NCERT Solutions for Class 4 EVS Chapter 7: How Things Work – Free PDF Download

Chapter 7 of the Class 4 EVS textbook Our Wondrous World is How Things Work. It introduces children to spinning objects, why things float or sink, and simple hands-on experiments and boat-making activities.

Last Updated: September 23, 2026

NCERT Textbook Questions and Answers – Chapter 7: How Things Work

Activity 1 (Page 105)

Q1: Do you think all objects can spin? Make a list of a few objects that can spin.
A: No, not all objects spin easily. Objects that can spin include a top, a wheel, a coin, a ceiling fan, and a spinning chair.

Q2: Collect objects from the given table, spin them, and complete an observation chart documenting their spinning behaviour.
A: Sample answer: a round coin spins smoothly and for a long time; a square eraser wobbles and stops quickly; a top spins fast and steadily due to its pointed base.

Activity 2 (Pages 106–107)

Q: Create spinners using cardboard, toothpicks, and pen tubes, then spin them and document your observations.
A: Cut a cardboard disc, push a toothpick or pen-tube through its centre hole, and spin it on a flat surface — students note how smoothly and how long each spinner spins.

Discuss (Page 108)

Q1: Which of the spinners did not spin properly? Discuss the possible reasons.
A: Spinners with an off-centre hole, an uneven shape, or a bent stick usually wobble and stop quickly instead of spinning smoothly.

Q2: Have you noticed the position of the hole in the first two spinners? Did this difference in the position of the hole make a difference in the spinning of these spinners?
A: Yes — a spinner with the hole exactly at the centre balances evenly and spins smoothly for longer, while one with an off-centre hole becomes unbalanced and stops quickly.

Activity 3 (Pages 110–111)

Q: Gather objects like leaves, nails, bowls, and bottles. Predict whether each will float or sink in water, then test and record results using ‘F’ and ‘S’.
A: Sample answer: leaf — F (float); nail — S (sink); empty plastic bottle (closed) — F (float); small stone — S (sink); an empty bowl placed carefully — F (float).

Discuss (Page 111)

Q: Did all the light objects float and all the heavy objects sink? Name the heavy objects that floated and lighter objects that sank.
A: No — a large, heavy but hollow object like a bowl or closed bottle can float because of its shape, while some small but dense objects like a nail or a coin sink even though they are light in weight.

Activity 4 (Page 112)

Q: Investigate whether the shape of an object influences whether it floats or sinks.
A: Sample answer: a flat sheet of aluminium foil floats, but the same foil crumpled into a tight ball sinks — showing that shape (not just the material) affects floating and sinking.

Activity 5 (Pages 113–114)

Q1: Design and construct boats using paper, cardboard, sticks, and clay in small groups, then display your creations.
A: Students build simple boats from the given materials, shaping them so they can float and hold small weights without sinking, then test them in a tub of water.

Q2: Compare your boat design with those created by other groups.
A: Sample answer: boats with a wider, flatter base floated more steadily and carried more weight than boats with a narrow or pointed base.

Let Us Reflect (Pages 115–116)

(Exact page wording should be cross-checked against your physical copy.)

Enquire About Something: Ravi noticed his spinner slows down and stops after a while. List at least two questions Ravi could ask to find out why.
A: Sample questions: “Why does the spinner slow down over time?” “Does friction with the ground or air cause it to stop?” “Would it spin longer on a smoother surface?”

Figure It Out (a): A lever/see-saw system is tilted toward side A. How can you balance it?
A: We can balance it by adding weight to side B, moving the load closer to the fulcrum on side A, or moving the pivot point until both sides balance.

Figure It Out (b): Explain methods to make floating objects sink and sinking objects float.
A: A floating object can be made to sink by adding weight to it or changing its shape to remove trapped air (like crumpling foil); a sinking object can be made to float by attaching it to something buoyant, like a piece of foam, or by changing its shape to trap air, like shaping clay into a boat.

Do an Activity: Classify the given objects into “float” and “sink” categories.
A: Students sort a fresh set of objects by testing them in water and placing each into a “float” or “sink” list based on the results.

Frequently Asked Questions

Why do we use simple machines?
Simple machines help us do work with less effort, by changing the amount, direction, or speed of the force we apply.

What is a fulcrum?
A fulcrum is the fixed point around which a lever pivots or turns when force is applied to it.

Written by Satish

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