This lesson covers the topic “Sound Waves”. In this lesson we will continue to study acoustics. First, let's repeat the definition of sound waves, then consider their frequency ranges and get acquainted with the concept of ultrasonic and infrasonic waves. We will also discuss the properties of sound waves in different media and learn what their characteristics are. .
Sound waves – these are mechanical vibrations that, spreading and interacting with the organ of hearing, are perceived by a person (Fig. 1).
Rice. 1. Sound wave
The branch of physics that deals with these waves is called acoustics. The profession of people who are popularly called “listeners” is acousticians. A sound wave is a wave propagating in an elastic medium, it is a longitudinal wave, and when it propagates in an elastic medium, compression and discharge alternate. It is transmitted over time over a distance (Fig. 2).
Rice. 2. Sound wave propagation
Sound waves include vibrations that occur with a frequency from 20 to 20,000 Hz. For these frequencies the corresponding wavelengths are 17 m (for 20 Hz) and 17 mm (for 20,000 Hz). This range will be called audible sound. These wavelengths are given for air, the speed of sound in which is equal to .
There are also ranges that acousticians deal with - infrasonic and ultrasonic. Infrasonic are those that have a frequency of less than 20 Hz. And ultrasonic ones are those that have a frequency greater than 20,000 Hz (Fig. 3).
Rice. 3. Sound wave ranges
Every educated person should be familiar with the frequency range of sound waves and know that if he goes for an ultrasound, the picture on the computer screen will be constructed with a frequency of more than 20,000 Hz.
Ultrasound – These are mechanical waves similar to sound waves, but with a frequency from 20 kHz to a billion hertz.
Waves with a frequency of more than a billion hertz are called hypersound.
Ultrasound is used to detect defects in cast parts. A stream of short ultrasonic signals is directed to the part being examined. In those places where there are no defects, the signals pass through the part without being registered by the receiver.
If there is a crack, an air cavity or other inhomogeneity in the part, then the ultrasonic signal is reflected from it and, returning, enters the receiver. This method is called ultrasonic flaw detection.
Other examples of ultrasound applications are ultrasound machines, ultrasound machines, ultrasound therapy.
Infrasound – mechanical waves similar to sound waves, but having a frequency of less than 20 Hz. They are not perceived by the human ear.
Natural sources of infrasound waves are storms, tsunamis, earthquakes, hurricanes, volcanic eruptions, and thunderstorms.
Infrasound is also an important wave that is used to vibrate the surface (for example, to destroy some large objects). We launch infrasound into the soil - and the soil breaks up. Where is this used? For example, in diamond mines, where they take ore that contains diamond components and crush it into small particles to find these diamond inclusions (Fig. 4).
Rice. 4. Application of infrasound
The speed of sound depends on environmental conditions and temperature (Fig. 5).
Rice. 5. Speed of sound wave propagation in various media
Please note: in air the speed of sound at is equal to , and at , the speed increases by . If you are a researcher, then this knowledge may be useful to you. You may even come up with some kind of temperature sensor that will record temperature differences by changing the speed of sound in the medium. We already know that the denser the medium, the more serious the interaction between particles of the medium, the faster the wave propagates. In the last paragraph we discussed this using the example of dry air and moist air. For water, the speed of sound propagation is . If you create a sound wave (knock on a tuning fork), then the speed of its propagation in water will be 4 times greater than in air. By water, information will reach 4 times faster than by air. And in steel it’s even faster: 
(Fig. 6).
Rice. 6. Sound wave propagation speed
You know from the epics that Ilya Muromets used (and all the heroes and ordinary Russian people and boys from Gaidar’s RVS) used a very interesting method of detecting an object that is approaching, but is still far away. The sound it makes when moving is not yet audible. Ilya Muromets, with his ear to the ground, can hear her. Why? Because sound is transmitted over solid ground at a higher speed, which means it will reach Ilya Muromets’ ear faster, and he will be able to prepare to meet the enemy.
