The speed of sound in powder. How much is the speed of sound in km per hour

The first attempts to understand the nature of the origin of sound were made more than two thousand years ago. In the works of the ancient Greek scholars Ptolemy and Aristotle, the correct assumptions are made that sound is generated by vibrations of the body. Moreover, Aristotle argued that the speed of sound is a measurable and finite quantity. Of course, in ancient Greece there were no technical possibilities for any exact measurements, therefore the speed of sound was relatively accurately measured only in the seventeenth century. To do this, we used the comparison method between the time the flash was detected from the shot and the time after which the sound reached the observer. As a result of numerous experiments, scientists came to the conclusion that sound propagates in 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 given medium directly depends on the density and temperature of this medium. So, the thinner the air, the slower the sound moves along it. In addition, the speed of sound is higher, the higher the temperature of the medium. To date, it is generally accepted that the speed of propagation of sound waves in 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 those altitudes where usually, the environmental characteristics are very different from normal. That is why in aviation, a universal concept is used, which is called the Mach number, named after the Austrian Ernst Mach. This number represents 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 greater 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 moving at subsonic speeds. Basically, this is due to a change in the aerodynamics of the aircraft, the deterioration of its controllability, heating of the body, as well as the resistance of the waves. These effects are observed only when the Mach number exceeds unity, that is, the object overcomes the sound barrier. At the moment, there are formulas that allow you to calculate the speed of sound at various air parameters, and, therefore, calculate the Mach number for different conditions.

Today, many new settlers, equipping the apartment, are forced to carry out additional work, including the soundproofing of their homes, because the standard materials used make it possible only to partially hide what is happening in your own house, 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 the premises, the layer adjacent to the load-bearing wall is made soundproof with “puffs” from above and below. It can reduce in decibels sometimes more than 10 times. Then basalt mats are laid, and plasterboard sheets, which reflect the sound outside the apartment, are placed on top. When a sound wave "flies" to such a structure, it damps in the insulator layers, which are porous and soft. If the sound has great power, then the materials absorbing it can even heat up.

Elastic substances, such as water, wood, metals, transmit well, therefore, we hear beautiful “singing” of musical instruments. And some nationalities in the past determined the approach, for example, of horsemen, putting their ears 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 may 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 translate speed into kilometers per hour, you need to multiply the figures by 3600 (seconds per hour) and divide by 1000 (meters per kilometer).

The speed of sound in km in an aqueous medium 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 it is already about 1490 m / s.

The salty medium differs by a known greater speed of sound vibrations.

Sound propagation in air also depends on temperature. With the 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 insulators for an apartment, we can find out that in a material such as cork, which is often used to reduce external noise, the speed of sound in km is only 1800 km / h (500 meters per second). It 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, its volume level decreases, because changes At the same time, the frequency remains the same, so we hear the female voice as female, and the male voice as male. 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 put a ringing alarm clock under the hood from which air is pumped. The greater the thinness of the air, the quieter the ringer is heard.

Sound speed - the propagation velocity of elastic waves in the 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, in gases the speed of sound is less than in liquids, and in liquids - 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 independent of the frequency of the wave and its amplitude; in cases where the speed of sound depends on the frequency, they speak of the dispersion of sound.

Encyclopedic YouTube

Already in ancient authors there is an indication that the sound is due to 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 shot. Using this method, various researchers (M. Mersenne, P. Gassendi, W. Derham, a group of scientists from the Paris Academy of Sciences - D. Cassini, Picard, Huygens, Römer) determined the value of the speed of sound (depending on the experimental conditions, 350-390 m /from). Theoretically, the question of the speed of sound was first considered by Newton in his “Beginnings”. Newton actually assumed isothermal sound propagation, so he received an underestimated estimate. The correct theoretical value of the speed of sound was obtained by Laplace. [ ]

Calculation of velocity in liquid and gas

The speed of sound in a homogeneous liquid (or gas) is calculated by the formula:

c \u003d 1 β ρ (\\ displaystyle c \u003d (\\ sqrt (\\ frac (1) (\\ beta \\ rho))))

In private derivatives:

c \u003d - v 2 (∂ p ∂ v) s \u003d - v 2 C p C v (∂ p ∂ v) T (\\ displaystyle c \u003d (\\ sqrt (-v ^ (2) \\ left ((\\ frac (\\ (\\ partial v)) \\ right) _ (T))))

where β (\\ displaystyle \\ beta) is the adiabatic compressibility of the medium; ρ (\\ displaystyle \\ rho) - density; C p (\\ displaystyle Cp) - isobaric heat capacity; C v (\\ displaystyle Cv) - isochoric heat capacity; p (\\ displaystyle p), v (\\ displaystyle v), T (\\ displaystyle T) - pressure, specific volume and temperature of the medium; s (\\ displaystyle s) is the entropy of the medium.

