Curiosity and scientific questions
At night you notice many insects circling a street lamp and wonder, "Why do they come to the light?" That wonder is where science begins.
A scientific question is one that we can answer by observing, measuring or doing an experiment. Science needs no big laboratory: a kitchen, a garden or a road is enough.
Key idea 1: Start with "Why?", "How?" and "What if?" — Then make the question focused by naming what you will change and what you will observe.
- Easy: "Why is my shadow longest in the evening?" is a good starting question.
- Medium: "Does a longer pencil roll farther down a slope?" names a change (length) and a result (distance).
- Exam-type: Make "Why do plants grow?" focused: "Does 50 mL or 100 mL of water every day make a bean plant taller in 10 days?"
In the figure: A testable question lets us change something and measure the result. An opinion about beauty or luck cannot be measured.
Key idea 2: Testable or not? — Ask "Can I change something and measure what happens?" If yes, it is a scientific question.
- Easy: "Does salt dissolve faster in hot water?" can be tested with two cups.
- Medium: "Which flower is the prettiest?" is an opinion, so it cannot be tested.
- Exam-type: "Is Monday luckier than Friday?" cannot be tested because luck cannot be measured.
Every answer in science opens new questions. Even a puffing roti is not fully understood by scientists.
Thinking that science needs costly machines. Curiosity and careful observation are enough to begin.
Ask "Can I change it and measure it?" Memory clue: C + M = testable (Change + Measure).
Spot the difference
| Point | Scientific question | Opinion question |
|---|---|---|
| Example | Does a plant bend towards light? | Which plant is the nicest? |
| Can we measure it? | Yes | No |
| Settled by | Observing or an experiment | Personal liking |
Practice questions
- 1What does science begin with?
- 2Name one place at home where simple experiments can be done.
- 3Is "Which season is the best?" a scientific question?
- 4Rewrite "Why do seeds grow?" as a focused, testable question.
- 5Is "Does a heavier stone sink faster in water?" testable? How?
- 6What are the "Probe and ponder" questions meant for?
- 7Priya asks, "Does cloth colour change how hot it gets in the sun?" Write a plan to test it.
- 8Why do scientists keep asking questions even after they find an answer?
Show answers (try them yourself first)
- 1Curiosity and questions such as "Why?" and "How?"
- 2The kitchen (also a garden or a balcony)
- 3No, it is an opinion and cannot be measured.
- 4For example: "Do bean seeds sprout faster in warm water than in cold water?"
- 5Yes: drop two stones of the same size but different weights into the same water and see which reaches the bottom first.
- 6To spark curiosity; they are not exam questions.
- 7Put cloths of different colours in the sun for the same time and measure each one's temperature.
- 8Every answer can open new questions, so knowledge keeps growing.
What to change and what to keep the same
Two friends compare paper planes. One uses thick paper and throws hard; the other uses thin paper and throws gently. Whose plane is better? We cannot tell, because many things were different.
A fair test changes only one thing, keeps all other conditions the same, and measures the result.
Key idea 1: Three jobs in every experiment — (1) the one thing we change, (2) the things we keep the same, (3) the result we observe or measure.
- Easy: Paper plane test: change the wing size.
- Medium: Keep the same paper and the same way of throwing.
- Exam-type: Toy car on a ramp: change the slope; keep the car and the floor same; measure the distance rolled.
In the figure: Follow the four steps in order. Skipping the second step makes the test unfair.
Key idea 2: Why only one change at a time? — If two things change together, we cannot tell which one caused the result.
- Easy: Change only the temperature of the water when testing how fast sugar dissolves.
- Medium: Kunal changed both water and soil in two pots, so he cannot say which one made pot B taller.
- Exam-type: Improve his plan: use the same soil in both pots and change only the amount of water.
Keeping notes of what you see and sense helps you compare later and think of new questions.
Changing the amount, the cup and the temperature all together and then blaming one of them.
Before you start, write: "I change __, I keep __ same, I measure __." Memory clue: C-S-M = Change one, Same rest, Measure result.
Spot the difference
| Part | Paper plane test | Plant test |
|---|---|---|
| Change one thing | wing size | amount of water |
| Keep the same | paper, way of throwing | soil, pot, light |
| Measure | distance flown | height in cm |
Practice questions
- 1How many things should be changed at a time in a fair test?
