What is the speed of sound in air, km/h? What is the speed of sound in km/h?

The highest speed is considered to be the speed of light in a vacuum, i.e. space free of matter. The scientific community accepted its value as 299,792,458 m/s (or 1,079,252,848.8 km/h). However, the most accurate measurement of the speed of light based on a standard meter, carried out in 1975, showed that it was 299,792,458 ± 1.2 m/s. At the speed of light it spreads like itself visible light, as well as other types of electromagnetic radiation, 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 over time. This speed does not depend either 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 elastic waves propagate. It is impossible to calculate the speed of sound in a vacuum, since sound cannot propagate under such conditions: there is no elastic medium in a vacuum, and elastic mechanical vibrations cannot arise. As a rule, sound travels slower in gases, a little faster in liquids, and most quickly in solids.

Thus, 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 equal (m/s):

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

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 scientists Ptolemy and Aristotle, correct assumptions are made that sound is generated by body vibrations. Moreover, Aristotle argued that the speed of sound is a measurable and finite quantity. Of course, in Ancient Greece There were no technical capabilities for any accurate measurements, so the speed of sound was measured relatively accurately only in the seventeenth century. For this purpose, a comparison method was used between the time of detection of the flash 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 travels in the air at a speed of 350 to 400 meters per second.

The researchers also found that 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 sound travels 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 air at normal conditions(at sea level at a temperature of 0ºС) is equal to 331 meters per second.

Mach number

IN real life the speed of sound is a significant parameter in aviation, however, at those altitudes where it is usually environment very different from normal. This is why aviation uses a universal concept 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 higher the Mach number will be, even if the speed of the object itself does not change.

Practical use This number is due to the fact that movement at speeds that are higher than the speed of sound is significantly different from movement at subsonic speeds. This is mainly due to changes in the aerodynamics of the aircraft, deterioration in its controllability, heating of the body, as well as wave resistance. These effects are observed only when the Mach number exceeds one, that is, the object breaks the sound barrier. On this 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.

Today, when setting up an apartment, many new residents are forced to spend additional work, including soundproofing your home, because The standard materials used make it possible to only partially hide what is going on in your own home, and not to be interested in the communication of your neighbors against your will.

In solids, it is affected at least by the density and elasticity of the substance resisting the wave. Therefore, when equipping premises, the layer adjacent to the load-bearing wall is made soundproof with “overlaps” at the top and bottom. It allows you to reduce decibels sometimes by more than 10 times. Then basalt mats are laid, and plasterboard sheets are placed on top, which reflect the sound outward from 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, so we hear beautiful “singing” musical instruments. And some peoples in the past determined the approach of, for example, horsemen, by 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 to 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 aquatic environment is different for substances with different salinities. 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.

A salty environment is characterized by a obviously higher speed of sound vibrations.

The propagation of sound in air also depends on temperature. With a value of 20 for this parameter, 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 learn that in a material such as cork, which is often used to reduce external noise levels, 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 passing, for example, a melody piece of music through some obstacle, its volume level decreases, because changes. At the same time, the frequency remains the same, thanks to which we hear a woman’s voice as a woman’s, and a man’s as a man’s. The most interesting place is where the speed of sound in km is close to zero. This is a vacuum in which waves of this type almost do not propagate. To demonstrate how this works, physicists place a ringing alarm clock under a hood from which the air is pumped out. The thinner the air, the quieter the bell is heard.

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 the given substance, in single crystals - on the direction of wave propagation. Usually independent of wave frequency and amplitude; in cases where the speed of sound depends on frequency, we speak of sound dispersion.

Encyclopedic YouTube

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 experimental determination sound speeds 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, Roemer) determined the value of the speed of sound (depending on the experimental conditions, 350-390 m /With). Theoretically, the question of the speed of sound was first considered by Newton in his Principia. 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 (Cp)(Cv))\left((\frac (\partial p) (\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) - 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.

Sacor 23-11-2005 11:50

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

Speed ​​of sound, speed of propagation of any fixed phase sound wave; also called phase velocity, as opposed to group velocity. S. z. usually the value is constant for a given substance under given external conditions and does not depend on the frequency of the wave and its amplitude. In cases where this is not fulfilled and S. z. depends on frequency, they talk about sound dispersion.


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

Sergey13 23-11-2005 12:20

at no. 320 m/s.