The most interesting sound waves are musical sounds and noises. What objects can create sound waves? If we take a wave source and an elastic medium, if we make the sound source vibrate harmoniously, then we will have a wonderful sound wave, which will be called musical sound. These sources of sound waves can be, for example, the strings of a guitar or piano. This may be a sound wave that is created in the air gap of a pipe (organ or pipe). From music lessons you know the notes: do, re, mi, fa, sol, la, si. In acoustics, they are called tones (Fig. 7).
Rice. 7. Musical tones
All objects that can produce tones will have features. How are they different? They differ in wavelength and frequency. If these sound waves are not created by harmoniously sounding bodies or are not connected into some kind of common orchestral piece, then such a quantity of sounds will be called noise.
Noise– random oscillations of various physical natures, characterized by the complexity of their temporal and spectral structure. The concept of noise is both domestic and physical, they are very similar, and therefore we introduce it as a separate important object of consideration.
Let's move on to quantitative estimates of sound waves. What are the characteristics of musical sound waves? These characteristics apply exclusively to harmonic sound vibrations. So, sound volume. How is sound volume determined? Let us consider the propagation of a sound wave in time or the oscillations of the source of the sound wave (Fig. 8).
Rice. 8. Sound volume
At the same time, if we did not add a lot of sound to the system (we hit a piano key quietly, for example), then there will be a quiet sound. If we loudly raise our hand high, we cause this sound by hitting the key, we get a loud sound. What does this depend on? A quiet sound has a smaller vibration amplitude than a loud sound.
The next important characteristic of musical sound and any other sound is height. What does the pitch of sound depend on? The height depends on the frequency. We can make the source oscillate frequently, or we can make it oscillate not very quickly (that is, perform fewer oscillations per unit time). Let's consider the time sweep of a high and low sound of the same amplitude (Fig. 9).
Rice. 9. Pitch
An interesting conclusion can be drawn. If a person sings in a bass voice, then his sound source (the vocal cords) vibrates several times slower than that of a person who sings soprano. In the second case, the vocal cords vibrate more often, and therefore more often cause pockets of compression and discharge in the propagation of the wave.
There is another interesting characteristic of sound waves that physicists do not study. This timbre. You know and easily distinguish the same piece of music performed on a balalaika or cello. How are these sounds or this performance different? At the beginning of the experiment, we asked people who produce sounds to make them of approximately the same amplitude, so that the volume of the sound is the same. It’s like in the case of an orchestra: if there is no need to highlight any instrument, everyone plays approximately the same, at the same strength. So the timbre of the balalaika and cello is different. If we were to draw the sound produced from one instrument from another using diagrams, they would be the same. But you can easily distinguish these instruments by their sound.
Another example of the importance of timbre. Imagine two singers who graduate from the same music university with the same teachers. They studied equally well, with straight A's. For some reason, one becomes an outstanding performer, while the other is dissatisfied with his career all his life. In fact, this is determined solely by their instrument, which causes vocal vibrations in the environment, i.e. their voices differ in timbre.
Bibliography
- Sokolovich Yu.A., Bogdanova G.S. Physics: a reference book with examples of problem solving. - 2nd edition repartition. - X.: Vesta: publishing house "Ranok", 2005. - 464 p.
- Peryshkin A.V., Gutnik E.M., Physics. 9th grade: textbook for general education. institutions/A.V. Peryshkin, E.M. Gutnik. - 14th ed., stereotype. - M.: Bustard, 2009. - 300 p.
- Internet portal “eduspb.com” ()
- Internet portal “msk.edu.ua” ()
- Internet portal “class-fizika.narod.ru” ()
Homework
- How does sound travel? What could be the source of sound?
- Can sound travel through space?
- Is every wave that reaches a person’s hearing organ perceived by him?
Questions.
