Sound sources. Sound vibrations
Man lives in the world of sounds. Sound for a person is a source of information. He warns people of danger. Sound in the form of music, birdsong gives us pleasure. We are pleased to hear a person with a pleasant voice. Sounds are important not only for humans, but also for animals, for which good sound capture helps to survive.
Soundare mechanical elastic waves propagating in gases, liquids, solids, which are invisible, but perceived by the human ear (the wave affects the eardrum). The sound wave is a longitudinal compression and rarefaction wave.
Cause of the sound- vibration (oscillations) of bodies, although these vibrations are often invisible to our eyes.
FORK- this is U-shaped metal plate, the ends of which can oscillate after hitting it. Published tuning fork The sound is very weak and can only be heard at a short distance. Resonator- a wooden box on which a tuning fork can be fixed, serves to amplify the sound. In this case, sound emission occurs not only from the tuning fork, but also from the surface of the resonator. However, the duration of the sound of the tuning fork on the resonator will be less than without it.
If we create a vacuum, will we be able to distinguish sounds? Robert Boyle placed a clock in a glass vessel in 1660. When he pumped out the air, he heard no sound. Experience proves that a medium is needed to propagate sound.
Sound can also propagate in liquid and solid media. Under the water you can clearly hear the impacts of stones. Put the clock on one end of the wooden board. By putting your ear to the other end, you can clearly hear the ticking of the clock.
The source of sound is necessarily an oscillating body. For example, a string on a guitar does not sound in its normal state, but as soon as we make it oscillate, a sound wave arises.
However, experience shows that not every vibrating body is a source of sound. For example, a weight suspended on a thread does not make a sound. Sound sources- physical bodies that oscillate, i.e. tremble or vibrate at a frequency of 16 to 20,000 times per second. Such waves are called sound.The vibrating body can be solid, such as a string or the earth's crust, gaseous, such as a jet of air in wind musical instruments, or liquid, such as waves on water.
Oscillations with a frequency less than 16 Hz are called infrasound. Oscillations with a frequency greater than 20,000 Hz are called ultrasound.
Sound wave(sound vibrations) are mechanical vibrations of molecules of a substance (for example, air) transmitted in space. Let's imagine how sound waves propagate in space. As a result of some perturbations (for example, as a result of vibrations of a loudspeaker cone or a guitar string) that cause movement and vibrations of air at a certain point in space, a pressure drop occurs in this place, since the air is compressed during movement, resulting in excess pressure. pushing the surrounding layers of air. These layers are compressed, which in turn creates excess pressure again, affecting the neighboring layers of air. So, as if along a chain, the initial perturbation in space is transmitted from one point to another. This process describes the mechanism of sound wave propagation in space. A body that creates a disturbance (vibration) of the air is called sound source.
The familiar concept for all of us sound" means only a set of sound vibrations perceived by the human hearing aid. About which vibrations a person perceives and which not, we will talk later.
Sound characteristics.
Sound vibrations, as well as all vibrations in general, as is known from physics, are characterized by amplitude (intensity), frequency and phase.
A sound wave can travel a wide variety of distances. Cannon fire is heard at 10-15 km, the neighing of horses and the barking of dogs - at 2-3 km, and the whisper is only a few meters away. These sounds are transmitted through the air. But not only air can be a conductor of sound.
Putting your ear to the rails, you can hear the noise of an approaching train much earlier and at a greater distance. This means that metal conducts sound faster and better than air. Water also conducts sound well. Having dived into the water, you can clearly hear how the stones knock against each other, how the pebbles rustle during the surf.
The property of water - to conduct sound well - is widely used for reconnaissance at sea during the war, as well as for measuring the depths of the sea.
A necessary condition for the propagation of sound waves is the presence of a material environment. In vacuum, sound waves do not propagate, since there are no particles transmitting interaction from the source of vibrations.
Therefore, on the Moon, due to the absence of an atmosphere, complete silence reigns. Even the fall of a meteorite on its surface is not audible to the observer.
With regard to sound waves, it is very important to mention such a characteristic as the speed of propagation.
Sound travels at different speeds in every medium.
The speed of sound in air is approximately 340 m/s.
The speed of sound in water is 1500 m/s.
The speed of sound in metals, in steel is 5000 m/s.
In warm air, the speed of sound is greater than in cold air, which leads to a change in the direction of sound propagation.
