1 km =1000m
1 m = 10 decimeter = 100 cm = 1000 mm = 10000000 micron = 1000000 nanometer.
That is, the conversion unit between adjacent meters, decimeters, centimeters and millimeters is 10, and the conversion unit between adjacent millimeters, micrometers and nanometers is 1000.
Rmb includes: propulsion rate: rewriting unit.
Money comes first, quantity comes last.
1 There are three kinds of banknotes below 0 yuan:1Yuan 2 yuan 5 yuan.
1 yuan * 10 sheets
2 *5
5 *2
1*8+2* 1 The multiplication sign is preceded by the face value of the money and followed by the quantity.
1*6+2*2
1*5+5* 1
1*4+2*3
1*3+5* 1+2* 1
1*2+2*4
1* 1+5* 1+2*2
Definition of 24-hour timing method
Ancient astronomers and physicists used sundials, sundials, water clocks and simple pendulums to time by observing the changes of the sun's shadow or water level. With the progress of science and technology, modern scientists have invented simple pendulum clock and synchronous oscillator, which use the oscillation period of simple pendulum or synchronous crystal to time. However, the above-mentioned time service method is easily influenced by environment, temperature, materials, electromagnetic field and even the observation angle of observers, and its stability is not good, so it must be corrected by the period of celestial bodies (earth rotation, revolution and moon revolution).
Before 1960, CIPM was based on the earth's rotation, and its definition was based on one-eighth of the average solar day. That is, 1 sec = 1/86400, and its stability is about 10-8.
From 1960 to 1967, CIPM was changed to be based on the revolution of the earth, and 1900 was defined as the average solar year. The definition of second is amended as: one second is 3 15525.947 of the average solar year. 1 sec = 1/3 1556925.9747 The stability of solar year in 1900 is about 10-9.
In the mid-20th century, due to the development of quantum mechanics, experiments and researches such as ultra-fine structure of spectrum, magnesium emission and laser, optical pumping, magnetic vibration of molecular beam, and separation of oscillation field were developed, which made quantum frequency standard replace celestial bodies. In 1967, CIPM defines one second as the duration of 9 192, 63 1 770 radiation periods, which corresponds to the transition between two ultra-fine energy levels in the ground state of cesium 133 atom (Cs 133). This second definition has been maintained to this day.
The definition of second can be realized by cesium atomic frequency standard, and its stability varies with the manufacturing method and maintenance environment of each standard. The stability of commercial cesium frequency standard HP-507 1 is about 10- 12. The stability of the atomic clock with absolute temperature scale of 10-6 degrees made by cesium atomic fountain in LPTF laboratory of France is about 10- 16.
The earth's rotation is not 24 hours, 24 hours is the result of the earth's rotation and revolution!
The earth turns once a day.
The time for the earth to rotate once (360 degrees) is 23 hours, 56 minutes and 04 seconds, which is a little less than what we usually say "one day and one night is 24 hours". Humans themselves can't feel the rotation of the earth, so they are used to calling sunrise and sunset a day before sunrise.
The ancient Egyptians divided the day into 24 hours. Every hour is divided into 60 minutes and every minute is divided into 60 seconds. So there are 24×60=86400 seconds in a day. These hours, minutes and seconds have become time units.
mass unit
In physics, "mass" refers to the amount of matter contained in an object. "Quality" in daily life refers to the quality of products. )
Quality unit reform
The situation of ancient mass units and length units is similar, and there are various forms. For example, Persia uses Garasa as the unit of mass, which is about 0.834kg, and Egypt uses Gade, which is about 9.33g g. According to the weights and measures system of Qin Dynasty in China, 1 stone = 4 jun, 1 jun = 30 kg, 1 kg = 16 liang. Compared with the modern international system of units, 1 kg is about 0? 256 kilograms. British units are pounds, ounces, drams and grains: 1 pound = 16 ounces = 265 drams = 7000 grains.
The British Empire made a weighing instrument out of pure platinum, which is a pure platinum cylinder with a height of about 1.35 inches and a diameter of 1. 1.5 inches.
The original unit of mass in kilograms was the length unit of meters adopted by France at the end of 18. The mass of 1 cubic decimeter of pure water at the maximum density (the temperature is about 4 degrees Celsius) is determined as 1 kg.
During the period of 1799, France made a prototype of platinum rice, and at the same time made a benchmark of platinum kilogram, which was kept in the Paris Archives.
Later, it was found that this benchmark is not completely equal to the mass of pure water with the maximum density of 1 cubic decimeter, but equal to 1? 000028 cubic decimeter. Therefore, after the Metric Congress of 1875, the alloy containing 90% platinum and 10% iridium was also used as the original kilogram, and one * * * was made into three. Compared with the original kilogram of platinum preserved by the Paris Archives Bureau, one of them was selected as the international original kilogram. The original international kilogram device was carefully kept in a special place by experts from the International Bureau of Metrology. It was covered with three layers of glass, and the outermost glass was pumped into a semi-vacuum to prevent air and impurities from entering. Subsequently, 40 platinum-iridium alloy cylinders were copied, compared with the original international kilogram device, and distributed to member States as national benchmarks. Like the rice prototype, the kilogram prototype also needs to be verified regularly to ensure the stability and reliability of the quality benchmark. 1 kg = 2kg = 2.205bp 1 kg = 0.5kg (kg) = 1.102bp1lb = 0.454kg (kg) = 0.907kg.