Circle of Learning • New NCERT textbook "Exploration" (2026-27) • All in-text questions and activities with answers + extra important questions
Activity 1.1 – Let Us Model
Suppose you ride a bicycle from your school to your home. You want to model the time it takes to go home from school. What details would you keep? What details could you ignore? Suggest why ignoring some details may actually be useful.
Answer
Details to keep (they affect the time a lot)
- The distance (length of the route) from school to home.
- Your average riding speed.
- The number of traffic signals, crossings or speed breakers where you must stop or slow down.
- Steep slopes (uphill stretches slow you down).
Details that can be ignored (they hardly change the time)
- The colour or brand of the bicycle.
- The weight of your school bag (small effect).
- Small turns and tiny bumps on the road.
- Light wind, the exact tyre pressure, the clothes you wear.
Why ignoring details is useful: If we try to include everything, the model becomes too complicated to work with and we may never get an answer. By keeping only the factors that matter most, we can quickly make a good estimate (time = distance ÷ average speed + time lost at stops). Later, if we need more accuracy, we can add more details step by step. This is exactly how scientists build models.
Pause and Ponder (In-text Questions)
Think of a prediction you or your family made recently (for example, the outcome of a cricket match). Was it based on evidence and reasoning, or mainly on guesswork? How can scientific thinking improve such predictions?
Answer
Sample answer: Before a cricket match, my family predicted that India would win. This was mainly guesswork based on support for our team, though we also remembered that India had won the last two matches.
Scientific thinking can improve such a prediction by:
- Collecting evidence – recent results of both teams, records at that ground, players' current form, pitch and weather report.
- Looking for patterns – e.g. how often the team batting first wins at that ground.
- Stating the prediction clearly so it can be tested, and checking afterwards whether it was right.
- If the prediction fails, re-examining assumptions (maybe dew or an injury was ignored) instead of blaming luck, so that the next prediction is better.
Describe one situation where an approximate answer is good enough, and one where you would need a very exact value.
Answer
Approximate answer is good enough: estimating how much rice to buy for a family for a month, or how long it will take to walk to the market. Being off by a little does not matter.
A very exact value is needed: the dose of a medicine for a patient, the amount of fuel needed for an aircraft, or the measurements of parts in a machine or bridge. A small error here can be dangerous. (The textbook's example of an aircraft running short of fuel because pounds were confused with kilograms shows why exact values and standard units matter.)
Choose a real-life object (maybe a pressure cooker or a mobile phone) or a problem (maybe a traffic jam near your school). Make a sketch listing what kind of ideas from physics, chemistry, biology, earth science, or mathematics are involved. Show how at least two branches of science connect with your example.
Answer
Example: Pressure cooker
Branch | Ideas involved |
Physics | Heat transfer, pressure, boiling point rises when pressure rises, the safety valve and whistle, conduction through the metal body. |
Chemistry | Burning of LPG (combustion), material of the cooker (aluminium/steel alloys), chemical changes in food during cooking. |
Biology | Softening of plant cell walls in dal and vegetables; killing of microbes at high temperature; nutrients in food. |
Mathematics | Volume of the cooker, how much water to add, timing (number of whistles). |
Connection: Physics tells us that higher pressure inside the cooker raises the boiling point of water above 100 °C. This higher temperature speeds up the chemical and biological changes (breaking down of starch and cell walls) in the food, so the food cooks faster. Thus physics, chemistry and biology work together in one everyday object.
(Draw a simple sketch of a pressure cooker in the middle of the page and draw arrows to boxes labelled Physics, Chemistry, Biology and Mathematics with the ideas above.)
Solved Examples from the Chapter (for revision)
Example 1.1 – A cricket shot: To model whether a ball hit for a six crosses the boundary, keep the mass of the ball and the speed and direction of the hit; ignore the brand of the bat, the colour of the ball and the grass on the field. Air resistance, spin and seam have smaller effects and can be left out of a simple model.
Example 1.2 – Checking predictions: To make "It will rain because the clouds look dark" testable, ask about measurable data and past patterns – humidity today versus the last time it rained, wind speed and direction, whether the temperature is dropping as before earlier rains.
Example 1.3 – Air breathed in a day: About 12–15 breaths per minute × 1440 minutes ≈ 20,000 breaths a day. One breath ≈ 0.5 litre, so we breathe about 10,000 litres of air every day.
Extra Important Questions
Multiple Choice Questions (1 mark)
1. In science, a model is
(a) an exact copy of a real system (b) a simplified way of looking at a real system (c) a guess without evidence (d) a toy
Answer: (b)
2. The symbol c for the speed of light comes from the Latin word
(a) circulus (b) celeritas (c) constans (d) clarus
Answer: (b) celeritas, meaning speed
Which of the following describes a regular pattern observed in nature?
Answer
(a) Law (b) Theory (c) Guess (d) Opinion
Answer: (a) Law
4. The speed of light is defined to be exactly
(a) 3,00,000 m/s (b) 299792458 m/s (c) 3 × 106 m/s (d) 186000 m/s
Answer: (b) 299792458 m/s
Short Answer Questions
Differentiate between a law, a theory and a principle in science, with one example each.
Answer
A law describes a regular pattern observed in nature, often with a mathematical relation – e.g. Newton's laws of motion explain the jerk felt when a bus stops suddenly. A theory explains why such patterns occur, based on evidence gathered over time – e.g. atomic theory explains how molecules form. A principle is a broad idea that helps us understand a situation – e.g. conservation of energy applied when climbing stairs.
"In science, a theory is just a guess." Do you agree? Explain.
Answer
No. A scientific theory is an explanation based on careful testing and critical examination of evidence. It is not an untested idea. Theories remain open to improvement when new evidence appears, which makes science reliable rather than weak.
Why do scientists use standard (SI) units?
Answer
Standard units mean the same amount everywhere, so results from different places can be compared, trade is fair and errors from conversions are avoided. Mixing units (like pounds and kilograms) can cause serious accidents.
Why do weather forecasts sometimes go wrong?
Answer
Weather depends on many changing factors such as temperature, pressure, humidity and wind. Very tiny differences in these conditions can grow over time and lead to very different outcomes. So forecasts are reliable for a few hours or days but less certain further ahead.
How would you scientifically check the claim "food should not be eaten during an eclipse"?
Answer
Ask testable questions: What physical change happens during an eclipse? (It is only a shadow.) Does the temperature change much? Does food spoil when kept in shade? Since no physical, chemical or biological mechanism supports the claim, it is not scientific.
"Failures are the greatest strength of science." Explain.
Answer
When predictions do not match observations, scientists re-examine their assumptions, models or measurements and improve them, based only on evidence. Because no theory is final and all ideas can be corrected by nature, science keeps getting more accurate.