Science as a way of thinking
A child sees steam rising from a hot cup of tea and asks, "Where does it come from?" That one question is where every science lesson begins.
Science is a never-ending process of asking questions, observing, experimenting and learning from the patterns of nature. It welcomes curiosity and stays open to the unknown. It is much more than a list of facts to memorise.
In the figure : Science works like a cycle: every answer can lead to a fresh question.
Rule 1: Science is a process, not just facts — Facts are the result; asking, testing and thinking are the way we reach them.
- Easy : Asking why a leaf is green starts a scientific enquiry.
- Medium : A fact learnt without any question behind it is memorised, not understood.
- Exam-type : An experiment that proves your guess right can still raise a new question.
Rule 2: Science looks for patterns — Careful observation of events that repeat helps us find rules of nature.
- Easy : Noticing that the Sun rises every day lets us expect it tomorrow.
- Medium : Seeing that ice melts every time it is warmed is finding a pattern.
- Exam-type : A pattern lets us predict, but the prediction must still be tested.
Science = questions + observation + experiments + thinking. Every answer can open a new question.
Thinking that science is only facts in a book. It is mainly a way of finding things out.
Memory clue: Q-O-E-T — Question, Observe, Experiment, Think, then repeat!
Spot the difference
| Idea | Meaning | Example |
|---|---|---|
| Curiosity | Wish to know more | Asking why the sky is blue |
| Observation | Looking carefully | Noting the shape of a leaf |
| Experiment | Testing an idea | Warming ice to see what happens |
Practice questions
- 1What is science?
- 2What does curiosity mean?
- 3Name two things a scientist does.
- 4Why is science called a process?
- 5How is a pattern useful to a scientist?
- 6Why should a prediction still be tested?
- 7A student only memorises definitions and never asks questions. Is she thinking like a scientist? Explain.
- 8Give one example of how an answer can lead to a new question.
Show answers (try them yourself first)
- 1A continuing process of asking questions, observing and experimenting to understand nature.
- 2A strong wish to know and understand things.
- 3Ask questions, observe, experiment (any two).
- 4Because it never ends; each finding leads to new questions and new tests.
- 5It helps to predict what may happen next.
- 6A prediction may be wrong; only a test can show whether it is right.
- 7No. A scientist asks questions and tests ideas instead of only memorising.
- 8Finding that plants need light may lead to asking how much light they need.
Asking good questions and exploring
When a cake does not rise, a baker does not just give up. She asks, "What did I change this time?" and tries again. A good question points to something we can find out.
A good question is clear, interesting and can be explored by observing or testing. A hypothesis is an idea or guess that can be tested. A fair test changes only one thing at a time. Results are recorded and a conclusion is drawn from them.
In the figure : A careful investigation goes from question to conclusion in steps.
Rule 1: Ask questions that can be explored — Questions that start with how, why and what happens if lead to experiments; some questions only ask for opinions.
- Easy : "Does a seed sprout faster in warm water?" can be tested.
- Medium : "Which flower looks prettiest?" is an opinion and cannot be tested.
- Exam-type : Turning a bare answer into a question shows that one answer can fit many questions.
Rule 2: Test fairly and record — Change only one thing at a time and keep everything else the same, then note down what you see.
- Easy : To test the effect of sunlight, give two plants the same water but different light.
- Medium : If water and light are both changed, you cannot tell which one caused the result.
- Exam-type : A table of observations makes the pattern in results easy to see.
Good question, clear guess, fair test, careful record, honest conclusion.
Changing many things together in one test. Then nobody knows what caused the result.
Memory clue: G-H-F-C — Good question, Hypothesis, Fair test, Conclusion.
Spot the difference
| Term | Meaning | Example |
|---|---|---|
| Observation | What we see or measure | The plant grew 3 cm |
| Hypothesis | A guess that can be tested | Plants grow better in light |
| Conclusion | What the results tell us | Light helped the plants grow |
Practice questions
- 1What is a hypothesis?
- 2What is a fair test?
- 3Why should results be recorded?
- 4Give an example of a question that can be tested.
- 5Why is "Which song is nicest?" not a scientific question?
- 6What happens if you change two things in one test?
- 7Make a fair test plan to find whether salt dissolves faster in hot water.
- 8Turn the answer "because it was cold" into two different questions.
Show answers (try them yourself first)
- 1An idea or guess that can be tested.
- 2A test in which only one thing is changed and all others stay the same.
- 3So that we can study the pattern and compare results later.
- 4Does a seed sprout faster in warm water?
- 5It is an opinion, so it cannot be tested.
- 6We cannot tell which change caused the result.
