NCERT Solutions Class 4 The World Around Us Chapter 7 How Things Work

F R E E S T U D Y M AT E R I A L F O R E V E R Y S T U D E N T

CLASS 4 · THE WORLD AROUND US

NCERT Solutions

Chapter 7: How Things Work

NCERT Textbook — Our Wondrous World

BOOK PAGES SECTIONS QUESTIONS MEDIUM

104 – 116 13 24 English

Solutions, notes, sample papers & more at 27 pages

Class 4 The World Around Us Chapter 7 How Things Work AglaSem · NCERT Solutions

CLASS 4 · THE WORLD AROUND US · OUR WONDROUS WORLD

NCERT Solutions — Chapter 7: How Things Work
Meera and Dhruv spin a coin, build paper spinners and float paper boats in a puddle. This page answers every
question, Discuss box and Activity in How Things Work, and fills in each recording table for you.

TEXTBOOK BOOK PAGES

Our Wondrous World (Class 4) 104 – 116

SECTIONS QUESTIONS

13 24

MEDIUM

English

In-text Questions — Page 104
How Things Work — the chapter begins

Q1 Have you ever wondered how these things work?

Yes, and it is worth wondering about. Every thing we use works in its own way.

A pencil writes because its soft dark tip rubs off on the paper.
A bag carries books because its cloth is strong and it has handles.
A coin spins because it is round and the same all the way round.

Why it happens: A thing works in a certain way because of its shape and the
material it is made of.

Tip: In this chapter, Meera and Dhruv find out how spinning things and floating
things work. You can try every activity at home too.

Q2 Do they always work the same way in all situations?

No. The same thing can behave differently in a different situation.

A coin spins for a long time on a smooth floor. On sand or on a cloth it stops at once.
A paper boat floats well at first. After some time the paper gets wet and the boat sinks.

Page 1 of 27

Class 4 The World Around Us Chapter 7 How Things Work AglaSem · NCERT Solutions

A piece of aluminium foil floats when it is spread out. The same piece sinks when it is
pressed into a tight ball.

Why it happens: When we change the shape of a thing, or the place we use it in, the
way it works also changes.

Q3 What changes might be needed to make them work even better?

Small changes can make a thing work much better. Here are three from this chapter.

1. Push the toothpick right through the centre of the card. The spinner then stands up and
spins for longer.
2. Make the paper boat wide and flat at the bottom. It then floats without tipping over.
3. Press the aluminium foil into a cup shape instead of a ball. It then floats instead of sinking.

Why it happens: Changing the shape changes how a thing balances and how it sits
on water.

Activity 1 — Page 105
Things that spin

ACTIVITY

Q1 Do you think all objects can spin? Make a list of a few objects that can spin.

No, all objects cannot spin. Only some things spin properly.

Coin Bangle Pencil Piece of stone Wooden Eraser
spinner (top)

Page 2 of 27

Class 4 The World Around Us Chapter 7 How Things Work AglaSem · NCERT Solutions

Set-up: spin each of these six things on a smooth, flat floor and watch it.

Things that can spin:

a coin
a bangle
a wooden top (lattu)
a plate or a small lid
a marble
a cardboard spinner with a toothpick

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

Why it happens: A thing spins well when it is round and looks the same from all
sides. A thing with flat sides and corners tips over instead of spinning.

Page 3 of 27

as e
Class 4 The World Around Us Chapter 7 How Things Work
a g l AglaSem · NCERT Solutions

co m
m.
Collect the objects mentioned in the table given below. Spin and observe them.
e
Q2

m l as
.co
Then, complete the table.

a g
se m
g l a
a OBJECTS I OBSERVE I WONDER I

com
THINK

e m . ag
Coin
a s
As it slows down, it Why does it start to shake

agl
begins to shake as it slows down?

m
Bangle As time passes, the

co
m.
sound…

m as e
.co
Pencil
a g l
se m Piece of Stone
g l a
a
Wooden

m a s
.co agl
Spinner (Top)

se m
Eraser
g l a
a
The table as it is printed in the book, with the first two lines partly filled in.

