My Science School

            There are many ways in which sound pollution affects a human being. It can cause hearing problems, sleep disorders, cardiovascular issues, and other health issues. Let us look at a few of them in detail.

            As you may know, unwanted sounds that our ears are not able to filter, may cause serious problems to the body. Certain sounds when exceed the limit, disturb our ears. For example, the sound of aeroplanes or horns.

            Constant exposure to such sounds can damage our ear drums, and cause hearing loss. Then there are sleep issues one develops due to loud sounds. If we are not able to sleep properly, it will in turn cause fatigue.

            Many studies in the past have suggested that the occurrence of aggressive behaviour and fatigue can be linked to noise pollution. In the later years of life, these conditions can possibly lead to chronic health issues.

 

          Like human beings, animals too are vulnerable to loud noises. A clear example can be seen if you have a pet dog at home. When it hears noises from firecrackers, for instance, it quickly moves to places that keeps it away from the sounds. Helpless animals like these get easily scared by high intensity sounds. 

          Not just for dogs, but for birds too, noise pollution proves to be costly. Often, sounds from planes, road traffic and machinery in urban areas destroy their habitats, and change their normal ways of life. For owls and bats in particular, unwanted sounds affect prey-hunting.

          Another species that get affected by sound pollution is elephants. Environmentalists warn that helicopter rides and other noisy events around their habitats can cause the animals to flee the area out of fear. This in turn, will affect the entire ecosystem.

          In fact, noise pollution is one of the many factors that contribute to the depletion of wildlife population. 

                Almost all species on Earth are prone to the hazards caused by sound pollution. Marine animals are no exception. Many studies have shown that loud sounds often cause major problems to the health of marine lives.

               It is true that many of these animals need sound to navigate, to find food and mates, and to communicate. Yet, when the sounds become noise, they find it unbearable.

               The main threats before them are military sonars, large ships, explosives, underwater construction and air guns. The effects caused by these factors are various. They include temporary and permanent hearing loss, disruption of communication, and subsequent stranding, habitat loss, serious injuries or even deaths from hemorrhaging and tissue trauma.

              While bigger fishes like whales and dolphins show a greater resistance, smaller ones and soft shelled species like prawns, molluscs etc, are more sensitive to noise. 

 

           As we saw earlier, the idea of waves can be best understood through the example of a stone thrown into still water. This act produces rings of small waves, or ripples on the surface of water. We can see them spread out in even, concentric circles, from the point where the stone falls.

          Depending on the size of the stone, the size of the circle too varies- the larger the object, the larger the waves. In this context, the movement of waves is produced by the up-and-down motion of particles in the water. Such waves are called ‘transverse waves’. Another example is the water waves in the ocean, which move up and down.

         Sound waves, on the other hand, move in a different pattern. Their vibration is caused by the back-and-forth movement of particles. Such waves are called

          ‘Longitudinal waves’. They travel in the same direction as the vibration, or disturbance that causes them. As the waves travel through a medium, the molecules or particles collide with each other in the same direction and the waves keep moving. 

            Supersonic speed refers to a speed greater than that of sound. A bullet fired from a modern-day gun is said to have this kind of speed. Another important example is the supersonic aircraft.

            As the name suggests, they are flights that travel faster than sound. Historically, they were developed in the second half of the 20th century. It is said that US Air Force Captain Charles E. ‘Chuck’ Yeager was the first person to fly an aircraft faster than the speed of sound, in 1947.

            One of the earliest and supersonic flights that was used as a passenger aeroplane was the Concorde. Its speed was twice the speed of sound, and was said to fly between London and New York in around three and a half hours! However, the flight is no longer used.

            An Indian example of a supersonic flight is the HAL Tejas, which is still in service. 

          Imagine yourself in a sea. You see different kinds of waves there - big ones, small ones, huge ones, and sometimes, scary ones too.

          The highest point of each wave is called the crest. Suppose you are floating on a wave crest, and can see the crest of another wave in front. Then, you are looking at the wavelength of those waves. In other words, wavelength is the distance between two identical points on two back-to-back waves. In this case, it is the distance between two crests. Similarly, there are also something known as troughs, which are the lowest part of a wave.

          The frequency of a wave, on the other hand, refers to the number of waves produced by a source each second. It could also denote the number of waves that pass a certain point each second. The unit of frequency is hertz (Hz). Kilohertz, megahertz and gigahertz are used when the waves have high frequencies.

          Both frequency and wavelength are related to the pitch of a sound, meaning they determine how high or low a sound is going to be. The greater the frequency, the shorter is the wavelength and, higher the pitch. 

          Put it simple, amplitude is the height of the peaks of a sound wave.

          Let’s try to understand the concept with the example of sea. Sometimes when you visit it, the sea looks calm. But sometimes, it gets rough with huge waves. As the waves develop, we can see some parts dipping down lower than the normal surface of water, and others rising higher than the same. The distance between this dip and the rise of a wave from the calm surface is generally referred to as amplitude.

          In the context of sound, amplitude is the size of vibrations, determining how loud a sound is to be. We know for a fact that larger vibrations create louder sounds.

         Intensity, as some of you might know already, describes the amount of energy in a sound. For example, a pistol shot has more intensity and produces more sound compared to a cork being pulled off a bottle. 

               From the very moment of birth, we, humans are capable of making sounds. First in the form of cries, then as incomplete words, and finally, as clear speech. There are many parts in our body that help us speak, or produce sounds.

              One of the main parts is the voice box, or larynx. It is a lump that remains close to our throat, and has two vocal cords stretching across it. They are the source for speech production in our body. That is, when air is exhaled from the lungs, it causes the vibration of the vocal cords. This in turn results in the production of sounds.