TL 23-11-2005 12:43

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

StartGameN 23-11-2005 12:48

StartGameN 23-11-2005 12:49

They answered at the same time

Sacor 23-11-2005 13:00

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

Kostya 23-11-2005 13:39

IMHO, you shouldn’t worry so much about this, you’re not interested in acoustics, but in shooting.

Sacor 23-11-2005 13:42

quote: Originally posted by Kostya:
IMHO, you shouldn’t worry so much about this, you’re not interested in acoustics, but in shooting.

Yes, it’s just interesting, otherwise everything is subsonic, supersonic, but how I dug it turned out to be completely ambiguous.

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

John Jack 23-11-2005 13:43

Cartridges also have a spread in initial velocity, and it also depends on temperature.

GreenG 23-11-2005 14:15


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

However, this is off

StartGameN 23-11-2005 14:40




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

However, this is off

Hunt 23-11-2005 14:48

What’s interesting to me is that while I was vacationing in the Urals, the maximum atmospheric pressure (for a month as a whole) never rose to the local parameters. At the moment there are 765 t-32. And what’s interesting is that the temperature is lower and the pressure is lower. Well... as far as I noted for myself, ... I don’t conduct constant observations. I also have a point. The tables were last year's for pressure 775 mm Hg. Maybe the lack of oxygen in our area is partially compensated by increased atmospheric pressure. I asked a question at my department, it turns out there is NO DATA! And these are the people who create decompression tables for people like me! And for military personnel, jogging (for physical exercise) is prohibited in our Palestines, because... lack of oxygen. I think if there is a lack of oxygen, it means that what is replaced is...nitrogen, that is, the density is different. And if you look at all this and count, you have to be a galactic class shooter. I decided for myself (while the Senor was poring over the calculator, and the customs office was working on my parcels): For 700, no, no, why bother firing cartridges.
So I wrote and thought. After all, he spat and swore more than once, well, what the hell with all this. Why go to the championship? Compete with whom?
...You read the forum and start talking again. Where to get bullets, matrices, etc.
CONCLUSION: A terrible dependence on communication with similar people who love weapons - homo... (I suggest finding a continuation of the expression)

GreenG 23-11-2005 16:02

quote: Originally posted by StartGameN:


I can develop it off - my diploma was called "Nonlinear acoustoelectromagnetic interactions in crystals with quadratic electrostriction"

StartGameN 23-11-2005 16:24

I’m not a theoretical physicist here, so there were no “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 stand here on the edge and listen? I won't interfere, honestly. Regards, Alexey

Antti 23-11-2005 16:39

quote: Originally posted by GreenG:


The main experimental method was apparently to hit the crystal with a magnet?

A square magnet on a curved crystal.

Sacor 23-11-2005 19:03

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

SVIREPPEY 23-11-2005 19:27

I'll tell you all this.
Ammunition is close to the speed of sound.22lr. We put a moder on the barrel (to remove the background sound) and fire at a hundred, for example. And then all the cartridges can be easily divided into subsonic (you can hear how it flies into the target - a slight “fart” occurs) and supersonic - when it hits the target it bangs so much that the whole idea with the mod goes down the drain. From subsonic I can mention tempo, biathlon, from imported ones - RWS Target (well, I don’t know many of them, and the choice in stores is not that good). From supersonic ones - for example, Lapua Standard, cheap, interesting, but very noisy cartridges. Then we take the initial speeds from the manufacturer’s website - and here is the approximate range where the speed of sound is at a given shooting temperature.

StartGameN 23-11-2005 19:56


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

In winter they wear hats and therefore their hearing becomes dull

STASIL0V 23-11-2005 20:25

But seriously: for what purpose is it necessary to know the real speed of sound for specific conditions (from a practical point of view)? the goal usually determines the means and methods/accuracy of measurement. For me, it seems like you don’t need to know this speed to hit a target or while hunting (unless, of course, without a muffler)...

Parshev 23-11-2005 20:38

In fact, the speed of sound is to some extent the limit for the stabilized flight of a bullet. If you look at an accelerating body, then up to the sound barrier the air resistance increases, just before the barrier quite sharply, and then, after passing the barrier, it drops sharply (that’s why aviators were so eager to achieve supersonic speed). When braking, the picture is built in 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 ambiguous.

The most interesting conclusion in the whole argument.

q123q 23-11-2005 20:44

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

For air k = 1.4 is the adiabatic index
R = 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=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 no more questions will arise.

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

Sacor 24-11-2005 10:32

Exhaustively, but doesn’t the speed of sound depend on density and pressure?

