There are a lot of people around us sound sources: musical and technical instruments, human vocal cords, sea waves, wind and others. Sound or, in other words, sound waves– these are mechanical vibrations of the medium with frequencies of 16 Hz – 20 kHz(see § 11-a).
Let's consider experience. By placing the alarm clock on a pad under the bell of the air pump, we will notice that the ticking will become quieter, but will still be audible. Having pumped out the air from under the bell, we will stop hearing the sound at all. This experiment confirms that sound travels through air and does not travel in a vacuum.
The speed of sound in air is relatively high: it ranges from 300 m/s at –50°C to 360 m/s at +50°C. This is 1.5 times faster than the speed of passenger aircraft. Sound travels much faster in liquids, and even faster in solids. In a steel rail, for example, the speed of sound is » 5000 m/s.
Take a look at the graphs of air pressure fluctuations at the mouth of a person singing the sounds “A” and “O”. As you can see, the vibrations are complex, consisting of several vibrations superimposed on each other. At the same time, clearly visible main fluctuations, the frequency of which is almost independent of the spoken sound. For a male voice this is approximately 200 Hz, for a female voice - 300 Hz.
l max = 360 m/s: 200 Hz » 2 m, l min = 300 m/s: 300 Hz » 1 m.
So, the sound wavelength of the voice depends on the air temperature and the fundamental frequency of the voice. Recalling our knowledge of diffraction, we will understand why people’s voices can be heard in the forest, even if they are blocked by trees: sounds with wavelengths of 1–2 m easily bend around tree trunks whose diameter is less than a meter.
Let us carry out an experiment confirming that the sources of sound are indeed oscillating bodies.
Let's take the device fork– a metal slingshot mounted on a box without a front wall for better radiation of sound waves. If you hit the ends of the slingshot of a tuning fork with a hammer, it will produce a “clean” sound called musical tone(for example, the note “A” of the first octave with a frequency of 440 Hz). Let us move a sounding tuning fork towards a light ball on a string, and it will immediately bounce to the side. This happens precisely because of the frequent vibrations of the ends of the tuning fork slingshot.
The reasons on which the frequency of vibration of a body depends are its elasticity and size. The larger the body size, the lower the frequency. Therefore, for example, elephants with large vocal cords emit low-frequency sounds (bass), and mice, whose vocal cords are much smaller, emit high-frequency sounds (squeak).
Not only how the body will sound, but also how it will capture sounds and respond to them depends on elasticity and size. The phenomenon of a sharp increase in the amplitude of oscillations when the frequency of an external influence coincides with the natural frequency of the body is called resonance (Lat. “reasonably” - I respond). Let's do an experiment to observe resonance.
Let's place two identical tuning forks side by side, turning them towards each other on those sides of the boxes where there are no walls. Let's hit the left tuning fork with a hammer. In a second we'll drown it out with our hands. We will hear the sound of the second tuning fork, which we did not strike. They say that the right tuning fork resonates, that is, it captures the energy of sound waves from the left tuning fork, as a result of which it increases the amplitude of its own vibrations.
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?
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 backwards. 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 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, 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 infrasound 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.
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 the 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, in addition to the vocal cords, you also need the tongue, lips, cheeks, soft palate and epiglottis.
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 sounds that are inaudible to the 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 many interesting features of these sound waves. Your classmates will tell us about these interesting facts (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 die out 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) a small factory was built next to the scientific center. Soon after its launch, strange phenomena were discovered in one of the scientific laboratories. After spending a couple of hours in its premises, the researcher became absolutely stupid: he had difficulty solving even a simple problem) .
And in conclusion, I suggest that you get the key words of the lesson from the cut letters by rearranging them.
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...
With the help of this video lesson you can study the topic “Sound Sources. Sound vibrations. Pitch, timbre, volume." In this lesson you will learn what sound is. We will also consider the ranges of sound vibrations perceived by human hearing. Let's determine what can be the source of sound and what conditions are necessary for its occurrence. We will also study such sound characteristics as pitch, timbre and volume.
The topic of the lesson is devoted to sound sources and sound vibrations. We will also talk about the characteristics of sound - pitch, volume and timbre. Before talking about sound, about sound waves, let's remember that mechanical waves propagate in elastic media. The part of longitudinal mechanical waves that is perceived by the human hearing organs is called sound, sound waves. Sound is the mechanical waves perceived by the human hearing organs that cause sound sensations .