co m
m .
o m l a se
.c a g
m
se each object on a smooth, flat floor. Watch it carefully, then write down what you saw. Here

g l aSpin
a is the table with every box filled in.

se m
com g l a
m . a
ase
agl

co m
m .
m l a se
.co agspinner (top)
Coin Bangle Pencil Piece of stone Wooden Eraser

se m
g l a
a c
.
Set-up: spin each of these six things on a smooth, flat floor and watch it.

s e m
m a
e m . co agl
g l as
a

co m
m .
m ase
.co


a g l Page 4 of 27

Class 4 The World Around Us Chapter 7 How Things Work AglaSem · NCERT Solutions

OBJECTS I OBSERVE I WONDER I THINK

Coin As it slows down, it begins to Why does it start to It cannot stay standing
shake shake as it slows when it turns slowly, so it
down? begins to fall

Bangle As time passes, the sound… Why does the sound The bangle lies flatter and
becomes faster and louder, and become faster at the flatter, so it taps the floor
then stops end? more often

Pencil It turns lying down on the table Why does it not stand A pencil is long and thin, so
and stops very soon up like the coin? it can only roll or turn flat

Piece of Stone It moves a little and stops at Why does it not spin at Its sides are bumpy and not
once all? the same all round

Wooden It stands upright and spins for a Why does it keep Its tip is pointed and it is the
Spinner (Top) long time standing while it spins? same on all sides

Eraser It does not spin properly; it Why will it not spin? It has flat sides and corners,
slides and stops so it cannot turn smoothly

Why it happens: A thing spins well when it is the same on all sides and rests on a
small point. The coin, the bangle and the top are like this; the pencil, the stone and
the eraser are not.

Try this: Spin a coin on a table and then on a woollen cloth. It spins for much longer
on the smooth table.

In-text Questions — Page 106
Let us make some spinners and explore

Q1 How does a top spin?

A top spins because we give it a quick twist and it then turns on its pointed tip.

Page 5 of 27

Class 4 The World Around Us Chapter 7 How Things Work AglaSem · NCERT Solutions

Set-up: wind the string round the top, hold the end and pull it sharply.

1. We wind a string around the top, or twist its stem sharply with our fingers.
2. The top starts turning round and round on its sharp tip.
3. Only the tiny tip touches the ground, so the top keeps turning for a long time.
4. Slowly it turns less and less, begins to shake, and then falls down.

Why it happens: The top stays standing because it is the same on all sides and turns
fast. When it slows down it can no longer stay upright, so it wobbles and falls.

Did you know? Spinning tops have been used in India for thousands of years.
Earlier they were made of clay. The lattu is a popular Indian top and is usually made
of wood.

Activity 2 — Pages 106–107

Page 6 of 27

Class 4 The World Around Us Chapter 7 How Things Work AglaSem · NCERT Solutions

Making spinners and testing them

ACTIVITY

Q1 Collect things, such as pieces of cardboard, toothpicks, an empty tube of a ballpoint
pen, and other small objects. Make the following spinners. Spin them and record
your observations.

What to do

1. Cut two round pieces and one square piece from thick cardboard, each about as wide as
your palm.
2. Make a small hole in the centre of the first round piece. Push a toothpick through it so a
little of the toothpick sticks out below.
3. Make the hole away from the centre in the second round piece and push a toothpick
through it.
4. Push a toothpick through the centre of the square piece.
5. Take one more round piece with the toothpick at the centre, and draw a small dark mark
near its edge.
6. Spin each one on a table and write down what you see.

Toothpick at Toothpick away A square spinner Circular spinner with
the centre from the centre a mark on its body

Set-up: push a toothpick through a piece of card. These are the four spinners to make.

The completed table

Page 7 of 27

Class 4 The World Around Us Chapter 7 How Things Work AglaSem · NCERT Solutions

CHANGE IN THE WHAT DO YOU OBSERVE? ANY OTHER OBSERVATIONS
SPINNER (SPINS/DOES NOT SPIN)

Toothpick at the centre Spins It stands upright and spins for a long time.
It looks the same from all sides.

Toothpick away from the Does not spin properly It wobbles at once and falls over very soon.
centre

A square spinner Spins While it is spinning it looks round, not
square.

