Overview
This opening chapter sets the tone for Grade 8 Science. In earlier years you learnt that science begins with wonder and that it keeps changing as new answers raise new questions. This year the focus is on investigation: learning how new facts are found, not only what the facts are. The chapter explains the two symbols printed on the pages of the textbook, the root and the kite, which stand for the solid ground of careful observation and the freedom of curiosity and imagination. It then walks through a real investigation from the kitchen: why a puri puffs up in hot oil and why one side is thinner than the other. Through this example you learn to ask a scientific question, to list what can be changed and what can be observed or measured, and to run a fair test by changing only one thing at a time. You also learn to repeat trials, record observations honestly in a table, find patterns and use them to ask the next question. Finally, the chapter gives a map of the year, from microbes and health to electricity, forces, weather, particles, light, the sky and our planet, showing how each topic links to the next.
हिंदी में पढ़ें
यह आरंभिक अध्याय सिखाता है कि वैज्ञानिक की तरह कैसे सोचें और काम करें: स्पष्ट प्रश्न पूछें, उचित परीक्षण की योजना बनाएँ, ईमानदारी से प्रेक्षण लिखें और हर उत्तर से अगला प्रश्न निकालें।
Learning Objectives
- Explain how investigation builds on wonder and on the changing nature of science
- Explain the root and kite symbols and why science needs both observation and imagination
- Frame focused, testable scientific questions from everyday observations
- Identify what is changed, what is observed or measured, and what is kept the same in an experiment
- Plan a fair test that changes only one factor at a time
- Repeat trials and find the average of simple readings
- Record observations honestly in a table and use patterns to ask new questions
- Describe the main areas of Grade 8 Science and how they are linked
Topics in this chapter
7 topics · tap a topic title to jump straight to it.
From wonder to investigation
1Think first
2The idea, in plain words
Think back to the questions that first made you curious about science. Why do leaves come in so many shapes? Why does milk turn into curd? In Grade 6, science began with exactly this kind of wonder: simple “why?” and “how?” questions about the world around you.
In Grade 7 you met a second idea: science keeps changing and growing. Every answer opens up new questions, and ideas that people once believed are slowly improved as they look more closely. Science is not a finished book of facts. It is a living activity.
Grade 8 takes the next step. This year the aim is not only to learn new facts but to learn how new facts are found. That is what we mean by investigation. An investigation is more than looking at something and asking a general question. It means:
- asking a focused question that can actually be tested,
- planning a simple experiment or a careful set of observations to answer it,
- recording what you see, honestly and carefully,
- using the results to improve your understanding, and then asking the next question.
Here is the difference in practice. “Why is the sky so interesting?” is a wonderful thought, but it is hard to test. “Does a wet cloth dry faster in the sun or in the shade?” is a focused question. You can hang two identical wet cloths, one in each place, and check them every fifteen minutes. The answer comes from your own observations, not from guessing.
Investigation also does not need a fancy laboratory. A kitchen, a garden, a balcony or a school ground is full of things to investigate. What you need is curiosity, patience, careful eyes, and the habit of asking “what happens if…?”.
Once you start thinking like an investigator, you stop being only a learner who receives answers. You become a young scientist who can find answers, check them, and share them with others.
3Worked example
- A general wonder: “Why is nature so varied?” A focused question: “Do seeds sprout faster in warm or in cold water?”
- Checking two identical wet cloths, one in sun and one in shade, every 15 minutes is a simple investigation.
- Asking “what happens if I add more yeast to the dough?” turns a kitchen into a place for experiments.
4Your turn
Which of these is a focused, testable question?
5Remember this
The root and the kite: observation and imagination
1Think first
2The idea, in plain words
The Curiosity textbook carries two small symbols on its pages. On the left-hand pages, at the bottom, there is a root. On the right-hand pages, at the top, there is a kite. They are there for a reason, and the reason is a lesson about how science works.
A root holds a plant firmly in the ground and draws water and nutrients from the soil. In science, the root stands for a solid foundation: careful observations, real measurements, what we already know, and our links with our environment, traditions and natural heritage. A scientist who ignores observations is like a plant without roots. Any wind of rumour can blow such an idea over.
A kite rises high and lets us see further. In science, the kite stands for curiosity and imagination: asking bold questions, guessing possible explanations, and thinking of new experiments. Without imagination, science would never move into the unknown.
