What is Sound?

A sound is a sensation that is perceived by us through our ear, the organs of hearing. In Physics terms, it travels as a wave and for that matter, is essentially a wave of compression. As it passes through a medium say, the air, the molecules of the air crowd together and then draw apart. The sensation of hearing results when such waves strike the ear.

Going by its wave nature, it very much resembles with light except that sound always require a medium through which it travels, but light can travel even in vacuum too.

However, like all compressional waves, sound waves can travel through any medium whatsoever except vacuum. The medium of sound travel thus, may be a solid, liquid or a gas such as air.

Sound is produced by vibration or movement say for example, the thin leather of the drum when beaten or hammered, it moves up and down, i.e. it vibrates, producing sound. Similarly, a guitar when plucked with the fingers, the string starts moving rapidly to and fro and thus, producing sound.

Several objects move either so slowly or so rapidly that the ear is not able to hear the sound produced by them. A ruler fixed at one end and plucked at the other will move to and fro, but may not produce sound of much intensity which can be heard because, the vibration is too slow. In the same vein, a bat also squeaks, but the sound it produces is caused by such a rapid vibration that our ears cannot detect it. It is said that the human ear can hear vibrations which are between 20 and 20,000 vibrations per second (or between 20Hz and 20,000 Hz). These are the limits of audibility, and the upper limit decreases with age.

Connecting concepts: How does sound travel in waves?

Every time a sound is made, there is some vibrating object somewhere. Something is moving back and forth rapidly thus, indicating that sound always starts with some vibrating object around. But the sound always requires a medium that could carry it from its source to the hearer. This medium thus could be anything from air, water and even the earth as such. A legend has to it that the ancient Indians used to put their ears down to the ground to hear a distant noise! In short, it can be said that no medium means no sound and this is the reason that the sound cannot travel in vacuum. Now the question that why does sound require a medium to travel through? The simple answer to this is that sound always travel in waves. As the vibrating objects somewhere vibrate, they cause the molecules or particles in the substance next to them to vibrate. Each particle then passes on the motion to the particle next to it and hence, the result is sound waves.

Since, the mediums in which sound travels can range anything from wood to water to air, obviously the sound waves will travel at different speeds in each of the given media. So, whenever do we raise a question and ask how fast does sound travel, we certainly have to ask: In what? Viewed thus, the speed of sound in air is about 335 meters per second that is approximately 750 miles per hour. But remember, this refers to the speed of sound when the temperature is at zero degrees centigrade thus concluding that as the temperature rises, the speed of sound will also rise. This is borne out of the fact that the speed of sound is always inversely proportional to the density of the medium i.e. more denser the medium is, less will be the speed of the sound in the said medium.  As the temperature rises, the density of the air decreases, hence, more shall be the speed of the sound. In the same vein, the speed of sound is much faster in water than in air say for example, when water is at a temperature of say, 8 degrees centigrade, sound travels through it at about 1435 meters per second or so called at 3210 miles per hour. Similarly, in steel, the sound travels at about 5000 meters per second or at 11,160 miles per hour.

It must however be kept in mind that the speed of sound has nothing to do with its being louder or otherwise, weak. Nor the speed of sound has anything to do with its pitch; high or low. Instead, the speed of sound depends entirely on the kind of media through which it is traveling. Try a trick to test the speed of sound in air and water. Clap two stones together when you are standing in water. Now go under water and do the same exercise again i.e. clap these two stones together again. You will be amazed to know that how much better sound travels through water than through the air as such….

What are Infrasonic & Ultrasonic waves?

Infrasonic are the longitudinal waves of frequency less than 20 Hertz i.e. the sound waves having less than 20 cycles or vibrations per second are called as infrasonic waves. During earthquake, infrasonic waves pass through the earth’s crust. The human heart also vibrates at infrasonic frequencies.

Ultrasonic on the other hand, refer to those longitudinal sound waves that have their frequency greater than 20,000 Hz (20 kHz). The vibrations of certain crystals (quartz, zinc oxide, barium titanate, etc.) under the influence of an applied alternating voltage produce ultrasonic frequencies of well up to about 10 kHz. Such energy conversions – mechanical vibrations to electrical or vice versa – are example of the piezoelectric effect. The human ear cannot hear ultrasonics, but dogs, birds, bats and dolphins can hear them. Dogs respond to dog whistles pitched at 25,000 Hz, inaudible to human whistle blowers and bats emit squeaks at 100,000 Hz and guide themselves in the dark by listening for their echoes from nearby obstructions.

