Sound vibrations and waves. Sound sources

Sound sources.

Sound vibrations

Lesson outline.

1. Organizational moment

Hello guys! Our lesson has a wide practical application in everyday practice. Therefore, your answers will depend on observation in life and on the 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, in front of you is a crossword puzzle, by solving which you will learn the key word of the lesson.

1st fragment: name a physical phenomenon

2nd snippet: name the physical process

3rd fragment: name the physical quantity

4th fragment: name the physical device

R	W	H
AT
			At
			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 “Sources of sound. Sound vibrations". In the lesson, you will learn what is the source of sound, what are sound vibrations, their occurrence and some practical applications in your life.

3. Explanation of new material.

Let's do an experiment. The purpose of the experiment: to find out the causes of sound.

Experience with a metal ruler(Appendix 2).

What did you observe? What can be the conclusion?

Conclusion: a vibrating body creates sound.

Let's do the following experiment. The purpose of the experiment: to find out whether sound is always created by a vibrating body.

The device that you see in front of you is called fork.

Experience with a tuning fork and tennis ball hung on a thread(Appendix 3) .

You hear the sound that the tuning fork makes, but the vibrations of the tuning fork are not noticeable. To make sure that the tuning fork oscillates, we carefully move it to a shady ball suspended on a thread and we will see that the vibrations of the tuning fork are transmitted to the ball, which has come into periodic motion.

Conclusion: sound is generated by any vibrating body.

We live in an ocean of sounds. Sound is produced by sound sources. There are both artificial and natural sound sources. Natural sources of sound include vocal cords (Appendix 1 - slide No. 6). The air we breathe leaves the lungs through the airways into the larynx. The larynx contains the vocal cords. Under the pressure of the exhaled air, they begin to oscillate. The role of the resonator is played by the mouth and nose, as well as the chest. For articulate speech, in addition to the vocal cords, the tongue, lips, cheeks, soft palate and epiglottis are also needed.

The natural sources of sound also include the buzzing of a mosquito, a fly, a bee ( fluttering wings).

Question:what creates the sound.

(The air in the balloon is under pressure when compressed. Then, it expands dramatically and creates a sound wave.)

So, sound creates not only a oscillating, but also a sharply expanding body. Obviously, in all cases of the appearance of sound, the layers of air move, i.e., a sound wave arises.

The sound wave is invisible, it can only be heard, as well as registered by 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 wave. What is this graph? ( sinusoid)

Let's experiment with a tuning fork with a feather. Hit the tuning fork with a rubber mallet. The students see the vibrations of the tuning fork, but do not hear the sound.

Question:Why are there vibrations, but you do not hear the sound?

It turns out guys, the human ear perceives sound ranges ranging from 16 Hz to Hz, this is an audible sound.

Listen to them through the computer and catch the change in the frequencies of the range (Appendix 5). Pay attention to how the shape of the sinusoid changes when the frequency of sound vibrations 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 the scheme of frequency ranges on the blackboard, draw it in a notebook (Appendix 5). By exploring infra and ultrasound, scientists have discovered many interesting features these sound waves. About these interesting facts your classmates will tell us (Appendix 6).

4. Consolidation of the studied material.

To consolidate the studied material in the lesson, I suggest playing the TRUE-FALSE game. I read the situation and you hold up a TRUE or FALSE sign and explain your answer.

Questions. 1. Is it true that any vibrating body is the source of sound? (right).

2. Is it true that music sounds louder in a hall filled with people than in an empty one? (incorrect, since the empty hall acts as a resonator for vibrations).

3. Is it true that a mosquito flaps its wings faster than a bumblebee? (true, because the sound produced by the mosquito is higher, therefore, the frequency of wing oscillations is also 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 the bats see with sound? (correct, since bats emit ultrasound and then listen to the reflected signal).

6. Is it true that some animals "predict" an earthquake using infrasound? (That's right, for example, elephants feel an earthquake in a few hours and are extremely excited at the same time).

7. Is it true that infrasound causes mental disorders in people? (that's right, in Marseille (France) a small factory was built near the scientific center. Shortly after its launch, one of the scientific laboratories discovered strange phenomena. After staying in her room for a couple of hours, the researcher became absolutely stupid: he could hardly solve even a simple problem).