Good investigation needs both at once.
| Root (stay grounded) | Kite (let ideas fly) | |
| What it means | Careful observation and measurement | Curiosity and creative thinking |
| Question it asks | What do I actually see? | What could explain it? What if…? |
| Danger if missing | Wild ideas never checked | Nothing new is ever discovered |
Look at an example. You notice that a puri puffs up in hot oil. The kite side of you guesses: “maybe steam forms inside the dough and pushes the layers apart”. The root side of you asks: “how can I check that? Does a puri with a hole pricked in it still puff?” The guess gives direction; the observation decides whether the guess survives.
The textbook also hides small patterns in the lines at the bottom of its pages. They are a reminder that science can be playful. Noticing small details, even on a page, is the first habit of a scientist.
Keep this pair in mind for the whole year: keep your feet on the ground of evidence, and let your ideas soar.
3Worked example
- Root: measuring how long a puri takes to puff, in seconds.
- Kite: guessing that trapped steam makes the puri swell.
- Using both: testing the steam idea by pricking a hole in the dough before frying.
4Your turn
In the root-and-kite idea, what does the kite stand for?
5Remember this
Asking a scientific question
1Think first
2The idea, in plain words
Every investigation starts with a question. But not every question can start an investigation. A scientific question is one that can be answered by observing, measuring or experimenting.
Take a question from the textbook’s first page: why is one side of a puri thinner than the other? As it stands, the question asks for a reason, and the reason is not easy to see directly. A scientist turns it into smaller questions that can be tested. One useful way is to ask: what are the different things that might change the way a puri puffs up?
A good scientific question usually has these features:
- It is about something you can observe or measure (puffing, time, height, colour, temperature).
- It points to something you can change (the oil temperature, the thickness of the dough).
- It is narrow enough to answer in a few trials, not a lifetime.
- It does not depend only on opinion, such as “which puri looks nicest?”.
Compare these pairs:
| Hard to test | Testable |
| Why does food cook? | Does rice cook faster with the lid on or off? |
| Why are puris tasty? | Does a thinner circle of dough puff up faster in hot oil? |
| Is the world getting warmer? | Has the average June temperature in our town changed over the last 30 years? (using weather records) |
Notice the last row. Some big questions, like whether the world is getting warmer, cannot be tested in a kitchen. Scientists still investigate them, by collecting careful measurements over many years and comparing them. So a scientific question does not always need an experiment; sometimes it needs systematic observation and records.
Asking a good question is a skill. With practice you will find that a sharp question makes the rest of the investigation much easier, because it tells you exactly what to change and what to watch.
3Worked example
- General: “Why does dough rise?” Testable: “Does dough with yeast rise more in a warm place than in a cold place?”
- General: “Why is the Moon’s shape different?” Testable: “How does the lit part of the Moon change, night by night, over two weeks?” (observation)
- Opinion, not testable: “Which flower is the prettiest?”
4Your turn
Which question can be answered by observation over time rather than by a kitchen experiment?
5Remember this
What we change and what we observe
1Think first
2The idea, in plain words
Once you have a question, the next step is to sort out two lists. The textbook puts it simply: what can we change or control in the experiment, and what can we observe to see whether the changes made any difference?
For the puri, the list of things we can change is long:
- the thickness and the size of the rolled circle of dough,
- the type of flour (atta, maida and so on),
- the temperature of the oil,
- the way the dough enters the oil: dropped straight down, slid in at an angle, or slid in slowly,
- whether the dough is fresh or stored, or has a hole pricked in it.
The things we can observe or measure are of two kinds. Some give a yes/no answer: did the puri puff up or not? Others give a number: how many seconds did it take to puff? How thick is the thinner side, in millimetres? Number answers let us compare results more exactly, but yes/no answers are also useful.
Scientists give these a name. The thing you choose to change is the changed factor (often called the independent variable). The thing you watch or measure is the observed factor (the dependent variable), because its value may depend on what you changed. All the other things that could affect the result, and that you keep the same, are the controlled factors.
| Investigation | Change | Observe / measure | Keep the same |
| Puri and oil heat | Oil temperature | Puffed? Time to puff (s) | Dough thickness, size, flour, how it is dropped |
| Drying clothes | Sun or shade | Time to dry (min) | Cloth, amount of water, wind |
| Sugar in water | Water temperature | Time to dissolve (s) | Amount of sugar and water, stirring |
Writing these three lists before you begin is like planning a journey before you set off. It keeps the experiment clear and makes the result easy to explain.
