In ancient times, humans basically walked on their legs, and if the distance was far, it could take many months or even a year.
In order to speed up the speed of walking, while liberating the feet, after all, long-term walking will make people tired, the feet will be worn out, therefore, the mount came into being, humans began to tame horses, cattle and other animals that can be driven to make long distances.
Later, people even invented carriages, ox carts and other tools that also need to rely on mounts, but animals also need to rest, but also need to eat and drink, the speed is also limited, if you need to go to distant places, it often takes ten days and a half months.
In modern times, with the development of the Industrial Revolution, the early carriages were no longer suitable for the development of Western cities, so the cable cars began to appear. The earliest cable car actually appeared in 1830, it was more as a function of transporting minecarts in mines, until 1873 was used in the city, reaching a speed of 10 to 20 kilometers per hour.
It is different from the modern electric sightseeing cable car, which has two rail-like running tracks under the modern cable car, relying on steam to provide power, forming cables that can move back and forth, and can stop and let tourists get off.
However, once the cable car fails, it will cause the entire line to be stopped for maintenance, which will delay for several hours, not only delaying the travel of guests, but also causing financial losses.
In order to travel conveniently, later people invented trains, cars, airplanes, etc. have been applied by humans to the current means of transportation, these great discoveries have facilitated people's daily lives, but also brought great benefits to many people.
And now, as the means of transport are developed faster and faster, some tools in a short period of time the distance of movement is very far, the general speed units such as meters / second or kilometers / h have gradually no longer applicable, therefore, scientists have added the speed unit of light, the speed of sound, etc. as a reference speed unit, Mach is the speed of sound-related units.
Perhaps many people have heard the word Mach, but they don't quite understand what it is. This is actually a unit of physics, but also the name of a physicist, just as in honor of Kelvin, Newton, Ampere, and other scientists, this unit of physics is also named after the first discoverer, Mach, to tell future generations who its "creator" really is.
Mach is actually the ratio of speed to the speed of sound, which is physically the speed at which sound propagates through the medium, and essentially, it is the propagation speed of a weak pressure disturbance in a certain medium under constant conditions.
Mach number 1 means 1 times the speed of sound, and because the speed of sound waves propagating in different media is different, often the greater the density of the medium, the faster the speed, therefore, Mach is not fixed, but will vary with different media.
Mach numbers are usually used in aircraft, rockets and other aircraft, because their speed is often very fast, can fly a long distance in a short period of time, ordinary speed units can no longer meet the measurement calculation, and the speed of light is too fast. At present, the speed of human aircraft is far from the speed of light, so it chooses to use the speed of sound to calculate.
If you want to get the Mach number velocity unit of the aircraft, you first need to take the altitude involved in the aircraft and the atmospheric environment it faces as a prerequisite, otherwise it is impossible to get the correct value.
Generally speaking, the Mach number in the high altitude is higher, because the stratospheric air at high altitude is relatively thin, the resistance of the air is also small, there is no change in the clouds, etc., and the visibility is higher. For example, above 10,000 meters, the speed of sound is about 1,062 kilometers per hour, while at sea level of 0 °C, the speed of sound here is about 1,193 kilometers per hour.
In general, if other factors are not taken into account, in an environment of 1 standard atmospheric pressure and 15 ° C, the speed of sound waves is 340 m / s, then Mach number 1 is 340 m / s, but it is only a relative value.
If the Mach number is less than 1, it means that the speed of the aircraft is less than the speed of sound, that is, subsonic, if the Mach number is greater than 1, the aircraft is faster than the speed of sound, that is, supersonic, when greater than or equal to 5, it means that the aircraft is at a supersonic speed.
At a rate of Mach 1 equals 340 meters per second, if Mach 15 is flown for an hour, that is, the speed of 340 multiplied by 15 gives 5100 meters per second, that is, it can fly 18,360 kilometers an hour.
In practice, on October 14, 1947, the United States first completed the flight of a supersonic test aircraft, which opened the door to related speed aircraft. When the aircraft is at supersonic speeds, the head squeezes and drains the air in front of it, creating a shock wave.
At the same time, the sound density waves emitted by the aircraft will also come to the tail because they cannot exceed the speed of the aircraft, forming a conical sound cone with the discharged air, thus forming a huge sonic boom.
People's aircraft speed is getting faster and faster, there are many aircraft have reached the speed of Mach 3, at this time the aircraft in addition to the sound explosion, but also because the speed is too fast, so that the fuselage of the aircraft and the air strong friction, the formation of ultra-high temperature air flow, so that the temperature of the aircraft rises, this situation is often referred to as "thermal barrier".
In general, the surface temperature of a mach speed aircraft can reach 350 ° C, which is stronger than the maximum temperature that can be tolerated by aluminum alloys widely used in aircraft, and only titanium alloys can be used.
When Mach reaches 6, because the speed is too high and the pressure is too small, if the pilot on the aircraft does not use a special pressure suit, it is likely to lead to black vision and even the danger of death.
On October 3, 1967, the U.S. X-15 supersonic aircraft reached a speed of Mach 6.72, or 7275 kilometers per hour. The United States has made relevant preparations long before the flight, and it is also equipped with a large number of thermal insulation materials.
However, after the flight, people found that many parts of the aircraft had melting problems, as if they had been burned by fire, and even the tail wing had even broken two holes. It is also for this reason that later manned aerial vehicles in the world used speeds of Mach 2 to 3.
"The world's martial arts are only fast and not broken", people have also been pursuing faster flying machines, but because of the current scientific limitations, human beings can not develop too fast flying machines. Only when human technology is more advanced can we create supersonic, even sub-light, light-speed vehicles, and this day may not be far away.