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Wednesday, 18 April 2012

Sound Waves and Its Charecteristics: Science Behind Sound


Sound is always made by some kind of movement.For example ,hitting your hand against a table or plucking a guitar string produces sound . There are many different kind of sounds,and they can be pleasant and unpleasant .Music has rhythm and is usually pleasant to hear .You might like pop music,But other may think it is noisy. Noise is any  sound that is unpleasant to a person .It is not usually as rhythmic as music.

When something vibrates it produces a sound. Vibrations are movements to and fro.The energy or strength of the vibrations is passed on to the tiny molecules in the surrounding air and makes them move.The stronger the vibrations , the louder the sounds.To make the molecules move requires energy.The further a sound travels the more molecules are moved.The energy of the vibrations is therefore slowly used up and the sound becomes quieter .This is called attenuation of sound.

The vibration moving through the air are called sound waves .You cannot see them , but they would look similar to the movement of corn in the wind.The corn stalks are blown over slightly .As they vibrate to and fro.Wave movements are seen to travel across the field although each corn stalk moves only a short distance

Sound waves move the molecules of air against each other .Each molecule bumps its Neighbour , which in turn bumps its neighbour.The molecules crowd together and then move back again.This crowding together causes a slight increase in pressure .As the molecules moves apart the pressure drop. A sound wave therefore produces a change in pressure as it travels through the air .If there were no air , as in outer space , sound would not travel and nothing could be heard.

Different Parts Of The Human Ear

It is only when the sound wave falls on the ear that a sound is heard.The flap of the outer ear is a funnel to collect the sound waves .These pass along a short tube to the ear drum. The second waves make the drum vibrate, causing tiny bones in contact with it to vibrate .These carry the sound to the inner ear.Here the vibrations are converted,by a shell shaped organ called the cochlea , into electrical messages. These are carried by nerves to the brain.


Tuning Fork Experiment to Know the Mechanism of Propagation Of Sound

If you turn the Tuning fork into state of vibration, then one side of the Tuning fork is vibrate along both sides (b and c) of fixed(a) position.During the vibration of Tuning fork it creates a sound wave on the air. Therefore sound propagate in air medium in the form of wave . During vibration when one side of the sound rod come into the outer side (b point) it produce pressure on the nearer air therefore the nearer air become compressed, then that part of air transmit it compression to the next part of the air .In this way the compression (c) is gradually transmitted throughout the air medium.Air in the behind area of the  every compression (c)  tend to expand due to partial emptiness it create rarefaction (r). In this way (through rarefaction(r) and compression(c)) sound propagate through air until it came to our ear or any other target

                                      Animated Video on Propagation of Sound through Tuning Fork


There are many way of producing a musical note.Percussion instruments are played by striking a surface in a particular manner .The surface of the bell is struck by a heavy  clapper .The oldest bell in the world found near Babylon, is over 3000 years old.The largest is the Tsar Kolokol (kings of bells) in the Kremlin,Moscow. Cast in 1734 it weighs 220 tons and stands on the ground Where it fell whilst being hanging in St Paul`s Cathedral,London.Big Ben (London ) and Great Tom (Oxford) are two other famous english bells .The most famous bell in the US is the Liberty Bell (Philadelphia). 


Different Parts Of The Human Ear

The ear has three parts, the outer ,inner and middle ear.In the middle ear, vibration of the ear drum move three tiny bones, the hammer, anvil and stirrup (these are named from their shapes). They carry sound to the cochlea in the inner ear.

Animated Video Establishing the Truth That no Sound can hear in absence of Air by Electric bell experiment
If an electric bell is put inside a jar and all the air is pumped out , no sound will be heard.The hammer can be seen to vibrate rapidly making the bell ring, but because there is no air the sound will not travel.
Establishing the Truth That no Sound can hear in absence of Air by Electric bell experiment


Different Types of Drums

A drum is a percussion instrument it consist of a piece of a skin, parchment plastic or nylon streached tightly over a wooden or metal frame .The bass drum is the largest orchestral and military drum . The diameter is much greater than the depth.Usually it is played with a felt-headed stick.


An echo occur when sound waves hit a barrier like a cliff, hill, or high wall . The wave bounce off and the sound  is heard again. This is called a reflected sound .The time between the sound and its echo is the time taken by the sound wave to hit the barrier and return to the listener.The sound wave loses energy as it travels so the echo is fainter than the original sound .