3Worked example
- Changed: oil temperature. Observed: whether the puri puffs. Kept the same: dough thickness.
- A yes/no observation: did the puri puff? A number observation: it took 6 seconds to puff.
- Changed: amount of water given to a plant. Observed: height after 10 days. Kept the same: pot, soil, sunlight, type of seed.
4Your turn
In an experiment on whether stirring helps salt dissolve, which is the observed (measured) factor?
5Remember this
A fair test: change one thing at a time
1Think first
2The idea, in plain words
Suppose Arjun fries two puris. The first is thin and goes into very hot oil. The second is thick and goes into oil that is only warm. The first puffs up quickly and the second does not. Can Arjun say the oil temperature made the difference? No. The thickness was different too, so he cannot tell which change caused the result.
This is why scientists run a fair test: change only one thing at a time, and keep every other condition the same. If you want to study the effect of the oil, you might use three pans: one with very hot oil, one with hot oil, and one with oil that is not very hot. Into each you drop circles of dough of the same thickness and size, made from the same dough, and dropped in the same way. Now if the results differ, the oil temperature is the only possible reason.
Two more habits make a fair test trustworthy:
- Repeat the trial. One puri may behave oddly by chance. Frying three puris for each oil and comparing them gives a more reliable answer. If the times are 42 s, 46 s and 44 s, the average is (42 + 46 + 44) ÷ 3 = 132 ÷ 3 = 44 s.
- Keep the conditions honest. Use the same pan size, the same amount of oil and the same person rolling the dough if possible.
Some things are hard to keep exactly the same. The oil cools a little each time a cold puri goes in, and no two rolled circles are perfectly alike. Scientists accept this and try to keep such differences small, and they mention them when they report the results.
Fair testing is not only for the kitchen. Doctors testing a medicine, farmers testing a fertiliser, and engineers testing a material all follow the same rule. It is one of the most important ideas in all of science.
Safety note: hot oil can cause serious burns. Any frying experiment must be done only by, or with, an adult, keeping your face and hands away from the pan.
- Average of repeated readings = sum of readings ÷ number of readings
3Worked example
- Fair: same dough thickness in three pans of oil at different temperatures.
- Unfair: a thin puri in hot oil compared with a thick puri in warm oil.
- Repeating: three trials of 42 s, 46 s and 44 s give an average of 44 s.
4Your turn
Sahil wants to test whether type of flour affects puffing. Which plan is a fair test?
5Remember this
Observing, recording and asking the next question
1Think first
2The idea, in plain words
An experiment is only as good as its records. While doing an investigation, a scientist writes down everything that is seen and sensed, not only the result that was expected. During frying, for example: did the oil splatter? Was there a smell? Did it smoke? How did the colour of the puri change? Such notes often explain surprises later.
A neat way to record is a table, made before the experiment starts:
| Oil | Trial | Puffed? (yes/no) | Time to puff (s) | Other notes |
| Very hot | 1 | |||
| Very hot | 2 | |||
| Hot | 1 | |||
| Not very hot | 1 |
Write the reading at once, as you see it. Do not wait until the end and fill it from memory, and never change a reading because it “looks wrong”. An unexpected reading is still a real result; repeat the trial to check it.
After the first round of experiments, look at your table and ask: what pattern do I see? Perhaps every puri in very hot oil puffed, and none in not-very-hot oil. That is a finding. Now try to explain it, using what you already know. Then something important happens: new questions appear.
- Do puris puff better when the dough is fresh or when it has been stored?
- What happens if I prick a hole in the dough before frying it?
- Does a phulka on an open flame puff for the same reason?
Each new question can start a new round of investigation. This loop of question → plan → test → record → explain → new question is called systematic investigation. It is how simple and very complicated experiments alike are done.
Here is a surprising fact the textbook shares: even the everyday puffing of a puri is not completely understood by scientists today. So there is still room for new investigators, perhaps you, to add to what we know.
3Worked example
- Notes during frying: oil splattered, smelled of wheat, puri turned golden in about a minute.
- A table prepared before the experiment, with columns for each trial.
- A new question after the first round: does pricking a hole stop the puri from puffing?
4Your turn
One reading in Rohan’s table is very different from the others. What should he do?
