What is the speed of sound? Speed of sound and its measurement.
For many, even years after graduating from school, it remains unknown what the actual speed of sound in air is. Some did not listen attentively to the teacher, while others simply did not fully understand the material being presented. Well, maybe it's time to fill this knowledge gap. Today we will not just indicate “dry” numbers, but will explain the mechanism itself that determines the speed of sound in air.
As you know, air is a collection of various gases. A little more than 78% is nitrogen, almost 21% is oxygen, the rest is carbon dioxide and Therefore, we will talk about the speed of sound propagation in a gaseous environment.
First, let's define it. Surely many have heard the expression “sound waves” or “sound vibrations”. Indeed, for example, the diffuser of a sound-reproducing speaker vibrates at a certain frequency, which is classified by the human hearing aid as sound. One of the laws of physics states that pressure in gases and liquids spreads without change in all directions. It follows that under ideal conditions the speed of sound in gases is uniform. Of course, in reality there is a natural attenuation. You need to remember this feature, since it is it that explains why the speed can change. But we are a little distracted from the main topic. So, if sound is vibration, what exactly is vibrating?
Any gas is a collection of atoms of a certain configuration. Unlike solids, there is a relatively large distance between the atoms in them (compared, for example, to the crystal lattice of metals). An analogy can be made with peas distributed over a container with a jelly-like mass. oscillations impart momentum to nearby gas atoms. They, in turn, like balls on a billiard table, “hit” neighboring ones, and the process repeats. The speed of sound in the air precisely determines the intensity of the root cause impulse. But this is only one component. The denser the atoms of a substance are located, the higher the speed of sound propagation in it. For example, the speed of sound in air is almost 10 times less than in monolithic granite. This is very easy to understand: in order for an atom in a gas to “reach” its neighbor and transfer momentum energy to it, it needs to overcome a certain distance.
Consequence: with increasing temperature, the speed of wave propagation increases. Despite the atoms’ own speed being higher, they move chaotically and collide more often. It is also true that compressed gas conducts sound much faster, but the champion is still liquefied. Calculation of the speed of sound in gases takes into account the initial density, compressibility, temperature and coefficient (gas constant). Actually, all this follows from the above.
Still, what is the speed of sound in air? Many have already guessed that it is impossible to give a definite answer. Here are just some basic data:
At zero at the zero point (sea level), the speed of sound is about 331 m/s;
By reducing the temperature to -20 degrees Celsius, you can “slow down” sound waves to 319 m/s, since initially atoms in space move more slowly;
Increasing it to 500 degrees accelerates the propagation of sound by almost one and a half times - up to 550 m/s.
However, the given data are approximate, since in addition to temperature, the ability of gases to conduct sound is also affected by pressure, space configuration (a room with objects or an open area), their own mobility, etc.
Currently, the property of the atmosphere to conduct sound is being actively studied. For example, one of the projects makes it possible to determine the temperature of air layers by recording the reflected (echo).
SOUND SPEED- speed of propagation of an elastic wave in the medium. Determined by the elasticity and density of the medium. For running without changing shape with speed With in the direction of the axis X, sound pressure R can be represented in the form p = p(x - - ct), Where t- time. For plane harmony, waves in a medium without dispersion and SZ. expressed in terms of frequency w and k Floy c = w/k. With speed With the harmonic phase propagates. waves, so With called also phase S. z. In media in which the shape of an arbitrary wave changes during propagation, harmonic. the waves nevertheless retain their shape, but the phase velocity turns out to be different for different frequencies, i.e. sound dispersion.In these cases the concept is also used group velocity. At large amplitudes, nonlinear effects appear (see. Nonlinear acoustics), leading to a change in any waves, including harmonic ones: the speed of propagation of each point of the wave profile depends on the pressure at this point, increasing with increasing pressure, which leads to distortion of the wave shape.
