In-text — Investigating the Puffing Puri — Exploring the Investigative World of Science

1. 13 marksCuriosity Grade 8, Chapter 1, page 6

   The chapter says the first step is to "try to ask a scientific question". What makes a question scientific, and what is the scientific question in the puri investigation?

   Hint. Look at how the book itself phrases it before listing anything.

   The book's own phrasing. It sets the question as: what are the different things that may change the way a puri puffs up when fried? Notice its shape — it does not ask for the ultimate cause, it asks what factors make a difference. That is a question you can get at by trying things.

   What makes it scientific. Three features:

   • It points at something you can actually do — fry puris under different conditions rather than argue about them
   • It has an answer that observation could change your mind about, since a factor either makes a difference or it does not
   • It is narrow enough to act on. 'Why do things puff?' leads nowhere; 'what changes how a puri puffs?' leads straight to a list of things to try

   The move that makes it work. A big mysterious question is broken into two practical lists — what can I change, and what can I watch — because those two lists are what an experiment actually consists of.

   ✦ Answer: the scientific question is "what different things may change the way a puri puffs up when fried?" — scientific because it is specific, answerable by doing rather than arguing, and could be settled by what you observe.

2. 23 marksCuriosity Grade 8, Chapter 1, page 6

   In the puri experiment, what are the things you can change or control? List them and explain why each might matter.

   Hint. The book gives four kinds of thing you can vary.

   The controllable factors, as the chapter lists them:

   What you can change	Why it might matter
   Thickness of the rolled dough	A thick disc may not inflate at all; a thin one may tear
   Size of the rolled dough	Changes how much steam has to spread across the sheet
   Type of flour (atta, maida, and so on)	Different flours form different gluten networks, which may or may not trap steam
   Temperature of the oil	Steam has to form fast enough to inflate the puri before the dough sets
   How it is dropped — vertically, at an angle, slowly	Decides which face meets the hot oil first, and how evenly

   What these have in common. Every one is something you decide before the experiment starts. That is what makes them controls rather than outcomes: you set them, and then you wait to see what follows.

   A practical note. Some are easy to vary precisely (thickness, flour), while others are hard to set exactly — oil temperature drifts as puris go in and out. Knowing which of your controls are shaky is part of doing the experiment honestly.

   ✦ Answer: the thickness and size of the rolled dough, the type of flour, the temperature of the oil, and the way the dough is dropped into it — all decided by you before frying begins.

3. 33 marksCuriosity Grade 8, Chapter 1, page 6

   What can you observe or measure in the puri experiment? How do observations of this kind differ from one another?

   Hint. The chapter points out that some answers are yes/no and others are numbers.

   The two kinds the chapter distinguishes.

   Yes/no observations — did it puff up at all? did the oil splatter? did a thick layer of dough still produce a thin side? These are quick to record and easy to agree on, but they are coarse: two puris that both 'puffed' may have puffed very differently.

   Measured quantities — how many seconds until it puffed? how thick is each wall? how wide did it inflate? A number carries far more information, because it lets you see a trend rather than just a difference, and it lets someone else check your result against theirs.

   Why you want both. A yes/no answer tells you whether an effect exists; a number tells you how big it is. Starting with 'did it puff?' is sensible, since there is no point timing something that never happens — but the investigation only becomes sharp once you are measuring.

   Do not throw away the incidental. The chapter also asks you to note whether the oil splattered, smelled or smoked. Those are not the outcome you set out to record, which is exactly why they are worth writing down.

   ✦ Answer: you can record yes/no observations (did it puff, did the oil splatter) and measured quantities (seconds taken to puff, wall thickness) — the first tells you whether something happens, the second tells you how much, so a good investigation uses both.

4. 44 marksCuriosity Grade 8, Chapter 1, page 6

   The chapter advises changing only one thing at a time while keeping the other conditions the same. Why does this matter? Illustrate with the oil-temperature test.

   Hint. Imagine changing two things at once and getting a different result. Which change caused it?

   The problem with changing two things. Suppose you fry one puri thin in very hot oil and another thick in cool oil, and only the first puffs. You have learned almost nothing, since the difference could be the thickness, or the temperature, or both working together, or one helping while the other hinders. The experiment cannot tell these apart, so it cannot answer anything.

   The chapter's own illustration. To test the effect of boiling hot, hot and not-very-hot oil, you would

   • use circles of dough of the same thickness
   • from the same flour and the same dough
   • of the same size
   • dropped in the same way

   and vary only the temperature. Then any difference in puffing can be pinned on the temperature, because it was the only thing free to differ.