Pitch, tone and volume
Sounds are different. To characterize the sound, special quantities are introduced: loudness, pitch and timbre of the sound.
The loudness of the sound depends on the amplitude of the oscillations: the larger the amplitude of the oscillations, the louder the sound. In addition, the perception of the loudness of sound by our ear depends on the frequency of vibrations in the sound wave. Higher frequency waves are perceived as louder.
The unit of sound volume is 1 Bel (in honor of Alexander Graham Bell, the inventor of the telephone). The loudness of a sound is 1 B if its power is 10 times the threshold of audibility.
In practice, loudness is measured in decibels (dB).
1 dB = 0.1B. 10 dB - whisper; 20–30 dB - noise standard in residential premises;
50 dB - conversation of medium volume;
70 dB - typewriter noise;
80 dB - the noise of a running truck engine;
120 dB - noise of a working tractor at a distance of 1 m
130 dB - pain threshold.
Sound above 180 dB can even cause a rupture of the eardrum.
sound frequency The angle wave determines the pitch. The higher the vibration frequency of the sound source, the higher the sound produced by it. Human voices are divided into several ranges according to their pitch.
Sounds from different x sources is a set of harmonic oscillations of different frequencies. Most componentthe last period (lowest frequency) is called the fundamental tone. The rest of the sound components are overtones. A set of these components creates a colorku, timbre of sound. The totality of overtones in the voices of different people is at least a little, but different,this defines the tone th voice.
According to legend, Pythago p all arranged musical sounds in a row, breakingthis series into parts - octaves, - and
octave - into 12 parts (7 mainnew and 5 semitones). There are 10 octaves in total, usually 7-8 octaves are used when performing musical works. Sounds with a frequency of more than 3000 Hz are not used as musical tones, they are too harsh and piercing.
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 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 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?
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 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.
The ears are a very delicate and delicate tool given to us by nature, so you should take care of it, since there is no replacement or analogue in the human body.
Sound, as we remember, are elastic longitudinal waves. And waves are generated by oscillating objects.
Sound source examples: oscillating ruler, one end of which is clamped, vibrating strings, speaker membrane.
But not always oscillating objects generate a 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 - 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 tympanic membrane (the membrane simply cannot oscillate with such a frequency).
High frequency sounds are felt more subtle, low frequency sounds more bassy.
If an oscillatory system performs harmonic oscillations of the same frequency, then its sound is called pure tone. Usually sound sources emit sounds of several frequencies at once - then the lowest frequency is called main tone, and the rest are called overtones. Overtones determine 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 you to compare sounds as “louder” and “less loud”. Loudness depends on many factors - it is frequency, on duration, on the individual characteristics of the listener. But most of all it depends on sound pressure, which is directly related to the amplitude of vibrations of the object that emits sound.
The unit of measure for loudness is called dream.
In practical problems, a quantity is usually used, called volume level or sound pressure level. This value is measured in white [B] or, more often, decibel [dB].
This value is logarithmically related to sound pressure - that is, a 10-fold increase in pressure increases the volume level by 1 dB.
The sound of leafing through a newspaper is about 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 the unusual applications of sound (more precisely, ultrasound) is echolocation. You can make a sound and measure the time after which the echo will come. The greater the distance to the obstacle, the greater the delay. Usually this method of measuring distances is used underwater, but bats use it directly in the air.
Echolocation distance is defined as follows:
2r=vt, where v is the speed of sound in the medium, t is the delay time before the echo, r is the distance to the obstacle.
Questions.
1. Tell us about the experiments depicted in figures 70-73. What conclusion follows from them?
In the first experiment (Fig. 70), a metal ruler clamped in a vise makes a sound when it vibrates.
In the second experiment (Fig. 71), one can observe the vibrations of the string, which also makes a sound.
In the third experiment (Fig. 72) the sound of a tuning fork is observed.
In the fourth experiment (Fig. 73), the vibrations of the tuning fork are "recorded" on a sooty plate. All these experiments demonstrate the oscillatory nature of the origin of sound. Sound comes from vibrations. In the fourth experiment, this can also be visually observed. The tip of the needle leaves a trace in the form close to a sinusoid. In this case, the sound does not appear from nowhere, but is generated by sound sources: a ruler, a string, a tuning fork.
2. What common property do all sound sources have?
Any source of sound is bound to oscillate.
3. Mechanical vibrations of what frequencies are called sound and why?
Sound vibrations are called mechanical vibrations with frequencies from 16 Hz to 20,000 Hz, because. in this frequency range they are perceived by a person.