Whales ,Porpoises, bats and some other living creatures can navigate and so locate their prey by using echoes. They emit a stream of sounds in all directions. The path of retuning echoes shows whereobstacles or prey are .

Echoes are useful to fishermen  for dectecting shoals of fish . Geologists use them to find minerals beneath the earth`s surface.

Acousticsis the study of the sound as it travels. It is specially concerned with the way sound travels in cinemas,concert hall , classrooms and any where sound must be clearly heard by  an audience.


In the year 1829 scientist Arago first detemine the velocity of sound in the air medium . In this experiment he installed two observer on the top of two hills which are separated by few miles. When one observer fire a gun another observer start his stop watch by seeing the light of the gunfire and stop his stop watch when he hear the sound of the gunfire.The Agrago again repeat the experiment few times. Then he noted that if the distance between the observers is x and the average time distance is t second then the velocity (V) of the sound in air medium is:-
V = ------

In this experiment anyone can find lots erreors because velocity of sound is depended on velocity of air .The velocity of sound much higher if the sound wave is along with air flow and the velocity of sound much lower if the sound wave is aganist the air flow. If the velocity of air is v then the velocity of sound along air flow is (V+v) (V = velocity of sound , v = velocity of air). The velocity of sound is (V-v) when sound wave flow aganist the air flow.Now we give stop watches and guns to the both observer. Now assume number 1 observer hear the gunfire sound in t1 second and number 2 observer hear the sound in t2 second . The air is flows from number 1 observer to number 2 then the formula is:-
                x                                                   x
V + v = ------               and            V-v = -------
                t1                                                  t2
                x         1              1
so  V = ------ (  ------  +  -------- )
                2          t1           t2


In a large room with wide hard unbroken walls. The sound echoes off the walls . The audience hears a jumble of noises making it impossible for even the slowest , clearest speaker to be understood .This is called reverberation .It can be reduced by padding the walls, hanging curtains and using padded seats..This absorb some of the sound and the echoes become less loud.There are fewer echoes in a full hall because people also absorb the sound.

The shape of a hall is specially designed so that , if possible every sound can be heard clearly by everyone there. Some of the sound is heard directly ; The rest is reflected off the walls and ceiling.The distances travel by these two sets of waves are carefully worked out to make the sound clear.

People  measure the depth of Ocean From Ship by Installing  different sound wave Measuring devices 

Sound must travel through a medium such as air. The molecules of the medium carry the vibrations from the source of sound to the listener`s ears; liquid and solid transmit sound even better than air.

Sound waves travel at a speed that depend on the medium. They travel faster in a denser medium such as water or glass,than in air .The speed of sound in air can be measured by placing an explosive charge 1 km from some one measuring instrument and the exploding it .The flash of the light is recorded by one instrument.A few second later a second instrument records the noise of explosion . Sound does not travel nearly as fast as light ,The time between the flash and the noise is found to be 3 seconds .This is time taken by sound to travel 1 km through air

                                                Ship animation what is measuring Ocean Depth

In thunderstorm , lightning is always seen before the clap of thunder is heard.This because light travels so much faster than sound .Count the number of seconds between the lighting flash and the first sound of thunder and divide the answer by three. This gives the distance .In kilometers, of the lightning


Picture showing Determination of Ocean Depth By measuring Sound Wave

The ocean depth can be found by measuring the time between sending out a sound signal and receiving the echo reflected from the ocean bed. Half this time ,multiplied by the speed of sound in sea water, gives the depth. Many readings can be taken in a short time. Install aquatic microphone(hydrophone) (H) below the ship Install a explosive (E)
below the ship another side of the hydrophone at same level.After explosion the sound propagated toward hydrophone
in two ways one through EH path, and other through EO path, which go to ocean depth then reflected toward hydrophone through OH path.Assume that time needed for EH path is t1 and time needed for (EO + OH) path is t2 and
velocity of the sound in ocean is Vw then the formula is:-

EH = Vw t1

EA = AH = Vw t1 / 2

EO + OH = Vw t2      (EO = OH)

EO = OH = Vw t2/2
                     ___________        Vw      __________
h  = OA = V EO|2 -  EA|2    = ---------  V t2|2 -  t1|2

If Hydrophone and explosive present at x distance then the final depth of ocean is:-

                            Vw        __________
D - x + h = x + --------  V  t2|2 --  t1|2      .