1. Tell about the experiments depicted in Figures 70-73. What conclusion follows from them?
In the first experiment (Fig. 70), a metal ruler clamped in a vice makes a sound when it vibrates.
In the second experiment (Fig. 71), one can observe vibrations of the string, which also produces sound.
In the third experiment (Fig. 72), the sound of a tuning fork is observed.
In the fourth experiment (Fig. 73), the vibrations of the tuning fork are “recorded” on a smoked plate. All these experiments demonstrate the oscillatory nature of the appearance of sound. Sound occurs as a result of vibrations. In the fourth experiment this can also be clearly observed. The tip of the needle leaves a trace in the form of a sinusoid. In this case, sound does not appear from nowhere, but is generated by sound sources: a ruler, a string, a tuning fork.
2. What common property do all sound sources have?
Any sound source necessarily vibrates.
3. Mechanical vibrations of what frequencies are called sound vibrations and why?
Sound vibrations are mechanical vibrations with frequencies from 16 Hz to 20,000 Hz, because in this frequency range they are perceived by humans.
4. What vibrations are called ultrasonic? infrasonic?
Vibrations with frequencies above 20,000 Hz are called ultrasonic, and with frequencies below 16 Hz - infrasonic.
5. Tell us about measuring the depth of the sea using echolocation.
Exercises.
1. We hear the sound of the flapping wings of a flying mosquito. but no flying bird. Why?
The vibration frequency of a mosquito's wings is 600 Hz (600 beats per second), a sparrow's is 13 Hz, and the human ear perceives sounds from 16 Hz.
Sound is caused by mechanical vibrations in elastic media and bodies, the frequencies of which lie in the range from 20 Hz to 20 kHz and which the human ear can perceive.
Accordingly, this mechanical vibration with the indicated frequencies is called sound and acoustic. Inaudible mechanical vibrations with frequencies below the sound range are called infrasonic, and with frequencies above the sound range they are called ultrasonic.
If a sounding body, for example an electric bell, is placed under the bell of an air pump, then as the air is pumped out the sound will become weaker and weaker and finally stop completely. The transmission of vibrations from the sounding body occurs through the air. Let us note that during its oscillations, the sounding body alternately compresses the air adjacent to the surface of the body, and, on the contrary, creates a vacuum in this layer. Thus, the propagation of sound in the air begins with fluctuations in air density at the surface of the vibrating body.
Musical tone. Volume and pitch
The sound that we hear when its source performs a harmonic oscillation is called musical tone or, for short, tone.
In any musical tone we can distinguish two qualities by ear: volume and pitch.
The simplest observations convince us that the tones of any given pitch are determined by the amplitude of the vibrations. The sound of a tuning fork gradually fades after striking it. This occurs together with the damping of oscillations, i.e. with a decrease in their amplitude. By hitting the tuning fork harder, i.e. By giving the vibrations a larger amplitude, we will hear a louder sound than with a weak blow. The same can be observed with a string and in general with any source of sound.
If we take several tuning forks of different sizes, it will not be difficult to arrange them by ear in order of increasing pitch. Thus, they will be arranged in size: the largest tuning fork gives the lowest sound, the smallest one gives the highest sound. Thus, the pitch of a tone is determined by the frequency of vibration. The higher the frequency and, therefore, the shorter the period of oscillation, the higher the sound we hear.
Acoustic resonance
Resonance phenomena can be observed in mechanical vibrations of any frequency, in particular in sound vibrations.
Let's place two identical tuning forks next to each other, with the holes of the boxes on which they are mounted facing each other. Boxes are needed because they amplify the sound of tuning forks. This occurs due to resonance between the tuning fork and the columns of air enclosed in the box; hence the boxes are called resonators or resonant boxes.
Let's hit one of the tuning forks and then muffle it with our fingers. We will hear how the second tuning fork sounds.
Let's take two different tuning forks, i.e. with different pitches, and repeat the experiment. Now each of the tuning forks will no longer respond to the sound of another tuning fork.