               However, there are other parts as well, that help in the process. The mouth and the nostrils are two of them. Yet another organ is the tongue. It plays a vital role in speech by moving into different shapes. Then there are the lips and the teeth, which help in the better expression of sounds. 

            The human ear is a wonderful organ that performs some of the most important functions in the body. It detects and analyzes sounds, and also maintains the sense of balance.

            Structurally, the external ear is created in a peculiar way. It has many twists and folds that help in enhancing certain sounds up to 100 times.

            Designed in a way as to make the skin maintain its funnel shape, a healthy ear enables the capturing of even the tiniest vibration.

            In addition, the ear can help determine sound direction. It can also decide the range of sounds we hear. However, as we grow old, we become less sensitive to sounds, and may not be able to hear high pitched sounds like the squeaking of a bat. But this could be picked up by a child. It has been found that a normal human can detect frequencies between 20 Hz and 20 kHz. 

                The concept of echo must be familiar to most of us. While standing in an empty space, if you let out a loud shout, you can hear a faint sound coming back after a few seconds. This reflected wave of sound that resembles the original is called the echo. It can be experienced when you are standing on top of mountains, in remote places, in big and empty rooms, in caves etc.

                The term echo is derived from the Greek word meaning sound. There are many factors influencing the creation of echoes. Typically, the sound waves can bounce off only if the objects they hit are smooth and hard. It is like a rubber ball bouncing off the ground. If the waves meet a soft surface, for example a cushion, they will be absorbed, and hence, no echo will be created.

                         There are multiple uses for echoes. They can be used to measure distance, velocity, and the shape of objects. It is to be noted that an improper arrangement of echoes will result in unclear sounds.

            The contributions made by the Ancient Greeks to the world of acoustics are unparalleled.

            One of them is the amphitheatre of Epidaurus, designed by Polykleitos the Younger, around the 4th century BC. The theatre had a tripartite structure, that is, an orchestra, auditorium, and stage building. There were also 34 rows of limestone seats that could accommodate 14,000 people.

            The acoustics of the place was such that a performer standing on the open-air stage could be heard in the back rows, almost 60 metres away.

            Experts attribute this rare feature to the arrangement of seats. According to them, the stepped row of seat structure was perfectly shaped so as to act as an acoustic filter. The seats suppressed low-frequency sounds that formed the major component background noise like the murmur of a crowd. This in turn, reflected high-frequency noises of the performers off the seats, and back toward the seated audience.

            We have read that most humans can hear sounds between 20 and 20,000 hertz. Ultrasounds are those above this limit or specifically, above 20,000 hertz. They are not different from the normal sound in terms of physical properties. But the only difference is that they can be heard and produced by only a few animals like bats, moths, dolphins etc. and not by humans. In other words, the range of ultrasound begins where our sonic range ends.

            The uses of ultrasound can be seen in electronic, navigational, industrial, medicinal and security applications. Let’s look at a few examples in brief.

            In some cases, ultrasound is used to detect objects or to measure distances. They are also helpful in testing products and structures.

            In addition to these, ultrasound is used in the field of medicine to view the internal organs of our body.

            There are quite a lot of animals that make use of ultrasound for purposes like navigation, communication, catching preys, avoiding obstacles etc. Let’s look at a few examples.

            Marine animals like dolphins and toothed whales are very famous for their sonar, which employs sounds from 250 Hz to 220 kHz.

            Then, there are the bats that have a variety of ultrasonic ranging techniques. They enable the mammals to detect preys and avoid obstacles, even in thick darkness.

            There are also many insects that have excellent ultrasonic hearing abilities. For example, like moths, beetles, lacewings, praying mantis etc. They use their skill to listen to echo locating bats. Upon hearing a bat, they make plans to escape being caught.

            Another group of animals that are responsive to ultrasonic sounds is mice. The next in the category of animals that can perceive high frequencies are dogs and cats.

             Sonar is the short form for Sound Navigation and Ranging. It is an ultrasonic system used in ships and other vessels for navigation, and locating objects underwater.

            As we know, sound waves travel faster than light through water. However, ordinary sound waves cannot travel longer distances, only ultrasonic waves can. Due to their high frequency and short wavelength, ultrasonic waves penetrate water to very long distances and it is this feature that is utilized in sonar.

            Let’s see how this works, in the case of a submarine. While deep in water, the vessel finds its way by sending out pulses of ultrasound and listening to the echoes. It is just like the phenomenon of echolocation in bats. Depending on the time it takes for the echoes to come back, the navigator of the vessel can figure out if there are any ships, submarines, or other obstacles nearby.

            This technique is also used by ships to calculate how deep the waters are by firing sound beams straight downward.

 

           The importance of ears is something we are all aware of. This organ is the receiver of sound in the human body and plays a very important role in communication.

           Structurally, the ear is made of three sections- the outer ear, the middle ear, and the inner ear. The outer ear is the visible external part which consists of the pinna and the ear canal. It gathers sounds and sends them to the middle ear through the ear canal.

           The middle ear is an air-filled cavity that turns sound waves into vibrations. It is separated from the external ear by the eardrum, a thin, cone-shaped piece of tissue. Past this drum, there are three small, but important bones in the middle ear. Collectively known as the ossicles, they are the malleus, incus and stapes.

           The third and final part of the ear is the inner ear. It consists of a tiny organ called the cochlea that converts the vibrations from the middle ear to nerve impulses. These impulses then travel to the brain, from where it gets converted as sound.