BIT 24-11-2005 12:41

[B] If you look at an accelerating body, then up to the sound barrier, air resistance increases, just before the barrier quite sharply, and then, after passing the barrier, it drops sharply (that’s why aviators were so eager to achieve supersonic speed).

I’ve already pretty much forgotten physics, but as far as I remember, air resistance increases with increasing speed, both before and after “sound”. Only at subsonic levels the main contribution is made by overcoming the force of friction with the air, and at supersonic levels this component sharply decreases, but the energy loss to create a shock wave increases. A. in general, energy losses are increasing, and the further, the more progressive.


Blackspring 24-11-2005 13:52

I agree with q123q. As we were taught, the norm at 0 Celsius is 330 m/s, plus 1 degree - plus 1 m/s, minus 1 degree - minus 1 m/s. Quite a working scheme for practical use.
Probably, the norm may vary depending on the pressure, but the change will still be approximately a degree-meter per second.
B.S.

StartGameN 24-11-2005 13:55

quote: Originally posted by Sacor:


It depends. But: there is Boyle’s law, according to which at a constant temperature p/p1=const, i.e. the change in density is directly proportional to the change in pressure

Parshev 24-11-2005 14:13


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

But I never knew.

It grows both before and after sound, and in different ways at different speeds, but falls at 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, so objects of different shapes cross the barrier in different ways. Before the sound, drop-shaped objects fly better, after the sound - with a sharp nose.


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 crossing the sound barrier, the TOTAL resistance force increases, and abruptly, due to a sharp increase in energy consumption for the formation of a shock wave. The contribution of the FRICTION FORCE (or rather, the resistance force due to turbulence behind the body) decreases sharply 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 drop-shaped body, streamlined at subsonic levels, creates a very powerful shock wave at supersonic temperatures, and experiences a much greater TOTAL drag force, compared to a pointed one but with a “blunted” rear part (which is practically irrelevant at supersonic temperatures). During the reverse transition, the rear non-streamlined part creates greater turbulence and a subsequent drag force compared to the teardrop-shaped body. In general, an entire section of general physics—hydrodynamics—is devoted to these processes, and it’s easier to read a textbook. And the scheme you outlined, as far as I can judge, does not correspond to reality.

Sincerely. BIT

GreenG 24-11-2005 15:38

quote: Originally posted by Parshev:


Before the sound, drop-shaped objects fly better, after the sound - with a sharp nose.

Hurray!
All that remains is to come up with a bullet that can fly nose forward at super sound and ass after crossing the barrier.

In the evening I’ll grab some cognac for my bright head!

Machete 24-11-2005 15:43

Inspired by the discussion (off).

Gentlemen, have you drunk cockroaches?

BIT 24-11-2005 15:56

Recipe, please.

Antti 24-11-2005 16:47




In general, an entire 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. Of course, there are different processes in water and in air, although there are some things in common.

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

In any case, there is a sharp change in the flow pattern at the barrier, disturbing the movement of the bullet - this is why it can 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 sound, additional unpredictable “disturbances” arise, leading to destabilization of the bullet and an increase in dispersion. Therefore, to achieve sporting goals, a supersonic small cartridge should under no circumstances be used (and even when hunting, the maximum possible accuracy will not hurt). What then is the advantage of supersonic cartridges? More (slightly) energy and therefore lethal force? And this comes at the expense of accuracy and more noise. Is it worth using supersonic 22lr at all?

gyrud 24-11-2005 21:42

quote: Originally posted by Hunt:
And for military personnel, jogging (for physical exercise) is prohibited in our Palestines, because... lack of oxygen. I think if there is a lack of oxygen, it means that it is replaced with...nitrogen,

It is impossible to talk about any replacement of oxygen with nitrogen because there is simply no replacement for it. Percentage composition atmospheric air the same at any pressure. Another thing is that at low pressure in the same liter of inhaled air there is actually less oxygen than at normal pressure, so oxygen deficiency develops. That is why pilots at altitudes above 3000m breathe through masks with an air mixture enriched up to 40% oxygen.


q123q 24-11-2005 22:04

quote: Originally posted by Sacor:
Exhaustively, but doesn’t the speed of sound depend on density and pressure?

Only through temperature.

Pressure and density, or rather their ratio, are strictly related to temperature
pressure/density = R*T
what R, T are, see 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

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?
However, I suspect that in air and water the picture may be somewhat different due to compressibility/incompressibility. Or not?

