"Higher, faster, stronger", this is one of the slogans of the Olympic movement. Human beings have always been exploring the limits of things. As the research deepens, we find that the world is always restricted by various physical rules, and various natural limits restrict our behavior. Perhaps the only thing that is free is our thoughts. Today we will talk about those important limits in nature and explore their impact on the movement and changes of everything. Let us first understand, what is speed?

Speed ??is a physical quantity that describes how fast an object moves. In physics, velocity is a vector (ignoring the actual meaning, which is a vector in mathematics), that is, it not only has numerical magnitude, but also has directionality. If speed only has magnitude but no direction, it is also called velocity in physics. In daily life, there is no such strict distinction between speed and speed. Regardless of whether there is direction or not, they are usually called speed.

The numerical value of speed v is the distance (s) traveled by the object in unit time (t), that is, v=s/t. The distance is the length of the movement trajectory of the object. It is a scalar quantity with only numerical magnitude but no direction. Common units of speed are kilometers per hour (km/h) and meters per second (m/s). In actual use, speed is sometimes divided into average speed and instantaneous speed. The difference between the two will not be explained. Just look at the name. The upper and lower limits of speed

In martial arts in the world, only fast ones cannot be broken. This is absolutely a wise saying. However, there are upper and lower limits to the speed of objects in nature, and they cannot accelerate without limit.

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 precise value is 299,792,458 meters per second. The speed of light is the fastest speed in the universe. The moving speed of any object in the universe with non-zero rest mass cannot reach or exceed the speed of light. The rest mass of a photon is 0. The speed of light has been this fast since its birth, and there is no acceleration process. However, the speed of an object moving in a medium can exceed the speed of light in the medium. When this super-light phenomenon occurs, Cherenkov radiation will be produced.

(Cherenkov radiation of blue glow, particles faster than the "speed of light")

The lower limit of speed is of course 0, which is absolute rest. The world is material, and matter is in motion. There are no absolutely static objects in nature. Therefore, the lower limit of speed is of course also unreachable. Movement is absolute, the description of movement is relative, and stillness is also relative. Humanity's pursuit of ultimate speed

Speed ??is very important to human survival and development. The ultimate speed that humans can achieve can, to a large extent, represent the level of human technological development.

When humans only relied on two legs to move, the average step length for adults was 50 centimeters, and the normal speed was about 1.5 meters. A person could walk more than 5 kilometers per hour.

The running speed of ordinary people is generally 3 to 5 times the normal walking speed, about 15 to 25 kilometers per hour. After physical strengthening training, running speed can be improved a lot. Bolt's fastest speed can reach 45 kilometers per hour. Cheetahs are the fastest animals on earth, reaching speeds of 120 kilometers per hour.

Since then, horseback riding has become the fastest way for humans to travel on land. In the cold weapon era, the Mongolian Empire relied on cavalry to flatten the Eurasian continent.

In modern times, with the increase in transportation means, human travel methods have become diversified, and the world suddenly feels smaller. The widespread use of internal combustion engines is the main driver. The invention of the airplane brought mankind from land to the sky, and then entered the age of flight. Modern cars can reach speeds of 100~120km/h when driving at high speeds. Humans have finally surpassed the champion cheetah in speed.

With the rapid development of aviation technology, human beings have doubled in speed. Due to the influence of sonic booms, there are no animals in nature that can fly faster than the speed of sound (at a low altitude of 15 degrees Celsius, the speed of sound in the air is about 340 meters per second). After long-term efforts, humans finally broke through the sound barrier. Now the fastest jetliner in the world can fly at a maximum speed of 800~1000km/h, which is close to Mach 1 (Mach 1 is approximately equal to 1200km/h).

In the field of aerospace, the successful launch of geosynchronous orbit satellites has meant that humans have reached the first cosmic speed, which is 7.9 kilometers per second. Since then, with the help of the planet's gravity, the speed of the Voyager 1 probe has successfully reached the third cosmic speed, which is 16.7 kilometers per second. Under the influence of the sun's gravity, the nearest Parker Solar Probe can reach a maximum speed of more than 100 kilometers per second at perihelion.

(Three major cosmic speeds)

(Parker Solar Probe) Summary

The speed of the fastest detector currently launched by mankind is less than the speed of light One ten thousandth of the speed, and this fastest speed also contains a lot of water, so it needs to rely on other celestial bodies for acceleration. Humanity's pursuit of extreme speed will not stop here. With the development of new propulsion technology, it should be able to reach one thousandth of the speed of light by the end of this century.

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