Chapter 1
Entering the World of
Secondary Science
Every question from the chapter — Examples, Activities, estimation tasks and Pause & Ponder — fully solved, with step-by-step working and hand-drawn diagrams.
In-text Questions
Examples, Activity & Curiosity / Estimation boxes
A cricket shot. Think of a cricket ball being hit for a six. You want to make a simple model. What details would you include? What would you ignore?
A model keeps only the details that affect the answer to our question and deliberately throws away the rest. Here the question is: “Will the ball cross the boundary without bouncing first?” So we keep what changes the flight path and ignore what does not.
✓ Keep (matters)
- Mass of the ball
- Speed with which it leaves the bat
- Direction / angle of the hit
✕ Ignore (no real effect)
- Brand of the bat
- Colour of the ball
- Amount of grass on the field
- Spin, seam stitching, air resistance — small effects, dropped in a simple model
As we build more complex models later, we can add the smaller effects (air resistance, spin) to gain greater accuracy. Ignoring details is not a mistake — it is done on purpose to keep the problem solvable.
You ride a bicycle from your school to your home and want to model the time it takes. What details would you keep? What could you ignore? Suggest why ignoring some details may actually be useful.
The only question we are answering is “roughly how long will the ride take?”. The simplest model is time ≈ distance ÷ average speed so we keep only what changes distance or speed.
✓ Keep
- Distance between school and home
- Your average cycling speed
- Number & length of stops (traffic signals, crossings)
- Road slope — uphill / downhill
✕ Ignore
- Colour or brand of the bicycle
- Clothes you are wearing
- Songs you hum on the way
- Each individual pedal stroke
Why ignoring is useful: If we tried to include every tiny detail (each pedal push, every gust of wind) the model would become impossibly complicated and we still wouldn’t get a better answer to “how long?”. Dropping the irrelevant details makes the model simple enough to actually calculate — and a quick estimate is exactly what we need.
How do we check predictions? Varsha tells Meghna, “It will rain this afternoon because the clouds look dark.” Think of questions Meghna could ask to make this prediction scientifically testable.
A scientifically testable prediction should rest on measurable evidence and past patterns — not on a single vague observation. Simple yes/no questions are usually not very useful. Meghna could ask:
- What was the condition of the sky the last time it actually rained?
- What is today’s humidity? Was it above 80 % the last time it rained?
- What is today’s wind speed and direction?
- Is the temperature dropping, the way it did before recent rains?
Each of these asks for data that can be measured and compared with what happened before — that is what turns a casual guess (“clouds look dark”) into a claim science can test.
Estimate how many litres of air you breathe in one day. Start from breaths per minute and the volume of one breath. Aim for a reasonable estimate, not an exact answer.
- Breaths per minute (at rest): about 12–15. Take ≈ 14.
- Minutes in a day: 60 × 24 = 1440 min
- Breaths per day: 14 × 1440 ≈ 20,000 breaths (roughly 18–22 thousand).
- Volume of one breath: a party balloon (≈ 2 L) fills in about 4–5 breaths, so one breath ≈ 2 L ÷ 4 ≈ 0.5 L
- Total air per day: 20,000 × 0.5 L = 10,000 L
Blowing up a balloon takes ≈ 20 s, so you could fill about 3 balloons a minute:
This is reasonably close to 10,000 L, so our estimate makes sense. (Of course you’d tire out instantly blowing balloons nonstop — restful breathing is far easier!)
How much rice would feed a family of four for a month? Assume all their calorie needs come from rice. (An adult needs ≈ 2000–2500 kcal/day.) Make a rough estimate.
- Calories per adult per day: take the middle value ≈ 2250 kcal
- Family of four per day: 4 × 2250 = 9,000 kcal
- For one month (≈ 30 days): 9,000 × 30 = 270,000 kcal
- Energy in rice: 100 g of uncooked rice gives about ≈ 350 kcal
- Rice needed: 270,000 ÷ 350 × 100 g ≈ 77,000 g ≈ 77 kg
Checking a “viral” claim: Is eating food harmful during an eclipse? Use simple scientific questions to test the claim.
- What physical change actually happens? An eclipse is only a play of shadows — the Moon temporarily blocks the Sun’s light. Nothing is added to or removed from the food.
- Does temperature change significantly? Only a small, brief dip in sunlight — not enough to affect food.
- Does food spoil in a shadow? No. Spoilage is caused by microbes and chemical reactions that need time, warmth and moisture — not the absence of sunlight for a few minutes.
Conclusion: There is no physical, chemical or biological mechanism by which an eclipse could make food harmful. The claim does not survive a few simple scientific questions — it is a myth.
Pause & Ponder
Open-ended reflection questions — model answers
Think of a prediction you or your family made recently (e.g. the outcome of a cricket match). Was it based on evidence and reasoning, or mainly on guesswork? How can scientific thinking improve such predictions?
Example prediction: “India will win today’s cricket match.”
Mostly guesswork if…
- “My favourite team always wins.”
- Based on hope, loyalty or a lucky feeling.
Evidence + reasoning if…
- Recent form & win record of both teams.
- Pitch and weather conditions.
- Player statistics and head-to-head history.
How scientific thinking improves it: gather relevant data, look for patterns from past matches, reason from that evidence rather than emotion, express the answer as a likelihood (not a certainty), and be ready to update the prediction as new information arrives. This separates a reasoned expectation from a pure guess.
Describe one situation where an approximate answer is good enough, and one where you would need a very exact value.
≈ Approximate is fine
- Estimating how much food to cook for guests.
- Roughly how long the journey to school will take.
- How much paint to buy for a wall.
= Exact value needed
- The dose of a medicine.
- Money in a bank transaction.
- Fuel loaded onto an aircraft.
- Chemical amounts in a lab reaction.
Choose a real-life object (e.g. a pressure cooker or mobile phone) or a problem (e.g. a traffic jam). Sketch the ideas from physics, chemistry, biology, earth science or mathematics involved. Show how at least two branches connect.
Physics → Chemistry: sealing the lid traps steam, so the pressure rises; higher pressure raises the boiling point of water well above 100 °C (this is the physics). That higher temperature then makes the chemical changes of cooking — starch softening and protein breakdown — happen much faster (this is the chemistry). So a single jet of steam links a physics idea (pressure–temperature) directly to a chemistry idea (reaction rate), which is exactly why food cooks faster in a pressure cooker.
