When a particle When a particle moves to and fro moves to and fro about its mean about its mean position , it is position , it is said to vibrate. said to vibrate.

This to and fro This to and fro motion is called motion is called a vibration. a vibration.

Every source of Every source of sound is a sound is a vibrating body. vibrating body.

A tuning fork is a U – A tuning fork is a U – shaped steel fork provided shaped steel fork provided with a steel handle. with a steel handle.

Prongs

Stem

The two arms of the U The two arms of the U are called prongs , are called prongs , whereas the handle is whereas the handle is called stem .called stem . It is a convenient source It is a convenient source of producing sound of producing sound vibrations in a vibrations in a laboratory.laboratory.

Take a small thermocol ball and Take a small thermocol ball and suspend it from an iron stand with suspend it from an iron stand with a light silk thread. a light silk thread.

Strike one of the prongs of the Strike one of the prongs of the tuning fork on the hard rubber pad tuning fork on the hard rubber pad and bring it close to your ear and and bring it close to your ear and you will be able to hear the sharp you will be able to hear the sharp humming sound of the tuning fork. humming sound of the tuning fork.

Now touch one prong of the Now touch one prong of the tuning fork to the thermocol ball . tuning fork to the thermocol ball .

You will observe that thermocol You will observe that thermocol ball flies outward. ball flies outward.

Thus, the experiment proves that Thus, the experiment proves that the sound produced by a tuning the sound produced by a tuning fork is due to the vibration of its fork is due to the vibration of its prongs .prongs .

Oscillatory Oscillatory motion – motion – This to This to and fro motion of and fro motion of the pendulum the pendulum about its mean about its mean position is called position is called one vibration. one vibration. This is also called This is also called oscillatory motion oscillatory motion ..Eg-Eg-A simple A simple pendulumpendulum. .

Amplitude –Amplitude – The maximum The maximum displacement of a vibrating displacement of a vibrating body from its mean position is body from its mean position is called its amplitude.called its amplitude.

It has been found that larger It has been found that larger the amplitude , more is the the amplitude , more is the loudness.loudness.

Eg – Eg – If a drum hit softly ,a soft If a drum hit softly ,a soft sound is produced, because sound is produced, because the amplitude is less . If the the amplitude is less . If the same drum is hit hard , a loud same drum is hit hard , a loud sound is produced as the sound is produced as the amplitude is very large.amplitude is very large.

SI unit of amplitude is metreSI unit of amplitude is metre

Frequency – Frequency – The number of vibrations produced by a vibrating The number of vibrations produced by a vibrating body in one second is called frequency. It is denoted by letter body in one second is called frequency. It is denoted by letter f .f .

The frequency of vibrations determines the shrillness or the The frequency of vibrations determines the shrillness or the pitch of any sound. If the frequency of vibration is low , we say pitch of any sound. If the frequency of vibration is low , we say the sound has low pitch or is bass. Conversely , if the frequency the sound has low pitch or is bass. Conversely , if the frequency of vibration is high , we say that the sound has high pitch or is of vibration is high , we say that the sound has high pitch or is shrill.shrill.

Eg – The voice of a child is shriller than that of an adult .Eg – The voice of a child is shriller than that of an adult .

The unit of frequency in SI The unit of frequency in SI system is system is Hertz . Hertz . When a When a vibrating body produce one vibrating body produce one vibration in one second , vibration in one second , then its frequency is said to then its frequency is said to be be oneone Hertz .Hertz .

If the frequency of a tuning If the frequency of a tuning fork is 256 Hz, it means it fork is 256 Hz, it means it is producing 256 vibrations is producing 256 vibrations in one second.in one second.

The time a vibrating body The time a vibrating body takes to complete one takes to complete one vibration is called its vibration is called its time time period. period.

It is denoted by letter ‘It is denoted by letter ‘t’t’.. If ‘f’ is the frequency of If ‘f’ is the frequency of

vibrating body and ‘t’ is the vibrating body and ‘t’ is the time period then: time period then:

‘‘f’ vibrations are completed in f’ vibrations are completed in 1s1s

:one vibration is completed in :one vibration is completed in = 1/f *s= 1/f *s

T=1/f i.e., Time period T=1/f i.e., Time period = 1/Frequency= 1/Frequency

If the frequency of the If the frequency of the vibrations is less than 20 vibrations is less than 20 Hz, then human ears Hz, then human ears cannot hear it. Such cannot hear it. Such vibrations are called vibrations are called infrasonic vibrations.infrasonic vibrations.

