Sound is produced by vibrations that travel in waves through a medium such as air, water or solid materials. Different musical instruments produce sound using different methods of vibration like vibrating vocal chords, air, strings or membranes. The characteristics of sound include intensity, pitch and tone which vary based on amplitude, frequency and quality of vibration. Sound travels faster in solids than liquids or gases and requires a medium to travel through. When sound waves hit a surface, they can bounce back through a process called echo.

2. 1. What is sound?
2. Where is sound?
3. How is sound for us?
4. What is the use of sound?

3. Sound is all around us. It is a
means of communication. Some
sounds, such as the siren of a
fire engine, an ambulance, or a
police car, alert us. Some of
them are pleasant, such as the
sound of a laughing baby or the
chirping of a bird. Some sounds
are unpleasant to us just like
shouting or crying.

4. 1. How is sound produced?
2. What is vibration?
3. What is sound wave?
4. How does we hear sound?

5. Sound is a form of energy. Energy is the
ability to do work. We can call sound
energy because sound makes movement
and other things. It is produced by rapid
vibrations. A vibration is a rapid to and
fro movement. When we speak or shout,
our vocal chords vibrate. These
vibrations go out in all directions
through the air waves. When the waves
reach our ears, they make our eardrums
vibrate too. If this vibration is within our
hearing range, we can hear the sound.
Vocal chord
eardrum

6. Guitar
Flute
Bugle
xylophone
Violin
Sitar
Drum Piano
1. What is necessary to produce sound?
2. How do musical instruments make sound?

7. Something must vibrate to produce sound.
In wind instruments, like the flute and
trumpet, vibrating air makes the sound.
Stringed instruments are played by
pressing the strings with finger tips and
plucking or bowing them. The pressure
changes the length of the strings, causing
them to vibrate at different frequencies
and making different sound. Shortening a
string produces a higher sound. Strings
also produce different sound depending on
their thickness. When a drum is beaten its
skin vibrates to make sound.

8. How does the sound travel?

9. Sound travels in the form of
wave. When any object
vibrates, it causes movement
in the air particles. These
particles bump into the
particles close to them,
which vibrate too, causing
them to move more air
particles. This movement,
called sound waves,
continues until the particles
run out of energy.
sound waves
air particles

10. What does happen when we are clapping?

11. When you clap your hands, it
makes the air moves in waves
like ocean waves. So sound
travels in the form of waves.
That do these waves look like?

12. What does happen when we throw
a stone in still water?

13. When a stone is thrown into a still
body of water, the waves travel
outward in the form of circles.
Sound waves travel through the air
in the same way. Just like the
waves in water, sound waves also
carry energy.

14. How does the sound wave travel?

15. Sound waves are longitudinal
waves. In a longitudinal wave,
particles of the medium are
displaced in a direction
parallel to the energy
transport. In the diagram you
can see that sound waves are
travelling along a path from
left to right but in reality,
sound waves spread out in all
directions.

16. What is tuning fork?
Explain rarefaction and compression?

17. The fine lines represent air molecules.
As the tuning fork vibrates it causes the
surrounding air molecules to vibrate in
a particular pattern. The vibrating air
molecules transfer their vibration to the
listener’s ear drum and cause it to
vibrate too.
In the diagram above you can see the
two parts of the sound waves,
compression and rarefaction. The
compression is the area of the sound
wave where the air particles are
crowded together. The rarefaction is the
area of the sound wave where the air
particles are spread out.

18. What does a vibrating object do?

19. A vibrating object compresses the surrounding air molecules, squeezing
them closer together, and then rarefies them, pulling them farther apart.
Air molecules themselves stay in the same average position. They do not
travel from the source of sound to the ear of the listener. Instead, each
individual molecule only moves a small distance when it vibrates but its
energy causes the molecule next to it to vibrate.

20. How does the noise occur?
What is regular repeating sound wave and
irregular repeating sound wave?

21. Irregularly repeating sound waves create noise, while regularly
repeating waves produce musical notes.
regularly repeating waves
irregularly repeating waves
noise

22. What is flick
and how it
effects the
object?

23. You can perform the following activity to demonstrate a sound wave.
Materials required:
 A rope
 A table, a tree, or a doorknob
Method:
1.Tie one end of a rope to a tree, door knob, or to the leg of your table.
2.Flick the free end up and down to see how waves move along the
rope.
When you flick the rope up and down, the flick moves along the rope
like a wave. The free end in your hand passes the movement to the
next part of the rope, which passes it again, and so on. This is how a
sound wave travels through the air.

