"Zou Jixiu has more than eight feet, and its shape is beautiful..." Wait, how high is eight feet? Xiaoming hurriedly checked the information, 3 feet equals 1 meter, eight feet is... 2.67 meters. It's also too "beautiful".
▲ How tall is eight feet?
In ancient times, the length units of many countries and regions were different. And for the convenience of measurement, it is often used as a part of the human body as a unit of length, such as:
Pharaoh of Ancient Egypt: It's easy to say, from my elbow to the tip of my middle finger is a wrist ruler, follow this to build a pyramid!
▲ Wrist ruler
Roman Charlemagne: Don't argue, my feet are a foot! (So how many feet are your height?) ）
▲ Feet
There are also units of length based on some common objects, such as:
King Edward II: Choose three of the largest grains from the ears of barley and line them head-to-head for an inch!
▲ Barley looks very similar to wheat
And so on, too many to count. This method of stipulating units of length is not uniform, each uses its own, and there are obstacles to communication.
▲The units are not unified, and there are problems with communication
The second is that it is inaccurate (the emperor is old, in case of osteoporosis or something...). ）。
So we need an object whose length does not change as a reference to specify the length unit. What's not to change in length? People slap their thighs: with the earth!
▲ The original definition of rice is related to the earth
In May 1790, a special committee of French scientists proposed that the distance from the Earth's equator to the North Pole through the meridian of Paris be used as a unit of length, the meter, which was approved by the French Parliament in 1791.
Didn't understand? The Earth is simply understood as a flat shaped circle, and a quarter of the circumference of the circle is the distance from the equator to the North Pole.
▲ Geographical knowledge, longitude and latitude lines, remember?
You must be curious, how did people measure this distance at that time? Space limitations, can not be elaborated. However, it is said that eratosenes in ancient Greece used astronomical, geographical, and mathematical knowledge to indirectly measure the circumference of the earth. Well, two thousand years ago, it was still very precise.
▲ One of the great masters of ancient Greece: Eratosenes
Far from it.
Subsequently, in 1799, according to the measurement results, a platinum rod with a rectangular section of 3.5 mm × 25 mm was made, and the distance between the two ends of the rod was set at 1 meter, and handed over to the French Archives Bureau for safekeeping, so it was also called "archival rice".
▲ Archive rice
On May 20, 1875, the French government came forward to convene a meeting of representatives of 20 national governments, and formally signed the Rice System Convention, which is recognized as an internationally accepted unit of measurement. At the same time, it was decided to establish the International Committee of Weights and Measures and the International Bureau of Weights and Measures.
At this point, our units of length are finally unified and very precise!
As for the later archives of the rice deformation was serious, people
Rice prototype was also manufactured from the archives (1872)
The preservation conditions of the rice prototype are specified in both (the First International Congress of Weights and Measures in 1889 and the Seventh Congress of Weights and Measures in 1927).
He completely abandoned the prototype meter and used the wavelength of light as the natural standard for length units (the Eleventh International Congress of Metrology, 1960).
Changed to "meter is 1/299 792 458 second interval of time interval for the length of travel of light in a vacuum" (17th International Congress of Metrology, 1983).
It's all an afterthought, and it's all about the constant pursuit of precision.
After meter (abbreviated as m) was determined, a group of brothers came over to support him. Let's get to know each other from the big to the small.
The eldest brother of the meter, kilometer (abbreviated km). Kilo means 103, 1km=1000m=103m. Kilometers have a nickname called "Kilometer", which is often posted on roadside signs.
▲ Traffic signs indicating distance
Mi's third brother, decimeter (abbreviated dm). Deci means one-tenth, 1dm = 10-1m. The presence of decimeters is relatively low, and 1 decimeter is about the width of a fist.
▲ The width of the fist is about 1dm
The fourth brother of the meter, centimeter (cm), abbreviated cm. centi means one percent, 1cm = 10-2m. Centimeters have a nickname called "centimeter", and the sense of existence is bursting, appearing on various scales.
▲Many scales are marked with cm
The fifth brother of the millimeter, millimeter (abbreviated as mm). Milli stands for one thousandth, 1mm = 10-3m. The various bullet calibers you know, such as 7.62, 5.56, etc., are in millimeters.
▲ 7.62mm bullet compared to 5.56mm bullet
The sixth brother of the meter, micrometer (abbreviated as μm). The English alphabet is not enough, borrowed the Greek letter μ (pronounced miu), indicating 10-6, 1 μm = 10-6 m. The famous PM2.5 refers to particulate matter with a diameter of less than or equal to 2.5 microns.
The seventh brother of the meter, nanometer (abbreviated nm). nano means 10-9, 1nm = 10-9m. As long as it is encountered, it is high-tech. The lithography machine that manufactures chips has reached the accuracy of 14nm in China and 5nm in foreign countries (we have to work hard, I believe it will surpass them).
▲Dutch ASML lithography machine
Length Seven Brothers has been gathered and can summon... Gourd up.
▲Memories of Teacher Daming's childhood
Just like different game levels, it's easier to beat with different characters, and we'll often encounter switching between these seven brothers. When converting units, it should be noted that both values and units participate in the operation. Don't write more or no units!
▲Unit conversion (daming teacher's height)
Summary of knowledge points
Conclusion: In the era of Zou Ji (Warring States period), 1 foot is 22~23cm, eight feet is more than eight feet, one meter and eight large, in that era, absolutely big!
Reference answer: Example question 1:B. Example 2: m;dm;cm;mm.