Exploring the Investigative World of Science Class 8: Questions, Variables and Fair Tests

What Exploring the Investigative World of Science is about

Key concepts

From wonder to a scientific question

Curiosity begins with broad questions: Why is the sky blue? Why does dough rise? To investigate, we turn a broad question into a focused, testable one that an experiment or careful observation can answer.

• Broad: 'Why does a puri puff up?'
• Focused: 'Does the temperature of the oil change how quickly a puri puffs up?'

A good investigative question names one thing to change and one thing to observe or measure. Questions about opinions ('Which puri tastes best?') or about things we cannot observe cannot be tested this way.

The chapter's 'Probe and ponder' questions (puri sides, grains of sand versus stars, the variety of life) are meant to spark curiosity, not to be learnt for an exam.

Worked example

Rewrite 'Why does milk go sour?' as a question that can be tested at home.

Try it first, then show the solutionSolution

1. Pick one thing you can change: the temperature at which milk is kept.
2. Pick one thing you can observe: the time taken for it to taste or smell sour (or to curdle).
3. Focused question: 'Does milk kept in a warm place turn sour faster than milk kept in a cool place?'

Answer: Does milk kept warm turn sour faster than milk kept cool?

What we change, what we observe, what we keep the same

Every investigation has three kinds of factors (often called variables):

• What we change on purpose (independent variable): for a puri, the oil temperature, dough thickness, type of flour, or the way the dough is dropped.
• What we observe or measure (dependent variable): whether the puri puffs (yes/no), the time it takes to puff (seconds), whether one side stays thin.
• What we keep the same (controlled variables): everything else, such as dough size and thickness, flour, amount of oil, and the way the dough is dropped, when we are testing oil temperature.

Some observations are yes/no or descriptive (qualitative); others are numbers (quantitative) such as time in seconds or size in centimetres.

Worked example

In the puri investigation, a student tests whether thicker dough puffs more slowly. Name the factor changed, the factor measured, and two factors kept the same.

Try it first, then show the solutionSolution

1. Changed: the thickness of the rolled dough.
2. Measured: the time taken (in seconds) for each puri to puff up.
3. Kept the same: the oil temperature and the size (diameter) of the dough circle; also the same flour and the same way of dropping it.

Answer: Change thickness; measure puffing time; keep oil temperature, size, flour and dropping method the same.

Fair tests: change one thing at a time

If two things change at once, you cannot tell which caused the difference. A fair test changes only one factor and keeps all others the same.

Example from the chapter: to see the effect of boiling-hot, hot and not-very-hot oil, use dough circles of the same thickness, dropped in the same way, so that only the oil temperature differs.

Unfair test: frying a thick maida puri in very hot oil and a thin atta puri in warm oil, then comparing puffing times. Thickness, flour and temperature all differ, so no conclusion about temperature is possible.

A fair test also uses the same measuring method each time and, where possible, repeats each condition.

Safety: hot oil and open flames can cause serious burns. Do any frying or flame test only with an adult doing the cooking, keep water away from hot oil, and watch from a safe distance.

Worked example

Ravi fries one puri from fresh dough in very hot oil and one from stored dough in warm oil. The fresh one puffs faster, so he says fresh dough puffs better. Is his test fair? How would you fix it?

Try it first, then show the solutionSolution

1. Two factors changed: freshness of dough and oil temperature.
2. So the faster puffing could be due to the hotter oil, not the fresh dough: the test is unfair.
3. Fix: fry both puris in oil at the same temperature, with the same size, thickness and flour, changing only fresh versus stored dough.

Answer: Not fair; keep the oil temperature (and everything else) the same and change only the dough's freshness.

Observing carefully and recording

Good investigators record everything they see and sense, not only the planned measurement. During frying, notes might include: Did the oil splatter? Was there smoke or a smell? Did the puri sink first and then rise?

• Measure where you can (seconds with a stopwatch, centimetres with a ruler).
• Repeat each condition and take the average (mean) of the readings, because single readings can be off. Puffing times of 8.2 s, 7.8 s and 8.0 s give a mean of $\frac{8.2+7.8+8.0}{3}=8.0$ s.
• Look out for a reading that is very different from the rest (perhaps a mistake), check it, and repeat if needed.
• Present results in a table so patterns are easy to see.

