Unit 6 : Light, Sound and Force

Vocabulary
1. luminous 8. noise
2. non-luminous 9. volume
3. shadow 10. push
4. soft 11. pull
5. pleasant 12. effect
6. loud 13. friction
7. unpleasant

Page 1 of 23
Answer the following questions
Q 1. Why can’t we see an object in a dark room?
We can’t see objects in a dark room because light doesn’t fall on them.
We can see objects when light falls on them.

Q 2. What are luminous objects ? Give examples.

Objects that give out light on their own are called luminous objects.

fire Lamp lighted bulb matchsticks sun

firefly liter lighted candle stars torch

Page 2 of 23
Q 3. What are non-luminous objects ? Give examples.
Objects that do not give out light on their own are called non- luminous objects
Eg: Moon, pencil, books, tables, chairs, boy, tree etc.

Q4. Define transparent, translucent and opaque objects with examples

Objects or materials that allow all light to pass through are called
transparent.
Eg. Water, glass etc.

Objects or materials that allow some light to pass through are called
translucent

Eg. Tracing paper, waxed paper etc.

Objects or materials that do not allow any light to pass through are called
opaque
Eg. wood, stone etc.

transparent. translucent opaque

Q 5. How are shadows formed ?

Light travels in a straight line as thin beams of rays.

Page 3 of 23
Shadows are formed when an opaque object or material blocks the path
of light. A shadow is always formed on the opposite side of the light.

Large shadow when the

opaque object is close to
the light.

Smaller shadow when the

opaque object is further
from the light.

Tiny shadow when an

opaque object is a long
way from the light.

Page 4 of 23
Q 6. Briefly describe the shape of shadows at different timings of the
day.

In the morning and evening, the shadow is long.

At noon the shadow is short.

1. The sun is low in the sky in the morning, so the shadows are long.
2. The sun is high in the sky at noon, so the shadows are short.
3. The sun is low in the sky in the evening, so the shadows are long.

SOUND
Page 5 of 23
Q7. What is sound ?
Sound refers to anything that can be heard.

Q8. How is sound produced?

Sound is produced when something vibrates or shakes.
The vibrations make the air shake.
The shaking air enters our ears which we hear as sound.

Page 6 of 23
Q 8. Name the different types of sound?
The different types of sound are
1. Soft sounds
2. Loud sounds
3. pleasant sounds
4. unpleasant sounds

a) Loud sounds are sounds that are high in volume.

b) Soft sounds are sounds that are low in volume.
c) Pleasant sounds are the types of sound which feels good or in
harmony with human hearing. It doesn’t cause noise pollution.
d) Unpleasant sounds are sounds which are not good for hearing and it
makes one irritating. It cause noise pollution.

1. can effectively reduce noise pollution.

2. Buildings can be designed with suitable noise absorbing material for the
walls, windows, and ceilings.
3. Workers should be provided with equipment’s such as ear plugs and
earmuffs for hearing protection.
Page 7 of 23
Page 8 of 23
FORCE
Q 10. What is force?
A push or pull applied on a body is called force.

Q 11. What are the effects of force on an object?

1. Force can move a resting object
2. Force can change the shape of an object
3. Force can stop a moving object
4. Force can change the direction of an object

Q 12. What is friction? Give an example

Friction is a special force that slows down movement.
When we roll a ball on the floor it slows down and finally stops.
Friction stops this moving ball.

Q 13. How does friction help us in our daily life ?

We are able to walk, write due to friction.

Page 9 of 23
Light, Sound and Force Practice Sheet
Choose the correct answer from the options
1. A natural source of light is sun
a. tube light b. sun c.torch
2. Which of the following is not a man-made source of light? firefly
a. firefly b. bulb c. CFL
3. A pleasant sound is chirping of birds.
a. horn b. chirping of birds c. drilling sound
4. Whispering is a soft sound.
a. loud b. unpleasant c. soft
5. You should play the music and TV at a low volume.
a. high volume b. very high-volume c. low volume
6. Force is defined as both push and pull.
a. push b. pull c. both push and pull
7. You can apply force to both.
a. change the shape b. stop the moving objects c.both
8. When we push or pull something we apply force and do work.
a. sleep b. do work c.do nothing
9. The force which slows down the movement is called friction.
a. friction b. motion c. rest
10. Force can do many things.
1. nothing b. one thing c.many things

Page 10 of 23
Fill in the blanks
1. Shadow is formed when an object blocks the path of light.
2. A natural source of light which is an animal is jellyfish/ glow worm.
3. A resting body can move when force is applied.
4. For drawing water from a well you apply pull force.
5. Noise is caused by an unpleasant sound.
6. Light travels in a straight line as thin beams of rays.
7. A candle is a non-luminous object.
8. We should speak softly.
9. We see non- luminous objects when light falls on them.

