A sound wave (sound vibrations) is a mechanical vibration of molecules of a substance (for example, air) transmitted in space.
But not every oscillating body is a source of sound. For example, an oscillating weight suspended on a thread or spring does not make a sound. A metal ruler will also stop sounding if you move it upward in a vice and thereby lengthen the free end so that its vibration frequency becomes less than 20 Hz. Research has shown that the human ear is capable of perceiving as sound mechanical vibrations of bodies occurring at a frequency from 20 Hz to 20,000 Hz. Therefore, vibrations whose frequencies are in this range are called sound. Mechanical vibrations whose frequency exceeds 20,000 Hz are called ultrasonic, and vibrations with frequencies less than 20 Hz are called infrasonic. It should be noted that the indicated boundaries of the sound range are arbitrary, since they depend on the age of people and individual characteristics their hearing aid. Typically, with age, the upper frequency limit of perceived sounds decreases significantly - some older people can hear sounds with frequencies not exceeding 6000 Hz. Children, on the contrary, can perceive sounds whose frequency is slightly higher than 20,000 Hz. Vibrations with frequencies greater than 20,000 Hz or less than 20 Hz are heard by some animals. The world is filled with a wide variety of sounds: the ticking of clocks and the hum of engines, the rustling of leaves and the howling of the wind, the singing of birds and the voices of people. People began to guess about how sounds are born and what they are a very long time ago. They noticed, for example, that sound is created by bodies vibrating in the air. More ancient Greek philosopher and the encyclopedist scientist Aristotle, based on observations, correctly explained the nature of sound, believing that a sounding body creates alternating compression and rarefaction of air. Thus, a vibrating string either compresses or rarefies the air, and thanks to the elasticity of the air, these alternating effects are transmitted further into space - from layer to layer, elastic waves arise. When they reach our ear, they impact the eardrums and cause the sensation of sound. By ear, a person perceives elastic waves with a frequency ranging from approximately 16 Hz to 20 kHz (1 Hz - 1 vibration per second). In accordance with this, elastic waves in any medium, the frequencies of which lie within the specified limits, are called sound waves or simply sound. In air at a temperature of 0° C and normal pressure sound travels at a speed of 330 m/s, in sea water - about 1500 m/s, in some metals the speed of sound reaches 7000 m/s. Elastic waves with a frequency of less than 16 Hz are called infrasound, and waves whose frequency exceeds 20 kHz are called ultrasound.
The source of sound in gases and liquids can be not only vibrating bodies. For example, a bullet and an arrow whistle in flight, the wind howls. And the roar of a turbojet aircraft consists not only of the noise of operating units - fan, compressor, turbine, combustion chamber, etc., but also of the noise of the jet stream, vortex, turbulent air flows that occur when flowing around the aircraft at high speeds. A body rushing rapidly through the air or water seems to break the flow flowing around it and periodically generates regions of rarefaction and compression in the medium. As a result, sound waves are generated. Sound can travel in the form of longitudinal and transverse waves. In gaseous and liquid media, only longitudinal waves arise when the oscillatory motion of particles occurs only in the direction in which the wave propagates. IN solids in addition to longitudinal ones, there are also transverse waves when the particles of the medium oscillate in directions perpendicular to the direction of propagation of the wave. There, striking the string perpendicular to its direction, we force a wave to run along the string. The human ear is not equally sensitive to sounds of different frequencies. It is most sensitive to frequencies from 1000 to 4000 Hz. At very high intensity, the waves are no longer perceived as sound, causing a sensation of pressing pain in the ears. The intensity of sound waves at which this occurs is called the pain threshold. The concepts of tone and timbre of sound are also important in the study of sound. Any real sound, be it a human voice or the playing of a musical instrument, is not a simple harmonic vibration, but a peculiar mixture of many harmonic vibrations with a certain set of frequencies. The one that has the most low frequency, are called the fundamental tone, others - overtones. Various quantities The overtones inherent in a particular sound give it a special coloring - timbre. The difference between one timbre and another is determined not only by the number, but also by the intensity of the overtones accompanying the sound of the fundamental tone. By timbre, we easily distinguish the sounds of a violin and a piano, a guitar and a flute, and recognize the voices of familiar people.