- 7Take two glasses with equal salt and equal water; use hot water in one and cold in the other; compare the time to dissolve.
- 8Why did the ice not melt? Why did we wear sweaters today?
Materials and their properties
Why is a lemon sour but a sugar cube sweet? Why does a spoon feel cold while a woollen cap feels warm? The answer lies in the properties of materials.
A property is a feature that helps us tell materials apart, such as taste, shine, hardness or whether electric current passes through. We study materials by testing their properties, and we sort them into groups like acidic, basic and neutral, conductors and insulators, and metals and non-metals.
In the figure : Different properties give different ways of sorting the same materials.
Rule 1: Properties help us sort materials — Testing one property at a time divides materials into groups.
- Easy : Lemon juice and vinegar are sour, so we say they are acidic.
- Medium : A metal spoon lets electric current pass; a rubber band does not.
- Exam-type : A property decides the use: copper for wires, plastic for covering them.
Rule 2: Many tests, many groups — The same object can belong to different groups under different tests.
- Easy : Iron is a metal and also a conductor of electricity.
- Medium : Sugar solution is neutral and also tastes sweet.
- Exam-type : Always choose the test that answers the question you are asking.
One property, one test, one grouping. The same material can be in many groups.
Thinking one property tells everything. A bitter taste does not always mean a base.
Memory clue: S-C-M — Sour-acid, Current-conductor, Metal-shiny.
Spot the difference
| Group | Test | Example |
|---|---|---|
| Acidic | Turns blue litmus red | Lemon juice |
| Conductor | Lets current pass | Copper wire |
| Metal | Shiny and malleable | Aluminium foil |
Practice questions
- 1What is a property of a material?
- 2Name one sour material.
- 3Give one conductor and one insulator.
- 4Why can one object be in more than one group?
- 5How is a sour taste related to acids?
- 6Why is plastic used to cover electric wires?
- 7A material is shiny, bends into sheets and carries current. Which group does it probably belong to?
- 8Why should we not taste unknown substances while testing?
Show answers (try them yourself first)
- 1A feature that helps tell materials apart.
- 2Lemon juice (or vinegar, tamarind water).
- 3Conductor: copper wire; insulator: rubber.
- 4Different tests look at different properties.
- 5Sour tasting substances usually contain acids.
- 6Plastic is an insulator, so it stops current passing to us.
- 7Metals.
- 8Some substances are harmful or poisonous.
Changes, heat and the water cycle
A scoop of ice cream melts in your hand, a pencil gets shorter when sharpened, and a banana turns yellow as it ripens. Some changes can be undone, and some cannot.
Changes in things around us can be reversible (can be undone, like ice melting to water and freezing again) or irreversible (cannot be undone, like a ripened fruit). Heat flows from a hotter object to a colder one. In nature, the Sun's heat evaporates water, clouds form, rain falls and some water seeps underground. This is the water cycle.
In the figure : Heat from the Sun keeps the water cycle going.
Rule 1: Changes can be reversible or not — Ask: can I get back the original thing?
- Easy : Melted wax can be solid again when it cools.
- Medium : A burnt match cannot become a fresh match.
- Exam-type : A change that forms a new substance is usually hard to reverse.
Rule 2: Heat moves from hot to cold — A hot object gives heat to a cold object until both have the same temperature.
- Easy : A hot spoon placed in cold water cools down.
- Medium : An ice cube melts in a warm room because it takes heat from the surroundings.
- Exam-type : In the water cycle, heat from the Sun makes sea water change to vapour.
Hot to cold is the way of heat. The Sun's heat drives the water cycle.
Thinking that cold flows into a hot object. In fact, heat flows out of the hot object.
Memory clue: E-C-R-S — Evaporate, Cloud, Rain, Seep.
Spot the difference
| Change | Reversible? | Example |
|---|---|---|
| Melting ice | Yes | Water freezes again |
| Ripening fruit | No | A ripe fruit cannot become raw |
| Rain falling | Part of a cycle | Water returns later by evaporation |
Practice questions
- 1What is a reversible change?
- 2Give one irreversible change.
- 3In which direction does heat flow?
- 4What does the Sun do in the water cycle?
- 5What happens to some of the rain water on land?
- 6Why does an ice cube melt faster in a warm room?
- 7A glass of cold juice becomes warm on the table. Explain using heat flow.
- 8Write the order of the water cycle in four steps.
Show answers (try them yourself first)
- 1A change that can be undone.
- 2Ripening of fruit (or burning of paper).
- 3From a hot object to a cold object.
- 4Its heat makes water evaporate from seas and rivers.
- 5Some of it trickles into the ground.
- 6The room is warmer, so more heat flows into the ice.