Speed of sound in gases and liquids. In gases and liquids, sound propagates in the form of volumetric compression-discharge waves. If the propagation process occurs adiabatically (which, as a rule, is the case), i.e., the change in temperature in the sound wave does not have time to level out even after 1 / 2
, period the heat from the heated (compressed) areas does not have time to move to the cold (rarefied) areas, then S. z. equal to 
, Where R is the pressure in the substance, is its density, and the index s shows that the derivative is taken at constant entropy. This S. z. called adiabatic. Expression for S. z. can also be written in one of the following forms:
Where TO hell - adiabatic. modulus of all-round compression of matter, - adiabatic. compressibility, 
- isothermal compressibility, = - the ratio of heat capacities at constant pressure and volume.
In bounded solids, in addition to longitudinal and transverse waves, there are other types of waves. Thus, along the free surface of a solid body or along its boundary with another medium, they propagate surface acoustic waves, the speed of which is less than the speed of body waves characteristic of a given material. For plates, rods and other solid acoustic materials. waveguides are characteristic normal waves The speed of which is determined not only by the properties of the substance, but also by the geometry of the body. So, for example, S. z. for a longitudinal wave in a rod with a st, the transverse dimensions of which are much smaller than the wavelength of sound, different from the S. z. in an unrestricted environment with l(Table 3): 
Methods for measuring S.z. can be divided into resonant, interferometric, pulsed and optical (see. Diffraction of light by ultrasound).Naib. Measurement accuracy is achieved using pulse-phase methods. Optical methods make it possible to measure S. z. at hypersonic frequencies (up to 10 11 -10 12 Hz). Accuracy abs. measurements S. z. on the best equipment approx. 10 -3%, while the accuracy is relative. measurements of the order of 10 -5% (for example, when studying the dependence With on temperature or magnetic fields or the concentration of impurities or defects).
Measurements of S. z. are used to define plurals. properties of matter, such as the ratio of heat capacities for gases, compressibility of gases and liquids, elastic moduli of solids, Debye temperature, etc. (see. Molecular acoustics). Determination of small changes in S. z. is sensitive. method of fixing impurities in gases and liquids. In solids, the measurement of S. z. and its dependence on different factors (temperature, magnetic field, etc.) allows you to study the structure of matter: the band structure of semiconductors, the structure of the Fermi surface in metals, etc.
Lit.: Landau L. D., L i f sh i c E. M., Theory of Elasticity, 4th ed., M., 1987; them, Hydrodynamics, 4th ed., M., 1988; Bergman L., and its application in science and technology, trans. from German, 2nd ed., M., 1957; Mikhailov I. G., Solovyov V. A., Syrnikov Yu. P., Fundamentals of molecular acoustics, M., 1964; Tables for calculating the speed of sound in sea water, L., 1965; Physical acoustics, ed. W. Mason, trans. from English, vol. 1, part A, M., 1966, ch. 4; t. 4, part B, M., 1970, ch. 7; Kolesnikov A.E., Ultrasonic measurements, 2nd ed., M., 1982; T r u e l l R., E l b a u m Ch., Ch i k B., Ultrasonic methods in solid state physics, trans. from English, M., 1972; Acoustic crystals, ed. M. P. Shaskolskoy, M., 1982; Krasilnikov V.A., Krylov V.V., Introduction to physical acoustics, M., 1984. A. L. Polyakova.
The warmer the water, the faster the speed of sound. When diving to greater depths, the speed of sound in water also increases. Kilometers per hour (km/h) is a non-system unit of speed measurement.
And in 1996, the first version of the site with instant calculations was launched. Already in ancient authors there is an indication that sound is caused by the oscillatory movement of the body (Ptolemy, Euclid). Aristotle notes that the speed of sound has a finite value, and correctly imagines the nature of sound.
Speed of sound in gases and vapors
In multiphase media, due to the phenomena of inelastic energy absorption, the speed of sound, generally speaking, depends on the oscillation frequency (that is, velocity dispersion is observed). For example, estimation of the velocity of elastic waves in a two-phase porous medium can be performed using the equations of the Bio-Nikolaevsky theory. At sufficiently high frequencies (above the Biot frequency), not only longitudinal and transverse waves, but also a longitudinal wave of the second kind arise in such a medium.