Applications galore of Ultrasonics

The uses of ultrasonics are many, ranging from cleaning silverware to catching burglars and drawing electronic portraits (sonograms) of unborn babies. Ultrasonic devices work by either delivering focused energy or detecting and measuring vibrations from an ultrasonic receiver.

Connecting concepts: What is ‘piezoelectric’ effect?

In simple terms, it refers to the appearance of an electric potential across certain faces of a crystal when the same is subjected to a certain mechanical pressure. Similarly, the other way round, when an electric field is applied on to the same crystal, the crystal undergoes what we call as mechanical distortion. It was the famous Pierre Curie and his brother, Jacques who discovered this phenomenon for the first time in crystals called Quartz and Rochelle salt in the year 1880 and named the one as piezo-electricity. Piezoelectric effect in fact, occurs in many crystals or crystalline substances such as barium titanate or zinc oxide etc. The phenomenon of piezo-electric effect occurring in crystalline solids can be explained by the fact of there being a displacement of ions from the unit cells of a crystal when the same is subjected to a pressure or a force of compression. As the ions from every unit cell of a crystal are displaced following compression, it amounts to the electric polarization of the unit cells. Since a crystal is noted for having a well ordered and regular arrangement of unit cells in its structure, these effects ultimately accumulate thereby, causing the appearance of an electric potential difference between certain faces of the crystal. Therefore, when an external electric field is applied to such a crystal, the ions in each unit cell are displaced by electrostatic forces thereby, resulting in the mechanical deformation of the whole crystal.

Delivering focused energy: Ultrasounds can be aimed, focused and reflected almost like light beams. Specific ultrasonic frequencies can be used for loosening the plaque from teeth as well as for causing kidney stones to be pulverized without affecting the kidney itself.

Detecting and measuring ultrasounds: Ultrasonics can be used for guarding banks, offices and factories. In this application, an ultrasonic beam is aimed and reflected so that it criss-crosses a room several times and then strikes a detector, a kind of ultrasonic microphone. An intruder walking into the path of the sound immediately sets off a remote signal.

Another kind of detecting and measuring is done by using ultrasound as a kind of X-ray, without the risks of x-ray exposure. A beam of ultrasound travels directly through a homogenous substance, but if it reaches a different substance (at an interface), the beam is reflected and forms a sonogram. In this way, ultrasonic detectors can locate cracks or bubbles in metal castings. Similarly, and much more important, interior organs of the body and fetuses can be located and outlined. For example, an echocardiograph machine clearly shows the opening and closing of the valves of the beating heart. Thus, we say that an ECG makes the use of ultrasonics for heart diagnostics.

The functioning of SONAR: (Sound Navigation & Ranging) is a method of investigating the depth of submerged objects by transmitting or sending ultrasonic waves onto them and receiving back the reflected ultrasonic waves. The time taken by the wave to travel to the object and returning back gives the distance of the object from the ship provided the speed of the ultrasonic wave in the medium is known. The reflected wave helps in studying the nature of the surfaces as well.

Modern fishing vessels are equipped with fish dens which can ultrasonically find the depth of fish schools. The dolphin can detect an individual fish and also its own kind from a distance of 50m. Bats can fly in darkness because of a sonar system of their own.

Why do we notice the lightening first rather than thud of a thunderstorm?

The answer to this question lies in the speed of the sound. During thunderstorms we see the lightning long before hearing the thunder, even though they are both produced at precisely the same instant. Also when a gun is fired to start a race of horses, we seem the smoke far off before we hear the sound of firing. All this goes to show that speed of light is much greater than that of sound. The speed of sound does not depend on wavelength and amplitude of the wave. Rather the speed of sound is inversely proportional to the density of the medium this means that greater the density of the medium lesser shall be the speed of the sound in that very medium. Say for example, the speed of sound in hydrogen is 4 times that in oxygen because of the oxygen being 16 times denser than hydrogen. At the same time, the speed or the velocity of sound is also independent of the pressure. With the increase of temperature, there is a decrease in density of the surrounding air and consequently, the velocity of sound increases. Velocity of sound in moist air is greater than that in dry air (which has more density than moist air). The velocity of sound decreases if the wind is blowing in a direction opposite to that of the sound wave.