And in conclusion, I suggest that from the cut letters, by rearranging, get keywords lesson.

KVZU - SOUND

RAMTNOKE - TUNING FORK

TRAKZUVLU - ULTRASOUND

FRAKVZUNI - INFRAZOUND

OKLABEINJA - VASCULATIONS

5. Summing up the lesson and homework.

Lesson results. In the lesson, we found out that:

That any vibrating body creates sound;

Sound propagates through the air as sound waves;

Sounds are audible and inaudible;

Ultrasound is an inaudible sound whose oscillation frequency is higher than 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 9 cells)

2. Continue reasoning:

I hear the sound: a) flies; b) a dropped object; c) thunderstorms, because ....

I do not hear the sound: a) from a climbing dove; b) from an eagle soaring in the sky, because ...

Before you understand what sound sources are, think about what sound is? We know that light is radiation. Reflected from objects, this radiation enters our eyes, and we can see it. Taste and smell are small particles of the body that are perceived by our respective receptors. What kind of sound is this animal?

Sounds are transmitted through the air

You must have seen how the guitar is played. Perhaps you yourself know how to do it. It is important that the strings make a different sound in the guitar when they are pulled. All right. But if you could put the guitar in a vacuum and pull the strings, then 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 was heard in airless space. From this follows a logical conclusion sound is transmitted through the air. Therefore, sound is something that happens to particles of air substances and sound-producing bodies.

Sound sources - vibrating 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. Sound sources are bodies that vibrate. These vibrations are transmitted by air molecules and our ear, perceiving these vibrations, interprets them into sound sensations that are understandable to us.

It is not difficult to check this. Take a glass or crystal goblet and put 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.

And now let several people wrap their arms around the glass as completely as possible, along with the leg, trying not to leave a single free area, except for the very small place to hit with a spoon. Hit the glass again. You will hardly hear any sound, and the one that will be will turn out to be weak and very short. What does it say?

In the first case, after the impact, the glass freely oscillated, 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 almost did not oscillate, and consequently, almost no sound was emitted.

The same goes for all other experiments you can think of and run. 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 various living beings generally differ very much.

Sounds are transmitted through the air

Sound sources - vibrating bodies

And now let several people wrap their arms around the glass as completely as possible, along with the leg, 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 turn out to be weak and very short. What does it say?

The same goes for all other experiments you can think of and run. 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.

Ears are a very thin and delicate instrument, given to us by nature, so you should take care of it, as replacements and analogues in human body does not exist.

The branch of physics that deals with sound vibrations is called acoustics.

The human ear is designed in such a way that it perceives vibrations with a frequency of 20 Hz to 20 kHz as sound. Low frequencies (sound from kick drum or organ pipe) are perceived by the ear as bass notes. The whistle or squeak of a mosquito corresponds to high frequencies. Oscillations with a frequency below 20 Hz are called infrasound, and with a frequency over 20 kHz - ultrasound. A person does not hear such vibrations, but there are animals that hear infrasounds coming from earth's crust before the earthquake. Hearing them, the animals leave the dangerous area.

In music, acoustic frequencies correspond to but there. The note "la" of the main octave (key C) corresponds to a frequency of 440 Hz. The note "la" of the next octave corresponds to a frequency of 880 Hz. And so all the other octaves differ in frequency exactly twice. Within each octave, 6 tones or 12 semitones are distinguished. Everyone tone has a frequency of yf2~ 1.12 different from the frequency of the previous tone, each semitone differs from the previous one in "$2 . We see that each next frequency differs from the previous one not by a few Hz, but by the same number once. Such a scale is called logarithmic, since the equal distance between the tones will be exactly on the logarithmic scale, where not the value itself is plotted, but its logarithm.

If the sound corresponds to one frequency v (or with = 2tcv), then it is called harmonic, or monochromatic. Purely harmonic sounds are rare. Almost always, sound contains a set of frequencies, i.e., its spectrum (see section 8 of this chapter) is complex. Musical vibrations always contain the fundamental tone cco \u003d 2n / T, where T is the period, and a set of overtones 2 (Oo, Zco 0, 4coo, etc. A set of overtones indicating their intensities in music is called timbre. Different musical instruments, different singers who strike the same note have different timbres. This gives them different colors.