- 7Heat flows from the warm air to the cold juice until both have the same temperature.
- 8Evaporation, cloud formation, rain, seeping underground or flowing in rivers.
Living things and life processes
A baby grows into a child, and a seedling grows into a tree. Both need food and air, and both change with time. These common needs are called life processes.
All living things carry out life processes such as taking food, breathing, growing, responding to surroundings and reproducing. In animals, food is broken down and the nutrients are carried to all parts of the body by blood. Plants make their own food using sunlight and also respire. Our bodies change rapidly in the middle-school years.
In the figure : Plants and animals both need food and air, but they get food differently.
Rule 1: Animals and plants both need food and air — Living things use food for energy and growth and use oxygen from air.
- Easy : A dog eats food and breathes air.
- Medium : A plant also takes in air and gives out some gases while living.
- Exam-type : Animals get ready-made food, but green plants make their own food.
Rule 2: Blood moves nutrients around — After digestion, the blood carries food material to every part of the body.
- Easy : The heart pumps blood through the body.
- Medium : Cells everywhere get nutrients because blood reaches them.
- Exam-type : Without circulation, only the cells near the gut would get food.
Every living thing eats, breathes, grows and reproduces. Plants make their own food; animals take food.
Believing that plants do not breathe. They do, but they also make their own food.
Memory clue: E-B-G-R — Eat, Breathe, Grow, Reproduce.
Spot the difference
| Living thing | How it gets food | Example |
|---|---|---|
| Animal | Eats ready-made food | Cow eating grass |
| Green plant | Makes food using sunlight | Mango tree |
| Human | Eats food, blood carries nutrients | A child eating roti |
Practice questions
- 1Name four life processes.
- 2How does food reach all parts of the body?
- 3How do green plants get food?
- 4Do plants breathe?
- 5Why do we need to eat?
- 6What changes do you notice in your body as you grow?
- 7Why can green plants make their own food but animals cannot?
- 8Give two ways in which plants and animals are alike.
Show answers (try them yourself first)
- 1Taking food, breathing, growing, reproducing.
- 2Blood carries digested food to all parts.
- 3By making it using sunlight.
- 4Yes, they take in and give out gases.
- 5Food gives energy and helps us grow.
- 6We become taller and our body shape changes.
- 7Green plants have chlorophyll and use sunlight; animals do not.
- 8Both need food and air, and both grow and reproduce.
Time, light and shadows
Long before clocks, people watched how a stick's shadow moved across the ground and knew whether it was morning or noon. Light and shadows told them the time.
A shadow forms when an object blocks light. The shadow's length and direction change as the Sun moves across the sky, so it can show the time of day (a shadow clock or sundial). Light helps us see things, and studying light has taught us a great deal about the universe. We measure time with clocks, and how fast something happens is its speed.
In the figure : A shadow changes length and direction as the Sun moves.
Rule 1: Shadows need light and an object — A shadow forms on the side opposite to the light source.
- Easy : Your shadow falls behind you when the Sun is in front of you.
- Medium : Moving a torch closer to a book makes the book's shadow larger.
- Exam-type : Shadows are used in puppet shows because they show the outline of the object.
Rule 2: Shadow tells the time — Long shadows appear in the morning and evening, and the shortest one near noon.
- Easy : Early morning shadows are long.
- Medium : At noon the shadow of a pole is the shortest.
- Exam-type : A sundial reads time from the direction of the shadow's tip.
Light + blocking object = shadow. Shadows are longest morning and evening, shortest at noon.
Thinking a shadow is a reflection or a colour. It is only an area without direct light.
Memory clue: M-N-E — Morning long, Noon short, Evening long.
Spot the difference
| Time of day | Shadow length | Direction |
|---|---|---|
| Morning | Long | Towards the west |
| Noon | Shortest | Near the object |
| Evening | Long | Towards the east |
Practice questions
- 1What is a shadow?
- 2When is a shadow shortest?
- 3Why are shadows long in the evening?
- 4What is a shadow clock?
- 5Why can't light pass through an opaque object?
- 6Why do early humans' shadow clocks work only in the daytime?
- 7A stick's shadow is 1 m long at 8 a.m. and 20 cm long at noon. Explain the change.
- 8Name two uses of light in daily life.
Show answers (try them yourself first)
- 1A dark area formed when an object blocks light.
- 2Around noon.
- 3The Sun is low in the sky, so the shadow stretches.
- 4A device that tells time from the shadow of a stick.
- 5Opaque materials block light.
- 6They need sunlight to cast a shadow.
- 7The Sun is low in the morning (longer shadow) and high at noon (shorter shadow).
- 8To see things and for lighting and photographs.