At our university there was a combined course in hydro- and aerodynamics, as well as a department of hydrodynamics. That's why I called this section abbreviated. You are of course right, processes in liquids and gases can proceed differently, although there is a lot in common.


BIT 25-11-2005 09:59


What then is the advantage of supersonic cartridges? More (slightly) energy and therefore lethal force? And this comes at the expense of accuracy and more noise. Is it worth using supersonic 22lr at all?

StartGameN 25-11-2005 12:44

The “accuracy” of a small cartridge is explained by the extremely low heating of the barrel and the unsheathed lead bullet, and not by the speed of its departure.

BIT 25-11-2005 15:05

I understand about heating. What about shelllessness? Greater manufacturing precision?

STASIL0V 25-11-2005 20:48

quote: Originally posted by BIT:


IMHO - ballistics, you mean trajectory. Less flight time means less external disturbances. In general, the question arises: Since the transition to subsonic air resistance sharply decreases, should the tipping moment also sharply decrease, and consequently the stability of the bullet increase? Is this why the small cartridge is one of the most accurate?

Machete 26-11-2005 02:31

quote: Originally posted by STASIL0V:


Opinions were divided. In your opinion, when a supersonic bullet comes out, it stabilizes when switching to subsonic. But 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 didn’t think to argue. He simply asked questions and, with his mouth open, listened.

Sacor 28-11-2005 14:45

quote: Originally posted by Machete:


In this case, Parshev is absolutely right - during the reverse transonic transition, the bullet is destabilized. That is why the maximum firing range for each specific cartridge in LongRange 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 is strongly destabilized somewhere at 20-30 m? And accuracy deteriorates significantly.

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

Initial value

Converted value

meter per second meter per hour meter per minute kilometer per hour 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 per minute yard per second mile per hour mile per minute miles per second knot knot (UK) speed of light in vacuum first cosmic speed second cosmic speed third cosmic speed speed of rotation of the Earth speed of sound in fresh water speed of sound in sea ​​water(20°C, depth 10 meters) Mach number (20°C, 1 atm) Mach number (SI standard)

American wire gauge

More about speed

General information

Speed ​​is a measure of the distance traveled in a certain time. Speed ​​can be a scalar quantity or a vector quantity - the direction of movement is taken into account. The speed of movement in a straight line is called linear, and in a circle - angular.

Speed ​​measurement

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

In the SI system, speed is measured in meters per second. Kilometers per hour are also widely used in metric system and miles per hour in the US and UK. When, in addition to the magnitude, the direction is also 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 ∆ t, has a finite speed v = u + a×∆ t.
• A body moving with constant acceleration a, with initial speed u and final speed v, has an average speed ∆ v = (u + v)/2.

Average speeds

Speed ​​of light and sound

According to the theory of relativity, the speed of light in a vacuum is the highest speed at which energy and information can travel. It is denoted by the constant c and is equal to c= 299,792,458 meters per second. Matter cannot move at the speed of light because it would 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 lowest in gases and 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 using 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 airplane speeds. This value is not constant; it depends on the state of the medium, which, in turn, depends on pressure and temperature. Supersonic speed is a speed exceeding Mach 1.

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 = 0.83–0.87.
• High-speed trains (like the Shinkansen in Japan): such trains reach maximum speeds of 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 to:



Human speed

• People walk at speeds 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 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 measurement of speed also takes into account the fourth dimension - space-time. This speed is called four-dimensional speed. Its direction may change, but its magnitude is constant and equal to c, that is, the speed of light. Four-dimensional speed is defined as

U = ∂x/∂τ,

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

Group speed

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

Hypersonic speed

Hypersonic speed is a speed exceeding 3000 meters per second, that is, many times faster than the speed of sound. Solid bodies moving at such speeds acquire the properties of liquids, since, thanks to inertia, the loads in this state are stronger than the forces that hold the molecules of a substance together during collisions with other bodies. At ultrahigh hypersonic speeds, two colliding solids turn into gas. In space, bodies move at exactly this 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 space. outer space. In such a collision, the skin of the spacecraft and the spacesuit suffer. Hardware developers are conducting hypersonic impact experiments in special laboratories to determine how severe impacts the suits, skins and other parts can withstand. spaceship, such as fuel tanks and solar panels, testing their durability. To do this, spacesuits and skin are exposed to impacts from various objects from a special installation at supersonic speeds exceeding 7500 meters per second.