For solutions and other complex physicochemical systems (for example, natural gas, oil), these expressions can give a very large error.

Solids

In the presence of interfaces, elastic energy can be transmitted by means of surface waves of various types, the speed of which differs from the velocity of longitudinal and transverse waves. The energy of these oscillations can be many times higher than the energy of body waves.

Sacor 23-11-2005 11:50

In principle, the question is not as simple as it seems, I found this definition:

The speed of sound, the speed of propagation of any fixed phase of a sound wave; also called phase velocity, in contrast to group velocity. S. z. usually a constant for a given substance under given external conditions and does not depend on the frequency of the wave and its amplitude. In those cases when this is not carried out and S. z. depends on the frequency, they talk about the dispersion of sound.

So what is the speed of sound in winter, in summer, in fog, in rain - these are now incomprehensible things to me ...

Sergey13 23-11-2005 12:20

at nu 320 m / s.

TL 23-11-2005 12:43

The denser the medium, the higher the propagation speed of the disturbance (sound) in the air is approx. 320-340m / s. (Falls with height) 1300-1500 m / s in water (salty / fresh) 5000 m / s in metal, etc. That is, with fog, the speed of sound will be higher, in winter also higher, etc.

Startgamen 23-11-2005 12:48

Startgamen 23-11-2005 12:49

At the same time answered

Sacor 23-11-2005 13:00

This means that the range is 320-340 m / s - the reference book looked, there, at 0 Celsius and a pressure of 1 atmosphere, the speed of sound in air is 331 m / s. So 340 in the cold, and 320 in the heat.
And now the most interesting, and what is the toll of the bullet speed of subsonic ammunition?
Here is the classification for small-caliber cartridges from Ada.ru, for example:
Standard (subsonic) cartridges speed up to 340 m / s
High velocity cartridges (high-speed) speed from 350 to 400 m / s
Cartridges of Hyper Velocity or Extra high velocity (superhigh-speed) speed from 400 m / s and above
That is, Eley Tenex 331 m / s Sob 325 m / s are considered subsonic, and the Standard 341 m / s is no longer. Although both these and these, in principle, lie in the same range of sound velocities. Like this?

Kostya 23-11-2005 13:39

IMHO do not bother with this, you are not fond of acoustics, but are fond of shooting.

Sacor 23-11-2005 13:42

quote: Originally posted by Kostya:
IMHO do not bother with this, you are not fond of acoustics, but are fond of shooting.

Yes, it’s just interesting, because all the subsonic is over-sounding, but as I dug it turned out everything was completely inappropriate.

By the way, what is the subsonic speed for silent shooting for the x54, x39, 9PM?

John jack 23-11-2005 13:43

The cartridges also have a spread of initial speed, and it also depends on the temperature.

Greeng 23-11-2005 14:15

Sound is an elastic longitudinal wave, the propagation speed of which depends on the properties of the environment. Those. higher terrain - lower air density - lower speed. Unlike light, a shear wave.
It is generally accepted that V \u003d 340 m / s (approximately).

However, this is off

Startgamen 23-11-2005 14:40

Current light has a transverse electromagnetic wave, and the sound is mechanical longitudinal. If I understand correctly, they are related by a description of the same mathematical function.
However, this is off

Hunt 23-11-2005 14:48

Here's what I’m interested in, the maximum atmospheric pressure (in general for a month) rested in the Urals has never risen to the parameters of the local ones. At the moment there is 765 t-32. And what's interesting is the temperature is lower and the pressure is lower. Well ... this as far as I noted for myself ... I do not conduct constant observations. I have a point. last year's tables were at a pressure of 775mm \\ rt \\ st. Maybe the lack of oxygen in our area is partially offset by increased atmospheric pressure. He asked a question at his department, it turns out there is NO DATA !. And these are people creating decompression tables for people like me! And for military jogging (physical exercises) in our Palestinians are prohibited, because lack of oxygen. I think if oxygen is deficient, then what is substituted by ... nitrogen, that is, and the density is different. And if you look at and consider all this, you must be a shooter of the galactic class. I decided for myself (while the Senior is piling over the calculator, and the customs over my parcels) I decided: For 700 no, no figs to shoot cartridges.
Here I wrote and thought. After all, he spat and promised more than once, well, what for all this. What to go to the Chepionat? Compete with whom?
... You read the forum and carries it again. Where to get bullets, matrices, etc.
CONCLUSION: A terrible dependence on communicating with similar people who love weapons - homo ... (I propose to find a continuation of the expression)