5Remember this
The journey ahead in Grade 8
1Think first
2The idea, in plain words
The opening chapter of Curiosity also gives a map of the year. Notice how each stop leads naturally to the next, and how the same investigative skills are used all the way through.
| Stop | Big question |
| Tiny living things | What lives in a single drop of water? Which microbes help us, and which make us ill? |
| Health | How do food, exercise, medicines and vaccines keep us healthy and help fight infections? |
| Electricity | How do the heating and magnetic effects of current warm us and run machines? |
| Forces | Why does a ball fall back down? Why does a car stop when brakes are applied? |
| Pressure and weather | How do small or large pressure differences make breezes, strong winds and cyclones? |
| Particles | What are materials made of, and why can particles in a gas move freely but not in a solid? |
| Elements, compounds, mixtures, solutions | How do particles combine or mix? How does sugar dissolve in tea? |
| Light | How do mirrors and lenses reflect and bend light? How do glasses help us see? |
| The sky and time | Why does the Moon show phases, and how did they give us calendars? |
| Nature’s balance | How do living things depend on air, water, sunlight and one another? |
| Our Earth | What makes Earth right for life, and how are humans changing its climate? |
Read the chain once more. Electricity does work through forces. Forces spread over an area give pressure, and pressure differences in air make winds. To understand why air exerts pressure, or why water boils at a particular temperature, we must zoom in to the particles of matter. Light that reflects from mirrors also reflects from the Moon, giving its phases and our calendars. Finally, everything comes together to ask what keeps life going on Earth.
The last stop carries a serious message. Earth is at just the right distance from the Sun for water to stay liquid, and its atmosphere gives us oxygen and shields us from harmful ultraviolet rays. Human activities can change Earth’s temperature and disturb its climate. People are part of the problem, and with science, people can also be part of the solution. Observing, measuring and experimenting, the skills of this chapter, are the tools for that work.
3Worked example
- Force and pressure explain why air moves as wind.
- Particles explain why air exerts pressure and why water boils at a fixed temperature.
- Observing the Moon’s phases helped people make the first calendars.
4Your turn
According to the map of the year, why do we study particles of matter?
5Remember this
Key Concepts
- Investigation
- A planned search for answers using focused questions, observations and experiments.
- Scientific question
- A question that can be answered by observing, measuring or experimenting.
- Experiment
- A planned test in which one factor is changed to see its effect on another.
- Observation
- Information gathered through the senses or instruments, recorded honestly.
- Measurement
- An observation given as a number with a unit, such as 6 seconds or 2 millimetres.
- Changed factor (independent variable)
- The one thing the investigator chooses to change in an experiment.
- Observed factor (dependent variable)
- The thing watched or measured to see whether the change made a difference.
- Controlled factors
- All the other conditions that are kept the same so the test is fair.
- Fair test
- An experiment in which only one factor is changed at a time and all others are kept the same.
- Trial
- One run of an experiment; repeating trials makes results more reliable.
- Average
- The sum of repeated readings divided by the number of readings.
- Record
- A written note or table of observations made at the time they are seen.
- Pattern
- A regular link found in the results, such as hotter oil giving faster puffing.
- Systematic investigation
- Working step by step: question, plan, test, record, explain, then ask a new question.
- Root (symbol)
- Stands for the solid ground of careful observation and existing knowledge.
- Kite (symbol)
- Stands for curiosity, imagination and new ideas that take science into the unknown.
End-of-Chapter Trial Paper & Test Questions
Topic-wise questions to test your understanding of every concept in this chapter.
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What does investigation in science mean? / विज्ञान में अन्वेषण का क्या अर्थ है?
Show answer
Investigation means finding out new facts for ourselves by asking a focused question, planning an experiment or careful observations, recording the results and using them to improve our understanding. / अन्वेषण का अर्थ है स्वयं नए तथ्य खोजना, जिसमें हम एक स्पष्ट प्रश्न पूछते हैं, प्रयोग या सावधान प्रेक्षण की योजना बनाते हैं, परिणाम लिखते हैं और उनसे अपनी समझ को बेहतर बनाते हैं।
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What do the root and the kite in the Curiosity textbook stand for? / पाठ्यपुस्तक ‘क्यूरियोसिटी’ में जड़ और पतंग किसके प्रतीक हैं?
Show answer
The root stands for a solid foundation of careful observation and knowledge, and the kite stands for curiosity and creative thinking. Good science needs both. / जड़ सावधान प्रेक्षण और ज्ञान की मज़बूत नींव का प्रतीक है, और पतंग जिज्ञासा तथा रचनात्मक सोच का प्रतीक है। अच्छे विज्ञान के लिए दोनों आवश्यक हैं।
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Give two things you could change while investigating how a puri puffs up. / पूरी के फूलने की जाँच करते समय आप कौन-सी दो चीज़ें बदल सकते हैं?