Solids are more elastic than liquids and gases; therefore speed of sound is more in solids, less in liquids and least in gases (even though solids have more density than liquids or gases generally). In air at 0⁰C the speed of sound is 330 meters per second, in water it is about 1450 m/s, in concrete, it is about 5000 m/s, and in steel it is about 6000 m/s.

Properties of sound waves

Just like the light or electromagnetic waves, sound waves also exhibit the similar properties such as reflection, refraction or diffraction etc. Each of these properties of sound waves is reflected in many natural phenomena around us say, for example:

I)     Reflection of Sound waves and “Echo”:

When ripples traveling on water surface strike a wide obstacle, such as a floating board, a new set of ripples are observed to start back from the obstacle. The waves herein this case are said to be reflected from it. In a similar way, sound waves may be reflected from walls, mountains & the ground etc. Reflection of sound waves obeys the same laws of reflection as those of light. One of the most pronounced effects and live examples of sound reflection observed in nature is the production of so called an echo…

Connecting concepts: What causes an ECHO?

Today, when you have a question about anything in nature, you expect to get a true, scientific answer. But in ancient times, people would make up legends to explain things. The legend that the early Greeks had to explain an echo is very charming. Would you like to know it? Here it is.

There was once a lovely nymph called Echo who had one bad fault – she talked too much. To punish her, the goddess Hera forbade her ever to speak without first being spoken to, and then only to repeat what she had heard. One day, Echo saw the handsome youth Narcissus. She fell in love with him at once, but he did not return her love. So Echo grew sadder and sadder and pined away, until nothing was left of her but her voice! And it is her voice which you hear when you speak and your words are repeated.

That sad legend doesn’t really explain an echo, of course. To understand what causes an echo, you have to know something about sound. Sound travels at a speed of about 335 meters per second in the open air. It travels in waves, much like ripples made by a pebble thrown into water. And sound waves go out in all directions from the source, like the light from an electric bulb.

Now, when a sound wave meets an obstacle, it may bounce back, or be reflected, just as light is reflected. When a sound wave is reflected in this way, it is heard as an echo. So an echo is nothing, but a sound repeated by reflection.

Not all obstacles can cause echoes, however. Some objects absorb the sound instead of reflecting it. This means the sound doesn’t bounce back or reflected. There is no echo thus. But usually, smooth, regular surfaces, such as a wall, a cliff, a side of a house, or a vaulted roof, will produce an echo.

Did you know that clouds reflect sounds and can cause echoes? In fact, when you hear the rumbling of thunder, it’s because the first sharp clap is being reflected again and again by the clouds to which we may also call as reverberation.

Thus, we see that the “echoes” are produced by the reflection of sound from a distant hard surface such as a wall or cliff. You are able to hear an echo separately from the original sound because; there is always a certain time interval (at least, 0.1 second) between the sound and its echo. An echo is also produced in a small room, but the time interval between the echo and original sound is so short that it is impossible for the ear to recognize the two as separate sounds. Hence, you seem to hear the two sounds at exactly the same time, but the echo makes the original sound richer and louder.

It has been found by calculation that the least distance one has to be from an obstacle in order to hear an echo distinctly from the original sound is about 55 ft or around 17 m. For any distance less than this, the echo cannot be heard separately. Furthermore, if a room is filled with cushioned chairs and people all over it, one would not be able to hear the echo any more, even if the room is huge & large enough. This is because the sound has been partly absorbed by the cushions of the chairs, the wood of the furniture and the clothes and bodies of the people around…          

Reverberation: The echo is sometimes heard more than once. This is possible in the still of the night or in a quiet & extremely silent valley where there are no other sounds. This continuous occurrence of echoes is known as reverberation. A clear example is that of the reverberation of thunder, which is due to the continuous reflection of sound between two or more clouds.

Just as a polished surface is the best reflector of light, so is true of the smooth & hard surfaces that are the best reflectors of sound. Therefore, in order to reduce the troublesome echoes in large halls, the walls may be roughened or covered with soft, thick or porous materials such as felt and heavy curtains which help absorbing the sound and stop the same from being reflected again and again. This arrangement is also used in broadcasting studios where echoes must be prevented in any case for a sound proof recording of programmes.

