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.
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 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. Natural sound sources include vocal cords (Appendix 1 - slide No. 6). The air we breathe leaves the lungs through Airways 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 sinusoid 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 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...
Sound is sound waves that cause vibrations of tiny particles of air, other gases, and liquid and solid media. Sound can only arise where there is a substance, no matter what state of aggregation it is in. In vacuum conditions, where there is no medium, sound does not propagate, because there are no particles that act as distributors of sound waves. For example, in space. Sound can be modified, altered, turning into other forms of energy. Thus, sound converted into radio waves or electrical energy can be transmitted over distances and recorded on information media.
Sound wave
The movements of objects and bodies almost always cause fluctuations in the environment. It doesn't matter whether it's water or air. During this process, the particles of the medium to which the vibrations of the body are transmitted also begin to vibrate. Sound waves arise. Moreover, movements are carried out in forward and backward directions, progressively replacing each other. Therefore, the sound wave is longitudinal. There is never any lateral movement up and down in it.
Characteristics of sound waves
Like any physical phenomenon, they have their own quantities, with the help of which properties can be described. The main characteristics of a sound wave are its frequency and amplitude. The first value shows how many waves are formed per second. The second determines the strength of the wave. Low-frequency sounds have low frequency values, and vice versa. The frequency of sound is measured in Hertz, and if it exceeds 20,000 Hz, then ultrasound occurs. There are plenty of examples of low-frequency and high-frequency sounds in nature and the world around us. The chirping of a nightingale, the rumble of thunder, the roar of a mountain river and others are all different sound frequencies. The amplitude of the wave directly depends on how loud the sound is. The volume, in turn, decreases with distance from the sound source. Accordingly, the further the wave is from the epicenter, the smaller the amplitude. In other words, the amplitude of a sound wave decreases with distance from the sound source.
Sound speed
This indicator of a sound wave is directly dependent on the nature of the medium in which it propagates. Both humidity and air temperature play a significant role here. In average weather conditions, the speed of sound is approximately 340 meters per second. In physics, there is such a thing as supersonic speed, which is always greater than the speed of sound. This is the speed at which sound waves travel when an aircraft moves. The plane moves at supersonic speed and even outruns the sound waves it creates. Due to the pressure gradually increasing behind the aircraft, a shock wave of sound is formed. The unit of measurement for this speed is interesting and few people know it. It's called Mach. Mach 1 is equal to the speed of sound. If a wave travels at Mach 2, then it travels twice as fast as the speed of sound.
Noises
IN Everyday life person there are constant noises. The noise level is measured in decibels. The movement of cars, the wind, the rustling of leaves, the interweaving of people's voices and other sound noises are our daily companions. But the human auditory analyzer has the ability to get used to such noise. However, there are also phenomena that even the adaptive abilities of the human ear cannot cope with. For example, noise exceeding 120 dB can cause pain. The loudest animal is the blue whale. When it makes sounds, it can be heard over 800 kilometers away.
Echo
How does an echo occur? Everything is very simple here. A sound wave has the ability to be reflected from different surfaces: from water, from a rock, from walls in an empty room. This wave returns to us, so we hear secondary sound. It is not as clear as the original one because some of the energy in the sound wave is dissipated as it travels toward the obstacle.
Echolocation
Sound reflection is used for various practical purposes. For example, echolocation. It is based on the fact that with the help of ultrasonic waves it is possible to determine the distance to the object from which these waves are reflected. Calculations are made by measuring the time it takes for ultrasound to travel to a location and return. Many animals have the ability to echolocation. For example, bats and dolphins use it to search for food. Echolocation has found another application in medicine. When examining with ultrasound, a picture is formed internal organs person. The basis of this method is that ultrasound, entering a medium other than air, returns back, thus forming an image.
Sound waves in music
Why do musical instruments make certain sounds? Guitar strumming, piano strumming, low tones of drums and trumpets, the charming thin voice of a flute. All these and many other sounds arise due to air vibrations or, in other words, due to the appearance of sound waves. But why is the sound of musical instruments so diverse? It turns out that this depends on several factors. The first is the shape of the tool, the second is the material from which it is made.
Let's look at this using string instruments as an example. They become a source of sound when the strings are touched. As a result, they begin to oscillate and send environment different sounds. The low sound of any stringed instrument is due to the greater thickness and length of the string, as well as the weakness of its tension. And vice versa, the more tightly the string is stretched, the thinner and shorter it is, the higher the sound obtained as a result of playing.
Microphone action
It is based on the conversion of sound wave energy into electrical energy. In this case, the current strength and the nature of the sound are directly dependent. Inside any microphone there is a thin plate made of metal. When exposed to sound, it begins to perform oscillatory movements. The spiral to which the plate is connected also vibrates, resulting in electricity. Why does he appear? This is because the microphone also has built-in magnets. When the spiral oscillates between its poles, an electric current is generated, which goes along the spiral and then to a sound column (loudspeaker) or to equipment for recording on an information medium (cassette, disk, computer). By the way, the microphone in the phone has a similar structure. But how do microphones work on landline and mobile phone? The initial phase is the same for them - the sound of the human voice transmits its vibrations to the microphone plate, then everything follows the scenario described above: a spiral, which, when moving, closes two poles, a current is created. What's next? With a landline telephone, everything is more or less clear - just like in a microphone, the sound, converted into electric current, runs through the wires. But what about cell phone or, for example, with a walkie-talkie? In these cases, the sound is converted into radio wave energy and hits the satellite. That's all.
Resonance phenomenon
Sometimes conditions are created when the amplitude of oscillations physical body increases sharply. This occurs due to the convergence of the values of the frequency of forced oscillations and the natural frequency of oscillations of the object (body). Resonance can be both beneficial and harmful. For example, to get a car out of a hole, it is started and pushed back and forth in order to cause resonance and give the car inertia. But there were also cases negative consequences resonance. For example, in St. Petersburg, about a hundred years ago, a bridge collapsed under soldiers marching in unison.
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 from 20 Hz to 20 kHz as sound. Low frequencies (the sound of a bass 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 above 20 kHz - ultrasound. Humans cannot hear such vibrations, but there are animals that hear infrasounds emanating 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 “A” of the main octave (key C) corresponds to a frequency of 440 Hz. The note “A” of the next octave corresponds to a frequency of 880 Hz. And so all other octaves differ in frequency by exactly two times. Within each octave there are 6 tones or 12 semitones. Every 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 subsequent frequency differs from the previous one not by a few Hz, but by the same number of times. This scale is called logarithmic because equal distance between tones will be precisely on a logarithmic scale, where it is not the value itself that 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, that is, its spectrum (see Section 8 of this chapter) is complex. Musical vibrations always contain a fundamental tone sso = 2i/T, where T is the period, and a set of overtones 2(Oo, 3so 0, 4coo, etc. A set of overtones with an indication of their intensities in music is called timbre. Different musical instruments, different singers playing 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, modern music uses this. Even the slow movement of any frequencies towards increasing or decreasing is used (ukulele).
In non-musical sounds, any combination of frequencies in the spectrum and their change over 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 quickly over time when pronouncing one 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 their voice, even if they pronounce the same words.