Show answer
We could change the thickness or size of the rolled dough, the type of flour, the temperature of the oil, or the way the dough is put into the oil. / हम बेली हुई लोई की मोटाई या आकार, आटे का प्रकार, तेल का तापमान, या लोई को तेल में डालने का तरीका बदल सकते हैं।
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Give one yes/no observation and one measured observation for the puri experiment. / पूरी वाले प्रयोग के लिए एक हाँ/नहीं वाला प्रेक्षण और एक मापा गया प्रेक्षण बताइए।
Show answer
A yes/no observation is whether the puri puffed up or not. A measured observation is the time it took to puff, in seconds. / हाँ/नहीं वाला प्रेक्षण है कि पूरी फूली या नहीं। मापा गया प्रेक्षण है कि उसे फूलने में कितने सेकंड लगे।
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What is a fair test? Why is it important? / उचित परीक्षण क्या है? यह क्यों महत्वपूर्ण है?
Show answer
A fair test is an experiment in which only one factor is changed at a time while all other conditions are kept the same. It is important because only then can a difference in the result be linked to the factor that was changed. / उचित परीक्षण वह प्रयोग है जिसमें एक समय में केवल एक कारक बदला जाता है और बाकी सभी परिस्थितियाँ समान रखी जाती हैं। यह इसलिए महत्वपूर्ण है क्योंकि तभी परिणाम में आए अंतर को बदले गए कारक से जोड़ा जा सकता है।
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To test the effect of oil temperature on a puri, what must be kept the same? / पूरी पर तेल के तापमान का प्रभाव जाँचने के लिए क्या समान रखना चाहिए?
Show answer
The dough circles must have the same thickness and size, be made from the same dough, and be put into the oil in the same way. / लोइयों की मोटाई और आकार समान हों, वे एक ही आटे से बनी हों, और उन्हें तेल में एक ही तरीके से डाला जाए।
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A puri took 12 s, 15 s and 15 s to puff in three trials. Find the average time. / तीन प्रयासों में एक पूरी को फूलने में 12 s, 15 s और 15 s लगे। औसत समय ज्ञात कीजिए।
Show answer
Average = (12 + 15 + 15) ÷ 3 = 42 ÷ 3 = 14 s. / औसत = (12 + 15 + 15) ÷ 3 = 42 ÷ 3 = 14 s।
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Why should observations be written down at the time of the experiment? / प्रयोग के समय ही प्रेक्षण क्यों लिख लेने चाहिए?
Show answer
Writing them at once avoids memory mistakes, keeps the record honest and includes surprises such as splattering or smoke that may help explain the result later. / तुरंत लिखने से याददाश्त की गलतियाँ नहीं होतीं, रिकॉर्ड ईमानदार रहता है और छींटे या धुआँ जैसी अनपेक्षित बातें भी दर्ज हो जाती हैं जो बाद में परिणाम समझाने में मदद करती हैं।
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Rewrite “Why does dough rise?” as a testable question. / “आटा क्यों फूलता है?” को एक परीक्षण योग्य प्रश्न के रूप में लिखिए।
Show answer
One testable question is: “Does dough with yeast rise more in a warm place than in a cold place in the same time?” Here we change the temperature and measure how much the dough rises. / एक परीक्षण योग्य प्रश्न है: “क्या खमीर वाला आटा समान समय में ठंडी जगह की अपेक्षा गर्म जगह पर अधिक फूलता है?” यहाँ हम तापमान बदलते हैं और आटे के फूलने को मापते हैं।
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What is meant by systematic investigation? / क्रमबद्ध अन्वेषण से क्या तात्पर्य है?
Show answer
Systematic investigation means working step by step: asking a question, planning, testing fairly, recording, explaining the result and then asking the next question that arises. / क्रमबद्ध अन्वेषण का अर्थ है चरणबद्ध तरीके से काम करना: प्रश्न पूछना, योजना बनाना, उचित परीक्षण करना, प्रेक्षण लिखना, परिणाम की व्याख्या करना और फिर उठने वाला अगला प्रश्न पूछना।
Related Laws & Principles
Explore allFoundational laws & principles behind this chapter. Each one opens a full page — what it says, why it matters, five practice questions and the mistakes to avoid.