Circular spinner with a Spins The mark is no longer seen as a dot. It
circular mark on its body looks like a ring going round and round.

Any other — a triangular Spins It also looks round while spinning, just like
spinner the square one.

Why it happens: A spinner spins well when the stick is at its centre, because then
both sides of the card weigh the same and it stays upright.

Tip: If your spinner still wobbles, try a shorter toothpick below the card, or push the
card so it sits flat and straight on the stick.

Discuss — Page 108
Which spinner spun properly?

DISCUSS

Q1 Which of the spinners did not spin properly? Discuss the possible reasons.

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

Page 8 of 27

ase
Class 4 The World Around Us Chapter 7 How Things Work
a g l AglaSem · NCERT Solutions

co m
e m.
m l as
m .co a g
l a se
a g

. comA square spinner ag
e m
Toothpick at Toothpick away Circular spinner with

l as
the centre from the centre a mark on its body

a g
Set-up: push a toothpick through a piece of card. These are the four spinners to make.

co m
Possible reasons we discussed:
se m.
o m l a
g is bigger and heavier.
m .c sides of the card around the stick are not the same. Oneaside
The two

l a se heavier side keeps pulling down, so the spinner leans over as it turns.
g
The
a The toothpick below the card may be too long or bent, so the spinner does not rest on one

s
small point.
m a
.co agl
The card may not be sitting flat and straight on the toothpick.

a s em
Why it happens: A spinnerag l turning only when it is balanced — the same on
keeps
every side of the stick.

co m
m .
o m l a se
.cHave you noticed the position of the hole in the first two
a g spinners? Did this
e m
las difference in the position of the hole make a difference in the spinning of these
Q2

ag spinners?

se m
com g l a
m . a
e

g l as a big difference.
Yes, the position of the hole made
a

co m
m .
m as e
.co a g l
se m
g l a
a c
m .
m a s e
.co agl
Toothpick at Toothpick away A square spinner Circular spinner with

em
the centre from the centre a mark on its body

a s
agl through a piece of card. These are the four spinners to make.
Set-up: push a toothpick

co m
m .
m ase
.co


a g l Page 9 of 27

Class 4 The World Around Us Chapter 7 How Things Work AglaSem · NCERT Solutions

SPINNER WHERE THE HOLE IS WHAT HAPPENED

First spinner At the centre It stayed upright and spun well

Second spinner Away from the centre It wobbled and fell over soon

The book says it plainly: the first spinner, with a hole at the centre, appears to be the same from
all sides. This spinner remains upright and spins, but that is not the case with the second
spinner.

Why it happens: When the hole is at the centre, the card on both sides of the stick is
equal, so nothing pulls the spinner to one side.

In-text Questions — Page 108
Spinners of other shapes

Q1 What other shapes can you try? Make spinners using different shapes of card
pieces, spin them, and observe what happens.

What to do

1. Cut cards in different shapes — a triangle, a rectangle, a pentagon, a star, a heart.
2. Find the middle of each shape and push a toothpick through it.
3. Spin each one on a table and look at it carefully while it turns.

Triangle Star Rectangle

Set-up: find the middle of each card shape and push the toothpick through it there.

Page 10 of 27

Class 4 The World Around Us Chapter 7 How Things Work AglaSem · NCERT Solutions

Sample answer: I made a triangle spinner, a star spinner and a rectangle spinner. Every one of
them looked round while it was spinning. The star spinner looked like a circle with a soft edge.
The rectangle spinner wobbled a little more than the others.

Why it happens: The shape turns so fast that our eyes cannot follow its corners. We
only see the path the corners make, and that path is a circle.

Tip: Fold the card in half twice to find its middle before making the hole. A hole at
the middle always spins better.

In-text Questions — Page 109
Colouring the spinner

Q1 What other changes can you make in your spinner? Can you colour it? How many
different ways can you colour it?

Yes, you can colour it — and you can colour it in very many ways. The book shows four of
them.

Four ways of colouring a round spinner, as shown in the book.

