Let's take a look first. What is speed?
Speed is a physical quantity that describes the speed of an object. Physically, speed is a vector (ignoring the practical meaning, that is, a mathematical vector), that is, it not only has numerical magnitude, but also has directionality. If speed has only magnitude and no direction, it is also called speed in physics. In daily life, there is not such a strict distinction between speed and speed. There is no direction, usually called speed.
The value of velocity v is the distance (s) that an object moves in unit time (t), that is, v = s/t, and the distance is the length of the object's trajectory, which is a scalar, with only a value and no direction. Common speed units are kilometers per hour (km/h) and meters per second (m/s). Speed is sometimes divided into average speed and instantaneous speed in the actual use process. We don't explain the difference between them, just look at the name.
Upper and lower limits of speed
The martial arts in the world are fast and unbreakable. This is absolutely wisdom. However, the speed of objects in nature has upper and lower limits, and it cannot be accelerated indefinitely.
The upper limit of speed is the speed of light (unless otherwise specified, the speed of light refers to the speed of light in a vacuum). The propagation speed of light in vacuum is about 300,000 kilometers per second, and the accurate value is 299,792,458 meters per second. The speed of light is the fastest in the universe. The speed of any object in the universe with non-zero rest mass cannot reach or exceed the speed of light. The rest mass of photons is zero, and the speed of light has been so fast since its birth, and there is no acceleration process. However, the moving speed of an object in a medium can exceed the speed of light. When this superluminal phenomenon occurs, Cherenkov radiation will be produced.
The blue glow radiated by Cherenkov, the particle speed exceeds the "light speed")
The lower limit of speed is of course 0, that is, absolute rest. The world is material, matter is moving, and there is no absolutely static object in nature. So the lower speed limit is of course unattainable. Motion is absolute, the description of motion is relative, and stillness is relative.
Man's Pursuit of Extreme Speed
Speed is very important for the survival and development of human beings, and the ultimate speed that human beings can achieve can represent the level of human scientific and technological development to a great extent.
When humans only walked on two legs, the average stride of adults was 50 cm, and the normal speed was about 1.5 m. A person can walk more than 5 kilometers per hour.
The average person's running speed is generally 3~5 times of the normal walking speed, about 15~25 kilometers per hour. After intensive physical training, the running speed can be improved a lot. The fastest instantaneous speed of the world's flying man Bolt can reach 45 kilometers per hour. Cheetah is the fastest animal on the earth, with an hourly speed of120km.
Since then, horseback riding has become the fastest way for human beings to travel on land. In the era of cold weapons, the Mongolian empire leveled Eurasia by cavalry.
In modern times, with the increase of transportation, the way of human travel has become diversified, and suddenly the world has become smaller. The widespread use of internal combustion engines is the main driving factor. The invention of the airplane made human beings enter the sky from land, and entered the era of flying. The speed of modern cars at high speed can reach 100~ 120km/h, and human beings finally surpass the running champion cheetah in speed.
With the rapid development of aviation technology, the speed of human beings has doubled. Due to the influence of sonic boom, there are no animals flying faster than the speed of sound in nature (at the low altitude of 15 degrees Celsius, the speed of sound in the air is about 340 meters per second). After long-term efforts, mankind finally broke through the sound barrier. At present, the fastest jet airliner in the world, the fastest speed can reach 800~ 1000km/h, close to 1 mach (1 mach is about 1200km/h).
In the aerospace field, the successful launch of geosynchronous orbit satellites has meant that human beings have reached the first cosmic speed, that is, 7.9 kilometers per second. After that, with the help of planetary gravity, the speed of Voyager 1 successfully reached third cosmic velocity, that is, 16.7 kilometers per second. Under the action of solar gravity, the nearest Parker solar probe can reach 100 km per second at perihelion.
(three cosmic speeds)
(Parker Solar Detector)
abstract
At present, the fastest detector launched by human beings is less than one tenth of the speed of light, and this fastest speed has a lot of water and needs to be accelerated by other celestial bodies. Man's pursuit of extreme speed will not stop there. With the development of new propulsion technology, it should reach one thousandth of the speed of light by the end of this century.
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