Circle the odd one. Give reasons for your answers.

(a) bulb chair sun
The Sun is a luminous object whereas the rest are non-luminous objects.

(b) soft loud pull

Pull is a type of force whereas the rest are types of noise.

(c) honking chirping screaming

Chirping is a pleasant sound whereas the rest are unpleasant sounds.

Page 11 of 23
Answer the following
1. What is force?
A push or pull applied on a body is called force.

2. How are shadows formed?

Light travels in a straight line as thin beams of rays.
Shadows are formed when an object blocks the path of light.

3. Differentiate between luminous and non- luminous objects with examples .

Luminous Objects Non- luminous objects

Objects that give out light on their Objects that do not give out light on
own are called luminous objects. their own are called non- luminous
Eg. Lighted bulb, lighted candle, objects.
lighted torch, sun, firefly , stars etc. Eg. Moon, pencil, books, chairs etc

4. How is a pleasant sound different from an unpleasant sound ?

Pleasant sounds Unpleasant sounds
Pleasant sounds are regular. Unpleasant sounds are irregular.
They are pleasing to our ears and They are not pleasing to our ears and
minds. minds.

5. What can we do to reduce noise ?

We can reduce noise
1. by speaking softly
2. by playing T.V and music system at a low volume.

Page 12 of 23
6. State the effects of force on any object.
1. Force can move a resting object
2. Force can change the shape of an object
3. Force can stop a moving object
4. Force can change the direction of an object

7. What is friction? Give one example.

Friction is a special force that slows down movement.
Eg: When we roll a ball on a floor it slows down and finally stops.
Friction stops this moving ball.

8. Are you able to do any work without applying any force ?

If yes, give examples, if no, give reasons.
The push or pull on any object is known as force.
Work is said to be done when the force applied on any object moves a distance
in a direction.
If there is no change in the position of the object, then no work is done.
Hence, force is necessary for doing work.

9. What are the effects of unpleasant sound or noise on children?

Noise can affect children very badly.
It can cause learning disabilities, attention difficulties, hypertension, stress
ulcers. Sudden exposure to loud noise is harmful to our ears and nervous
system.

10. Give two examples of man-made sources of light.?

The sources of light may be natural or man-made.
Candles and bulbs are two examples of man-made sources of light.
They have to be lit or turned on by humans.

11. Give two examples of pleasant sound.

The soft sound that makes us happy is pleasant.
The chirping of birds and buzz of bees are two examples of pleasant sound.
Page 13 of 23
12. Give two examples of noise or unpleasant sound.
The loud sound that is harmful to our ears and nervous system is unpleasant.
The sound of crackers and horns of vehicles are some examples of unpleasant
sounds.
It creates disturbance whenever they are produced.

13. Choose the activity which is correct for which we apply force:
1. Hitting the ball.
2. Throwing a toy.
3. Growing grass.
4. Watching TV
5. Ironing a shirt.

Page 14 of 23
Q1. Name the different types of sound?
The different types of sound are
1. Loud sounds are sounds that are high in volume.
2. Soft sounds are sounds that are low in volume.
3. Pleasant sounds are the types of sound which feels good or in harmony
with human hearing. It doesn’t cause noise pollution.
Eg: music, birds chirping
4. Unpleasant sounds are sounds which are not good for hearing and it
makes one irritating. It causes noise pollution.
Eg:
a) loud sound of TV and radio
b) loud sound of machines in factories,
c) loud music in parties
d) honking of horns on vehicles

Q2. What is Pitch?

Pitch is called the highness and lowness of a sound.
The higher the frequency, the higher the pitch.
The lower the frequency, the lower the pitch.

Q3. What is noise ?

Lound and unpleasant sound is called noise.
Noise causes noise pollution.
Q4. List sources of noise pollution in your surroundings.
There are various sources which cause sound pollution in our
surroundings,
1. loud sound of TV., radio,
2. loud sound of machines in factories,
3. loud music in parties
4. honking of horns on vehicles

Q5. What is a music?

a. Music are pleasant sound which feels good or in harmony with human
hearing.

Page 15 of 23
b. Music doesn’t cause noise pollution.
c. Music need musical instruments to play.

Can music become noise sometimes ?

Music becomes noise sometimes when we play it in high volume.

Q6. How can we reduce noise?

