1 sound speed. We calculate the speed of sound in km

Today, many newcomers, equipping an apartment, are forced to carry out additional work, including soundproofing their home, because the standard materials used make it possible to only partially hide what is happening in your own home, and not be interested in the communication of neighbors against your will.

In solids, at least the density and elasticity of the substance opposing the wave affects. Therefore, when equipping rooms, the layer adjacent to the load-bearing wall is made soundproof with "overlaps" from above and below. It allows you to reduce in decibels sometimes more than 10 times. Then basalt mats are laid, and on top - gypsum plasterboard sheets that reflect sound outside the apartment. When a sound wave “flies up” to such a structure, it is attenuated in the insulator layers, which are porous and soft. If the sound is strong, the materials that absorb it may even heat up.

Elastic substances, such as water, wood, metals, transmit well, therefore we hear the wonderful "singing" of musical instruments. And some nationalities in the past determined the approach, for example, of riders, putting their ear to the ground, which is also quite elastic.

The speed of sound in km depends on the characteristics of the medium in which it propagates. In particular, the process can be affected by its pressure, chemical composition, temperature, elasticity, density and other parameters. For example, in a steel sheet, a sound wave travels at a speed of 5100 meters per second, in glass - about 5000 m / s, in wood and granite - about 4000 m / s. To convert speed into kilometers per hour, you need to multiply the indicators by 3600 (seconds per hour) and divide by 1000 (meters per kilometer).

The speed of sound in km in an aquatic environment is different for substances with different salinity. For fresh water at a temperature of 10 degrees Celsius, it is about 1450 m / s, and at a temperature of 20 degrees Celsius and the same pressure - already about 1490 m / s.

The salty environment is distinguished by a deliberately higher speed of passage of sound vibrations.

Sound propagation in air also depends on temperature. With a value of this parameter equal to 20, sound waves travel at a speed of about 340 m / s, which is about 1200 km / h. And at zero degrees, the speed slows down to 332 m / s. Returning to our apartment insulators, we can find out that in a material such as cork, which is often used to reduce the level of external noise, the speed of sound in km is only 1800 km / h (500 meters per second). This is ten times lower than this characteristic in steel parts.

A sound wave is a longitudinal vibration of the medium in which it propagates. When, for example, a melody of a piece of music passes through an obstacle, the level of its volume decreases, because changes In this case, the frequency remains the same, due to which we hear a woman's voice as a woman's, and a man's as a man's. The most interesting is the place where the speed of sound in km is close to zero. This is a vacuum in which waves of this type hardly propagate. To demonstrate how this works, physicists place a ringing alarm clock under a bell from which air is pumped out. The more rarefied the air, the quieter the bell is heard.

The highest speed is the speed of light in a vacuum, that is, space free of matter. The scientific community accepted its value as 299 792 458 m / s (or 1,079 252 848.8 km / h). At the same time, the most accurate measurement of the speed of light on the basis of a reference meter, carried out in 1975, showed that it is 299 792 458 ± 1.2 m / s. Visible light itself, as well as other types of electromagnetic radiation, such as radio waves, X-rays, and gamma quanta, propagate at the speed of light.

The speed of light in a vacuum is a fundamental physical constant, that is, its value does not depend on any external parameters and does not change with time. This speed does not depend on the movement of the wave source or on the observer's frame of reference.

What is the speed of sound?

The speed of sound differs depending on the medium in which the elastic waves propagate. It is impossible to calculate the speed of sound in vacuum, since sound cannot propagate under such conditions: there is no elastic medium in vacuum, and elastic mechanical vibrations cannot arise. As a rule, sound propagates more slowly in gas, slightly faster in liquid, and most rapidly in solids.

So, according to the Physical Encyclopedia edited by Prokhorov, the speed of sound in some gases at 0 ° C and normal pressure (101325 Pa) is (m / s):

The speed of sound in some liquids at 20 ° C is (m / s):

Longitudinal and transverse elastic waves propagate in a solid medium, and the velocity of the longitudinal waves is always greater than the transverse ones. The speed of sound in some solids is (m / s):

The first attempts to understand the origin of sound were made over two thousand years ago. In the writings of the ancient Greek scientists Ptolemy and Aristotle, correct assumptions are made that sound is generated by body vibrations. Moreover, Aristotle argued that the speed of sound is measurable and finite. Of course in Ancient Greece there was no technical capability for any accurate measurements, so the speed of sound was relatively accurately measured only in the seventeenth century. For this, a comparison method was used between the flash detection time from the shot and the time after which the sound reached the observer. As a result of numerous experiments, scientists have come to the conclusion that sound travels in the air at a speed of 350 to 400 meters per second.

The researchers also found that the value of the speed of propagation of sound waves in a particular medium directly depends on the density and temperature of this medium. So, the thinner the air, the slower the sound moves through it. In addition, the higher the temperature of the medium, the higher the speed of sound. Today it is generally accepted that the speed of propagation of sound waves in the air under normal conditions (at sea level at a temperature of 0 ° C) is 331 meters per second.

Mach number

In real life, the speed of sound is a significant parameter in aviation, but at altitudes where it is usual, the environmental characteristics are very different from normal. That is why aviation uses a universal concept called the Mach number, named after the Austrian Ernst Mach. This number is the speed of the object divided by the local speed of sound. Obviously, the lower the speed of sound in a medium with specific parameters, the larger the Mach number will be, even if the speed of the object itself does not change.

The practical application of this number is due to the fact that movement at a speed that is higher than the speed of sound differs significantly from movement at subsonic speeds. Basically, this is due to changes in the aerodynamics of the aircraft, deterioration of its controllability, heating of the hull, as well as wave resistance. These effects are observed only when the Mach number exceeds one, that is, the object overcomes the sound barrier. At the moment, there are formulas that allow you to calculate the speed of sound for certain air parameters, and, therefore, calculate the Mach number for different conditions.