It is not difficult to explain this result. The vibrations of one tuning fork act through the air with some force on the second tuning fork, causing it to perform its forced vibrations. Since tuning fork 1 performs a harmonic oscillation, the force acting on tuning fork 2 will change according to the law of harmonic oscillation with the frequency of tuning fork 1. If the frequency of the force is different, then the forced oscillations will be so weak that we will not hear them.
Noises
We hear a musical sound (note) when the vibration is periodic. For example, this kind of sound is produced by a piano string. If you hit several keys at the same time, i.e. make several notes sound, then the sensation of musical sound will remain, but the difference between consonant (pleasant to the ear) and dissonant (unpleasant) notes will clearly appear. It turns out that those notes whose periods are in the ratio of small numbers are consonant. For example, consonance is obtained with a period ratio of 2:3 (fifth), 3:4 (quanta), 4:5 (major third), etc. If the periods are related as large numbers, for example 19:23, then the result is dissonance - a musical, but unpleasant sound. We will move even further away from the periodicity of oscillations if we hit many keys at the same time. The sound will already be noise-like.
Noise is characterized by a strong non-periodicity of the oscillation shape: either it is a long oscillation, but very complex in shape (hissing, creaking), or individual emissions (clicks, knocks). From this point of view, noises should also include sounds expressed by consonants (hissing, labial, etc.).
In all cases, noise vibrations consist of a huge number of harmonic vibrations with different frequencies.
Thus, the spectrum of a harmonic vibration consists of one single frequency. For a periodic oscillation, the spectrum consists of a set of frequencies - the main one and its multiples. In consonant consonances we have a spectrum consisting of several such sets of frequencies, with the main ones being related as small integers. In dissonant consonances, the fundamental frequencies are no longer in such simple relationships. The more different frequencies there are in the spectrum, the closer we come to noise. Typical noises have spectra in which there are extremely many frequencies.
Integrated lesson in physics, music and computer science.
The purpose of the lesson:
Introduce students to the concept of “sound”, the characteristics of sound; will teach you to distinguish sounds by volume, timbre, and show how these characteristics are related to the frequency and amplitude of vibrations; show the connection between physics and music.
Target
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Preview:
9th grade. Lesson 36
Sound sources. Sound vibrations. Problem solving.
The purpose of the lesson: Introduce students to the concept of “sound”, the characteristics of sound; teach to distinguish sounds by volume, tone, timbre; show how these characteristics are related to the frequency and amplitude of vibrations; show the connection between physics and music.
During the classes.
- Organizing time.
- Updating knowledge.
Slide 1
- Frontal survey
1. What are mechanical waves?
2. What are the two types of mechanical waves?
3. What is period, frequency, wavelength, wave speed? What connection exists between them?
- Independent work.
3. Studying new material.
Teacher. In previous classes, we began to study mechanical waves in order to further become familiar with electromagnetic waves. Although they have different names and different physical natures, they are described by the same parameters and equations. Today we will get acquainted with another type of mechanical waves. You will write down their name after you solve a logical problem (the method of solving such problems is called “brainstorming”).
The English have a fairy tale: “The devil caught three travelers and agreed to let them go if they gave him an impossible task. One asked to turn a growing tree into gold, the other asked to make a river flow back. The devil was joking, he dealt with it and took the souls of both travelers for himself. There is a third traveler left..." Guys, put yourself in the place of this traveler and offer the devil an impossible task. (Different versions are offered.) “...And the third one whistled and said: “Sew a button on this!” - and the devil was put to shame.”
What is whistling?
Students. Sound.
Slide 2 (lesson topic)
Slide 3
The world of sounds is so diverse,
Rich, beautiful, diverse,
But we are all tormented by the question
Where do sounds come from?
Why do our ears delight everywhere?
It's time to think seriously.