In pure water, the speed of sound is about 1500 m/s (see the Colladon-Sturm experiment) and increases with increasing temperature. An object moving at a speed of 1 km/h travels one kilometer in one hour. If you do not find yourself in the list of suppliers, notice an error, or have additional numerical data for colleagues on the topic, please let us know.
The information presented on the site is not official and is provided for informational purposes only. On the ground, the passage of the shock wave is perceived as a bang, similar to the sound of a gunshot. Having exceeded the speed of sound, the plane passes through this area of increased air density, as if piercing it - breaking the sound barrier. For a long time, breaking the sound barrier seemed to be a serious problem in the development of aviation.
flight Mach numbers M(∞), slightly higher than the critical number M*. The reason is that at numbers M(∞) > M* a wave crisis occurs, accompanied by the appearance of wave resistance. 1) gates in fortresses.
Why is it dark in space? Is it true that stars fall? A speed whose Mach number exceeds 5 is called hypersonic. Supersonic speed is the speed of movement of a body (gas flow) exceeding the speed of sound under identical conditions.
See what “SUPERSONIC SPEED” is in other dictionaries:
Sound travels much faster in solids than in water or air. A wave is, in a sense, the movement of something spreading in space. A wave is a process of movement in space of state change. Let's imagine how sound waves propagate in space. These layers are compressed, which in turn again creates excess pressure, affecting neighboring layers of air.
This phenomenon is used in ultrasonic flaw detection of metals. The table shows that as the wavelength decreases, the size of defects in the metal (cavities, foreign inclusions) that can be detected by an ultrasound beam decreases.
The fact is that when moving at flight speeds above 450 km/h, wave drag begins to be added to the usual air resistance, which is proportional to the square of the speed. Wave drag increases sharply as the aircraft speed approaches the speed of sound, several times higher than the drag associated with friction and the formation of vortices.
What is the speed of sound?
In addition to speed, wave resistance directly depends on the shape of the body. So, the swept wing noticeably reduces the wave drag. A further increase in the angle of attack during maneuvering leads to the spread of stall throughout the entire wing, loss of controllability and stalling of the aircraft into a tailspin. A forward-swept wing is partially free of this drawback.
When creating a forward-swept wing, complex problems arose, primarily associated with elastic positive divergence (or simply with twisting and subsequent destruction of the wing). Wings made of aluminum and even steel alloys blown through supersonic tubes were destroyed. It wasn't until the 1980s that composite materials emerged that could combat twisting by using specially oriented windings of carbon fibers.
For sound to propagate, an elastic medium is required. In a vacuum, sound waves cannot propagate, since there is nothing there to vibrate. At a temperature of 20 °C it is equal to 343 m/s, i.e. 1235 km/h. Note that it is to this value that the speed of a bullet fired from a Kalashnikov assault rifle decreases at a distance of 800 m.
Sound travels at different speeds in different gases. Enter the value you want to convert (speed of sound in air). In the areas of modern technology and business, the winner is the one who manages to do everything quickly.
Sound speed- the speed of propagation of elastic waves in a medium: both longitudinal (in gases, liquids or solids) and transverse, shear (in solids). It is determined by the elasticity and density of the medium: as a rule, the speed of sound in gases is less than in liquids, and in liquids it is less than in solids. Also, in gases, the speed of sound depends on the temperature of a given substance, in single crystals - on the direction of wave propagation. Usually does not depend on the frequency of the wave and its amplitude; in cases where the speed of sound depends on frequency, we speak of sound dispersion.