   A further precaution. One puri per temperature is not enough, since dough is not perfectly uniform and one puri may behave oddly by chance. Fry three or four at each temperature and see whether the pattern holds — a result that appears every time is worth far more than one that appeared once.

   ✦ Answer: because if two things change together you cannot tell which one caused the difference — holding thickness, size, flour and drop-method fixed while varying only the oil temperature is what makes the result attributable to temperature.

5. 53 marksCuriosity Grade 8, Chapter 1, page 7

   Why is it a good idea to keep notes of everything you see and sense during an experiment, including things you were not looking for?

   Hint. The chapter mentions splattering, smell and smoke — none of which is the puffing you set out to study.

   Memory is not a record. By the tenth puri you will not reliably recall which one took longer, or which batch smoked. Written notes made at the time are evidence; recollection afterwards is not, because it quietly reshapes itself to fit whatever you have since decided you believe.

   The unexpected often matters most. The chapter asks: did the oil splatter, smell, or smoke? None of that is the puffing you set out to measure. But smoking oil tells you the temperature went past where you meant it to be, splattering points to water on the dough, and a change in smell may mean the oil has been used too long. Each of these can explain an odd result that would otherwise look like a mystery.

   Notes let someone else repeat it. An experiment that cannot be repeated cannot be checked. Recording your flour, your rolling thickness, your oil and your method is what turns a one-off kitchen success into something a classmate can test against.

   They also generate the next question. Most follow-up questions come from something noticed and written down in passing, not from the plan you started with.

   ✦ Answer: because notes made at the time are evidence and memory is not — and because incidental observations like splattering, smell or smoke often explain surprising results, let others repeat your work, and supply the next question.

6. 63 marksCuriosity Grade 8, Chapter 1, page 7

   After one round of experiments you may think of more questions. What further questions does the chapter suggest, and what does this say about how investigation works?

   Hint. The chapter gives two, both about things you had not thought to vary at first.

   The two the chapter offers.

   • Do puris puff better when made fresh or from stored dough? — a factor that was not on the original list at all, since the first list assumed dough was just dough
   • What happens if I prick a hole in the puri before frying? — a deliberate interference, and a sharp test of the steam idea, because if trapped steam is what inflates the puri, letting it escape should stop the puffing

   What this reveals about investigation. It does not run in a straight line from question to answer and stop. Each round of experiments produces results and new questions, and the new questions are usually better than the ones you began with, because now you know something. The chapter's phrase for this whole approach is systematic investigation.

   Why the pricking question is especially good. It does not merely add another factor to the list — it tests an explanation. A question that could prove a proposed explanation wrong is worth more than one that just gathers more observations.

   ✦ Answer: whether fresh or stored dough puffs better, and what happens if you prick the puri before frying — showing that investigation is a cycle, where each round's results raise sharper questions than the ones you started with.

Solutions written by the tuition.in editorial team and checked against NCERT Curiosity — Textbook of Science for Grade 8 (hecu101.pdf), Chapter 1 'Exploring the Investigative World of Science', pages 1-7, Reprint 2026-27. HAND-WRITTEN throughout. CHAPTER STRUCTURE VERIFIED AGAINST THE PRINTED CONTENTS PAGE (hecu1ps.pdf p.18), which lists all 13 chapters and their start pages. This chapter carries NO exercise section and NO numbered questions - it is a seven-page opening letter to the student. Its assessable content is the four 'Probe and ponder' prompts on page 1, the worked puri investigation on pages 6-7, and the framing material on pages 2-5, and the 14 questions here cover exactly those. TWO POINTS OF SCIENTIFIC HONESTY. First, the book states explicitly that puri puffing 'is not really completely understood by scientists today', so the solution presents the uneven-setting account as a hypothesis to be tested and says plainly that it is not settled science. Second, the sand-versus-stars comparison was worked as a Fermi estimate in Python rather than asserted: a 0.5 mm grain at 60% packing gives about 5e9 grains per cubic metre, and the shortest quoted world coastline (356,000 km) with a 30 m wide, 5 m deep beach gives about 5.3e10 cubic metres, hence about 3e20 grains; the most sand-unfavourable assumptions (1 mm grains, shortest coastline) still give 3e19, against 1e11 to 4e11 stars in the Milky Way - a gap of about 1e8 that no reasonable change of assumptions closes. The solution also flags that the familiar opposite claim compares sand against the ~1e22 stars of the observable universe, not our galaxy, and notes the coastline paradox as the reason the coastline figure itself ranges from 356,000 to 1,160,000 km.. Questions are referenced from the NCERT textbook for identification.