Experiments show that the human ear and human hearing organs perceive vibrations with frequencies from 16 Hz to 20,000 Hz. It is this range that we call sound. Of course, there are waves whose frequency is less than 16 Hz (infrasound) and more than 20,000 Hz (ultrasound). But this range, these sections are not perceived by the human ear.
Rice. 1. Hearing range of the human ear
As we said, the areas of infrasound and ultrasound are not perceived by the human hearing organs. Although they can be perceived, for example, by some animals and insects.
What's happened ? Sound sources can be any body that vibrates at a sound frequency (from 16 to 20,000 Hz)
Rice. 2. An oscillating ruler clamped in a vice can be a source of sound.
Let's turn to experience and see how a sound wave is formed. To do this we need a metal ruler, which we will clamp in a vice. Now, when we act on the ruler, we will be able to observe vibrations, but we will not hear any sound. And yet a mechanical wave is created around the ruler. Please note that when the ruler is moved to one side, an air seal is formed here. In the other direction there is also a seal. Air vacuum forms between these seals. Longitudinal wave - this is a sound wave consisting of compactions and rarefaction of air. The oscillation frequency of the ruler in this case is less than the sound frequency, so we do not hear this wave, this sound. Based on the experience we have just observed, at the end of the 18th century, a device called a tuning fork was created.
Rice. 3. Propagation of longitudinal sound waves from a tuning fork
As we have seen, sound appears as a result of vibrations of a body with a sound frequency. Sound waves propagate in all directions. There must be a medium between the human hearing aid and the source of sound waves. This medium can be gaseous, liquid, or solid, but it must be particles capable of transmitting vibrations. The process of transmitting sound waves must necessarily occur where there is matter. If there is no substance, we will not hear any sound.
For sound to exist you need:
1. Sound source
2. Wednesday
3. Hearing aid
4. Frequency 16-20000Hz
5. Intensity
Now let's move on to discussing sound characteristics. The first is pitch. Sound height - characteristic that is determined by the frequency of oscillations. The higher the frequency of the body that produces vibrations, the higher the sound will be. Let's look again at the ruler held in a vice. As we have already said, we saw vibrations, but did not hear any sound. If we now make the length of the ruler shorter, we will hear the sound, but it will be much more difficult to see the vibrations. Look at the line. If we act on it now, we will not hear any sound, but we will observe vibrations. If we shorten the ruler, we will hear a sound of a certain pitch. We can make the length of the ruler even shorter, then we will hear a sound of even higher pitch (frequency). We can observe the same thing with tuning forks. If we take a large tuning fork (also called a demonstration fork) and hit the legs of such a tuning fork, we can observe the vibration, but we will not hear the sound. If we take another tuning fork, then when we hit it we will hear a certain sound. And the next tuning fork, a real tuning fork, which is used to tune musical instruments. It makes a sound corresponding to the note A, or, as they also say, 440 Hz.
The next characteristic is the timbre of the sound. Timbre called sound color. How can this characteristic be illustrated? Timbre is the difference between two identical sounds performed by different musical instruments. You all know that we only have seven notes. If we hear the same note A played on a violin and on a piano, we can tell them apart. We can immediately tell which instrument created this sound. It is this feature - the color of the sound - that characterizes the timbre. It must be said that timbre depends on what sound vibrations are reproduced, in addition to the fundamental tone. The fact is that arbitrary sound vibrations are quite complex. They consist of a set of individual vibrations, they say vibration spectrum. It is the reproduction of additional vibrations (overtones) that characterizes the beauty of the sound of a particular voice or instrument. Timbre is one of the main and brightest manifestations of sound.
Another characteristic is volume. The volume of sound depends on the amplitude of vibrations. Let's take a look and make sure that loudness is related to the amplitude of vibrations. So, let's take a tuning fork. Let's do the following: if you hit the tuning fork weakly, the amplitude of vibrations will be small and the sound will be quiet. If you now hit the tuning fork harder, the sound will be much louder. This is due to the fact that the amplitude of the oscillations will be much greater. The perception of sound is a subjective thing, it depends on what kind of hearing aid is used and how a person feels.
List of additional literature:
Is the sound so familiar to you? // Quantum. - 1992. - No. 8. - P. 40-41. Kikoin A.K. About musical sounds and their sources // Quantum. - 1985. - No. 9. - P. 26-28. Elementary physics textbook. Ed. G.S. Landsberg. T. 3. - M., 1974.
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