- 2What should happen to all the other conditions?
- 3In a test on dissolving sugar, name a thing that can be measured.
- 4In a test of stirring speed on dissolving salt, what must be kept the same?
- 5A plant is kept in the dark and another in light, but one gets more water. Is it a fair test?
- 6What can Kunal conclude if he changed water and soil together?
- 7Design a fair test for "Does a thicker string hold more weight?" Name what you change, keep the same and measure.
- 8A friend changes the oil temperature and the dough size together. How can the test be improved?
Show answers (try them yourself first)
- 1Only one.
- 2They are kept the same.
- 3The time taken to dissolve (or the temperature).
- 4The amount and temperature of the water, and the amount of salt.
- 5No; water is also different, so two things change.
- 6Nothing definite; the cause cannot be separated.
- 7Change thickness; keep length and material same; measure the weight held.
- 8Change only one of them at a time and keep the other the same.
Observing, measuring and recording
A teacher says, "The plant grew a lot." Another says, "The plant grew 6 cm in a week." The second sentence is more useful because anyone can check and compare it.
Observing means noticing carefully with our senses and tools. A measurement is a number with a unit. A record is a note written at once, so that nothing is forgotten.
Key idea 1: Two kinds of observations — Some have only yes/no answers; others give a number that we can measure.
- Easy: "Did the seed sprout?" is a yes/no observation.
- Medium: "The seed sprouted in 4 days" gives a number.
- Exam-type: Improve "Did the ice melt?" by also noting the time taken in seconds.
In the figure: The hotter the water, the smaller the time. Numbers let us see this pattern at once.
Key idea 2: A good record — It has numbers with units, the conditions of the experiment, and everything we saw or sensed. Tools: stopwatch (time, s), ruler (length, cm), thermometer (temperature, °C), balance (mass, g).
- Easy: "The plant is 12 cm tall."
- Medium: "100 mL water at 45 °C, sugar dissolved in 35 s."
- Exam-type: "It was nice" is an opinion; "The water turned pink in 10 s" is an observation.
Keep the notes of a try that failed too: failures also teach us something.
Writing "warm" or "fast" instead of a number such as 45 °C or 12 s.
If you can use a number, use a number. Memory clue: NUT = Number, Unit, Time of writing (write it at once).
Spot the difference
| Point | Yes/no observation | Numerical observation |
|---|---|---|
| Example | Did it melt? | It melted in 95 s |
| Gives | only two answers | an exact amount |
| Easy to compare? | not much | very easy |
Practice questions
- 1Which instrument measures time?
- 2In which unit do we usually measure the height of a plant?
- 3Is "The stick is 15 cm long" a measurement?
- 4Which is the better note: "It melted" or "It melted in 95 s"?
- 5Which tool will you use to measure temperature?
- 6Sugar dissolved in 60 s, 35 s and 15 s at 20 °C, 40 °C and 60 °C. What pattern do you see?
- 7Two students measure the same pencil and get 14 cm and 15 cm. What should they do?
- 8Rewrite "The water was warm and the sugar went fast" as a good record.
Show answers (try them yourself first)
- 1A stopwatch (or clock).
- 2Centimetres (cm).
- 3Yes, it has a number and a unit.
- 4"It melted in 95 s", because it gives a number.
- 5A thermometer.
- 6Hotter water dissolves sugar faster.
- 7Measure again carefully starting from the zero mark.
- 8For example: "Water at 45 °C; one spoon of sugar dissolved in 35 s."
Systematic investigation and how science grows
A gardener sees that tomato plants near the wall flower earlier. She guesses that warmth is the reason, moves some pots, and records the dates. She is investigating step by step.
A systematic investigation is a planned, step-by-step way of finding answers. Each answer usually raises new questions, so science keeps growing and changing.
Key idea 1: The steps — Ask a question, plan and experiment, observe and record, explain using the observations, then ask new questions.
- Easy: The first step is always a question.
- Medium: The explanation must come from what we observed, not from what we hoped to see.
- Exam-type: If the result differs from your guess, accept the observation and rethink the explanation.
In the figure: The last step leads back to the first one, so the cycle keeps going.
Key idea 2: Root and kite — The root on the left-hand pages is the strong foundation of careful observation; the kite on the right-hand pages is free, creative thinking.