Other changes you can make:

Make the card bigger or smaller.
Use a longer or a shorter toothpick below the card.
Cut the card in a new shape.
Stick a small paper flag on the top.
Paint the spinner in a new pattern — rings, dots, stripes or slices.

Page 11 of 27

Class 4 The World Around Us Chapter 7 How Things Work AglaSem · NCERT Solutions

Sample answer: I coloured one spinner with two colours turn by turn, one with four colours,
one with all seven colours of a rainbow, and one with only dots. So there is no fixed number —
you can colour a spinner in as many ways as you can think of.

Why it happens: Colour does not change how the spinner turns. It only changes
what we see while it is turning.

Q2 Colour the spinners in different ways, spin them and observe what happens. What
happens to the colours on the spinner when it is painted with different colours and
then spun?

The separate colours are no longer seen. They mix together and the spinner looks like one
single colour.

Four ways of colouring a round spinner, as shown in the book.

SPINNER WHEN IT IS STILL WHEN IT IS SPINNING FAST

Purple and blue slices Eight separate slices One soft blue-purple colour all over

Yellow and red slices Eight separate slices One orange-ish colour all over

Many colours together Eight different colours One pale, dull colour, close to grey or white

Why it happens: The spinner turns so fast that our eyes cannot follow each colour
one by one. We see all the colours together, so they look mixed into one.

Try this: Spin it slowly at first and then faster. The colours stay separate while it is
slow and mix only when it turns fast.

Page 12 of 27

Class 4 The World Around Us Chapter 7 How Things Work AglaSem · NCERT Solutions

Q3 Many things around us spin, such as ceiling fans and potter’s wheels. What other
things have you observed spinning?

Many things around us spin. Here are ones you can see every day.

WHERE THINGS THAT SPIN

At home Ceiling fan, table fan, mixer jar, washing machine drum, wall clock hands

On the road Wheels of a cycle, a bus and a bullock cart; the steering wheel

At work Potter’s wheel, charkha (spinning wheel), grinding stone (chakki), windmill

At play Lattu (top), merry-go-round, a hula hoop, a spinning coin

In nature A falling maple-type seed, a whirling leaf in the wind

Why it happens: All these things turn round and round about a fixed centre, just like
our cardboard spinner turns about its toothpick.

Did you know? A charkha (spinning wheel) is used to twist cotton fibre into thread.
Mahatma Gandhi used the charkha to make handmade clothes.

In-text Questions — Page 110
Floating and Sinking

Q1 You can try this out at home. Make a paper boat and float it in a bowl. Observe
whether your boat floats properly like in Picture 1 or flips like in Picture 2?

What to do

1. Fold a paper boat from an old newspaper sheet.
2. Fill a bowl with water and place the boat on the water very gently.
3. Watch it for a minute. See whether it stays upright or turns over on its side.

Page 13 of 27

as e
Class 4 The World Around Us Chapter 7 How Things Work
a g l AglaSem · NCERT Solutions

co m
e m.
m l as
m .co a g
l a se
a g

com
e m . ag
g l as
a

co m
m.
Picture 1 Picture 2
m as e
.co a g l
Picture 1 and Picture 2 show a paper boat put into a bowl of water.

a s em
a l you will see:
gWhat
m a s
agl
A boat with a wide, flat bottom and equal sides floats upright, as in Picture 1.

m .co
A boat that is narrow or badly folded, or one that is pushed in from one side, tips over, as in
Picture 2.
l a se
a g
After some time the paper soaks up water, becomes soft, and the boat slowly sinks.

Sample answer: My first boat floated properly like Picture 1. When I made a second boat with
co m
thin paper, it leaned to one side and flipped over like Picture 2.
m .
o m l a se
.c it happens: A boat stays upright when its two sides aareg the same and its
m
asebottom is wide. If one side is heavier, the boat leans over and flips.
Why

agl
se m
com g l a
. a
Activity 3 — Pages 110–111sem
a
agl

co m
m .
m as e
.co a g l
se m
g l a
a c
m .
m a s e
e m . co agl
g l as
a

com
m .
m ase
.co


a g l Page 14 of 27

Class 4 The World Around Us Chapter 7 How Things Work AglaSem · NCERT Solutions

Which things float and which sink?