4. What vibrations are called ultrasonic? infrasonic?
Oscillations with frequencies above 20,000 Hz are called ultrasonic, and those with frequencies below 16 Hz are called infrasonic.
5. Tell us about measuring the depth of the sea using echolocation.
Exercises.
1. We hear the sound of the flapping wings of a flying mosquito. but a flying bird does not. Why?
The oscillation frequency of the wings of a mosquito is 600 Hz (600 strokes per second), a sparrow is 13 Hz, and the human ear perceives sounds from 16 Hz.
With the help of this video lesson, you can learn the topic “Sound sources. Sound vibrations. Pitch, tone, volume. In this lesson, you will learn what sound is. We will also consider the ranges of sound vibrations perceived by human hearing. Let us determine what can be the source of sound and what conditions are necessary for its occurrence. We will also study such characteristics of sound as pitch, timbre and loudness.
The topic of the lesson is devoted to sound sources, 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. Part of the longitudinal mechanical waves, which is perceived by the human hearing organs, is called sound, sound waves. Sound is mechanical waves that are perceived by human hearing organs, which cause sound sensations. .
Experiments show that the human ear, human hearing organs perceive vibrations with frequencies from 16 Hz to 20,000 Hz. It is this range that we call the sound range. 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. Human ear hearing range
As we said, the areas of infrasound and ultrasound are not perceived by human hearing organs. Although they can be perceived, for example, by some animals, insects.
What ? Sound sources can be any bodies that oscillate with sound frequency (from 16 to 20,000 Hz)
Rice. 2. An oscillating ruler clamped in a vise can be a source of sound
Let us turn to experience and see how a sound wave is formed. To do this, we need a metal ruler, which we clamp in a vise. Now, acting on the ruler, we can observe vibrations, but we do not hear any sound. And yet, a mechanical wave is created around the ruler. Note that when the ruler moves to one side, an air seal forms here. On the other side, there is also a seal. Between these seals, an air vacuum is formed. Longitudinal wave - this is a sound wave, consisting of seals and air discharges. The vibration frequency of the ruler in this case is less than the audio frequency, so we do not hear this wave, this sound. Based on the experience that we have just observed, at the end of the 18th century an instrument 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 the 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, solid, but it must be particles capable of transmitting vibrations. The process of transmission of sound waves must necessarily occur where there is matter. If there is no substance, we will not hear any sound.
For sound to exist:
1. Sound source
2. Wednesday
3. Hearing aid
4. Frequency 16-20000Hz
5. Intensity
Now let's move on to discussing the characteristics of sound. The first is the pitch. Sound pitch - characteristic, which is determined by the frequency of oscillation. The higher the frequency of the body that produces vibrations, the higher the sound will be. Let's turn again to the ruler, clamped in a vise. As we have already said, we saw the vibrations, but did not hear the sound. If now the length of the ruler is made smaller, then 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 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 the sound of even higher pitch (frequency). We can observe the same thing with tuning forks. If we take a large tuning fork (it is also called a demonstration tuning fork) and hit the legs of such a tuning fork, we can observe the oscillation, but we will not hear the sound. If we take another tuning fork, then, by striking it, we will hear a certain sound. And the next tuning fork, a real tuning fork, which is used to tune musical instruments. It produces a sound corresponding to the note la, or, as they 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 played by different musical instruments. You all know that we have only seven notes. If we hear the same note A, taken on the violin and on the piano, then we will distinguish them. 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 the 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 striking manifestations of sound.
Another feature is volume. The loudness of the sound depends on the amplitude of the vibrations. Let's take a look and make sure that the loudness is related to the amplitude of the vibrations. So, let's take a tuning fork. Let's do the following: if you hit the tuning fork weakly, then the oscillation amplitude will be small and the sound will be quiet. If now the tuning fork is hit harder, then the sound is much louder. This is due to the fact that the amplitude of oscillations will be much larger. The perception of sound is a subjective thing, it depends on what the hearing aid is like, what the person's well-being is like.
List of additional literature:
Are you familiar with the sound? // Quantum. - 1992. - No. 8. - C. 40-41. Kikoin A.K. On musical sounds and their sources // Kvant. - 1985. - No. 9. - S. 26-28. Elementary textbook of physics. Ed. G.S. Landsberg. T. 3. - M., 1974.
