Sound plays an important role in our
It helps us to communicate with one
We hear a variety of sounds in our
You must have hears the sound
produced by musical instruments like
flute, tabala, harmonium, etc.
Sound Is Produced By A
The to and fro or back and forth motion
of an object is called vibration.
When a tightly stretched band is plucked,
it vibrates and produces sound. When it
stops vibrating, it does not produce any
We see that vibrating object produces
In some cases, the vibrations are easily
visible to us. But in most cases, their
amplitude is so small that we cannot see
them. However we can feel them
Sound Produced By Humans
In humans, the sound is produced by the
voice box or the larynx.
The bump that seems to move when you
swallow is known as voice box.
It is at the upper end of the windpipe.
Two vocal cords, are stretched across
the voice box or larynx in such a way
that it leaves a narrow slit between them
for passage of air.
When the lungs force the air through the
slit, the vocal cord vibrate, producing
Muscles attached to the vocal cords
can make the cord tight or loose.
When the vocal cords are tight and
thin, the type and quantity of voice is
different from that when they are thick.
Sound Needs A Medium For
Activity - 1
Take a metal glass tumbler. Make sure
that it is dry. Place a cell phone in it.
Ask your friend to give a ring on the
cell phone. Listen to the ring carefully.
Now, surround the rim of the tumbler
with your hands. Put your mouth on
the opening between your hands.
Indicate to your friend to give a ring
again. Listen to the ring wile sucking
air from the tumbler.
If you had been able to suck all the air
in the tumbler, the sound would stop
Actually, sound needs a medium to
When air has been removed
completely from the vessel, it is said
that there is vacuum in the vessel.
The sound cannot travel through
Activity – 2
Does sound travel through water ?
Take a bucket. Fill it with clean water.
Take a small bell in one hand. Shake
this bell inside the water to produce
sound. Make sure that the bell does
not touch the body of the bucket.
Place your ear gently on the water
surface. You can hear the sound of the
bell. This indicates that sound travel
Activity – 3
Does sound travel through solids ?
Take a meter scale and hold it in one
end of your ear. Ask your friend to
gently tap or scratch the other end of
the scale. You can hear the sound of
Vibrating objects produce sound and it
is carried in all directions in a medium
We Hear Sound Through Our
The shape of the outer part of the ear is
like a funnel.
When sound enters it, it travels down a
canal at the end of which a thin
membrane is stretched tightly. It is called
the eardrum. It performs an important
The eardrum is like a stretched rubber
sheet. Sound vibrations make the
The eardrum send vibrations to the inner
ear. From there the signal goes to brain.
That is how we hear.
Amplitude, Time Period And
Frequency Of A Vibration
The to and fro motion is vibration, this
motion is also called oscillatory
The number of oscillations per second
is called the frequency of oscillation.
Frequency is expressed in hertz. Its
symbol is Hz.
A frequency of 1 Hz is one oscillation
Amplitude and frequency are two
important properties of any sound.
The loudness of sound depends on its
When the amplitude of a vibration is
large, the sound produced is loud.
When the amplitude is small, the
sound produced is feeble.
The frequency determines the shrillness
or pitch of a sound.
If frequency of vibration is higher we say
that the sound is shrill and has a higher
pitch. If the frequency of vibration is
lower, we say that the sound has a lower
E.g. A drum vibrates with low frequency.
Therefore it produces a low pitched
sound. On the other hand, a whistle has
a high frequency and therefore,
produces a sound of higher pitch.
Audible And Inaudible Sounds
The sounds of frequencies less than 20
vibrations per second (20 Hz) cannot be
detected by a human ear. Such sounds
are called inaudible.
On the higher side, sound of frequencies
higher than about 20,000 vibrations per
second (20 kHz) are also not audible to
The range of audible frequencies in
human ears is roughly from 20 to 20,000
Noise And Music
Unpleasant sounds are called noise.
In a classroom all the children starts to
speak together they produces noise.
We enjoy musical sound. The musical
sound is one which is pleasing to ear.
Similarly, presence of excessive or
unwanted sounds is called noise
Major causes of noise pollution are
sound of vehicles, explosions
including bursting of crackers,
machines, loudspeakers etc.
Television and transistor radio at high
volumes, some kitchen appliances,
desert coolers, air conditioners, all
Harms Of Noise Pollution
The presence of excessive noise in
the surroundings may cause many
health related problems.
Lack of sleep, hypertension (high
blood pressure), anxiety and many
more health disorders may be caused
by noise pollution.
A person who is exposed to loud
sound continuously may get
temporary or permanent impairment of
Measures To Limit Noise
To control noise, we must control
sources of noise.
Silencing devices must be installed in
aircraft engines, transport vehicles,
industrial machines and home
All noisy operations must be
conducted away from any residential
Noise producing industries must be
Use of automobile horns should be
TV and music systems should be run
at low volumes.
Trees must be planted along the roads
and around buildings to cut down on
the sounds reaching the residents,
thus reducing the harmful effects of