This math book is 26 meters long. The lamp is 50 cm long. This room is 3 cm high. This word is 6 meters thick. This big tree is 8 meters high. Classroom length10cm.
What is length:
Length is a measure of one-dimensional space and the distance from point to point. Usually, when measuring the side length of a straight line in two-dimensional space, the one with a larger length value is called long, which is neither greater than its value nor wider than the one on the "side". So width is actually a measure of length, so the height of "vertical length" is measured in three-dimensional space. * * * There are kilometers, kilometers, kilometers, meters, inches, centimeters and millimeters.
At the international metrology conference held in 1967, one second is no longer just the swing of a pendulum or the rotation of the second hand of a quartz clock, but the natural microwave oscillation frequency of cesium atoms is 9 19263 1770 times.
Congress defined one second as the number of these oscillations of cesium atoms, and this standard has been used to this day. "It is more accurate because the movement inside the atom is less affected by the outside world, and a vibrating atomic system will not change its vibration frequency because of the change of external conditions."
Academician Wang Yuzhu of Shanghai Institute of Optics and Mechanics, China Academy of Sciences said that the invention of the first cesium atomic clock shortened the clock difference from one thousandth of a second per day for self-oscillating clocks and one thousandth of a second per day for quartz clocks to less than one second in 300,000 years.
What scientists need to do is to accurately record these oscillations through electronic system. When it reaches 9 19263 1770, it will be known that there is one second. In fact, one second is also divided into 9 19263 1770 intervals, and the corresponding accuracy of one second is the ninth place after the decimal point.
Length measurement:
The measurement of length is the most basic measurement, and the most commonly used tool is the scale. The international unit of length refers to the dimension length of space, and the unit is meter (m). Commonly used units are kilometer (km), decimeter (dm), centimeter (cm), millimeter (mm), micron (micron) and nanometer (nm).
Decimal system between adjacent units: 1km, 1000m, 10m, 10dm, 10cm, 10mm, 1000mm. When converting length units, small units are converted into large units by multiplication and large units are converted into small units by division.