1. The nature of sound. Conditions necessary for the existence of sound
Teacher. We live in a world of sounds that allow us to receive information about what is happening around us.
They try to whisper scraps of posters,
The iron roofs are trying to scream,
And the water in the pipes tries to sing,
And so the wires hum powerlessly...
K.Ya.Vanshenkin.
What is sound? How can I get it? Physics answers all these questions.
Slide 4
What is acoustics?
Acoustics is a branch of physics that deals with the study of sound, its properties, and sound phenomena.
Sound waves carry energy, which, like other types of energy, can be used by humans. But the main thing is the huge range of expressive means that speech and music possess. Since ancient times, sounds have served people as a means of communication and communication with each other, a means of understanding the world and mastering the secrets of nature. Sounds are our constant companions. They have different effects on people: they delight and irritate, they calm and give strength, they caress the ear and frighten with their unexpectedness. (The recording of “Rostov Bells” is turned on.)
The famous bells of the four-arched belfry, built in 1682–1687, sounded. in the city of Rostov the Great, the city of the glory of the past. Rostov bells are performed by five bell ringers, and the tongue of the largest bell, “Sysoya,” is rocked by two people. Thirteen bells are arranged in a row. The bell ringers position themselves so that they can see each other and agree on the beat.
Since ancient times, the ringing of bells has accompanied the life of the people. Veliky Novgorod, Pskov, and Moscow have long been famous for their bells, but there was no such “orchestra” as in Rostov. What causes the sound?
Slide 5
Cause of the sound? - vibration (oscillations) of bodies, although these vibrations are often invisible to our eyes.
Sound sources - oscillating bodies.
However, not all oscillating bodies are sources of sound. Let's make sure of this.
Experience 1. "Day of Disobedience"
“You can’t do that! Don't click the ruler! Now if you break the ruler, how will you measure segments in mathematics?” How often did we hear this at school! But now we will have a day of disobedience. In this experiment, you are not only allowed to click the ruler on the edge of the table. After all, this is also physics!
Materials: ruler, table.
Sequencing.
Place the ruler on the table so that half of it hangs over the edge of the table. Press the end that lies on the table firmly with your hand, locking it in place. With your other hand, lift the free end of the ruler (just not too much so as not to break it) and let go. Listen to the resulting buzzing sound.
Now move the ruler a little so as to reduce the length of the hanging part. Bend and release the ruler again. What was the sound like? Is he the same as last time?
Scientific explanation.
As you probably already guessed, the humming sound is produced by vibration of the part of the ruler that hangs over the edge of the table. The part that is pressed to the table cannot vibrate and therefore does not make sounds at all. The shorter the vibrating end of the ruler, the higher the sound produced,the longer, the lower the sound.
Slide 6
Sound is mechanical elastic waves, spreading in gases, liquids, solids.
Waves that cause the sensation of sound, withfrequency from 16 Hz to 20,000 Hz
called sound waves (mainly longitudinal).
Slide 7
The propagation of sound can be compared to the propagation of a wave in water. Only the role of a stone thrown into water is played by an oscillating body, and instead of the surface of the water, sound waves propagate in the air. Each vibration of the tuning fork branch creates one condensation and one rarefaction in the air. The alternation of such condensations and rarefactions is a sound wave.
Slide 8
To hear the sound required:
1. sound source;
2. elastic medium between it and the ear;
3. a certain range of vibration frequencies of the sound source - between 16 Hz and 20 kHz,
4. sufficient power of sound waves for the ear to perceive.
Slide 9
There are two types of sound sources: artificial and natural, find them in the riddles:
Slides 10 – 12
1. Flying past the ear,
He buzzes to me: “I’m not a fly.”
The nose is long
Who will kill him?
He will shed his blood.
(Mosquito).
3. Little songbird in the forest
lives,
Cleans feathers
(Bird).
4. Walks back and forth
Never gets tired.
To everyone who comes,
She offers her hand.