- Oscillation frequency called the number of complete oscillations per second. The unit of frequency measurement is 1 hertz (Hz). 1 hertz corresponds to one complete (in one direction or the other) oscillation, occurring in one second.
- Period is the time (s) during which one complete oscillation occurs. The higher the frequency of oscillations, the shorter their period, i.e. f=1/T. Thus, the frequency of oscillations is greater, the shorter their period, and vice versa. The human voice creates sound vibrations with a frequency of 80 to 12,000 Hz, and the ear perceives sound vibrations in the range of 16-20,000 Hz.
- Amplitude vibration is the greatest deviation of an oscillating body from its original (quiet) position. The greater the amplitude of the vibration, the louder the sound. The sounds of human speech are complex sound vibrations, consisting of one or another number of simple vibrations, varying in frequency and amplitude. Each speech sound has its own unique combination of vibrations of different frequencies and amplitudes. Therefore, the shape of vibrations of one speech sound is noticeably different from the shape of another, which shows graphs of vibrations during the pronunciation of the sounds a, o and y.
A person characterizes any sounds in accordance with his perception by volume level and pitch.
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." During 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 towards a shady ball suspended on a thread and we will 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. TO natural sources sound 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 physical devices. 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 is this schedule? (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 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 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 the bats see with 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. In 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, around the ruler it is created mechanical wave. 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.
Sound, as we remember, are elastic longitudinal waves. And waves are generated by oscillating objects.
Examples of sound sources: an oscillating ruler, one end of which is clamped, oscillating strings, a speaker membrane.
But oscillating objects do not always generate sound audible to the ear - if the frequency of their oscillations is below 16 Hz, then they generate infrasound, and if more than 20 kHz, then ultrasound.
Ultrasound and infrasound are, from the point of view of physics, the same elastic vibrations of the medium as ordinary sound, but the ear is not able to perceive them, since these frequencies are too far from the resonant frequency of the eardrum (the eardrum simply cannot vibrate with such a frequency).
High frequency sounds are felt as thinner, low frequency sounds as bassier.
If an oscillatory system performs harmonic oscillations of one frequency, then its sound is called in a clear tone. Usually sound sources produce sounds of several frequencies at once - then the lowest frequency is called main tone, and the rest are called overtones. Overtones are determined timbre sound - it is because of them that we can easily distinguish a piano from a violin, even when their fundamental frequency is the same.
Volume sound is a subjective sensation that allows us to compare sounds as “louder” and “less loud.” Volume depends on many factors - frequency, duration, and the individual characteristics of the listener. But most of all it depends on sound pressure, which is directly related to the vibration amplitude of the object that produces the sound.
The unit of measurement for loudness is called dream.
IN practical problems usually use a quantity called volume level or sound pressure level. This value is measured in belah [B] or, more often, in decibels [dB].
This value depends logarithmically on the sound pressure - that is, an increase in pressure 10 times increases the volume level by 1 dB.
The sound of flipping through a newspaper is approximately 20 dB, an alarm clock is 80 dB, the sound of an airplane taking off is 100-120 dB (on the verge of pain).
One of unusual applications sound (more precisely ultrasound) is echolocation. You can make a sound and measure the time it takes for the echo to come. The greater the distance to the obstacle, the greater the delay will be. This method of measuring distances is usually used underwater, but bats use it directly in the air.
The echolocation distance is determined as follows:
2r = vt, where v is the speed of sound in the medium, t is the delay time to the echo, r is the distance to the obstacle.
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 and sound-producing bodies.
Sources of sound - oscillating bodies
Further. 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 knock 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 for a very 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.