Chapter - 13, Sound, Science, Class 8

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Chapter - 13, Sound, Science, Class 8

WHAT IS SOUND?
INTRODUCTION TO SOUND
SOUND-PRODUCING MUSICAL INSTRUMENTS
SOUND PROPERTIES
HOW DO HUMANS PRODUCE SOUND?
HOW SOUND PROPAGATE IN A MEDIUM?
SOUNDS BY HUMANS
THERE ARE THREE MAJOR PARTS OF THE HUMAN EAR
AMPLITUDE, TIME PERIOD, AND FREQUENCY
THE LOUDNESS OF A SOUND
PITCH OF THE SOUND
AUDIBLE AND INAUDIBLE SOUNDS
NOISE AND MUSIC
NOISE POLLUTION
CAUSES OF NOISE POLLUTION
EFFECTS OF NOISE POLLUTION
PREVENTION OF NOISE POLLUTION

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1. Chapter –13
Sound
By Shivam Parmar
(Entrepreneur)
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2. WHAT IS SOUND?
•A sound is a form of energy that
is produced when air molecules
vibrate in a particular pattern
called waves. Hence, the sound
is a wave.
•Vibration can be described as a
back and forth motion of an
object.
•Depending upon the vibrations,
a sound is produced. Sound
cannot be produced without any
vibration.

3. INTRODUCTION
TO SOUND
•The sound is produced by vibrating objects.
•They travel from one place to another in the
form of waves. Hence, the name sound waves.

4. SOUND
PRODUCING
MUSICAL
INSTRUMENTS

5. SOUND PROPERTIES
•Sound needs a medium to
propagate. The matter or
material through which sounds
propagates is called a medium.
•Sound cannot travel in a
vacuum, as it lacks any medium
of transmission.
•The moon does not have an
atmosphere, hence, you can
hear on the moon.

6. HOW DO HUMANS PRODUCE SOUND?
•Human beings have a voice box
or larynx which is present in
their throat on the upper side of
the windpipe.
•The larynx has two vocal cords
which have a narrow slit
between them so that air can
pass through it.
•As the lungs throw the air out of
the windpipe, it passes through
the slit and hence allows the
production of sound as the vocal
cords start vibrating.

7. •The vocal cord muscles also play a role in the production of
sound.
•Their thickness and tightness describe the quality or type of the
voice a person has.
•The vocal cords in males are of length 20 mm and females have
15mm long vocal cords. Children, on the other hand, have very
short length vocal cords. Hence, the voices, their quality and
their type are always different in women, men and children.

8. HOW SOUNDPROPAGATE
IN A MEDIUM?
•Sound needs some vibration of
molecules to travel.
•Solids, liquids and gases all have
molecules present in them which
allow the propagation of sound.
•These molecules or particles in
solids, liquids and gases are
packed in varied ways.
•Solids have tightly packed
particles in them and hence they
allow fast propagation of sound
through them.

9. Liquids have slightly loosely packed
particles and hence it takes a little
time for sound to travel in water or
through a liquid.
Gases have completely loosely
packed particles and hence sound
takes the most time in travelling
through the air.

10. SOUNDS BY
HUMANS
•We know that sounds are
produced as waves in the air or
any other medium.
•As these sound waves travel to
our ears they convert them
into electrical signals or
messages that our brain can
understand.
•Our ears have a special
structure that allows this
function.

11. THERE ARE THREE MAJOR PARTS OF THE HUMAN EAR
1. The Outer Ear
2. The Middle Ear
3. The Inner Ear

13. AMPLITUDE, TIME PERIOD AND FREQUENCY
•The magnitude of disturbance in the
medium on either side of the mean
value is called asAmplitude(A). Larger
the amplitude, louder the sound.
•The number of oscillations per second
is calledfrequency.Expressed in
Hertz(Hz).
•Time taken for one complete
oscillation to travel across a point.
•T = 1/f. (Seconds)

14. THE LOUDNESS OF A SOUND
•The loudness of a sound depends
upon the amplitude of the sound.
•The higher the amplitude, the higher
is the displacement of the particles
and the higher is the loudness of the
sound.
•The loudness of the sound is directly
proportional to the square of its
amplitude.
•The SI unit for measuring the
loudness of a sound in decibels (dB).

16. PITCH OF THE SOUND
•Every person has a different sound quality.
•Also, every musical instrument vibrates to
produce a different kind of sound. This
quality of sound is characterized by its
Different quality of sounds may have
same pitch and loudness.
•The pitch of a sound depends upon the
frequency of the sound wave.
•The pitch would be higher if the
frequency of the sound is high.

17. AUDIBLE AND
INAUDIBLE SOUNDS
•Audible range = 20Hz to 20kHz
known as the Sonic range.
•Below 20 Hz (inaudible) →
Infrasonic range
•Above 20 kHz (inaudible) →
Ultrasonic range

18. NOISE AND MUSIC
•Noisecan be regarded as an unpleasant
sound. Noise consists of sound waves of
varied frequencies which have no
particular periodic pattern of repetition.
Therefore, noise is regarded as a mixture
of sound waves with irregular
frequencies.
•Music, on the other hand, is a pleasant
sound that has a clear pitch. Musical
sound can be created by arranging and
combining different sounds in a
particular order. The frequencies of a
musical sound are harmonious in nature.

19. NOISE POLLUTION
•Noise pollution can be defined as
the presence of undesirable and
unpleasant sounds in the earth's
environment.
•Human beings can bear sounds
ranging up to 85 decibels only.
Above that, any noise can
damage our hearing power.
•Generally, any sound that has a
frequency of more than 30 dB is
considered noise.

20. •The unwanted noise causes an
adverse effect on the health of the
organisms present on the earth.
•According to the World Health
Organization, the maximum sound
limit that is ideal for cities is 45 dB
only.
•However, it has been found that the
sound range in many big cities of the
world lies up to 90 dB.
•Hence noise pollution is common in
many cities today and even rural
areas to a great extent.

21. CAUSES OF NOISE
POLLUTION
•Construction Noise
•Neighbourhood Noise
•Industrial Noise
•Natural Sounds
•Transport Noise
•Bursting of Fireworks

22. EFFECTS OF NOISE POLLUTION
•Excessive noise in the surroundings can lead to
serious health problems such as hypertension,
lack of sleep or insomnia, anxiety, lack of memory,
stress, irritation and even nervous breakdown.
•It can lead to temporary or permanent hearing
loss in human beings as well as animals.
•Excessive noise leads to increased blood pressure.
It increases cholesterol levels in the blood and
therefore increases the chances of cardiovascular
diseases in a person.
•If sound intensity is more than 180 dB it can lead
to the death of a person.

23. PREVENTION OF
NOISE POLLUTION
•Factories and other industries
should be set up at a distance from
residential areas.
•Silencing devices should be
incorporated into heavy vehicles
such as aircraft, industrial
equipment, machinery and other
home appliances.
•Use of horns should be minimized
especially near public places such as
hospitals, religious places and
schools.

24. •Trees should be planted in
huge numbers as they can
absorb unwanted noise from
the environment.
•People who work in noisy
conditions such as industries
and mines should be provided
earplugs to protect their ears.

25. Thank You
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