An admixture of non-multiple frequencies is also possible. In classical European music, this is considered dissonant. However, it is used in modern music. Even the slow movement of any frequencies in the direction of increase or decrease is used (ukulele).

In non-musical sounds, any combination of frequencies in the spectrum and their change in time are possible. The spectrum of such sounds can be continuous (see section 8). If the intensities for all frequencies are approximately the same, then such a sound is called " White noise» (the term is taken from optics, where White color is the totality of all frequencies).

The sounds of human speech are very complex. They have a complex spectrum that changes rapidly over time when pronouncing a single sound, word, and entire phrase. This gives speech sounds different intonations and accents. As a result, it is possible to distinguish one person from another by voice, even if they pronounce the same words.

A sound wave (sound vibrations) is a mechanical vibration of the 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 up in a vise and thereby lengthen the free end so that its oscillation frequency becomes less than 20 Hz. Studies have shown that the human ear is able to perceive as sound the mechanical vibrations of bodies occurring at a frequency of 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 features their hearing aid. Usually, 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 more than 20,000 Hz. Oscillations whose frequencies are 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 rumble of motors, the rustling of leaves and the howling of the wind, the singing of birds and the voices of people. About how sounds are born, and what they represent, people began to guess 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 encyclopedic scientist Aristotle, based on observations, correctly explained the nature of sound, believing that the sounding body creates alternate compression and rarefaction of air. Thus, an oscillating string now compresses, then rarefies the air, and due to the elasticity of the air, these alternating influences are transmitted further into space - from layer to layer, elastic waves arise. Reaching our ear, they act on the eardrums and cause the sensation of sound. By ear, a person perceives elastic waves having a frequency ranging from about 16 Hz to 20 kHz (1 Hz - 1 oscillation per second). In accordance with this, elastic waves in any medium whose frequencies lie within the indicated limits are called sound waves or simply sound. In air at a temperature of 0 ° C and normal pressure, sound propagates 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 - a fan, compressor, turbine, combustion chamber, etc., but also of the noise of a jet stream, vortex, turbulent air flows that occur when the aircraft flows around at high speeds. A body rapidly rushing through the air or water, as it were, breaks the flow around it, periodically generates areas of rarefaction and compression in the medium. The result is sound waves. Sound can propagate in the form of longitudinal and transverse waves. In a gaseous and liquid medium, only longitudinal waves arise when oscillating motion particles occurs only in the direction in which the wave propagates. AT 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 wave propagation. There, striking the string perpendicular to its direction, we make the wave run along the string. The human ear is not equally receptive 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 feeling of pressing pain in the ears. The intensity of the sound waves at which this happens is called the threshold. pain sensation. 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 a game musical instrument, is not a simple harmonic oscillation, but a kind of mixture of many harmonic vibrations with a certain set of frequencies. The one with the lowest frequency is called the fundamental tone, the others are overtones. A different number of overtones inherent in a particular sound gives it a special color - timbre. The difference between one timbre and another is due not only to the number, but also to the intensity of the overtones that accompany the sound of the fundamental tone. By timbre, we can easily distinguish the sounds of the violin and piano, guitar and flute, we recognize the voices of familiar people.

Oscillation frequency called the number of complete oscillations per second. The unit of frequency is 1 hertz (Hz). 1 hertz corresponds to one full (in one and the other direction) oscillation occurring in one second.
Period called the time (s) during which one complete oscillation occurs. The higher the oscillation frequency, 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 hearing perceives sound vibrations in the range of 16-20,000 Hz.
Amplitude oscillations are called the greatest deviation of an oscillating body from its original (calm) position. The larger the vibration amplitude, the louder the sound. The sounds of human speech are complex sound vibrations, consisting of one or another number of simple vibrations, different in frequency and amplitude. Each sound of speech has only its own combination of vibrations of different frequencies and amplitudes. Therefore, the form of vibrations of one sound of speech differs markedly from the form of another, which shows the graphs of vibrations during the pronunciation of the sounds a, o and y.

A person characterizes any sounds in accordance with his perception in terms of volume and height.