ACTIVITY

Q1 Collect objects, such as a leaf, an iron nail, an empty bowl (katori), a plastic bottle
with a lid, pieces of stone, aluminium foil and other things of your choice. Fill a
bucket with water. Before dropping the things listed in the table, guess whether
things will float or sink. You may try other things too. Then, observe what happens
when it is actually dropped in water. You can write ‘F’ for objects that float and ‘S’
for objects that sink.

ITEMS BEFORE DROPPING AFTER DROPPING

WHAT IS WHY DO WHAT IS YOUR WHAT COULD
YOUR YOU OBSERVATION? BE THE
GUESS? THINK REASON?
SO?

Leaf F It is light F It is light

Iron nail or
pin

Empty steel
bowl

A piece of
stone

Empty
bottle with
a closed lid

Bottle full of
water with a
closed lid

The table as it is printed in the book, with the leaf row already filled in as an example.

What to do

1. Fill a bucket with water and keep all the things ready beside it.
2. First guess for each thing — will it float (F) or sink (S)? Write the guess and the reason.

Page 15 of 27

Class 4 The World Around Us Chapter 7 How Things Work AglaSem · NCERT Solutions

3. Now put the things in the water one by one, gently.
4. Write down what really happened and what you think the reason is.

Leaf Iron nail Empty steel A piece of Empty bottle Bottle full of water
Bucket of water or pin bowl (katori) stone with closed lid with closed lid

Set-up: fill a bucket with water and keep these things beside it, one at a time.

The completed table

ITEMS BEFORE BEFORE AFTER DROPPING AFTER
DROPPING — DROPPING — — WHAT IS YOUR DROPPING —
WHAT IS YOUR WHY DO YOU OBSERVATION? WHAT COULD
GUESS? THINK SO? BE THE
REASON?

Leaf F It is light F It is light

Iron nail S It is made of iron S Iron is heavy for its
or pin and feels heavy small size, so it goes
down

Empty S Steel is heavy F It is empty, and its
steel bowl cup shape holds air
inside

A piece of S It is hard and S It is heavy for its
stone heavy small size

Empty F It is light and full F The closed bottle is
bottle of air full of air, so it stays
with a on top
closed lid

Bottle full S It is full of water S There is no air
of water and feels heavy inside it now, so it
with a goes down
closed lid

Page 16 of 27

Class 4 The World Around Us Chapter 7 How Things Work AglaSem · NCERT Solutions

Why it happens: The book says it after the activity — some heavy objects like iron
nails sink, while lighter ones like leaves float. But the empty steel bowl is heavy and
still floats, so weight alone does not decide it.

Tip: Lower the steel bowl into the water slowly and keep it straight. If it tilts, water
goes in and then it sinks.

Discuss — Page 111
Heavy things and light things

DISCUSS

Q1 Did all the light objects float and all the heavy objects sink? Name the heavy objects
that floated and lighter objects that sank.

No. Some heavy things floated and some light things sank.

HEAVY THINGS THAT FLOATED LIGHT THINGS THAT SANK

Empty steel bowl (katori) A small pin

A big empty plastic bottle with the lid closed An eraser

A wooden plank A small marble

So the book’s own words are right: Floating or sinking of an object cannot be decided based just on
whether it is heavy or light. It also depends on other factors.

Why it happens: The empty steel bowl floats because it is hollow and holds air. A pin
is light but it is solid metal packed into a very small space, so it sinks.

Check it yourself: A big ship made of iron floats, but a tiny iron nail sinks. Size and
shape matter, not weight alone.

Activity 4 — Page 112

Page 17 of 27

Class 4 The World Around Us Chapter 7 How Things Work AglaSem · NCERT Solutions

Does shape play a role?

ACTIVITY

Q1 Let us find out whether shape plays a role in floating and sinking.

What to do

1. Cut three pieces of aluminium foil of the same size.
2. Leave the first piece spread out flat.
3. Press the second piece tightly into a small ball, squeezing out as much air as you can.
4. Bend the third piece into a cup shape, like a small katori.
5. Guess first, then put each piece gently into a bowl of water and watch.

pressed tightly in a cup-like
Bowl of water spread out into a ball shape

Set-up: take three equal pieces of aluminium foil and give each one a different shape.