We can reduce noise
1. by speaking softly.
2. by playing T.V and music system at a low volume.

Q7. Trees act as noise barriers by absorbing sound and help in reducing noise
pollution.
Q8.. A well planted group of trees can reduce noise pollution by up to 10
decibels.

Q9. What are the solution For Noise Pollution?

1. Planting bushes and trees.
2. Regular servicing and tuning of automobiles

FORCE
Q1. What is force?
A push or pull applied on a body is called force.

Q2. What are the effects of force on an object?

What will happen when you apply force on an
object?
1. Force can move a resting object
2. Force can change the shape of an object
3. Force can stop a moving object
4. Force can change the direction of an object

Q3. What is friction? Give an example

Friction is a special force that slows down movement.
Eg: Friction stops a moving ball.

Q4. How does friction help us in our daily life?

1. Friction helps us in our daily life in different ways:
2. Friction helps us to write on a notebook / blackboard / whiteboard.
3. Friction helps us to drive vehicles on the road.
Page 16 of 23
 4. Friction helps us to light a matchstick.
5. Friction helps us to hold our shoe to the ground.
6. Friction applies brakes to stop a moving object.

Q5. What are the causes of friction? OR What are the disadvantages of friction?
1. Friction produces heat.
2. Friction produces sound.
3. Friction wears out the rubbing surface.
4. Friction damage to the parts of machines.
5. Friction reduces the speed of moving objects, so more force is required.
6. Friction does not allow the free movement of objects.

Q6. A pencil eraser uses friction to rub off mistakes written in pencil lead.

Q7. Tyres of wheels are threaded why?

Will it be easy to apply break if not threaded?
1. Tyres of wheels are threaded because it increases the friction between the
tyre and the road.
2. It gives better grip.
3. It prevents skidding.
4. It is not easy to apply break if not threaded.

Q8. We sprinkle powder on the carom board before the game why?
We sprinkle powder on the carom board before the game because it decreases
the friction between the carom board and the Stricker.

Friction can be increased by Friction can be decreased by

1. threading 1. using lubricants.
2. scratching 2. using wheels.
3. making a surface rough 3. using ball bearing in machines.

1. Friction slows down the movement of an object.

2. The shadow is formed on the opposite side of the light source.
3. The shortest shadows are formed at noon.
4. The longest shadows are formed in the evening and morning.
5. We hear all kinds of sounds with the help of ears.
6. Unpleasant sounds disturb you.
7. Friction slows movement.
8. Noise is an unpleasant sound.
9. Loud and unpleasant sound is noise.
10. Who helps us to make sounds? Our tongue
11. The sun is the main souce of light and heat on earth.
12. The force helps us to move objects.
13. Force changes the shape of the objects.

Page 17 of 23
Move closer to you  PULL
Move object away from you  PUSH

Force Of Push Or Pull > Force Of Friction

Things slide  Less friction

Things do not move  More friction

1. Give two examples each of situation in which you push or pull to change the
state of motion of objects.
(i) We apply brakes to a moving bicycle.
(ii) We pull a chair to change its position.

2. Give two examples of situations in which applied force causes a change in

the shape of an object.
1. Making toys from clay.
2. A lady making chapatis.

3. Fill in the blanks in the following statements.

(a) To draw water from a well we have to pull at the rope.
(c) To move a loaded trolley we have to push it.

4. A blacksmith hammers a hot piece of iron while making a tool.

How does the force due to hammering affect the piece of iron?
The blacksmith hammers a hot piece of iron, the hitting force changes the
shape of iron into a tool.

5. Friction depends on the nature of surfaces.

6. Friction produces heat.
7. Sprinkling powder on the carom board reduces or decreases friction.
8. Sliding friction is less than static friction.
9. Name the force that always opposes the applied force. = Frictional force

Page 18 of 23
10. Give examples to show that friction is both a friend and a foe.
Friction is friend:
1. Friction helps us to write on a notebook / blackboard / whiteboard.
2. Friction helps us to catch different objects
3. Friction helps us to drive vehicles on the road.
4. Friction helps us to light a matchstick.
5. Friction helps us to hold our shoe to the ground.
6. Friction applies brakes to stop a moving object.

Friction is foe:
1. Friction produces heat.
2. Friction produces sound.
3. Friction wears out the rubbing surface.
4. Friction damage to the parts of machines.
5. Friction reduces the speed of moving objects so more force is required.
6. Friction does not allow the free movement of objects.

7. Iqbal has to push a lighter box and Seema has to push a similar heavier box
on the same floor. Who will have to apply a larger force and why?
Seema pushes a heavier box. So, she needs to apply larger force due to more
friction.

