Sources of sound vibrations. Sound sources
Sound sources. Sound vibrations
Man lives in a world of sounds. Sound for humans is a source of information. He warns people about danger. Sound in the form of music, birdsong gives us pleasure. We enjoy listening to a person with a pleasant voice. Sounds are important not only for humans, but also for animals, for which good sound detection helps them survive.
Sound – these are mechanical elastic waves propagating in gases, liquids, and solids.
Reason for the sound - vibration (oscillations) of bodies, although these vibrations are often invisible to our eyes.
Sound sources
- physical bodies, which fluctuate, i.e. tremble or vibrate at a frequency
from 16 to 20,000 times per second. The vibrating body can be solid, for example, a string
or earth's crust, gaseous, for example, a stream of air in wind musical instruments
or liquid, for example, waves on water.
Volume
Loudness depends on the amplitude of vibrations in the sound wave. The unit of sound volume is 1 Bel (in honor of Alexander Graham Bell, the inventor of the telephone). In practice, loudness is measured in decibels (dB). 1 dB = 0.1B.
10 dB – whisper;
20–30 dB
– noise standards in residential premises;
50 dB– medium volume conversation;
80 d B
– the noise of a running truck engine;
130 dB– pain threshold
Sound louder than 180 dB can even cause eardrum rupture.
High sounds represented by high-frequency waves - for example, birdsong.
Low sounds These are low-frequency waves, such as the sound of a large truck engine.
Sound waves- These are elastic waves that cause a person to experience sound.
A sound wave can travel a wide variety of distances. Gunfire can be heard at 10-15 km, the neighing of horses and barking dogs - at 2-3 km, and whispers only at a few meters. These sounds are transmitted through the air. But not only air can be a conductor of sound.
By placing your ear to the rails, you can hear the sound of an approaching train much earlier and at a greater distance. This means that metal conducts sound faster and better than air. Water also conducts sound well. Having dived into the water, you can clearly hear the stones knocking against each other, the noise of the pebbles during the surf.
The property of water - it conducts sound well - is widely used for reconnaissance at sea during war, as well as for measuring sea depths.
A necessary condition for the propagation of sound waves is the presence of a material medium. In a vacuum, sound waves do not propagate, since there are no particles there that transmit the interaction from the source of vibrations.
Therefore, due to the lack of atmosphere, complete silence reigns on the Moon. Even the fall of a meteorite on its surface is not audible to the observer.
In each medium, sound travels at different speeds.
Speed of sound in air- approximately 340 m/s.
Speed of sound in water- 1500 m/s.
Speed of sound in metals, steel- 5000 m/s.
In warm air, the speed of sound is greater than in cold air, which leads to a change in the direction of sound propagation.
FORK
- This U-shaped metal plate, the ends of which can vibrate after being struck.
Published tuning fork the sound is very weak and can only be heard at a short distance.
Resonator- a wooden box on which a tuning fork can be attached serves to amplify the sound.
In this case, sound emission occurs not only from the tuning fork, but also from the surface of the resonator.
However, the duration of the sound of a tuning fork on a resonator will be shorter than without it.
E X O
A loud sound, reflected from obstacles, returns to the source of sound after a few moments, and we hear echo.
By multiplying the speed of sound by the time elapsed from its origin to its return, you can determine twice the distance from the sound source to the obstacle.
This method of determining the distance to objects is used in echolocation.
Some animals, for example bats,
also use the phenomenon of sound reflection using the echolocation method
Echolocation is based on the property of sound reflection.
Sound - running mechanical wave on and transfers energy.
However, the power of simultaneous conversation of all people on the globe is hardly more than the power of one Moskvich car!
Ultrasound.
· Vibrations with frequencies exceeding 20,000 Hz are called ultrasound. Ultrasound is widely used in science and technology.
· The liquid boils when an ultrasonic wave passes through (cavitation). In this case, water hammer occurs. Ultrasounds can tear pieces off the surface of metal and crush solids. Ultrasound can be used to mix immiscible liquids. This is how emulsions in oil are prepared. Under the influence of ultrasound, saponification of fats occurs. Washing devices are designed on this principle.