The completed table

ALUMINIUM BEFORE BEFORE AFTER DROPPING AFTER
FOIL WHEN— DROPPING — DROPPING — — WHAT IS YOUR DROPPING —
WHAT IS WHY DO YOU OBSERVATION? WHAT COULD
YOUR GUESS? THINK SO? BE THE
REASON?

spread out F It is thin and light F It lies spread wide
on the water

pressed tightly F It is the same foil, S All the foil is
into a ball so it should still squeezed into a
float small space and no
air is left inside

in a cup-like F A cup is like a F The cup holds air
shape small boat inside it

Page 18 of 27

ase
Class 4 The World Around Us Chapter 7 How Things Work
a g l AglaSem · NCERT Solutions

What this activity teaches: the book states it plainly — By changing the shape, we can make an
co m
object float or sink. When aluminium foil was spread out or made in the shape of a cup, it floated.
e m.
m l as
.co g
However, when it was made into a ball, it sank.

em a
a s
gl it happens: The foil weighs the same in all three tests. Only its shape changed,
aand
Why
that alone decided whether it floated or sank.

. com ag
m trapped inside, the ball may float too.
Tip: Press the ball really tightly. If airestays
s
a
agl

co m
Activity 5 — Pages 113–114
em.
m l as
.co a g
Let us create some boats

se m
l a
ACTIVITY

g
a
m
Let us create some boats: • Collect some paper, cardboard boxes, ice-cream sticks,
a s
.co agl
Q1

em
clay, adhesive tape, etc. • Create groups of three to four students. • Think of how

a s
agl that your boat is different from boats made by other
you can make a boat using some of the materials that you have. • Draw a picture. •
Prepare a boat. Try to ensure
groups. • Organise an exhibition of boats in the class.

co m
m .
m step by step as e
What.to codo, a g l
s e m
agla 1. Sit in a group of three or four. Put all your material on one desk.
m
2. Talk about what your boat will look like. Decide its shape and its size.

m flat so it does not tip over. l a se
coand
3. Draw a picture of your boat in your notebook first, and mark which material goes where.
. a g
4. Build the boat. Make the bottom wide
5. Seal the joints well with tapeaors m so water cannot get in.
eclay
l
aganything
6. Test it in a tub of water. Fix that leaks or tips.

m
7. Put all the boats on one table with name cards, and invite the other classes to see them.

. co
em
m l as
m .co a g
l a se
ag
.c
s e m
m a
e m . co agl
g l as
a
A boat made with A boat made of a Boats made using
ice-cream sticks coconut shell walnut shells

com
m .
m ase
.co


a g l Page 19 of 27

Class 4 The World Around Us Chapter 7 How Things Work AglaSem · NCERT Solutions

Three kinds of boats shown in the book that a group can make.

Sample answer: Our group made a raft from twelve ice-cream sticks. We laid the sticks side by
side and joined them with two sticks across the back and adhesive tape. We pressed a small
lump of clay in the middle to hold a paper flag. The raft floated flat on the water and did not tip
even when we put two erasers on it.

Why it happens: A boat floats because it is hollow or flat and wide, so it spreads its
weight over a lot of water — exactly like the foil cup in Activity 4.

Tip: Coconut shells, walnut shells and a big leaf all make good boats. They are
hollow and light.

Q2 Compare your boat with others’ boats.

Fill in the table after looking at your boat and at two or three other groups’ boats.
A completed sample table

STRENGTHS OF YOUR BOAT CHALLENGES OF YOUR BOAT

Its bottom is wide and flat, so it does not tip over Water slowly comes in between the sticks

Ice-cream sticks are strong, so the boat does not break It is heavy, so it sits low in the water

It can carry two erasers without sinking The tape comes off after it is wet for a long time

What we noticed when we compared:

The paper boat was the lightest but it became soft and sank first.
The coconut-shell boat floated best because it is hollow.
The clay boat sank when it was rolled into a lump, and floated when it was made like a bowl.