Picture showing Underground Oil Exploration by examining Reflected sound wave pattern from underground explotion

An underground explosion directs sounds downwards. Oil reflects a certain pattern of echoes. Which are recorded by a sensitive instrument called a seismograph. The geologist can therefore locate the oil and find the best place to sink a well.


Wind instruments that are called pipes are the trombone, trumpet,bugle,,tuba, flute,piccolo, clarinet and saxophone. When you blow into one , the column of air inside vibrates, producing a note.

Picture Showing Different sound wave pattern within different open and closed pipes

Air can be made to vibrate as it is blown into the pipe by making it move past a sharp edge.This edge causes eddies or wave in the air column .If you could see  them , they would looks like the waveson a flag flapping in the wind.

The frequency (number of vibrations each second ) of the vibrations depends on the length of the air column inside the pipe.The shorter the air column , the higher the frequency , or pitch, of the note produced.By opening or closing holes at different places on the tube, the length of the vibrating air  column is altered which changes the pitch.

Picture showing different types of Flutes

Pipes are called open pipes if both ends are open and closed pipes if one end is closed off .An open pipe and a closed pipe of the same length have different tones.In an open pipe the frequency,and therefore the pitch , is twice that of closed pipe of the same size .This is because the waves have a different shape in the two pipes .At an open end the molecules of air have their largest vibrations. At closed end they do not vibrate at all.

Showing different flutes and Sound wave pattern from Flutes

The wave inside the pipes can have different wavelengths- as long as there is a node (no vibrations) at a closed end and an antinode (greatest number of vibrations) at an open end. As the wave-length get shorter, the frequency or pitch of the note gets higher.This means that when you blow down a pipe, you produce a main note , called the fundamental, and other fainter notes of higher pitch .These are called overtones.The overtones give an instrument its characteristic sound. The organ is the largest of all musical instruments. It covers the widest frequency range ,and has greatest variety of tone.
Air is blown into the many pipes ,either by hand bellows or now mainly by motor driven fans.The long wide organ pipes make low pitched sounds and the short narrow pipes make high pitched sounds.


A diagram of a wave . Where the lines cross. The molecules are at the rest , this is called a node (N) . Where the lines are widest apart the molecules are vibrating most and have their greatest energy . This is called an antinode (A). The wavelength of a wave is the distance between nodes or between antinodes.

Waves in open and closed pipes the fundamental note has the longest wavelength and thus the lowest pitch or frequency. The frequency of the overtone are whole number multiply of the frequency of the fundamental.


Any sound that we consider pleasant to hear is said to be musical.Music is the sound made by orchestra, a musical instrument ,a singer or a choir.

The ancient greeks were the first people to study music scientifically .They put together a series of musical sounds in ascending (higher) and descending (lower) pitch to make a scale.


Picture showing different Musical Instruments

Musical instruments can be put into 4 main sections : strings, percussion, wind and electric instruments. The different design and shapes of the instruments and the different materials from which are made causes them to have different sounds. A violin made of thick good quality of wood will make different sounds from a similar looking of thinner or poor quality of wood.

                                                    Sounds from different musical Instruments

Two other important factors are an instruments size and the musician`s skill .

In good music , only the desired vibrations are heard .If the vibration has the right pitch and amplitude (loudness) , a musician should be able to Recognise which note is being played , for example the note"A" of the musical scale.


Each musical note has a definite pitch or frequency that is the same for every instrument. It is called the fundamental
frequency .The note on a piano has the same fundamental frequency as the note played on the Guiter or a is produced 440 vibrations of the string or air column in one second.

No musical instrument produces a perfectly pure note of one frequency.Instead it produces a number of fainter overtones at the same time as the fundamental frequency . These overtones can have 2, 3 ,4,5,6 times the frequency of the fundamental. Different instrument produce different amounts of some or all of these overtones.This is why each instrument has a definite and recognizable sound.