The Acoustics of Buildings:  Reverberation is particularly noticeable in cathedrals and other large buildings where multiple sound reflections can occur from walls, roof and floor. Excessive reverberation in a concert hall is undesirable, as it causes music and speech to sound confused and indistinct. On the other hand, it is also not desirable to have no reverberation at all, for in its absence sound seems weak. The very characteristic of a building in relation to sound are called its “acoustics” and the pioneering work in this field was carried out in the early twentieth century by Professor W.C. Sabine of Harvard University. The most important property of a concert hall is its reverberation time that is defined as time taken for sound of a specified standard intensity to die away until it just becomes inaudible. This was very useful in planning new concert halls. Sabine related this “reverberation time” to the volume of a hall, the surface area of its walls, ceilings and so on and also the sound reflecting properties of these surfaces.

Noted that for certain special purposes, e.g. investigation of the properties of loudspeakers and other sound equipments, it is necessary to have rooms whose walls absorb completely all sound energy falling upon them. This is achieved by lining the walls, ceilings and floor with an-echoic wedges composed of glass fibre encased in muslin. In modern building practices, the spaces in the walls between the floors and ceilings are usually filled with some inelastic material which absorbs the sound instead of transmitting or reflecting it.

II)    Refraction of Sound: Why do we hear sounds louder at night than during the day time?At night, some distant sounds, such as traffic sounds are often heard louder than they are during the day time. This has been attributed to what we call as the refraction of sound waves. Why? The scientific reason behind this is that after sunset, the air near the ground cools down more than the air above it and just because, the sound travels more slowly in cold air than it is in warm air therefore, the sound waves from the source of sound are refracted back towards the ground. During the day however, the upper air is usually cooler than that near the ground and sounds tend to travel upwards.

III)   Diffraction and Interference in sound waves: Audible sounds have wavelengths from about 1.5 cm (frequency 20 kHz) up to 15 meters (frequency 20 Hz.) and so suffer diffraction by objects of similar size, such as a doorway 1 m wide. This explains why we can hear sound round corners.

Sound waves of the same frequency from two loud-speakers (supplied by one signal generator) produce a steady interference pattern. As you walk past the speakers you can hear the resulting variations in the loudness of the sound due to the waves reinforcing and canceling one another. The beats are produced when two notes of almost equal pitch are sounded together such that the loudness of the resulting sound rises and falls regularly and what that is being heard is called as beats. Noted that these beats are essentially produced as a result of the interference of sound waves and do render an added evidence in favour of the wave nature of the sound…

Characteristics of Sound: (Question asked in GS-pre-2000)

 Sounds can be distinguished from one another by three different characteristics: pitch, loudness and quality.

(i)    Pitch is that characteristic of a sound by which a high or shrill note can be distinguished from a low or a flat one. If the pitch is higher, the sound is said to be shrill and if it is less, the sound is described as flat. Pitch always depends upon the frequency i.e. higher the frequency of a given sound, higher shall be its pitch. All musical notes have a definite pitch. The voice of a woman is invariably of a higher pitch as that of a man.         

(ii)   Loudness is determined by the amplitude (energy) of vibration of the sound-making object. Thus, greater the energy carried by a sound wave, the greater is the intensity of that very sound.

 The intensity of a sound, as is received at any given place is measured in a unit called as decibel. Some common sounds and their noise levels in decibels (db) are like this: Ordinary conversation= (60 db); Telephone bell & Alarm clock= (70 db); Heavy traffic= (100db); Rock music & Siren of an Ambulance= (120 db); Jet aircraft= (140-150 db) and Machine gunfire= (170 db). 

The threshold of pain is about 120 db.

Connecting concepts: What is Decibel?

Decibel is a unit for comparing the levels of electric or acoustic power or in other words, to measure the loudness of sounds. It is in fact, more convenient to express them i.e. loudness of a sound as ratios rather than in their absolute magnitudes. Consider, for instance, the loudness of two sounds like the roar of a Ramjet engine and a barely audible human whisper. The absolute magnitude of total power that they produce in the air around them may be measured in watts. Therefore, the power of the former is 100,000 watts, while that of the latter is only 0.000,000,001 watt. Given thus, it can be said that the Ramjet engine roar is essentially, 100 trillion times louder than that of the barely audible, human whisper.

