| 单词 | second |
| 释义 | second 1. One sixtieth (1⁄60) of a minute. 2. In the International Systems of Units (SI), the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom.This is the base unit of time for atomic clocks, which are the basis for the UTC time scale and the calibration of other clocks, frequency counters, and frequency standards.This refers to a cesium atom at rest, at sea level, at a temperature of 0 K (0 Kelvin, or absolute zero). This measurement is highly stable, unlike the natural frequency standards such as the rotation of the Earth on its axis, the rotation of the Earth around the sun, and electrical and mechanical vibrations such as pen-dulums, tuning forks, and vibrations of quartz crystals. See also SI and UTC. |
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