Worked example

Four trials of the time for an ice cube to melt on a steel plate gave 15, 16, 15 and 30 minutes. What is odd about the data, and what should you do?

Try it first, then show the solutionSolution

1. Three readings are close (15 to 16 min); 30 min is far from them.
2. Including it gives a mean of 19 min, which does not represent the others.
3. Check what was different in that trial (bigger cube, cooler room), repeat it; if it was a mistake, use the other three: mean about 15.3 min.

Answer: The 30-minute reading is an odd one out; check and repeat it rather than average it blindly.

Results lead to new questions

An investigation rarely ends with one answer. After one round of experiments, new questions appear:

• Do puris puff better from fresh or stored dough?
• What happens if a hole is pricked in the dough before frying?

This is how all experiments work, from kitchen tests to research laboratories: question → plan → observe and measure → analyse → conclude → new questions. Science keeps refining its ideas.

The chapter points out that even why a puri puffs (and why one side is thinner) is not yet completely understood by scientists, a reminder that everyday things can hold open questions.

Root and kite: the book's page design pairs a root (solid observation and connection to environment and heritage) with a kite (curiosity soaring). Investigation works best when both are balanced.

Worked example

After finding that puris in hotter oil puff faster, write two new questions an investigator might ask next.

Try it first, then show the solutionSolution

1. Change a different factor: 'Does pricking a hole in the dough stop it from puffing?'
2. Look deeper at the cause: 'Does the steam formed inside the dough make it puff, and does wetter dough puff more?'

Answer: For example: Does a pricked puri still puff? Does a wetter dough puff more?

The journey ahead in Grade 8

The chapter previews how the year's topics connect:

• Microbes in a drop of water, helpful and harmful; then health: nutrition, exercise, medicines and vaccines.
• Electricity: heating effect (heaters) and magnetic effect (motors).
• Forces that change motion, then pressure, which drives winds, storms and cyclones.
• Particles of matter (close in solids, free in gases); elements, compounds and mixtures; solutions such as sugar in tea.
• Light: reflection in plane and curved mirrors, bending in lenses, the phases of the Moon, and how observing the sky gave us calendars.
• Ecosystems: how living things depend on air, water, sunlight and each other.
• Earth: why it is 'just right' for life (distance from the Sun, liquid water, an atmosphere giving oxygen and blocking harmful ultraviolet rays), and how human activities affect climate.

The thread through all of them is the same toolkit: observe, measure, experiment, explain.

Worked example

Match each question to the topic of the year it belongs to: (a) Why does a heater coil glow? (b) Why does the visible part of the Moon change each night? (c) How does sugar disappear in tea?

Try it first, then show the solutionSolution

1. (a) Heating effect of electric current (electricity).
2. (b) Positions of the Earth, Moon and Sun (light and keeping time with the skies).
3. (c) Dissolving: solutes, solvents and solutions.

Answer: (a) electricity (b) Moon's phases and the sky (c) solutions.

Science in real life: Exploring the Investigative World of Science

Each concept, met in an everyday situation. Read the situation, try the problem, then check the solution. The one-line hook is what to remember.

Topics in this chapter

• Asking a Scientific Question and Choosing What to Change and Observe
• Fair Testing and Systematic Investigation

Exploring the Investigative World of Science: formulas and key facts

Investigation cycle

$\text{question}\to \text{plan}\to \text{observe}\to \text{analyse}\to \text{conclude}\to \text{new question}$

Fair test rule

$\text{change one factor; keep all others the same}$

Mean of repeated readings

$\text{mean}=\frac{\text{sum of readings}}{\text{number of readings}}$

Percentage of a sample

$\frac{\text{number showing the result}}{\text{total}}\times 100$

Three kinds of factors

$\text{changed}\mid \text{measured or observed}\mid \text{kept the same}$

Exploring the Investigative World of Science: diagrams to practise

Practise each one on paper: draw it from the checklist, then tick off every label.

How the school exam asks Exploring the Investigative World of Science

The question patterns to expect, and the method that works for each.

