Second
From Engineering
The second (symbol: s) is the SI base unit of time. It is often abbreviated sec. in non-SI usage.
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[edit] Definition
The second is the duration of 9 192 631 770 [[Period (physics) [[1]] of the radiation corresponding to the transition between the two Hyperfine structure [[2]] of the ground state [[3]] of the caesium-133 [[4]] atom [[5]].
[edit] Origin
Originally, the second was known as a "second minute", meaning the second minute (i.e. small) division of an hour. The first division was known as a "prime minute" and is equivalent to the minute we know today.
[edit] Conversions
- 60 seconds = 1 minute [[6]]
- 3 600 seconds = 1 hour [[7]]
- 86.4 kiloseconds (86 400 seconds) = 1 day [[8]] (in the SI sense)
[edit] Explanation
See also explanation at [[9]]
The definition of the second was later refined at the 1997 meeting of the Bureau International des Poids et Mesures [[10]] to include the statement
- This definition refers to a caesium atom at rest at a temperature of 0 K.
[edit] See also
[edit] External links
- Official BIPM definition of the second
- Public domain article about definition of seconds and leap seconds
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