(Door).
5. Two brothers
They are knocking on the same bottom.
But they don’t just beat -
They sing a song together.
(Drum).
6. Cow graze on the meadow
The hostess has gone
Hanging up a little bell.
What is this? Guess it!
(Bell).
6. On a wooden triangle
Three strings pulled
They picked it up and started playing -
The legs began to dance on their own.
(Balalaika).
8. The device is small,
But such an amazing one.
If my friend is far away,
It's easy for me to talk to him.
(Telephone).
Musical sounds are produced by various musical instruments. The sound sources in them are different, so musical instruments are divided into several groups:
Slides 13–16
- Percussion – tambourines, drums, xylophones, etc. (Here, tensioned material, metal plates, etc. vibrate when struck by a stick or hand);
- Wind instruments - flutes, bugles and fanfares, clarinets, horns, trumpets (vibrations of the air column inside the instrument
- Strings – violin, guitar, etc..
- Keyboards - pianos, harpsichords (vibrations of the strings are caused by hitting them with hammers);
Thus, according to the effect they have on us, all sounds are divided into two groups: musical sounds and noises. How are they different from each other?
The distinction between music and noise is quite difficult, since what may seem like music to one may just be noise to another. Some consider opera to be completely unmusical, while others, on the contrary, see the limit of perfection in music. The neighing of horses or the creaking of a wagon loaded with timber may be noise to most people, but music to the timber merchant. To loving parents, the cry of a newborn baby may seem like music; to others, such sounds are just noise.
However, most people would agree that the sounds coming from the vibrating strings, reeds, tuning fork and vibrating vocal cords of the singer are musical. But if so. What is essential in exciting a musical sound or tone?
Our experience shows that for musical sound it is essential that the vibrations occur at regular intervals. Vibrations of a tuning fork, strings, etc. have such a character; vibrations of trains, timber cars, etc. occur at irregular, uneven intervals, and the sounds they produce are only noise. Noise differs from a musical tone in that it does not correspond to any specific frequency of vibration and, therefore, to a specific pitch of sound. Noise contains vibrations of various frequencies. With the development of industry and modern high-speed transport, a new problem has emerged - the fight against noise. Even a new concept of “noise pollution” of the environment has emerged.
Slide17 R. Rozhdestvensky gave a very accurate and succinct image of current reality:
Aerodromes,
Piers and platforms,
Forests without birds and land without water...
Less and less of the surrounding nature,
More and more - the environment.
Noise, especially at high intensity, is not only annoying and tiring - it can also seriously undermine your health.
The most dangerous thing is long-term exposure to intense noise on a person’s hearing, which can lead to partial or complete hearing loss. Medical statistics show that hearing loss has taken a leading place in the structure of occupational diseases in recent years and has no tendency to decline.
Therefore, it is important to know the characteristics of human perception of sound, acceptable noise levels from the point of view of ensuring health, high productivity and comfort, as well as means and methods of dealing with noise.
Negative effects of noise on humans and protection from it.
Harmful effects of noise on the human body.
Slide 18
The manifestations of the harmful effects of noise on the human body are very diverse.
Prolonged exposure to intense noise(above 80 dB) on a person’s hearing leads to its partial or complete loss. Depending on the duration and intensity of noise exposure, a greater or lesser decrease in the sensitivity of the hearing organs occurs, expressed as a temporary shift in the hearing threshold, which disappears after the end of the noise exposure, and with a long duration and (or) noise intensity, irreversible changes occur.hearing loss (hard of hearing), characterized by a constant change in the hearing threshold.
There are the following degrees of hearing loss:
Slide 19
- I degree (mild hearing loss) – hearing loss in the area of speech frequencies is 10 - 20 dB, at a frequency of 4000 Hz - 20 - 60 dB;
- II degree (moderate hearing loss) – hearing loss in the area of speech frequencies is 21 - 30 dB, at a frequency of 4000 Hz - 20 - 65 dB;
- III degree (significant hearing loss) - hearing loss in the area of speech frequencies is 31 dB or more, at a frequency of 4000 Hz - 20 - 78 dB.