Greeng 23-11-2005 16:02

quote: Originally posted by StartGameN:
I can off develop - my diploma was called "Nonlinear acoustoelectromagnetic interactions in crystals with quadratic electrostriction"

Startgamen 23-11-2005 16:24

I’m not a theoretical physicist, so there weren’t any “experiments”. There was an attempt to take into account the second derivative and explain the occurrence of resonance.
But the idea is right

Khabarovsk 23-11-2005 16:34

Can I listen to you from the edge here? I won’t interfere, chesslovo. Regards, Alexey

Antti 23-11-2005 16:39

quote: Originally posted by GreenG:
was the main experimental method, apparently, tapping a crystal with a magnet?

Square magnet on a curved crystal.

Sacor 23-11-2005 19:03

Then another question, why does the sound of a shot seem louder in winter than in summer?

SVIREPPEY 23-11-2005 19:27

I’ll tell you all this.
Of the ammunition, the speed of sound is close. 22lr. We put moder on the trunk (to remove the sound background) and shoot at a hundred, for example. And then all the cartridges can be easily divided into subsonic (you hear how it flies into the target — such a light “fart” takes place) and supersonic — when it hits the target, it bangs so that the whole idea with moderator flies down the drain. From subsystem I can note the pace, biathlon, from imported ones - RWS Target (well, I know little of them, and the choice is not that in stores). From supersonic - for example, Lapua Standard, cheap, interesting, but very noisy cartridges. Then we take the initial speeds from the manufacturer’s website - and here's an approximate range where the speed of sound is at a given firing temperature.

Startgamen 23-11-2005 19:56

Then another question, why does the sound of a shot seem louder in winter than in summer?

In winter, the mustache walks in hats and therefore the hearing is dulled

STASIL0V 23-11-2005 20:25

But seriously: for what purpose is it necessary to know the real speed of sound for specific conditions (in the sense from a practical point of view)? the target usually determines the means and methods / accuracy of the measurement. For me, since it’s kind of like hitting a target or hunting, it doesn’t need to know the speed (unless of course without a silencer) ...

Parshev 23-11-2005 20:38

In fact, the speed of sound is to some extent the limit for a stabilized flight of a bullet. If you look at the accelerated body, then the air resistance rises to the sound barrier, quite sharply before the barrier itself, and then, after passing through the barrier, drops sharply (because aviators were so eager to achieve supersonic). When braking, the picture is built in the reverse order. That is, when the speed ceases to be supersonic, the bullet experiences a sharp jump in air resistance and can go somersault.

vyacheslav 23-11-2005 20:38

everything turned out to be completely inappropriately.

The most interesting conclusion in the entire discussion.

q123q 23-11-2005 20:44

And so, comrades, the speed of sound directly depends on temperature, the higher the temperature, the greater the speed of sound, and not the other way around as noted at the beginning of the topic.
*************** /------- |
sound speed a \u003d \\ / k * R * T (this root is so designated)

For air, k \u003d 1.4 is an adiabatic exponent
R \u003d 287 - specific gas constant for air
T - temperature in Kelvin (0 degrees Celsius corresponds to 273.15 degrees Kelvin)
That is, at 0 Celsius a \u003d 331.3 m / s

Thus, in the range of -20 +20 Celsius, the speed of sound varies in the ranges from 318.9 to 343.2 m / s

I think more questions will not arise.

As for why all this is necessary, it is necessary when studying flow regimes.

Sacor 24-11-2005 10:32

Exhaustively, but does the speed of sound depend on density or pressure?

BIT 24-11-2005 12:41

[B] If you look at the accelerated body, then the air resistance rises to the sound barrier, rather sharply before the barrier, and then, after passing through the barrier, drops sharply (because the aviators were so eager to achieve supersonic).

I have already pretty much forgotten physics, but as far as I remember, air resistance increases with increasing speed both before and after the “sound”. It is only at subsonic that the main contribution is made by overcoming the frictional force against air, and at supersonic this component sharply decreases, but the energy losses due to the creation of a shock wave increase. A. On the whole, energy losses increase, and the further, the more progressive.