- Easy: Root = foundation of knowledge; kite = curiosity taking flight.
- Medium: Good science needs both together.
- Exam-type: Imagine why something happens, then test it with careful records.
Even simple things such as the puffing of a fried puri are not completely understood, so there is always more to find out.
Hiding or changing a result because it does not match the guess.
Follow the cycle: Ask, Plan, Test, Note, Explain, Repeat. Memory clue: "A Plan To Note Every Result".
Spot the difference
| Point | Root | Kite |
|---|---|---|
| Stands for | strong foundation, careful observation | creative thinking, curiosity |
| Seen on | left-hand pages | right-hand pages |
| Reminds us to | stay grounded in facts | let ideas soar |
Practice questions
- 1What does "systematic investigation" mean?
- 2What is the first step of an investigation?
- 3What does the root symbol stand for?
- 4Write the steps of an investigation in the correct order.
- 5What should you do if the result is different from your guess?
- 6Why do scientific ideas change over time?
- 7Seeds sprouted faster in warm water. Write a good follow-up question.
- 8Explain how the root and the kite together describe good science.
Show answers (try them yourself first)
- 1A planned, step-by-step way of finding answers.
- 2Asking a question.
- 3The strong foundation of knowledge and careful observation.
- 4Ask, plan and experiment, observe and record, explain, ask new questions.
- 5Accept the observation and rethink the explanation.
- 6New observations can improve our earlier understanding.
- 7For example: "Is there a temperature so hot that the seeds do not sprout?"
- 8Observation keeps us grounded in facts; creative ideas let us ask new questions.
Our journey through Grade 8 science
Before a long trip we look at a road map to see where each stop comes. This section is the road map of the whole book.
The Grade 8 chapters move from the very small (microbes and particles) to the whole planet (ecosystems and Earth), and each chapter connects to the next.
Key idea 1: From small to big — Microbes and health come first, then electricity, forces, pressure and winds, then particles and materials, solutions, light, the Moon and calendars, ecosystems and finally Earth.
- Easy: The year starts with a drop of water full of tiny organisms.
- Medium: Electric current has a heating effect and a magnetic effect.
- Exam-type: Pressure differences in air explain gentle breezes, strong winds and cyclones.
In the figure: Each chip is a part of the journey. Read left to right and then down.
Key idea 2: Everything is connected — Particles help us understand air pressure and solutions; light explains mirrors, lenses and the Moon's phases; the Moon's cycles gave us the first calendars; ecosystems and Earth bring it all together.
- Easy: Sugar dissolving in tea is a solution.
- Medium: The positions of the Earth, Moon and Sun give the Moon's phases.
- Exam-type: Small changes in Earth's temperature from human activity can disturb the climate.
The same method of asking, observing and explaining is used in every chapter.
Treating each chapter as a separate island; look for links between them.
Think "small to big": microbes, matter, motion, light, Moon, Earth. Memory clue: "My Mother Makes Lovely Moon-cakes, Every day" gives Microbes, Matter, Motion, Light, Moon, Earth.
Spot the difference
| Group | Big idea |
|---|---|
| Living world | microbes, health, ecosystems |
| Forces and electricity | current, forces, pressure, winds |
| Matter | particles, mixtures, solutions |
| Light and sky | mirrors, lenses, Moon, calendars |
Practice questions
- 1Which two effects of electric current are studied?
- 2What is everything around us made of?
- 3Name three groups into which materials are classified.
- 4What causes the phases of the Moon?
- 5Why were the first calendars linked to the sky?
- 6Which feature of Earth keeps water liquid?
- 7Explain how pressure differences are connected to winds and cyclones.
- 8Why is it important to study particles before studying solutions?
Show answers (try them yourself first)
- 1The heating effect and the magnetic effect.
- 2Tiny particles.
- 3Elements, compounds and mixtures.
- 4The relative positions of the Earth, Moon and Sun.
- 5People watched the repeating cycles of the Sun and the Moon.
- 6Its distance from the Sun (with an atmosphere that keeps it comfortable).
- 7A small pressure difference gives a breeze; a larger one gives strong winds and sometimes cyclones.
- 8A solution forms when particles of one substance mix evenly with those of another, so we need to know about particles first.