Speed of sound in air

For many, even years after graduation, it remains unknown what the speed of sound in the air really is . Someone inattentively listened to the teacher, and someone just did not fully understand the material presented. Well, maybe it's time to fill this gap in knowledge. Today we are not just pointing out "dry" figures, but we will explain the mechanism itself, which determines the speed of sound in the air.

As you know, air is a collection of different gases. A little more than 78% is nitrogen, almost 21% is oxygen, the rest is carbon dioxide and inert gases. Consequently, we are talking about the speed of sound propagation in a gaseous medium.

First, let's define what sound is. Surely many people have heard the saying "sound waves" or "sound vibrations". Indeed, for example, the diffuser of a sound reproducing column oscillates with a certain frequency, which is classified as a sound by the human hearing aid. One of the laws of physics says that the pressure in gases and liquids propagates without changing in all directions. It follows that under ideal conditions the velocity of sound in gases is uniform. Of course, in reality its natural attenuation takes place. You need to remember this feature, since it explains why speed can change. But we are a bit distracted from the main topic. So, if the sound is an oscillation, then what exactly is vibrating?

Any gas is a set of atoms of a certain configuration. In contrast to solids, between atoms in them is a relatively large distance (compared, for example, with the crystal lattice of metals). It is possible to give an analogy with peas distributed in a container with a jelly-like mass. The source of sound vibrations informs the impulse of movement to the nearest atoms of the gas. They, in turn, like balls on a billiard table, "strike" at neighboring ones, and the process repeats. The speed of sound in the air determines the intensity of the primary-cause pulse. But this is only one component. The denser the atoms of matter are, the higher the speed of sound propagation in it. For example, the speed of sound in the air is almost 10 times less than in monolithic granite. This is very easy to understand: for an atom in a gas to "fly" to a neighboring one and transfer energy to it, it must overcome a certain distance.

Consequence: with increasing temperature, the velocity of wave propagation increases. Despite the thermal expansion, the natural velocity of the atoms is higher, they move chaotically and more often collide. It is also true that compressed gas conducts sound much faster, but the champion is still the liquefied aggregate state. In calculating the speed of sound in gases, the initial density, compressibility, temperature and coefficient (gas constant) are taken into account. Actually, all this follows from the foregoing.

After all, what is the speed of sound in the air? Many have already guessed that it is impossible to give an unambiguous answer. We give only some basic data:

- at zero degrees Celsius at the zero point (sea level), the speed of sound is about 331 m / s;

- By lowering the temperature to -20 degrees Celsius, you can "slow down" sound waves to 319 m / s, since initially the 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 apart from the temperature, the pressure of the gases, the configuration of the space (the room with objects or the open area), the own mobility, etc., also influence the sound.

At present, the property of the atmosphere to conduct sound is actively investigated. For example, one of the projects allows you to determine the temperature of the air layers by recording a reflected sound signal (echo).