If the frequency of If the frequency of vibration is between 20 Hz vibration is between 20 Hz TO 20,00 Hz, then they TO 20,00 Hz, then they can be perceived by the can be perceived by the human ear . Such human ear . Such vibrations are called vibrations are called sonic vibrations.sonic vibrations.

However, if the frequency However, if the frequency of vibrations is above of vibrations is above 20,000 Hz then human ear 20,000 Hz then human ear cannot perceive them . cannot perceive them . Such vibrations are called Such vibrations are called ultrasonic soundsultrasonic sounds . .

Dogs can hear upto the Dogs can hear upto the frequency of 40,000Hz. frequency of 40,000Hz. Dogs can respond to a Dogs can respond to a whistle which produce whistle which produce ultrasonic vibrations and is ultrasonic vibrations and is called called Galton whistleGalton whistle..

Bats produce vibrations in Bats produce vibrations in the frequency range of 50 the frequency range of 50 Hz to 80,000Hz. Bats have Hz to 80,000Hz. Bats have very weak eyes . When very weak eyes . When bats fly in the night, they bats fly in the night, they produce ultrasonic vibration produce ultrasonic vibration . When these vibrations . When these vibrations strike the insect, they are strike the insect, they are reflected back .on receiving reflected back .on receiving the reflected sound, the bat the reflected sound, the bat can locate the insect.can locate the insect.

Dolphins also use ultrasonic Dolphins also use ultrasonic sounds to locate their sounds to locate their preyprey..

Ultrasonic Ultrasonic vibrations are vibrations are used for imaging used for imaging internal organs internal organs of human body.of human body.

Ultrasonic Ultrasonic vibrators are vibrators are used to used to drive rat and drive rat and cockroaches cockroaches from from godown.godown.

These vibrations are These vibrations are used in relieving pain in used in relieving pain in joints and muscles.joints and muscles.

These vibrations are These vibrations are used in detecting flaws in used in detecting flaws in articlesarticles made from made from metals. Etcmetals. Etc..

The speed of sound in steel is around 5100 m/s.The speed of sound in steel is around 5100 m/s. By knowing the speed of sound in water , we can find By knowing the speed of sound in water , we can find

the depth of the sea .the depth of the sea . The speed of sound in water is around 1600 m/s.The speed of sound in water is around 1600 m/s. Sound energy travels fastest in solidsSound energy travels fastest in solids Sound is slower in liquidsSound is slower in liquids It is slowest in gases . In air ,the speed is around 330 It is slowest in gases . In air ,the speed is around 330

m/s.m/s.

We have learnt that sound travels through We have learnt that sound travels through solids, liquids and gases . But sound solids, liquids and gases . But sound cannot travel through vacuum.cannot travel through vacuum.

A material medium is necessary for the A material medium is necessary for the propagation of sound.propagation of sound.

Shining objects like mirror , metal or hard objects like Shining objects like mirror , metal or hard objects like building or stone reflect sound. However, materials building or stone reflect sound. However, materials with loose texture absorb sound. Eg- with loose texture absorb sound. Eg- curtains, curtains, gunny bag ,straw, carpets, e.t.c. absorb sound.gunny bag ,straw, carpets, e.t.c. absorb sound.

Auditoriums are carpeted and their walls are coated Auditoriums are carpeted and their walls are coated with some rough materials, so that they do not with some rough materials, so that they do not reflect any sound.reflect any sound.

Different objects produce Different objects produce different sounds because different sounds because either they have different either they have different loudness or different pitches loudness or different pitches or both. Eg- The sound of a or both. Eg- The sound of a girl is more shrill as compared girl is more shrill as compared to the sound of a boy.to the sound of a boy.

Loudness – Loudness – Loudness is the Loudness is the characteristic of a sound characteristic of a sound which distinguishes a feeble which distinguishes a feeble sound from a loud sound of sound from a loud sound of the same frequency.the same frequency.

The loudness of sound The loudness of sound depends upon the amplitude depends upon the amplitude of the vibrating body. of the vibrating body.

Pitch- Pitch- The voice of a woman is more shrill than the The voice of a woman is more shrill than the voice of a man . A shrill sound is called voice of a man . A shrill sound is called high pitch high pitch sound, sound, whereas a soft or shrill sound is called whereas a soft or shrill sound is called low low pitch sound. pitch sound. Pitch is the effect produced in the Pitch is the effect produced in the ear due to the sound of some particular frequency. ear due to the sound of some particular frequency. Pitch depends upon the frequency of a vibrating Pitch depends upon the frequency of a vibrating body, i.e., higher the pitch , the more is the body, i.e., higher the pitch , the more is the frequency and the lower the pitch, the less is the frequency and the lower the pitch, the less is the frequency.frequency.

