
(d) Megnad Saha
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(a) Aryabhata
Explanation
Aryabhata, a famous mathematician and astronomer, explained the occurrence of eclipses.

Thinking Like a Scientist
Anyone can be a little scientist
All it takes is curiosity
Ask why, how and what
Use observation and experiments
Draw conclusions based on evidence
Example 1 — Mita's question
plants near the window grew taller
she wondered if sunlight mattered
so she designed an experiment
Example 2 — Mita's conclusion
sunny plant grew tall and green
dim-light plant stayed short and pale
sunlight helps plants make food
Important Points
Mita kept water, room and air conditions the same so only light differed.
By asking a question, experimenting, observing and concluding, Mita thought like a scientist.
Scientific thinking helps us solve problems and decide based on evidence, not guesses.
Definition — Scientific Thinking
Scientific thinking means investigating the world through a systematic approach and making decisions based on evidence rather than guesses.
Our Home — The Planet Earth
Earth is the planet where life exists
Liquid water supports life here
The ozone layer and gravity help too
Such factors make a planet habitable
Human activity harms nature's balance
Example 1 — Factors for life
presence of liquid water
an ozone layer for protection
gravity to hold the atmosphere
Example 2 — Harm to nature
rising sea levels and flooding
loss of biodiversity
severe pollution causing diseases
Important Points
Some factors decide if a planet is habitable or not.
Microorganisms like fungi and bacteria help remove waste from nature.
Human activities interfere with nature's balance, seen in rising seas and pollution.
Definition — Habitable Planet
A habitable planet means a planet, like the Earth, where factors such as liquid water, an ozone layer and gravity allow life to exist.
Q 1
Objective Type Questions Q3(e) - Page 14 Lakhmir Singh
Question
State whether true or false: Rising water level can flood the low-lying areas.
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True
Explanation
Rising sea levels, caused by human activity, can flood low-lying areas.