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Class 9 Science Chapter 1: Entering the World of Secondary Science, 8 practice questions with answers

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These are 8 practice questions on Chapter 1, Exploration: Entering the World of Secondary Science, of the new NCERT Class 9 Science textbook, Exploration (First Edition, April 2026). This short chapter is about how science works rather than about one topic, so the questions test the thinking skills it describes: models and the details they leave out, laws, theories and principles, why units matter, quick estimates, and what to do when a prediction fails. Each has a worked answer and the textbook page it comes from. Try each one before you open the answer.

These questions are our own, drafted with AI help. The two calculations were re-computed by a test script and none of the numbers is taken from the chapter, but no practising teacher has reviewed them yet. If you find a mistake, please tell us.

What the chapter says you need

Facts from the NCERT textbook (Exploration: Textbook of Science for Grade 9, Chapter 1, printed pages 1 to 7):

Models

Question 1. Say what is being left out on purpose in each model: (a) a metro route map draws each line as a straight coloured line with the stations evenly spaced along it; (b) a water molecule is drawn as one large ball joined by two sticks to two small balls.

Answer: (a) The map leaves out the real distances between stations, the bends in the track and everything on the land above; it keeps only the order of the stations and where the lines meet at interchanges, which is all a passenger needs to plan a trip. (b) The molecule is not really made of balls and sticks; the drawing ignores what the atoms actually look like and shows only which atoms there are and how they are bonded. Both are models: simplified pictures that keep what matters for the question. (Models, page 2.)

Question 2. A model says that a crumpled paper ball and a steel ball dropped together from the same height, held at arm's length above a cushion on the floor, should land at the same time. When students try it, the paper ball lands a little later. Is the model useless? What should the students do?

Answer: no, the model is not useless; they should re-examine its assumptions. The simple model left out air resistance on purpose, to show the basic effect of gravity. Air resistance has a much larger effect on a light paper ball than on a steel ball, so the model works well for the steel ball but needs that extra detail for the paper ball. When a prediction does not match the observation, scientists re-examine the assumptions, the model or the measurements, and improve the model. (Ignoring air resistance in a model, page 2; checking predictions against observations, page 4.)

Laws, theories and principles

Question 3. Is each statement best called a law, a theory or a principle? (a) "Whenever we push a heavy box harder, it speeds up more": a regular pattern seen again and again. (b) "Matter is made of tiny particles that are always moving; this is why the smell of incense spreads across a room." (c) Using the idea that energy is never lost, only changed, to explain why a swing slows down unless it is pushed.

Answer: (a) law; (b) theory; (c) principle. A law usually describes a regular pattern observed in nature. A theory goes further and explains why something happens, based on evidence. A principle is a broad idea that helps us make sense of a given situation: the chapter calls this one the principle of conservation of energy (page 4). Applied to the swing, its energy is not lost but turns into heat and sound, through air resistance and friction at the hooks, so it slows down unless someone pushes it. (Laws, page 3; theories and principles, page 4.)

Question 4. Your cousin says, "It's only a theory, so it is just a guess." How would you correct this, using what the chapter says about theories?

Answer: In science, a theory is not a guess or an untested idea. It is an explanation based on careful testing and critical examination of evidence. It can still be improved or changed when new evidence comes in, and that openness is what makes science reliable. (Theories, page 4.)

Units and estimates

Question 5. Two students measure the speed of the same car. One writes "63" and the other writes "17.5". Both are right. Explain how, and say what each should have added.

Answer: one used km/h, the other m/s; each should have written the unit. 63 km/h = 63 × 1000 m ÷ 3600 s = 17.5 m/s. Check: 17.5 × 3.6 = 63. A number without its unit can be read wrongly; quantities in science have defined units, and using SI units (here, m/s) everywhere avoids conversion mix-ups. (Symbols and units, page 2; SI units, page 3.)

Question 6. A stack of new notebook paper is 42 mm thick, and one sheet is about 0.07 mm thick. Roughly how many sheets are in the stack? A friend guesses 6000. Does that make sense?

Answer: about 600 sheets; 6000 does not make sense. Number of sheets ≈ 42 ÷ 0.07 = 600. Check: 600 × 0.07 = 42 mm. For 6000 sheets, the stack would be about 6000 × 0.07 = 420 mm thick, ten times the measured height, so a quick estimate shows the guess is impossible. (Understanding the situation, identifying the quantities and estimating, page 5.)

Predictions and connections

Question 7. Two students make claims about a tulsi plant on the window sill. Student A: "This plant is happy." Student B: "This plant will grow taller in a sunny window than in a dark corner." Which claim can be tested scientifically, and what would you measure?

Answer: Student B's. It makes a prediction that can be checked with measurable evidence: grow similar plants in the two places, measure their heights over the same weeks, and compare. "Happy" cannot be measured, so A's claim cannot be tested. (Predictions and measurable evidence, page 4.)

Question 8. Why does the chapter say that the division of science into physics, chemistry, biology and earth science is "made by us"? Give one reason from the chapter.

Answer: The natural world has no such boundaries; the divisions only help us organise knowledge. Most real-world problems, such as understanding climate change, developing medicines or designing sustainable technologies, need ideas from several branches at once, and science also connects with mathematics, technology, the arts and social sciences. (Branches of science, page 6.)

Practise more, and check your marks

Where CMDLearn fits

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Sources

All opened and read on 22 October 2026. Page numbers are the printed page numbers of the textbook; printed page = PDF page + 0.

The ideas are from the textbook pages above. The questions, worked answers and checks are our own, and both calculations were re-computed by script. This guide is general information; follow your teacher and the textbook.