Tricks to remember Exploring the Investigative World of Science

Short memory aids. Say each one aloud once, then use it on a question the same day.

• C-M-S

  Change one, Measure one, Same for the rest.

  Use it when: Planning any fair test.

• Root and kite

  Roots keep you grounded in observation; the kite lets your ideas fly. You need both.

  Use it when: Remembering the book's message about investigation.

• Three times, then average

  Repeat each condition at least three times and take the mean.

  Use it when: Reliable results.

• Answers breed questions

  Every conclusion should end with a new 'What if...?'

  Use it when: The investigation cycle.

Exploring the Investigative World of Science: exam-level solved questions

Ordered from exam level to HOTS. Cover the solution, write your own, then compare step by step.

Case-study practice (Section E style)

Read the situation, then answer every part. In a school exam set on the board pattern this is a 4-mark question split into 1 + 1 + 2 marks.

Where the marks are

How a typical answer is split into step marks. Show every step: a right final answer alone rarely earns full marks.

Where students lose marks in Exploring the Investigative World of Science

The slips examiners see most often, and what to write instead.

• ✗Mistake: Changing more than one factor

  Students want quick results.

  Wrong working

  Thin puri in hot oil versus thick puri in warm oil: the thin one puffs faster, so thin dough puffs faster.

  Right working

  Keep the oil temperature the same and change only the thickness; otherwise the result may be due to the oil.

  ✓Do this: Write down the one factor you change before starting.

  Usually costs: The conclusion mark.

• ✗Mistake: Mixing up what is changed and what is measured

  Both are 'things in the experiment'.

  Wrong working

  In testing oil temperature, the measured factor is the oil temperature.

  Right working

  Oil temperature is changed; the time to puff (or whether it puffs) is measured.

  ✓Do this: The measured factor is the result you record, usually in the last columns of your table.

  Usually costs: 1 mark.

• ✗Mistake: Relying on a single trial

  One reading seems enough.

  Wrong working

  The puri in hot oil puffed in 12 s once, so hot oil always takes 12 s.

  Right working

  Repeat (for example 3 times), average the times, and note any odd readings.

  ✓Do this: Plan repeats and a mean column in the table.

  Usually costs: 1 mark in planning questions.

• ✗Mistake: Over-general conclusions

  A small test is stretched to everything.

  Wrong working

  Hot oil puffs puris faster, so all fried foods cook faster in hotter oil without any problem.

  Right working

  Conclude only what was tested: within this range, puris in hotter oil puffed faster.

  ✓Do this: Limit your conclusion to the conditions tested.

  Usually costs: 1 mark.

Practice questions on Exploring the Investigative World of Science

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

1. Q1 · 1 mark · MCQExam level

   In a fair test, how many factors are changed on purpose?
   (a) None
   (b) One
   (c) Two
   (d) All

   Hint

   Fair test rule.

   Answer

   (b) One

2. Q2 · 1 mark · MCQExam level

   The time taken for a puri to puff is a
   (a) factor kept the same
   (b) factor changed
   (c) measured observation
   (d) prediction

   Hint

   It is recorded as a result.

   Answer

   (c) measured observation

3. Q3 · 2 marks · Very short answerExam level

   Give one qualitative and one quantitative observation you could record while frying puris.

   Hint

   Descriptive versus number.

   Answer

   Qualitative: the oil splattered (or the puri puffed). Quantitative: it took 8 seconds to puff.

4. Q4 · 1 mark · Very short answerExam level

   Rewrite 'Why do some clothes dry faster?' as a testable question.

   Hint

   One change, one measurement.

   Answer

   For example: Does a cotton cloth dry faster than a woollen cloth of the same size and wetness in the same place?

5. Q5 · 2 marks · Very short answerHarder exam level

   Trial times (s) for a ball to roll down a ramp were 3.4, 3.6 and 3.5. Find the mean.

   Hint

   Add and divide by 3.

   Answer

   $\frac{10.5}{3}=3.5$ s

6. Q6 · 3 marks · Short answerHarder exam level

   Kiran tests whether salt affects how fast ice melts, but puts salted ice in the sun and unsalted ice in the shade. Explain the problem and correct it.

   Hint

   Two factors changed.