8. Explain why sportsmen use shoes with spikes?

Sportsmen use shoes with spike to increase the friction between shoes and
surface. The shoes do not slip while they run or play.

9. You spill a bucket of soapy water on a marble floor accidently.

Would it make it easier or more difficult for you to walk on the floor? Why?
a) Soapy water reduces friction.
b) Our foot cannot make a proper grip on the floor.
c) It makes us difficult to walk on the floor.

10. Suppose your writing desk is tilted a little, a book kept on it starts sliding
down.
Show the direction of frictional force acting on its.
The book moves downwards.
The frictional force is acting opposite to the movement of book.
So it acts upwards.

1. At what time of the day is our shadow long?

In the morning and evening of the day is our shadow long because the sun is
low in the sky in the morning and evening.
2. At what time of the day is our shadow short?
At afternoon of the day is our shadow long because the sun is high in the sky
in the afternoon.
1. Suppose you are in a dark room. Can you see objects in the room? Can you
see objects outside the room? Explain.
Page 19 of 23
 We can’t see objects in a dark room because light doesn’t fall on them.
We can see objects outside the room because light falls on them

2. Is the light from a far away object able to travel to our eyes through opaque
objects?
No, light cannot pass through opaque objects

3. What type of objects a chair, a painting and a shoe are?

A chair, a painting and a shoe are opaque objects because we cannot see
through them.

4. Can we see any object in a completely dark room?

No, we cannot see anything in a completely dark room because light doesn’t
fall on them.

5. How do we see the object around us?

We can see objects around us when light falls on them.

6. In a completely dark room, if you hold up a mirror in front of you, will you
see a reflection of yourself in the mirror?
In a completely dark room, if we hold up a mirror in front of us, we cannot
see a reflection of ourself in the mirror because we can see objects around
us only when light falls on them.

7. Do the shadows look different in color when the colours of the objects are
different?
No, the shadows are same for different colour of objects, it is always black.
8. Name the things other than source of light and opaque object required to
see the shadow? cardboard, wall and ground.
9. Do you observe a shadow when there is just a source of light and nothing
else in a room?
No, we cannot see the shadow without any opaque object.

10. Do you observe your shadow in a dark room or at night when there is no
light?
No, we cannot observe any shadow without any source of light.

11. What do we see on the ground, when a sunlight falls on the opaque
objects?
We see the shadows of objects.

12. What are shadows?

When a light falls on the opaque objects.
We see dark patches formed on the ground
A shadow is formed on the opposite side of the light.

Choose the correct answer. Sound can travel through

(a) gases only (b) solids only (c) liquids only (d) solids, liquids
and gases.
Page 20 of 23
Ans: (d) Solids, liquids and gases.

Voice of which of the following is likely to have minimum frequency?

(a) Baby girl (b) Baby boy (c) A man (d) A
woman

Explain in what way noise pollution is harmful to humans.

Noise pollution can cause temporary or permanent deafening.
Noise pollution can causes headache, high blood pressure and lack of sleep.

Page 21 of 23
Noise Music

It is unpleasant sound. It is pleasant sound.

It leads to noise pollution. No such pollution takes place.

It is hazardous to health. It is good for health.

No special instruments are required Special instruments are required to

to produce noise. play music.

What is the difference between noise and music? Can music become noise
sometimes?

Q3. We cannot hear in SPACE OR MOON OR VACUUM. Why?

1. Sound is produced by vibrating air or vibrations.
2. Space or moon or vacuum has no air to vibrate.
3. Sound does not travel in space or moon or vacuum.
4. So we cannot hear sound in space or moon or vacuum.

Lightning and thunder take place in the sky at the same time and at the same
distance from us. Lightning is seen earlier and thunder is heard latter. Can
you explain why?
Lightning and thundering take place in the sky at same time and at the same
distance us but lightning is seen earlier than thunder is heard because light
travels faster than sound.

Which of the following mechanical systems will produce the maximum

amount of heat because of friction?

A B C D

The maximum and the minimum friction offered by the ground will be for the
situations
A) I and II B) III and IV C) II and III D) I and IV
Correct Answer: B

The picture of four people pushing four heavy boxes of equal weight on a
surface in four different situations I, II, III, and IV respectively, is shown in
the given figure

Page 22 of 23
.
The maximum and the minimum friction offered by the ground will be for the
situations
A) I and II B) III and IV C) II and III D) I and IV
Correct Answer: B

Which of the following actions involves a push?

Correct Answer: A

Page 23 of 23