Blackspring 24-11-2005 13:52

I agree with q123q. We were taught - the norm at 0 centigrade is 330 m / s, plus 1 degree - plus 1 m / s, minus 1 degree - minus 1 m / s. It is a working scheme for practical use.
Probably, the norm may vary with pressure, but the change will still be approximately a degree meter per second.
BS

Startgamen 24-11-2005 13:55

quote: Originally posted by Sacor:

Depends, depends. But: there is such a Boyle law, according to which at a constant temperature p / p1 \u003d const, i.e. density change is directly proportional to pressure change

Parshev 24-11-2005 14:13

Originally posted by Parshev:
[B]
I have already pretty much forgotten physics, but as far as I remember, air resistance increases with increasing speed both before and after the “sound”. .

And I never knew.

It grows both before the sound and after the sound, and in different ways at different speeds, but falls on the sound barrier. That is, 10 m / s before the speed of sound, the resistance is higher than when 10 m / s after the speed of sound. Then it grows again.
Of course, the nature of this resistance is different, therefore objects of different shapes cross the barrier in different ways. Drop-like objects fly better before the sound, with a sharp nose after the sound.

BIT 24-11-2005 14:54

Originally posted by Parshev:
[B]

That is, 10 m / s before the speed of sound, the resistance is higher than when 10 m / s after the speed of sound. Then it grows again.

Not certainly in that way. When the sound barrier passes, the TOTAL resistance force increases, moreover, abruptly, due to a sharp increase in energy consumption for the formation of a shock wave. The contribution of the FRICTION FORCE (more precisely, the resistance force due to turbulence behind the body) sharply decreases due to a sharp decrease in the density of the medium in the boundary layer and behind the body. Therefore, the optimal body shape at subsonic becomes suboptimal at supersonic, and vice versa. A supersonic teardrop-shaped body flowing around in the sound creates a very powerful shock wave, and experiences a much greater TOTAL resistance force compared to the pointed but with a “blunt” back part (which is practically irrelevant in supersonic). In the reverse transition, the rear non-streamlined part creates greater turbulence compared to the teardrop-shaped body and, therefore, drag force. In general, a whole section of general physics is devoted to these processes - hydrodynamics, and it is easier to read the textbook. And the scheme you have outlined, as far as I can tell, is not true.

Sincerely. BIT

Greeng 24-11-2005 15:38

quote: Originally posted by Parshev:
Drop-like objects fly better before the sound, with a sharp nose after the sound.

Hooray!
It remains to come up with a bullet that can fly nose forward in excess of sound and w .. sing after crossing the barrier.

In the evening I’m stomping cognac for my bright head!

Machete 24-11-2005 15:43

Inspired by discussion (off).

Gentlemen, did you drink a cockroach?

BIT 24-11-2005 15:56

Recipe, pliz.

Antti 24-11-2005 16:47

In general, a whole section of general physics is devoted to these processes - hydrodynamics ...

What does Hydra have to do with it?

Parshev 24-11-2005 18:35

What does Hydra have to do with it?

And the name is beautiful. Nothing, of course, has different processes in water and in the air, although there is a common one.

Here you can see what happens with the drag coefficient on the sound barrier (3rd graph):
http://kursy.rsuh.ru/aero/html/kurs_580_0.html

In any case - on the barrier there is a sharp change in the flow pattern, disturbing the movement of the bullet - this may be useful to know the speed of sound.

STASIL0V 24-11-2005 20:05

Returning again to the practical plane, it turns out that when switching to subsonic, additional little-predictable “disturbances” arise that lead to the destabilization of the bullet and the increase in scatter. Therefore, in order to achieve sporting goals, a supersonic small cartridge cannot be used in any case (and the maximum possible accuracy will not hinder hunting). What then is the advantage of supersonic cartridges? More (not much) energy and therefore lethal force? And this is due to accuracy and even more noise. Is it worth it to use supersonic 22lr at all?

gyrud 24-11-2005 21:42

quote: Originally posted by Hunt:
And for military jogging (physical exercises) in our Palestinians are prohibited, because lack of oxygen. I think if there is a lack of oxygen, then it’s replaced by ... nitrogen,

One cannot speak of any substitution of nitrogen for nitrogen. there is simply no substitution for it. The percentage of atmospheric air is the same at any pressure. Another thing is that under reduced pressure in the same liter of inhaled air there is actually less oxygen than at normal pressure, and oxygen deficiency develops. That is why pilots at altitudes above 3000m breathe through masks with an air mixture enriched with up to 40% oxygen.

q123q 24-11-2005 22:04

quote: Originally posted by Sacor:
Exhaustively, but does the speed of sound depend on density or pressure?

