SOUND
* Sound is produced by the vibration
of materials.
* Oscillatory/vibratory motion is a
type of motion where body moves to and fro or back and forth repeatedly about a
mean/central position.
* Vibration or oscillation is one
complete to and fro or back and forth motion of oscillating body about its mean
position.
* Musical instruments are forced to
vibrate by plucking string, striking membrane, beating string, etc and it is
the vibration of the instrument that we hear.
* In human, the sound is produced by
vocal cords present in voice box (larynx) located at the upper end of the
windpipe. Vocal cords vibrate to produce sound when lungs force air through the
cord’s slit. Muscles attached to the vocal cords make the cords tight or loose.
Quality of voice depends on nature of the cord muscle. Tight and thin cord muscle
has different voice from loose and thick muscle.
* Sound travels through a medium
(gas, liquid or solid). It can’t travel in vacuum.
* Human ear has three main parts:
1.
OUTER
EAR: Has canal with eardrum (stretched membrane like stretched rubber sheet).
2.
MIDDLE
EAR: Has set of three bones linked together and attached to ear drum.
3.
INNER
EAR: Inner ear changes received vibrations from middle ear into nerve impulses.
Nerve impulses are carried by auditory nerves to brain.
* Human hear sound through ears.
* Musical sound is characteristic sound
which produces pleasant sensation on ear.
* Musical instruments are generally
of following types
TYPES OF
MUSICAL INSTRUMENT
|
NATURE OF
SOUND PRODUCTION
|
EXAMPLES
|
String
Instruments
|
Vibration of
string produce sound
|
Sitar
|
Wind/Reed
Instruments
|
Column of air
is vibrated by blowing directly
through tubes
|
Flute,
|
Membrane
Instrument
|
Vibration of
skin or membrane mounted on the instruments
|
Tabla, Drum
|
Ghana Vadya
|
Beaten or
struck to produce musical sound
|
Cymbals, Jal
Tarang
|
* Noise is sound which produce
unpleasant sensation on the ears.
* Time period is defined as time
taken by a vibrating body to complete one oscillation.
* Frequency is the number of
oscillations completed by a vibrating body in one second. Unit of frequency is hertz
(Hz).
* Frequency determines the shrillness/pitch
of sound. If the frequency of the vibration is higher, higher is the pitch and
shriller is the sound.
* Amplitude is maximum displacement
of an oscillating body from its central position.
* Human voice can produce sounds with
frequency between 60Hz-13,000Hz. Normal human ear can hear sound of frequency
between 20Hz-20,000Hz. Such sound is called audible. Inaudible sound has
frequencies lower than 20Hz.
* The sound of frequency greater than
20,000Hz is called Ultrasonic.
* Loudness of sound depends on the
amplitude of vibration. It is proportional to the square of the amplitude of
the vibration producing the sound. It is, if amplitude becomes twice, the
loudness increases by a factor of 4. Loudness is expressed in a unit of decibel
(dB).
When amplitude of
vibration is large, sound produced is loud.
* Above 80dB the noise becomes
physically painful.
* Noise pollution is caused due to
vehicles, machines, crackers, explosions, loudspeakers including television and
radio at high volumes, aeroplanes, factory, etc
* Harm of excessive noise pollution
ü Lack of sleep
ü Hypertension(High blood pressure)
ü Anxiety
ü Impairment of hearing temporary or
even permanently
* Measures to limit noise pollution
ü Silencing devices must be installed
in air craft engines, transport vehicles, Industrial machines and home
appliance.
ü Noise producing industries should
be set up away from residential areas.
ü Airport, railway stations and bus
stations should be made away from residential areas.
ü Use of automobile horns should be
minimized.
ü TV, music systems should be run at
low volumes.
ü Trees must be planted along the
roads and around building.
ü Use of high noise creating crackers
should be avoided.
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