 But in this regard, one thing that remains to be something of paramount importance is that when measurement extends over such a wide range, it is more convenient to use a ‘geometric ratio scale’ rather than using an ordinary arithmetic scale provided by the series of whole numbers 0, 1, 2, 3…, we conventionally use for counting. In the geometric ratio scale, numbers increase in a geometric fashion like, 1, 10, 100, 1000, 10,000 just like cells of the body divide… So if we denote them as powers of ten to designate the respective figures of 10, 100 and so on and represent them namely 10⁰, 10¹, 10², 10³, 10⁴… respectively, we can use their power indices, 0, 1, 2, 3, 4.. to indicate their magnitude in a new unit called as “bel”. Since a decibel is one tenth of a bel, the same numbers, 1, 10, 100, 1000, 10,000... may also be denoted as 0, 10, 20, 30, 40... Decibels respectively.

Accordingly, if we reckon the loudness of the human whispers at the threshold of hearing as zero decibel, then that of the Ramjet roar (10¹⁴ times louder) than that of the human whisper, will be 140 decibels. Likewise, the strength of the human voice at the conversational level (10⁴ times stronger) will be 40 decibels such that every increase of ten decibels meaning a ten-fold rise in its loudness.

In brief, decibel unit is to sound what degree of temperature is to heat.

(iii)   Quality of a sound is that characteristic which distinguishes two sounds of the same loudness and frequency when coming from two different instruments. The quality of a musical sound depends on the “wave form” mostly. Thus, we can easily distinguish between the sounds of sitar and violin by their wave forms though they may be of exactly the same loudness and frequency.

Resonance in sound waves: Why does a big bang inside a closed room shatter the window panes?

The above effect is attributed to another characteristic of sound waves what we call as “Resonance”. Resonance in a practical sense is a particular case of forced vibration. When a body A is vibrating near another body B which has the same natural frequency as that of the A, then the body B will also start to vibrate of its own accord. As such, B is then said to vibrate in resonance or in tune with A.

In 1939, in USA, the ‘Tacoma suspension bridge’ collapsed because of mechanical resonance. A high-speed wind set the air over the bridge vibrating at a frequency close to the natural frequency of the vibration of the bridge. As a consequence, the bridge started oscillating and after several hours of a steady increase in amplitude of vibration due to resonance, the bridge eventually collapsed.

Soldiers are specifically trained to march in exact coordination with each other as well as in their steps so as to maintain a steady rhythm. If soldiers in formation march over a suspension bridge, the frequency of their steps may sometime match with that of the natural frequency of the bridge and could become a cause of a dangerous resonance. Therefore, by training, all soldiers are being trained as how to break the rhythm of their marching while crossing over a suspension (or otherwise, even a weak) bridge.

Windows rattle when a low flying aeroplane passes overhead. This however, occurs if the natural frequency of vibration of the window happens to be the same as one of the frequencies that make up the noise of the planes’ engine.

Similarly, when there is a loud explosion in a room, we find that the window panes in the room (especially if the windows are shut) vibrate strongly. If however, the explosion is large & loud enough; the windows might even be shattered into pieces. In the same way, when a bomb is dropped, houses which are at some distance from the spot fall flat on to the ground.

Interstingly, our radio also works on the same principle of resonance. The action of tuning in a radio set is made to adjust the value of the capacitance in a circuit until it has the same natural period of oscillation for electricity as that of the incoming signal. The small alternating e.m.f. thus set up in the aerial, is then able to build up similar e.m.f of large amplitude in the tuned circuit…

Connecting concepts: What is Doppler’s Effect?

Doppler’s effect is the apparent variation in the frequency of any emitted wave, such as a wave of light or sound, as the source of the wave approaches or moves away, relative to an observer. The effect takes its name from the Austrian physicist Christian Johann Doppler, who first stated the physical principle in 1842. Doppler’s principle explains why, a source of sound of a constant pitch moving towards an observer seems higher in pitch, whereas a source moving away seems lower. This change in pitch of the sound can be heard by an observer listening to the whistle of an express train from a station platform or another train. The lines in the spectrum of a luminous body such as a star are similarly shifted towards the violet end of the spectrum if the distance between the star and the earth is decreasing and it shifts towards the red end if the distance is increasing. By measuring this shift, the relative motion of the earth and the star can be calculated. In short, the Doppler Effect describes that when the source, the medium and the observer are in motion and as the source and observer move together, the apparent frequency of the sound is higher than that is actually produced by the source. On the other hand, as they move apart from each other, the same gets lower.

What is Red Shift?