24. What are intensity, pitch, and tone?

25. There are many different
sounds in the environment.
Some are loud, such as the
sound made by a jet engine.
Some, such as whispers, are
soft. Every one of us has a
different voice. Imagine
listening to the sounds of
birds, different musical
instruments, and a lion’s roar.
What makes them different
from each other?

26. The variation between sounds
is caused by their different
characteristics. These are
intensity, pitch, and tone.
Sound intensity is a measure of
the energy of a sound wave.
The intensity depends upon the
amplitude of the waves. The
more energy a sound wave
carries, the higher the
amplitude is; the higher the
amplitude, the higher the
intensity.

27. Pitch is how high or low a sound
is. It depends upon the
frequency of the waves, the
higher the frequency, the higher
the pitch; the lower the
frequency, the lower the pitch.
The sounds produced by a drum
have much lower frequencies
that those produced by a whistle.
The frequencies of some sounds
are shown. Can you identify
which one has the highest pitch
and which one the lowest?

28. Tone is a particular
quality that tells the
way a sound is
heard.

29. What is medium of sound?

30. Can you hear sound under water?
Yes, but you cannot hear any sound
in space. Why is this?

31. It is because sound is always
produced by a vibrating body.
Water is made up of particles
which can vibrate to produce and
carry sound waves. In outer space
there are no particles to vibrate, so
sound cannot travel there.
A substance that makes the
transfer of energy from one
location to another possible,
especially in the form of waves, is
called a medium. Sound waves
require a medium to spread and
travel through.

33. Most of the sounds we hear
travel through the air, but sound
waves can also move through
water, wood, and metal or any
other solid. All these materials
have particles that can vibrate.
Without a medium there are no
particles to carry the sound
waves. Air is an example of a
gaseous medium. In a telephone
made by paper cups and a string,
sound travels through the string
that is tied to both the cups. This
is an example of a solid medium.

34. How does the speed of sound
effect by the medium?

35. The speed of sound depends on the nature and properties of the
medium through which it is travelling. The closer the molecules
are in a medium, the faster the sound will travel through it. Metals
carry sound waves faster than water. Sound travels 10 to 15 times
faster in metals than in gases; in liquids it travels 4 to 5 times
faster than in dry air. It is easier for sound waves to travel through
solids than through liquids because the molecules are closer
together and more tightly bonded in solids. Similarly, it is harder
for sound to travel through gases than through liquids, because
gaseous molecules are farther apart. That is why the speed of
sound is faster in solid materials and slower in liquids or gases

36. What is the fastest thing in the universe?

37. Whether the medium sound is travelling through, its speed is always slower that the speed of light.
Light is the fastest phenomenon in the universe. That is why, in a thunder storm, we see lightning
before hearing the thunder.

38. What is the bouncing of sound and what does it called?

39. In the previous unit you learned that
when light hits a surface it bounces
back. Sound waves behave
similarly. When sound waves hit a
hard surface such as the side of a
mountain or the walls of an empty
room, they bounce back. This is
called echo of sound. A repetition of
sound produced by the reflection of
sound waves from a wall, mountain,
or other obstructing surface
is called an echo.

40. Can we hear echo all the time you speak?

41. You cannot hear an echo every
time you speak, there are certain
conditions in which an echo is
heard. You cannot hear an echo in
a well-furnished room. There are
materials which, instead of
reflecting sound, absorb it. These
materials may be curtains, carpet,
a bed, or cushions. Echoes are
produced when sound travels
from its source to a solid object
such as a wall and bounces back.

42. What are the uses of echo?

43. Echoes
can be
very
helpful.
Echoes
are used
in
medicine.

44. In order to explore the bottom of the
ocean, scientists use equipment that
creates echoes. This equipment sends
sounds to the ocean floor, and the
sound bounce back in different
patterns. The scientists then use
special equipment to turn the echoes
into pictures that show what the
ocean floor looks like. Just as echoes
sound different in different parts of a
room or valley, the deep-sea
equipment hears echoes that sound
different in different areas of the
ocean; shallower areas produce
different echoes from deeper places.

45. Some animals, such as
bats, dolphins, and whales,
use a similar method to
find out what is around
them.

46. Bats emit high-pitched sounds
that bounce off objects and
return to them, helping them
gather information about the
size and location of the object.