Why it happens: The book says it too — some boats are strong and hard to break,
while others break easily; some tip over easily, while others keep better balance.

Page 20 of 27

Class 4 The World Around Us Chapter 7 How Things Work AglaSem · NCERT Solutions

Q3 Think about how you can improve your boat.

Here are changes that really make a boat better. Try one change at a time and test it.

1. Make the bottom wider and flatter. A wide bottom keeps the boat from tipping over.
2. Seal every joint. Cover the gaps with tape or a thin layer of clay so no water comes in.
3. Keep both sides the same. If one side is heavier, the boat leans and flips.
4. Use lighter material. Thermocol, cork and a coconut shell float much better than thick clay.
5. Raise the sides a little. Higher sides keep water and waves out.
6. Place the load in the middle. Weight kept in the centre keeps the boat level.

Narrow bottom — it tips over Wide, flat bottom — it stays level
Two boats of the same size put into water, one with a narrow bottom and one with a wide, flat
bottom.

Why it happens: Each of these changes works on the boat’s shape and balance —
and shape is what decides whether a thing floats or sinks.

Check it yourself: Put one coin at a time in your boat. Count how many coins it can
carry before it sinks. Then improve the boat and count again.

Let us reflect — Pages 115–116

Page 21 of 27

Class 4 The World Around Us Chapter 7 How Things Work AglaSem · NCERT Solutions

End-of-chapter questions

LET US REFLECT

Q1 Enquire about something: When Ravi spins a spinner, he notices that it slows down
and eventually stops. He is curious about this and asks his teacher some questions.
List at least two questions that he could ask.

Ravi can ask any questions that help him find out why the spinner stops. Here are good ones.

spins fast begins to shake stops and falls

A spinner, moments after it is started and a little later.

1. Why does the spinner slow down and stop on its own?
2. What can I do to make it spin for a longer time?
3. Will it spin longer on a smooth table than on a rough mat?
4. Does a bigger spinner spin longer than a smaller one?
5. Why does the spinner begin to shake just before it stops?
6. Will a sharper, thinner tip make it spin longer?

Sample answer: Ravi could ask — “Why does the spinner slow down and stop by itself?” and
“What should I change so that it spins for a longer time?”

Why it happens: A good question names one thing you can change and test — the
floor, the size, the tip — so you can try it out and find the answer yourself.

Tip: The book does not expect a perfect explanation here. It wants you to think of
questions and then try them out.

Page 22 of 27

Class 4 The World Around Us Chapter 7 How Things Work AglaSem · NCERT Solutions

Q2 Figure it out: (a) The following figure is bending towards the side ‘A’. What should be
done to balance it?

B

A

Two sticks are tied in a cross and hung from one thread. Paper toys hang from some of
the threads.

Hang something on side B of the same weight as the paper toy hanging on side A — then
the two sides will be equal and the sticks will hang level.

Page 23 of 27

as e
Class 4 The World Around Us Chapter 7 How Things Work
a g l AglaSem · NCERT Solutions

co m
e m.
m l as
m .co a g
l a se
a g B

co m
e m . ag
g l as
a

co m
em.
c o m g l as
. a
a s
Aem
ag l

m a s
m .co agl
l a se
a g
Two sticks are tied in a cross and hung from one thread. Paper toys hang from some of the threads.

Any one of these will balance it:
co m
m .
m
1. Tie a paper toy of the same weight to the empty thread at end B.
as e
.co a g l
em
2. Take off the toy hanging at end A, so that both ends carry nothing.

l a s3. Move the toy at A nearer to the centre, and the one at B further out.
ag 4. Make the toy at A lighter, for example by using a smaller piece of paper.

se m
o m g l a
m .cside B carries nothing, so side A goes down.
Why it happens: The stick hangs level only when both sides pull down equally. Right
a
a
now side A carries a paper toy
l seand
ag
m
Try this: Hang a ruler from a thread tied at its middle. Hang one eraser on the left
. co
m
and it dips. Hang the same eraser on the right too, and it becomes level.