Red shift is a shift in the wavelength of light emitted by a cosmic object toward the longer (red) wavelengths of object’s spectrum. Light acts like a wave, and its wavelength is the distance between crests of successive waves. The term red shift comes from the first detected shifts in wavelengths of light, but such shifts also occur at radio and other electromagnetic wavelengths. When a red shift occurs, all wavelengths are lengthened by the same fraction. A red shift is expressed as a percent-age increase over the normal wavelength. An example of a red shift can be seen in the spectra of quasars, extremely powerful sources of radio and light waves. A series of bright spectral lines caused by hydrogen appears in the spectrum of Quasar 3C 273 (Object 273 in the 3^rd Cambridge catalogue of radio sources). The wavelength of each line of 3C 273 is 15.8 per cent longer than normal. Thus, the red shift of the quasar is 15.8 per cent. In essence, the bottom line of the red shift remains in the fact that If the star and the earth are moving closer to one another, more light pulses are received in a given time interval, and the colour emitted from the star appears to be shifted towards the violet end of the spectrum. When the distance between the earth and the star is increasing, the observed light is shifted towards the red end of the spectrum.

What is Sonic Boom?

The pressure disturbances created by a plane flying below the speed of sound such that such pressure disturbances end up traveling faster than the plane itself and consequently, the sound of plane can be heard by the people on the ground as if it were coming towards them. May it be noted that the sound of a plane flying at a speed faster than the speed of sound, i.e. it is flying at supersonic speed cannot be heard on the ground until the aircraft has passed by. Nevertheless, after a supersonic aircraft has flown overhead, people on the ground may hear a kind of sharp “boom” or “bang” what we call as “sonic boom.”

Connecting concepts: What is Mach number?

Mach numbers are generally used to describe the speed of sound in air particularly just because, the speed of sound in air is not always the same owing to the presence of layers of the air of different densities at successive heights from the ground. Given thus, the speed of sound always depends on the altitude and temperature of the air. At sea level & at 15⁰C, sound travels at a speed of about 1,190 kmph. With higher altitude, as the air up there in the atmosphere gets cooler and consequently, increases in its density, the speed of sound thus, decreases. At 12,000 meters, the speed of sound is about 1,060 kmph.

 Flights faster than Mach 1 speed, the speed of sound is called supersonic and the flight as being supersonic flight. However, Flights slower than mach 1 is accordingly called as subsonic flights.

It is (sonic boom) caused by the shock waves from a plane: the plane moves as fast as the pressure disturbances it creates, and these disturbances ‘pile up’ in front and form a shock wave. At least two shock waves are created: one from the front and the other from the rear of the plane, but as the two waves, arrive close together, only a single boom may be heard.                

What is the Sound Barrier?

The name “sound barrier” is actually a wrong way to describe a condition that exists when planes travel at certain speeds. A kind of “barrier” was expected sometime in the distant past by the scientists when planes reached the speed of sound i.e. must be flying at 335 meters per second that is the actual speed of sound in open air. Unfortunately, in the actual sense, no such barrier actually developed at all!

In order to understand this, let’s start with a plane traveling at an ordinary low-speed flight i.e. it may be flying below the speed of sound in air. As the plane moves forward, the front parts of the plane send out a pressure wave. This pressure wave is being caused by the building up of particles of air as the plane moves forward.

Now this pressure wave goes out ahead of the plane at the speed of sound whereas, the plane is flying at a lesser speed than the speed of sound. It is i.e. “the pressure wave” therefore, is moving faster than the plane itself, which, as we said above, is moving at an ordinary speed. As this pressure wave rushes ahead of the plane, it causes the air to move smoothly over the wing surfaces of the so called low speed flying plane.

Now let’s say the plane is now traveling at the speed of sound. The air ahead receives no pressure wave in advance of the plane just because, both the plane and the pressure wave are moving forward at the same speed. So the pressure wave herein this case builds up, but in front of the wing rather than ahead of it as noted above.

The result being, a shock wave, and this creates great stresses in the wing of the plane. Before planes actually flew at the speed of sound and even faster, it was expected that these shock waves and stresses would create a kind of “barrier” for the plane – a “sound barrier.” But no such barrier developed or actually found to have developed ever since aeronautical engineers were able to design planes & aircrafts to overcome it.

Incidentally, the loud “boom” what has also been referred to as “sonic boom” that is heard when a plane passes through the “sound barrier” is caused by the shock wave as described above particularly, – when the speed of the pressure wave and the speed of the plane are the same. A sonic boom may easily shatter window panes. The faster or lower a plane flies, the stronger the shock wave and thus, louder the sonic boom will be…