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Already in ancient authors there is an indication that sound is caused by the oscillatory movement of the body (Ptolemy, Euclid). Aristotle notes that the speed of sound has a finite value, and correctly imagines the nature of sound. Attempts to experimentally determine the speed of sound date back to the first half of the 17th century. F. Bacon in the New Organon pointed out the possibility of determining the speed of sound by comparing the time intervals between a flash of light and the sound of a gunshot. Using this method, various researchers (M. Mersenne, P. Gassendi, W. Derham, a group of scientists from the Paris Academy of Sciences - D. Cassini, J. Picard, Huygens, Roemer) determined the value of the speed of sound (depending on the experimental conditions, 350- 390 m/s). Theoretically, the question of the speed of sound was first considered by I. Newton in his “Principles”. Newton actually assumed that sound propagation is isothermal, and therefore received an underestimate. The correct theoretical value for the speed of sound was obtained by Laplace.
Calculation of speed in liquid and gas
The speed of sound in a homogeneous liquid (or gas) is calculated by the formula:
c = 1 β ρ (\displaystyle c=(\sqrt (\frac (1)(\beta \rho ))))In partial derivatives:
c = − v 2 (∂ p ∂ v) s = − v 2 C p C v (∂ p ∂ v) T (\displaystyle c=(\sqrt (-v^(2)\left((\frac (\ partial p)(\partial v))\right)_(s)))=(\sqrt (-v^(2)(\frac (C_(p))(C_(v)))\left((\ frac (\partial p)(\partial v))\right)_(T))))Where β (\displaystyle \beta )- adiabatic compressibility of the medium; ρ (\displaystyle \rho )- density; C p (\displaystyle C_(p))- isobaric heat capacity; C v (\displaystyle C_(v))- isochoric heat capacity; p (\displaystyle p), v (\displaystyle v), T (\displaystyle T)- pressure, specific volume and temperature of the medium; s (\displaystyle s)- entropy of the medium.
For solutions and other complex physical and chemical systems (for example, natural gas, oil), these expressions can give a very large error.
Solids
In the presence of interfaces, elastic energy can be transferred through surface waves of various types, the speed of which differs from the speed of longitudinal and transverse waves. The energy of these oscillations can be many times greater than the energy of body waves.
Probably many of you have heard about such a concept as the speed of sound. I hope most of you understand what this is. And even if not, we’ll figure it out now.
What is speed?
Firstly, you need to understand that speed is a physical quantity that shows how far a body can travel per unit time. From this definition it follows that a car moving at a speed of 70 km/h, in 99% of cases, can travel 70 kilometers in one clockwise revolution (that is, in an hour). In 1% of cases we'll discount the fact that it may break down on the road or the road will end. The car is clear. Instead of a car, you can take other objects: a person is running, a stone is flying, a jerboa is jumping, etc. All these bodies are real objects that can be seen and even touched. But the sound is not a stone or an airplane, where does it get its speed?
The concept consists of two words. We've already dealt with the first one. Now let's move on to the second. What is sound?
Sound is something that we can hear, that is, it is a physical phenomenon. This phenomenon occurs as a result of the spread sound wave in solid, liquid or gaseous media. The sound wave is very similar to an ordinary sea wave, which everyone has seen live or on TV (it’s not for nothing that they were called the same - wave). But more accurately, you can imagine a sound wave as circles on water that appear after throwing a pebble. After all, sound travels equally in all directions! If you shout at a glass of water, they will take you to the madhouse. You will be able to see the sound!!! In the form of circles on the surface of the water.
That is sound wave- this is essentially the vibration of the atoms of the medium in which sound propagates. This is why windows shake from loud music.
Now we know what speed is and what sound is, so let's connect these concepts together!
The speed of sound is a value that shows how far a sound wave can travel per unit time.
As we have already figured out, for a sound wave to move, it is necessary (air, water, a solid body) to vibrate. This is why there is no sound in space! Since there are no atoms there (practically none, there are a few, but very few)! And the most interesting thing is that sound travels in air at a speed of 340 m/s, in water at a speed of 1500 m/s, and in solids at speeds of 3000-6000 m/s. This is not surprising, since the smaller the distance between the atoms, the faster the sound travels.