m as e
.co a g l
se m
g l a
a (b) How would you make a floating object sink and a sinking object float?
c
.
Q3

s e m
m a
e m . co agl
g l as
Change its shape, or change what is inside it. That is the whole idea of this chapter.
a

co m
m .
m ase
.co


a g l Page 24 of 27

Class 4 The World Around Us Chapter 7 How Things Work AglaSem · NCERT Solutions

WHAT I WANT WHAT I WOULD DO EXAMPLE FROM THE CHAPTER

Make a floating Press it tightly into a small ball, so Flat aluminium foil floats; the same foil pressed
object sink no air is left inside into a ball sinks

Make a floating Fill it with water and close it An empty bottle with a closed lid floats; the
object sink same bottle full of water sinks

Make a floating Put something heavy inside it, or Put stones into a floating katori and it goes
object sink push it right under down

Make a sinking Spread it out flat or bend it into a A foil ball sinks; open it out into a cup and it
object float cup or boat shape floats

Make a sinking Place it on something that floats A coin sinks; put it in a paper boat and it stays
object float on top

Why it happens: The book states it clearly — By changing the shape, we can make an
object float or sink. A wide or cup-like shape holds air and rests on the water; a tight,
small shape does not.

Q4 Do an activity: Classify the objects below based on whether they float or sink in
water. Wax, Marble, Thermocol, Candle, Coin, Cork, Leaf, Eraser, Spoon, Ice-cube,
Potato, Tomato, Pumpkin, Lemon

Put each one gently into a bucket of water and watch. Here is the completed answer.

Page 25 of 27

Class 4 The World Around Us Chapter 7 How Things Work AglaSem · NCERT Solutions

THINGS THAT FLOAT THINGS THAT SINK

Wax Marble

Thermocol Coin

Candle Eraser

Cork Spoon

Leaf Potato

Ice-cube

Tomato

Pumpkin

Lemon

Nine things float and five things sink.

Why it happens: Wax, cork, thermocol and ice are light for their size, so they stay on
top. A pumpkin and a lemon are big but have some air inside, so they float too. A
marble, a coin, a steel spoon and an eraser are heavy for their small size, so they go
down. A potato has no air inside and sinks.

Check it yourself: A candle is made of wax, so it floats just like a lump of wax. A big
pumpkin floats even though it is much heavier than a small marble that sinks —
weight alone does not decide it.

Chapter at a glance
Some things spin well and some do not. A coin, a bangle and a wooden top spin; an eraser
does not spin properly.
A spinner spins best when the toothpick goes right through its centre. Then it looks the
same from all sides and stays upright.
A square spinner looks round while it is spinning, and many colours painted on a spinner
mix into one colour.
Some heavy things float and some light things sink. So floating cannot be decided by weight
alone.

Page 26 of 27

Class 4 The World Around Us Chapter 7 How Things Work AglaSem · NCERT Solutions

Shape matters. Aluminium foil floats when it is spread out or shaped like a cup, but it sinks
when it is pressed into a tight ball.
Many things around us spin — ceiling fans, a potter’s wheel, the charkha and the lattu.

Quick revision

WHAT WE TRIED WHAT WE WHAT WE SAW WHY IT HAPPENS
CHANGED

Coin Spun it standing on its It shakes as it slows It cannot stay standing when it
edge down turns slowly

Spinner Toothpick at the centre Stands upright and It looks the same from all sides
spins well

Spinner Toothpick away from the It wobbles and falls Its two sides are not the same
centre

Square spinner Shape of the card It looks round while It turns too fast for our eyes to
spinning follow

Coloured spinner Painted in many colours The colours mix into The colours move too fast for
one colour our eyes

Leaf Put in water Floats It is light

Iron nail Put in water Sinks It is heavy

Empty steel bowl Put in water gently Floats It is empty and holds air inside

Bottle full of water, lid Put in water Sinks It is full of water, so it is heavy
closed

Aluminium foil Spread out flat Floats It lies spread wide on the water

Aluminium foil Pressed tightly into a Sinks All the foil is squeezed into a
ball small space

Aluminium foil Made into a cup shape Floats The cup holds air inside it

Page 27 of 27