Noise- A sound does not Noise- A sound does not have a pleasing have a pleasing sensation on the ears is sensation on the ears is calledcalled noise. noise. Scientifically, Scientifically, a noise is produced by a noise is produced by irregular vibrations. Eg- sound irregular vibrations. Eg- sound of too many people talking at of too many people talking at one time, bark of a dog.one time, bark of a dog.

Music – A sound which has a Music – A sound which has a pleasing sensation on the pleasing sensation on the ears is called ears is called musicmusic. . Scientifically , a musical Scientifically , a musical vibration is produced by vibration is produced by regular vibrations. Eg- the regular vibrations. Eg- the prong of the tuning fork of a prong of the tuning fork of a sitar vibrates at regular sitar vibrates at regular intervals and is called intervals and is called music .music .

The loudness of sound is measured in decibels (dB). It signifies the The loudness of sound is measured in decibels (dB). It signifies the sound pressure level. Human ears can pick up sound from 10 dB to 180 sound pressure level. Human ears can pick up sound from 10 dB to 180 dB . A human being can tolerate loudness of 80 dB . The sound above dB . A human being can tolerate loudness of 80 dB . The sound above 80 dB is painful and causes various health problems.80 dB is painful and causes various health problems.

The disturbance produced in the The disturbance produced in the environment by undesirable , loud and environment by undesirable , loud and harsh sound from various sources is called harsh sound from various sources is called noise pollution.noise pollution.

The noise pollution at a particular place is The noise pollution at a particular place is determined by the following factors:determined by the following factors:

(I) Loudness of the sound.(I) Loudness of the sound. (2) Duration of noise.(2) Duration of noise.

Noise in homes - 1. Noise in homes - 1. televisiontelevision , , 2. 2. power musicpower music systemsystem, 3., 3.desert desert coolercooler, 4. , 4. vacuum cleanervacuum cleaner, 5. , 5. typetype writer.writer.

Noise in surroundings – 1. Noise in surroundings – 1. loud loud speakers atspeakers at marriagesmarriages , 2. , 2.exploding exploding crackerscrackers, 3. , 3. hawkershawkers,4. ,4. publicity publicity announcementsannouncements..

Noise in factories – Noise in factories – All factories All factories big or small use machines , which big or small use machines , which invariably produce noise.invariably produce noise.

Noise due to transportation – Noise due to transportation – 1. 1. train , 2 . All kinds of petrol and train , 2 . All kinds of petrol and diesel vehicles , 3 . Aeroplanes diesel vehicles , 3 . Aeroplanes

Noise in surroundings interferes Noise in surroundings interferes in conversation with another in conversation with another person.person.

A long exposure to noise may A long exposure to noise may result in loss of hearing.result in loss of hearing.

It causes anger , tension , It causes anger , tension , headaches , irritability and headaches , irritability and nervous tension.nervous tension.

It can cause loss of night vision It can cause loss of night vision as well as colour as well as colour blindness. ,e.t.c.blindness. ,e.t.c.

Factories should be relocated far away from Factories should be relocated far away from residential areas .residential areas .

Use of loudspeakers for various social or religious Use of loudspeakers for various social or religious events should be banned . events should be banned .

At homes ,T.V., radio , e.t.c. should be played at low At homes ,T.V., radio , e.t.c. should be played at low volume.volume.

Heavy vehicles should not be allowed in residential Heavy vehicles should not be allowed in residential areas.areas.

Stringed Instruments (Tantu Stringed Instruments (Tantu vadya)vadya)

1.Violin, 2. Guitar , 3. Sitar , 4. Veena1.Violin, 2. Guitar , 3. Sitar , 4. Veena

Wind Instruments (Sushir Wind Instruments (Sushir Vadya)Vadya)

1.Flute, 2. Shahnai, 3.Bugle1.Flute, 2. Shahnai, 3.Bugle

Membrane Instruments Membrane Instruments (Avanaddhu Vadya)(Avanaddhu Vadya)

1. Dholak, 2. Tabla,3. Mridangam,4. 1. Dholak, 2. Tabla,3. Mridangam,4. Drums.Drums.

Ghana VadyaGhana Vadya 1. Jal Tarang , 2. Mud Pot1. Jal Tarang , 2. Mud Pot