NCERT Solutions for Class 4 The World Around Us Chapter 7 How Things Work (PDF) – 2027

Yes. Every thing works in its own way because of its shape and the material it is made of. For example, a pencil writes because its soft tip rubs off on the paper, and a coin spins because it is round.

No. The same thing can work differently in a different situation. A coin spins for a long time on a smooth floor, but on a cloth it stops at once. A paper boat floats at first, but sinks when its paper gets wet.

Small changes in shape and balance can make things work better.

• Push the toothpick through the centre of a spinner.
• Make a paper boat wide and flat at the bottom.
• Press aluminium foil into a cup shape, not a ball.

No, all objects cannot spin properly.

Objects that can spin: a coin, a bangle, a wooden top (lattu), a small lid, a marble and a cardboard spinner.

Objects that do not spin properly: an eraser, a book, a brick and a matchbox.

Completed table (the first line is from the book; write what you really see):

We give the top a quick, sharp twist (or pull its wound string). It then turns round and round on its pointed tip. Only the tiny tip touches the ground, so it keeps spinning for a long time. As it slows down, it shakes and then falls.

Completed table

The spinner with the toothpick away from the centre did not spin properly. It wobbled and fell over soon.

Reason: The card is not the same on all sides of the toothpick. One side is bigger and heavier, so it pulls the spinner down to that side.

Yes, it made a big difference. In the first spinner the hole is at the centre, so it looks the same from all sides. It stayed upright and spun well. In the second spinner the hole is away from the centre, so it wobbled and fell.

I made spinners shaped like a triangle, a star and a rectangle, with the toothpick through the middle of each. Every one of them looked round while it was spinning, just like the square spinner.

Yes, we can colour it, in as many ways as we like — there is no fixed number. We can colour it in slices of two colours, in many colours, in rings or in dots.

Other changes: make the card bigger or smaller, use a longer or shorter toothpick, or cut the card in a new shape.

The separate colours can no longer be seen. They mix together, and the spinning spinner looks like one single colour.

Other things I have seen spinning: a table fan, the wheels of a bicycle and a bus, a washing machine drum, the hands of a clock, a charkha, a chakki (grinding stone), a windmill, a lattu and a merry-go-round.

My paper boat floated properly, like in Picture 1, because I folded it neatly and its two sides were equal. A second boat that I folded unevenly leaned to one side and flipped, like in Picture 2.

Completed table (F = floats, S = sinks; the guesses are a sample):

No. Not all light objects floated, and not all heavy objects sank.

Completed table (F = floats, S = sinks):

Conclusion: By changing the shape, we can make an object float or sink.

Our group of four made a raft from twelve ice-cream sticks laid side by side and joined with adhesive tape. We stuck a paper flag in a small lump of clay in the middle. We kept its bottom wide and flat, so it floated without tipping. We showed it at our class exhibition.

Sample table

I can improve my boat by:

1. making its bottom wider and flatter, so it does not tip over;
2. sealing the gaps with tape or clay, so no water gets in;
3. keeping both sides equal and the load in the middle;
4. using light materials such as thermocol or cork.

Ravi could ask:

1. Why does the spinner slow down and stop by itself?
2. What can I change so that it spins for a longer time?
3. Will it spin longer on a smooth table than on a rough mat?

Hang a paper toy of the same weight on the empty thread at end B. Then both ends of the stick carry equal weight, and it hangs level. (Or take the toy off end A.)

To make a floating object sink: press it tightly into a ball (like foil), or fill it with water (like the bottle).

To make a sinking object float: change its shape — spread it out, or make it like a cup or a boat (like the foil ball opened into a cup).

Nine things float and five things sink.