Widely used ultrasound in hydroacoustics. Ultrasounds of high frequency are absorbed very weakly by water and can spread over tens of kilometers. If they meet the bottom, iceberg or other solid, they are reflected and give an echo of great power. An ultrasonic echo sounder is designed on this principle.
In metal ultrasound spreads practically without absorption. Using the ultrasonic location method, it is possible to detect the smallest defects inside a part of large thickness.
· The crushing effect of ultrasound is used for the manufacture of ultrasonic soldering irons.
Ultrasonic waves, sent from the ship, are reflected from the sunken object. The computer detects the time the echo appears and determines the location of the object.
· Ultrasound is used in medicine and biology for echolocation, for identifying and treating tumors and some defects in body tissues, in surgery and traumatology for dissecting soft and bone tissues during various operations, for welding broken bones, for destroying cells (high power ultrasound).
Infrasound and its impact on humans.
Vibrations with frequencies below 16 Hz are called infrasound.
In nature, infrasound occurs due to the vortex movement of air in the atmosphere or as a result of slow vibrations of various bodies. Infrasound is characterized by weak absorption. Therefore, it spreads over long distances. The human body reacts painfully to infrasonic vibrations. At external influences, caused by mechanical vibration or sound wave at frequencies of 4-8 Hz, a person feels the movement of internal organs, at a frequency of 12 Hz - an attack of seasickness.
· Highest intensity infrasonic vibrations create machines and mechanisms that have surfaces large sizes, performing low-frequency mechanical vibrations (infrasound of mechanical origin) or turbulent flows of gases and liquids (infrasound of aerodynamic or hydrodynamic origin).
Before you understand what sound sources there are, think about what sound is? We know that light is radiation. Reflecting from objects, this radiation reaches our eyes, and we can see it. Taste and smell are small particles of bodies that are perceived by our respective receptors. What kind of animal is this sound?
Sounds are transmitted through the air
You've probably seen how the guitar is played. Perhaps you can do this yourself. Another important thing is the sound the strings make in a guitar when you pluck them. That's right. But if you could place a guitar in a vacuum and pluck the strings, you would be very surprised that the guitar would not make any sound.
Such experiments were carried out with a wide variety of bodies, and the result was always the same: no sound could be heard in airless space. The logical conclusion follows that sound is transmitted through the air. Therefore, sound is something that happens to particles of air substances and bodies that produce sound.
Sources of sound - oscillating bodies
Next. As a result of a wide variety of numerous experiments, it was possible to establish that sound arises due to the vibration of bodies. Sources of sound are bodies that vibrate. These vibrations are transmitted by air molecules and our ear, perceiving these vibrations, interprets them into sensations of sound that we understand.
It's not difficult to check. Take a glass or crystal goblet and place it on the table. Tap it lightly with a metal spoon. You will hear a long thin sound. Now touch the glass with your hand and tap again. The sound will change and become much shorter.
Now let several people wrap their hands around the glass as completely as possible, along with the stem, trying not to leave a single free area, except completely small place for hitting with a spoon. Hit the glass again. You will hardly hear any sound, and the one that will be will be weak and very short. What does this mean?
In the first case, after the impact, the glass oscillated freely, its vibrations were transmitted through the air and reached our ears. In the second case, most of the vibrations were absorbed by our hand, and the sound became much shorter as the vibrations of the body decreased. In the third case, almost all vibrations of the body were instantly absorbed by the hands of all participants and the body hardly vibrated, and therefore made almost no sound.
The same goes for all other experiments you can think of and conduct. Vibrations of bodies, transmitted to air molecules, will be perceived by our ears and interpreted by the brain.
Sound vibrations of different frequencies
So sound is vibration. Sound sources transmit sound vibrations through the air to us. Why then do we not hear all the vibrations of all objects? Because vibrations come in different frequencies.
The sound perceived by the human ear is sound vibrations with a frequency of approximately 16 Hz to 20 kHz. Children hear sounds of higher frequencies than adults, and the ranges of perception of different living creatures generally vary greatly.
Sound sources.
Sound vibrations
Lesson summary.
1.Organizational moment
Hello guys! Our lesson has wide practical application in everyday practice. Therefore, your answers will depend on your observation skills in life and your ability to analyze your observations.