   Answer

   Both salt and place changed, so faster melting could be due to the sun. Keep both in the same place (same temperature) with ice cubes of the same size, changing only whether salt is added; repeat each.

7. Q7 · 2 marks · Very short answerHarder exam level

   List three factors you would keep the same when testing whether the type of flour affects how a puri puffs.

   Hint

   Everything except flour.

   Answer

   Oil temperature, dough size and thickness, the way the dough is dropped (also the amount of oil).

8. Q8 · 3 marks · Short answerHarder exam level

   Out of 25 seeds kept moist, 20 sprouted; out of 25 kept in a dark cupboard (also moist), 21 sprouted. What percentage sprouted in each? What does this suggest about light and sprouting in this test?

   Hint

   Percentages.

   Answer

   80% and 84%. The results are very similar, so in this test light did not make much difference to sprouting; water mattered more (from other tests).

9. Q9 · 2 marks · Very short answerHarder exam level

   Draw (describe) a results table for testing three oil temperatures with three trials each, including units and a column for other observations.

   Hint

   Factor changed first, mean last.

   Answer

   Columns: Oil temperature | Time to puff, trial 1 (s) | trial 2 (s) | trial 3 (s) | Mean (s) | Other observations. Rows: warm, hot, very hot.

10. Q10 · 5 marks · Long answerHarder exam level

    Plan an investigation to find out whether the thickness of a phulka affects whether it puffs on a flame. Include the question, factors, method, repeats, table and how you will conclude.

    Hint

    Use C-M-S.

    Answer

    Question: does thickness affect puffing? Change: thickness (for example 1 mm, 2 mm, 3 mm). Keep the same: dough, diameter, flame size, time on the tawa before the flame. Safety: an adult handles the flame and the hot tawa. Measure: puffs or not, and time to puff, three phulkas each; mean time. Table: thickness | trials | mean | notes. Conclude only for the thicknesses tested and list new questions.

11. Q11 · 3 marks · Short answerHOTS / competency

    A student concludes from one test that 'heavier balls always roll faster'. Give two reasons why this conclusion is not justified.

    Hint

    Repeats and other factors.

    Answer

    Only one test was done (no repeats), and other factors (size, surface, ramp angle, how the ball was released) may not have been kept the same; also 'always' goes beyond the conditions tested.

12. Q12 · 2 marks · Very short answerHOTS / competency

    The chapter says even a puffing puri is not completely understood by scientists. Explain what this tells you about science.

    Hint

    Open questions.

    Answer

    Science is not a finished list of facts; even everyday events can hold open questions, and investigation keeps going as new questions arise.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1. 1.What does the chapter want you to learn this year, beyond facts?Show answer

   How to find new facts by investigating.

2. 2.What is a testable question?Show answer

   A focused question naming one thing to change and one thing to observe or measure.

3. 3.Name two things you could change when investigating puri puffing.Show answer

   Any two of: dough thickness, size, type of flour, oil temperature, the way the dough is dropped.

4. 4.Name two things you could observe or measure.Show answer

   Whether the puri puffs (yes/no) and the time taken to puff.

5. 5.What is a fair test?Show answer

   A test in which only one factor is changed and all others are kept the same.

6. 6.Why repeat trials?Show answer

   To get a more reliable mean and to spot odd readings.

7. 7.What do the root and the kite in the page design stand for?Show answer

   The root stands for a solid foundation of knowledge and observation; the kite for curiosity taking flight.

8. 8.Is the puffing of a puri fully understood by scientists?Show answer

   No, the chapter says it is not completely understood.

Quick revision checklist

The night before the exam: can you do each of these without looking?

• ☐Can you turn a broad question into a testable one?
• ☐Can you name the changed, measured and kept-same factors in an investigation?
• ☐Can you spot an unfair test and fix it?
• ☐Can you find the mean of repeated trials?
• ☐Can you spot an odd reading in data?
• ☐Can you draw a results table with units?
• ☐Can you write a conclusion limited to what was tested?
• ☐Can you suggest new questions after an investigation?
• ☐Can you explain the root and kite symbols?
• ☐Can you match everyday questions to the year's chapters?

Exploring the Investigative World of Science: frequently asked questions