The Earth, Moon and Sun
You wake up in bright daylight while a friend on the other side of the Earth is going to sleep. The Earth keeps turning, so someone is always having day and someone night.
The Earth rotates on its own axis once in about 24 hours, causing day and night. The Moon revolves around the Earth, and the Earth revolves around the Sun, taking about a year. When the Moon comes between the Sun and Earth, a solar eclipse may occur; when Earth comes between the Sun and Moon, a lunar eclipse may occur.
In the figure : Three motions explain day and night, the year and eclipses.
Rule 1: Rotation gives day and night — The side of the Earth facing the Sun has day; the other side has night.
- Easy : Earth completes one rotation in about one day.
- Medium : Sunrise happens where the Earth turns into the Sun's light.
- Exam-type : The Sun does not move around the Earth; the Earth's rotation makes it appear to.
Rule 2: Eclipses are shadows of Earth and Moon — Alignment of the Sun, Moon and Earth casts shadows.
- Easy : A solar eclipse is seen when the Moon blocks the Sun.
- Medium : A lunar eclipse is seen when Earth's shadow falls on the Moon.
- Exam-type : Eclipses are rare because the three bodies must be in a line.
Rotation = day and night. Revolution of the Earth = year. Moon in front of Sun = solar eclipse.
Believing the Sun goes around the Earth. The Earth's rotation makes the Sun seem to move.
Memory clue: R-D-R-Y — Rotation Day-night, Revolution Year.
Spot the difference
| Motion | Who moves | Result |
|---|---|---|
| Rotation | Earth on its axis | Day and night |
| Revolution | Earth around Sun | One year |
| Revolution | Moon around Earth | Phases and eclipses |
Practice questions
- 1What is rotation?
- 2What is revolution?
- 3How long does the Earth take to rotate once?
- 4What causes day and night?
- 5When does a solar eclipse occur?
- 6When does a lunar eclipse occur?
- 7Why do we not see an eclipse every month?
- 8Why does the Sun seem to move across the sky?
Show answers (try them yourself first)
- 1Spinning of a body on its own axis.
- 2Movement of one body around another.
- 3About 24 hours.
- 4Rotation of the Earth.
- 5When the Moon comes between the Sun and the Earth.
- 6When the Earth comes between the Sun and the Moon.
- 7The three bodies must be in a line, which does not happen every month.
- 8Because the Earth rotates.
Science, society and sustainability
A town throws a lot of plastic into a river, and fish begin to disappear. People use more water than the rain refills, and wells dry up. What we do changes what happens in nature.
Human activities are linked to events in the natural world and to the society we live in. Science helps us understand these links and offers ways to solve problems such as pollution. Sustainability means meeting our needs in a way that does not harm the environment for the future.
In the figure : Science and responsible action together protect the environment.
Rule 1: Our actions affect nature — Cutting trees, burning fuel and dumping waste change the air, water and soil.
- Easy : Dumping waste in a river harms fish.
- Medium : Burning too much fuel adds smoke to the air.
- Exam-type : Neutralising acidic factory waste before release can protect a lake.
Rule 2: Science can help us act responsibly — Understanding causes lets us choose better ways.
- Easy : Using a cloth bag instead of a plastic bag reduces waste.
- Medium : Solar panels use sunlight instead of burning fuel.
- Exam-type : Scientists measure water quality to decide how to treat it.
Science gives understanding; responsibility gives action. Reduce, reuse, recycle.
Thinking one person's small actions do not matter. Many small actions together make a big difference.
Memory clue: R-R-R — Reduce, Reuse, Recycle.
Spot the difference
| Action | Effect | Better choice |
|---|---|---|
| Dumping waste | Pollutes water | Treat waste first |
| Using plastic bags | Adds waste | Use cloth bags |
| Burning fuel | Pollutes air | Use clean energy |
Practice questions
- 1What is sustainability?
- 2Give two ways humans affect nature.
- 3What does "reduce" mean?
- 4How can science help solve pollution?
- 5Why should factory waste be treated before release?
- 6Name two things you can reuse.
- 7Explain how saving water at home helps the environment.
- 8Why is it called responsibility, not just discovery, in science?
Show answers (try them yourself first)
- 1Meeting our needs without harming the environment for the future.
- 2Cutting trees and dumping waste (or burning fuel).
- 3To use less of something.
- 4By finding causes and ways to clean or prevent it.
- 5Harmful waste can kill living things in lakes and rivers.
- 6Jars, cloth bags, old bottles (any two).
- 7Less water is taken from rivers and wells, so more remains for nature.
- 8Because discoveries can affect people and the planet, so we must use them wisely.