2. Repetition of basic knowledge.
Slides No. 1, 2, 3, 4, 5 are displayed on the projector screen (Appendix 1).
Guys, here is a crossword puzzle, after solving it you will learn the key word of the lesson.
1st fragment: name a physical phenomenon
2nd fragment: name the physical process
3rd fragment: name a physical quantity
4th fragment: name a physical device
R | Z | N | ||||||||
IN | ||||||||||
U | ||||||||||
TO |
Pay attention to the highlighted word. This word is “SOUND”, it is the key word of the lesson. Our lesson is devoted to sound and sound vibrations. So, the topic of the lesson is “Sound Sources. Sound vibrations." In the lesson you will learn what is the source of sound, what sound vibrations are, their occurrence and some practical applications in your life.
3. Explanation of new material.
Let's conduct an experiment. Purpose of the experiment: to find out the causes of sound.
Experiment with a metal ruler(Appendix 2).
What did you observe? What can be concluded?
Conclusion: a vibrating body creates sound.
Let's carry out the following experiment. Purpose of the experiment: to find out whether sound is always created by a vibrating body.
The device you see in front of you is called fork.
Experiment with a tuning fork and a tennis ball hanging on a string(Appendix 3) .
You hear the sound that the tuning fork makes, but the vibration of the tuning fork is not noticeable. To make sure that the tuning fork is oscillating, we carefully move it to a shady ball suspended on a thread and see that the oscillations of the tuning fork are transferred to the ball, which begins to move periodically.
Conclusion: sound is generated by any vibrating body.
We live in an ocean of sounds. Sound is created by sound sources. There are both artificial and natural sources of sound. Natural sound sources include vocal cords (Appendix 1 - slide No. 6). The air we breathe leaves the lungs through respiratory tract into the larynx. The larynx contains the vocal cords. Under the pressure of exhaled air they begin to oscillate. The role of the resonator is played by the oral and nasal cavities, as well as the chest. For articulate speech except vocal cords the tongue, lips, cheeks, soft palate and epiglottis are also necessary.
Natural sources of sound also include the buzzing of a mosquito, fly, bee ( wings flutter).
Question:what creates sound.
(The air in the ball is under pressure in a compressed state. Then it expands sharply and creates a sound wave.)
So, sound creates not only a oscillating, but also a sharply expanding body. Obviously, in all cases of sound occurrence, layers of air move, i.e., a sound wave arises.
The sound wave is invisible, it can only be heard and also registered by physical instruments. To register and study the properties of a sound wave, we use a computer, which is currently widely used by physicists for research. A special research program is installed on the computer, and a microphone is connected that picks up sound vibrations (Appendix 4). Look at the screen. On the screen you see a graphical representation of the sound vibration. What does this graph represent? ( sinusoid)
Let's conduct an experiment with a tuning fork with a feather. We hit the tuning fork with a rubber mallet. Students see the vibration of the tuning fork, but do not hear any sound.
Question:Why are there vibrations, but you don’t hear the sound?
It turns out, guys, that the human ear perceives sound ranges ranging from 16 Hz to Hz, this is audible sound.
Listen to them through a computer and notice the change in the frequencies of the range (Appendix 5). Pay attention to how the shape of the sine wave changes when the frequency of sound oscillations changes (the oscillation period decreases, and therefore the frequency increases).
There are unheard sounds for human ear. These are infrasound (oscillation range less than 16 Hz) and ultrasound (range greater than Hz). You see a diagram of frequency ranges on the board, sketch it in your notebook (Appendix 5). By studying infra and ultrasound, scientists have discovered a lot interesting features these sound waves. About these interesting facts Your classmates will tell us (Appendix 6).
4. Consolidation of the studied material.
To reinforce the material learned in class, I suggest playing a TRUE-FALSE game. I read out the situation and you hold up a sign that says TRUE or FALSE and explain your answer.
Questions. 1. Is it true that the source of sound is any oscillating body? (right).
2. Is it true that in a hall filled with people the music sounds louder than in an empty one? (wrong, because the empty hall acts as a vibration resonator).
3. Is it true that a mosquito flaps its wings faster than a bumblebee? (correct, because the sound produced by a mosquito is higher, therefore the frequency of wing vibrations is higher).