The effect of noise on the human body is not limited to the effect on the organ of hearing. Through the fibers of the auditory nerves, noise irritation is transmitted to the central and autonomic nervous systems, and through them it affects the internal organs, leading to significant changes in the functional state of the body, affecting the mental state of a person, causing a feeling of anxiety and irritation. A person exposed to intense (more than 80 dB) noise spends on average 10–20% more physical and neuropsychic effort to maintain the output he achieved at a sound level below 70 dB. An increase of 10–15% in the overall incidence of workers in noisy industries was established. The effect on the autonomic nervous system is evident even at low sound levels (40 – 70 dB). Of the autonomic reactions, the most pronounced is the disturbance of peripheral circulation due to the narrowing of the capillaries of the skin and mucous membranes, as well as an increase in blood pressure (at sound levels above 85 dB).
The impact of noise on the central nervous system causes an increase in the latent (hidden) period of the visual motor reaction, leads to disruption of the mobility of nervous processes, changes in electroencephalographic parameters, disrupts the bioelectric activity of the brain with the manifestation of general functional changes in the body (even with noise of 50 - 60 dB), significantly changes the biopotentials of the brain, their dynamics, causes biochemical changes in the structures of the brain.
For impulsive and irregular noisesnoise exposure increases.
Changes in the functional state of the central and autonomic nervous systems occur much earlier and at lower noise levels than a decrease in auditory sensitivity.
Slide 20
Currently, “noise disease” is characterized by a complex of symptoms:
- decreased hearing sensitivity;
- changes in digestive function, expressed in decreased acidity;
- cardiovascular failure;
- neuroendocrine disorders.
Those working in conditions of prolonged noise exposure experience irritability, headaches, dizziness, memory loss, increased fatigue, decreased appetite, ear pain, etc. Exposure to noise can cause negative changes in a person’s emotional state, including stressful ones. All this reduces a person’s performance and productivity, quality and safety of work. It has been established that in work that requires increased attention, when the sound level increases from 70 to 90 dB, labor productivity decreases by 20%.
Slide 21 (Film digital drugs)
Slide 22
Ultrasounds ( above 20,000 Hz) also cause hearing damage, although the human ear does not respond to them. Powerful ultrasound affects nerve cells in the brain and spinal cord, causing a burning sensation in the external auditory canal and a feeling of nausea.
No less dangerous are infrasonic exposure to acoustic vibrations (less than 20 Hz). At sufficient intensity, infrasounds can affect the vestibular system, reducing auditory sensitivity and increasing fatigue and irritability, and lead to loss of coordination. A special role is played by infrafrequency oscillations with a frequency of 7 Hz. As a result of their coincidence with the natural frequency of the alpha rhythm of the brain, not only hearing impairment is observed, but internal bleeding may also occur. Infrasounds (6 8 Hz) can lead to cardiac and circulatory problems.
Slides 23 – 24
PRESERVATION OF HEARING
Plug your ears with your thumbs, carefully place your index fingers on the eyelids of your closed eyes. The middle fingers squeeze the nostrils. The ring fingers and both little fingers lie on the lips, which are folded into a tube and extended forward. Inhale smoothly through your mouth so that your cheeks puff out. After inhaling, tilt your head and hold your breath. Then slowly raise your head, open your eyes and exhale through your nose.
2. Exercise "Tree" for silence - very simple.You can speak only if a direct question is asked in the correct form. Questions: “Well, how are you?”, “What are you doing?”, “Am I going, or what?” - do not work. After a while, the questioner begins to feel like a vile provocateur and with his question: “What time is it?” - he sorts it out himself.. And silence sets in. Exercise helps conserve energy, sharpen hearing and concentration.
