Tuesday 26 June 2012

SOUND


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.



                        


Sound enters funnel shaped outer part of ear and travels down a canal to eardrum which vibrates, sends vibration to inner ear. Inner ear changes received vibrations from middle ear into nerve impulses. Nerve impulses are carried by auditory nerves to brain. Brain interprets impulses and sound is heard.
*       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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