Only through temperature.

Pressure and density, or rather their ratio is strictly related to temperature
pressure / density \u003d R * T
what is R, T see in my post above.

That is, the speed of sound is an unambiguous function of temperature.

Parshev 25-11-2005 03:03

It seems to me that the ratio of pressure and density is strictly related to temperature only in adiabatic processes.
Are climate changes in temperature and atmospheric pressure such?

Startgamen 25-11-2005 03:28

The correct question.
Answer: climate change is not an adiabatic process.
But some kind of model must be used ...

BIT 25-11-2005 09:55

quote: Originally posted by Antti:
What does Hydra have to do with it?
Someone I suspect that in air and water the picture may vary slightly due to compressibility / incompressibility. Or not?

We at the university had a combined course in hydro- and aerodynamics and also the department of hydrodynamics. Therefore, I called this section in abbreviated form. You are certainly right, processes in liquids and gases can proceed in different ways, although there are a lot of similarities.

BIT 25-11-2005 09:59

What then is the advantage of supersonic cartridges? More (not much) energy and therefore lethal force? And this is due to accuracy and even more noise. Is it worth it to use supersonic 22lr at all?

Startgamen 25-11-2005 12:44

The "accuracy" of the small cartridge is due to the extremely weak heating of the barrel and the non-shell lead bullet, and not to the speed of its departure.

BIT 25-11-2005 15:05

About heating is understandable. And what about the cloudlessness? Greater manufacturing accuracy?

STASIL0V 25-11-2005 20:48

quote: Originally posted by BIT:
IMHO - ballistics, tobish trajectory. Less flying time - less external disturbances. But in general, the question arises: since when switching to subsonic air resistance sharply decreases, the overturning moment should also sharply decrease, and therefore increase the stability of the bullet? Is this why the small cartridge is one of the most accurate?
Machete 26-11-2005 02:31
quote: Originally posted by STASIL0V:
Opinions are divided. In your opinion, a supersonic bullet is stabilized when switching to subsonic. And according to Parshev, on the contrary, an additional disturbing effect arises that worsens stabilization.

Dr. Watson 26-11-2005 12:11
Exactly.
BIT 28-11-2005 12:37
And I did not think to argue. He simply asked questions and, opening his mouth, listened.
Sacor 28-11-2005 14:45
quote: Originally posted by Machete:
In this case, Parshev is absolutely right - with a reverse transonic transition, the bullet is destabilized. That is why the maximum firing range for each particular cartridge in the Long Range is determined by the distance of the reverse transonic transition.

It turns out that a small-caliber bullet fired at a speed of 350 m / s somewhere on 20-30 m is highly destabilized? And accuracy is deteriorating significantly.

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1 kilometer per hour [km / h] \u003d 0.0001873459079907 the speed of sound in fresh water

Initial value

Converted value

meter per second meter per hour meter per minute kilometer per minute kilometer per second centimeter per hour centimeter per minute centimeter per second millimeter per hour millimeter per minute millimeter per second foot per hour foot per minute foot per second yard per hour yard in minute yard per second mile per hour mile per minute mile per second knot knot (Brit.) speed of light in vacuum first space speed second space speed third space speed Earth's rotation speed sound speed in fresh water sound speed in sea water (20 ° C, depth 10 meters) Mach number (20 ° C, 1 atm) Mach number (SI standard)

American wire gauge

Speed \u200b\u200bdetails

General information

Speed \u200b\u200b- a measure of the distance traveled over a given time. The speed can be a scalar quantity and a vector quantity - in this case, the direction of motion is taken into account. The speed of movement in a straight line is called linear, and in a circle - angular.

Speed \u200b\u200bmeasurement

Average speed v find by dividing the total distance traveled ∆ x for the total time ∆ t: v = ∆x/∆t.

In the SI system, speed is measured in meters per second. Kilometers per hour in the metric system and miles per hour in the USA and Great Britain are also widely used. When in addition to the magnitude the direction is indicated, for example, 10 meters per second to the north, then we are talking about vector velocity.