Musical scales are made up of groups of 12 notes called semi notes .The notes are arranged on a scale which rises from low to high pitch. Each group of notes is called octave .Each note of octave has a frequency that is 1.0595 times higher than the frequency of the note immediately below it. If you multiply 1.0595 by itself 12 times you get the answer 2 .This mean that the note one octave above another one has twice its frequency .The frequency of upper C is 532.2 vibrations per second .Twice that of middle C.

Lord Rayleigh was one of the Britain`s greatest scientists. He worked out a new method of measuring the strength and loudness( amplitude) of sound vibrations. He wrote the Theory of sound  which describes the movement of sound producing objects,and how they cause the surrounding air to vibrate.


The waveforms of the notes of different instruments. The waveforms are found by adding the amplitides of the fundamental and the various overtones.The fainter the overtones, the smaller the amplitudes.Each instrument has a different waveform because of the different overtones present.



Music is made all over the world on a bewildering variety of instruments. Here is a collection of variety of instruments.The vina and sitar are also lutes, while the sarangi is played with a bow and the strings stopped with the fingers which move along them to make the notes slide.


Different sound Levels of different Noises

Any sound that a person find unpleasant can be called noise. A noise to one person ,however might be thought  a nice sound by some body else .In scientific terms noise is sound made by an irregular pattern of waves.

There are many things which could  make our world unpleasantly ,even dangerously noisy .Therefore include jet taking off , road drills and heavy traffic. Laws forbid the making of noise above a certain level.

You may have noticed that a car born or or fire engine siren seem to have higher pitch as the vehicle rushes toward you.
This is most noticeable as the vehicle reaches you .At the moment the pitch of the horn or siren suddenly drops to a much lower note.

Sound waves moves outward from the horn .The waves moving in the same direction as the vehicle travel towards you at the speed of the sound plus the speed of the vehicle .So as the car comes toward you .More than the normal number of sound waves reach you each second . The frequency of the waves is higher than it would be if the vehicle were not moving .The pitch of the note is also higher .

When the car has passed you the sound wave reach you at the normal speed of sound minus the speed of the car .Fewer sound waves reach you per second so the frequency is lower than when the vehicle is stationery .The pitch of the note is lower. This is why the pitch suddenly drops as the vehicle passes you


Picture showing Doppler Effects

This seeming change in pitch of a moving sound source is called the Doppler effect .It is named after Johann Doppler who worked out the reason for it in 1842. The Doppler effect also occurs with light waves.

         Animated movie Showing Doppler Effect : Sound Of a Car engine during Near and Away Position

If a source of light , such as a star , is moving toward or away from an observer, the normal frequency of the light waves is increased or decreased .This effect is very useful in astronomy for calculating the velocities of stars.

One very recent noise is the sonic boom produced by supersonic aircraft .As an aircraft flies ,It pushes in front of it in waves .These are like the waves you see moving forward and outward from the bow of moving ship. As the aircraft flies
faster it pushes the waves of air against each other .This forms a wall or barrier of compressed air in front of the aircraft

At about 1200 km per hour (750 mph) an aircraft reaches the speed of sound.At this moment power full air pressure wave at the nose of the Air Craft disturbed and turn into a sound wave .A noise like tremendous clap of thunder is heard directly below the aircraft .This is called the sonic boom. 

As the car engine rushes away from you buzzing its horn, fewer sound waves reach you than when it approached you. The pitch of the horn`s note drops suddenly as it passes you.

A Scale of noises: A loudness of a noise is found by measuring the energy of a sound wave.Loudness is usually measured in decibels. A sound of zero decibels is just too faint for the human ear to hear. Lorries are not allowed to make a noise above 90 decibels. Sound above 140 decibels are dangerous to the unprotected ear.


There are many aircraft that can fly faster than the speed of sound. Most of these are military aircraft.The world`s fastest jet aircraft is the Lockheed SR-71 . This American plane has reached a speed of 3520 Km per hour (2200 mph). Concorde was developed jointly Britain and France and is the only supersonic passenger plane.It travels at more than twice the speed of sound, reaching London from New York in about three hours.


                                      Animated Oscilloscope Reading For different types of Sounds

This is the machine which produce graphical representation of any sound note.In case of hi-pitched sound it produce closely space many waves . In case of low pitched sound it produce distant space few waves.In case of soft sound it produce very low Highted waves. In case of loud sound it produce high highted waves.

Oscilloscope Reading sound From Tape Recorder

Real Oscilloscope Machine

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