4. Is it true that the vibrations of a sounding tuning fork decay faster if its leg is placed on a table? (correct, because the vibrations of the tuning fork are transmitted to the table).
5. Is it true that bats see using sound? (correct, because bats emit ultrasound and then listen to the reflected signal).
6. Is it true that some animals “predict” earthquakes using infrasound? (true, for example, elephants feel an earthquake several hours in advance and are extremely excited).
7. Is it true that infrasound causes mental disorders in people? (that's right, in Marseille (France) next to scientific center A small factory was built. Soon after its launch, strange phenomena were discovered in one of the scientific laboratories. After staying in her room for a couple of hours, the researcher became absolutely stupid: he had difficulty solving even a simple problem).
And in conclusion, I suggest that from the cut letters, by rearranging, you get keywords lesson.
KVZU – SOUND
RAMTNOCKE – TUNING FORK
TRYAKZUVLU – ULTRASOUND
FRAKVZUNI - INFRASOUND
OKLABEINYA – OSCILLATIONS
5. Summing up the lesson and homework.
Lesson summary. During the lesson we found out that:
That any vibrating body creates sound;
Sound travels through the air in the form of sound waves;
Sounds are audible and inaudible;
Ultrasound is an inaudible sound whose vibration frequency is above 20 kHz;
Infrasound is an inaudible sound with an oscillation frequency below 16 Hz;
Ultrasound is widely used in science and technology.
Homework:
1. §34, ex. 29 (Peryshkin 9th grade)
2. Continue the reasoning:
I hear the sound of: a) flies; b) a fallen object; c) thunderstorms, because...
I don’t hear the sound: a) from a climbing dove; b) from an eagle soaring in the sky, because...
Integrated lesson in physics, music and computer science.
Objective 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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9th grade. Lesson 36
Sound sources. Sound vibrations. Problem solving.
Objective 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.
Progress of the lesson.
- Organizational moment.
- 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 get acquainted with electromagnetic waves. Although they have different names, various physical nature, but are described by the same parameters and equations. Today we will get acquainted with another species 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 backwards. The devil, jokingly, 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 expressive means that speech and music have. 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 pacify 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 bell ringing 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.
Sequence of actions.
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 your 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 went
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. Noise contains vibrations of various frequencies. With the development of industry and modern high-speed transport, new problem- combating 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 of high intensity, is not only annoying and tiring - it can also seriously undermine your health.
The most dangerous is prolonged exposure to intense noise on a person’s hearing, which can lead to partial or complete loss hearing Medical statistics shows that hearing loss in recent years takes a leading place in the structure occupational diseases and has no tendency to decrease.
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) intensity of noise, 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 fiber auditory nerves noise irritation is transmitted to the central and autonomic nervous systems, and through them affects internal organs, leading to significant changes in functional state body, affects mental state 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 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 a violation of peripheral circulation due to narrowing of the capillaries skin and mucous membranes, as well as increased 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 visual motor reaction, leads to impaired mobility nervous processes, changes in electroencephalographic parameters, violates bioelectrical activity brain with manifestations of general functional changes in the body (even at a noise level of 50–60 dB), significantly changes the biopotentials of the brain, their dynamics, and 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 hearing sensitivity.
Slide 20
Currently " noise sickness"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, loss of appetite, ear pain, etc. Exposure to noise can cause negative changes emotional state person, even stressful. All this reduces a person’s performance and productivity, quality and safety of work. It has been established that in work requiring 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 brain and spinal cord, causes a burning sensation in the external ear canal and a feeling of nausea.
No less dangerous are infrasonic exposure to acoustic vibrations (less than 20 Hz). With sufficient intensity, infrasounds can affect vestibular apparatus, reducing auditory sensitivity and increasing fatigue and irritability, and lead to impaired 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 can also occur internal bleeding. Infrasounds (6 8 Hz) can lead to cardiac and circulatory problems.
Slides 23 – 24
PRESERVATION OF HEARING
Cover your ears thumbs, index fingers carefully place on the eyelids of closed eyes. The middle fingers squeeze the nostrils. 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 preserve energy, sharpen hearing and concentration.
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 sine wave. In this case, sound does not appear from nowhere, but is generated by sound sources: a ruler, a string, a tuning fork.
2. How 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.