The speed of bodies moving with acceleration can be found using the formulas:

a, with initial speed u during the period ∆ thas final speed v = u + a×∆ t.
A body moving with constant acceleration a, with initial speed u and final speed vhas an average velocity ∆ v = (u + v)/2.

Average speeds

Speed \u200b\u200bof light and sound

According to the theory of relativity, the speed of light in vacuum is the highest speed with which energy and information can move. It is denoted by a constant c and equals c \u003d 299,792,458 meters per second. Matter cannot move at the speed of light, because this will require an infinite amount of energy, which is impossible.

The speed of sound is usually measured in an elastic medium, and is equal to 343.2 meters per second in dry air at a temperature of 20 ° C. The speed of sound is the lowest in gases, and the highest in solids. It depends on the density, elasticity, and shear modulus of the substance (which shows the degree of deformation of the substance under shear load). Mach number M is the ratio of the speed of a body in a liquid or gas medium to the speed of sound in this medium. It can be calculated by the formula:

M = v/a,

where a is the speed of sound in the medium, and v - body speed. Mach number is commonly used in determining speeds close to the speed of sound, such as the speeds of airplanes. This value is variable; it depends on the state of the medium, which, in turn, depends on pressure and temperature. Supersonic speed - speed exceeding 1 Mach.

Vehicle speed

Below are some vehicle speeds.

Passenger aircraft with turbofan engines: the cruising speed of passenger aircraft is from 244 to 257 meters per second, which corresponds to 878–926 kilometers per hour or M \u003d 0.83–0.87.
High-speed trains (like the Shinkansen in Japan): these trains reach maximum speeds from 36 to 122 meters per second, that is, from 130 to 440 kilometers per hour.

Animal speed

The maximum speeds of some animals are approximately equal:

Human speed

People walk at a speed of about 1.4 meters per second or 5 kilometers per hour, and run at speeds of up to about 8.3 meters per second, or up to 30 kilometers per hour.

Examples of different speeds

Four-dimensional speed

In classical mechanics, vector velocity is measured in three-dimensional space. According to the special theory of relativity, space is four-dimensional, and the fourth dimension, space-time, is also taken into account in the measurement of speed. This speed is called four-dimensional speed. Its direction may vary, but the value is constant and equal to c, that is, the speed of light. Four-dimensional speed is defined as

U \u003d ∂x / ∂τ,

where x represents the world line — a curve in space-time along which the body moves, and τ is the “proper time” equal to the interval along the world line.

Group speed

Group velocity is the wave propagation velocity that describes the propagation velocity of a wave group and determines the velocity of wave energy transfer. It can be calculated as ∂ ω /∂kwhere k is the wave number, and ω - angular frequency. K measured in radians / meter, and the scalar frequency of the waves ω - in radians per second.

Hypersonic speed

Hypersonic speed is a speed exceeding 3000 meters per second, that is, many times higher than the speed of sound. Solids moving at this speed acquire the properties of liquids, because due to inertia, the loads in this state are stronger than the forces that hold the molecules of the substance together during a collision with other bodies. At ultrahigh hypersonic speeds, two colliding solids turn into gas. In space, bodies move at such a speed, and engineers designing spacecraft, orbital stations and spacesuits must take into account the possibility of a station or astronaut colliding with space debris and other objects when working in outer space. In such a collision, the plating of the spacecraft and the spacesuit suffer. Equipment developers conduct collision experiments at hypersonic speeds in special laboratories to determine how strong the collisions can withstand spacesuits, as well as cladding and other parts of the spacecraft, such as fuel tanks and solar panels, checking their strength. To do this, the spacesuits and lining are subjected to impacts by various objects from a special installation with supersonic speeds exceeding 7500 meters per second.

The highest speed is considered to be the speed of light in a vacuum, that is, a space free of matter. The scientific community accepted its value 299 792 458 m / s (or 1 079 252 848.8 km / h). In this case, the most accurate measurement of the speed of light based on a reference meter, carried out in 1975, showed that it is 299 792 458 ± 1.2 m / s. With the speed of light, both visible light itself and other types of electromagnetic radiation propagate, for example, radio waves, x-rays, gamma rays.

The speed of light in a vacuum is a fundamental physical constant, i.e., 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, nor on the observer's reference frame.

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 a vacuum, because sound cannot propagate under such conditions: there is no elastic medium in a vacuum, and elastic mechanical vibrations cannot occur. As a rule, the sound propagates more slowly in a gas, a little faster - in a liquid, most quickly - 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):

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

	Longitudinal wave	Transverse wave






Aluminium alloy