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A shake is an informal metric unit of
A shake is an informal metric unit of time
Time is the continuous progression of existence that occurs in an apparently irreversible process, irreversible succession from the past, through the present, and into the future. It is a component quantity of various measurements used to sequ ...
equal to 10 nanosecond
A nanosecond (ns) is a unit of time in the International System of Units (SI) equal to one billionth of a second, that is, of a second, or seconds.
The term combines the SI prefix ''nano-'' indicating a 1 billionth submultiple of an SI unit (e ...
s, or 10−8 second
The second (symbol: s) is a unit of time derived from the division of the day first into 24 hours, then to 60 minutes, and finally to 60 seconds each (24 × 60 × 60 = 86400). The current and formal definition in the International System of U ...
s. It was originally coined for use in nuclear physics
Nuclear physics is the field of physics that studies atomic nuclei and their constituents and interactions, in addition to the study of other forms of nuclear matter.
Nuclear physics should not be confused with atomic physics, which studies th ...
, helping to conveniently express the timing of various events in a nuclear reaction.
Etymology
Like many informal units having to do with nuclear physics, it arose fromtop secret
Classified information is confidential material that a government deems to be sensitive information which must be protected from unauthorized disclosure that requires special handling and dissemination controls. Access is restricted by law or ...
operations of the Manhattan Project
The Manhattan Project was a research and development program undertaken during World War II to produce the first nuclear weapons. It was led by the United States in collaboration with the United Kingdom and Canada.
From 1942 to 1946, the ...
during World War II
World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...
. The word "shake" was taken from the idiomatic expression
An idiom is a phrase or expression that largely or exclusively carries a figurative or non-literal meaning, rather than making any literal sense. Categorized as formulaic language, an idiomatic expression's meaning is different from the lite ...
"in two shakes of a lamb's tail", which indicates a very short time interval.
The phrase "a couple of shakes", in reference to the measurement of time, may have been popularized by Richard Barham
Richard Harris Barham (6 December 1788 – 17 June 1845) was an English cleric of the Church of England, a novelist and a humorous poet. He was known generally by his pseudonym Thomas Ingoldsby and as the author of ''The Ingoldsby Legends''.
...
's ''Ingoldsby Legends
''The Ingoldsby Legends'' (full title: ''The Ingoldsby Legends, or Mirth and Marvels'') is a collection of myths, legends, ghost stories and poems written supposedly by Thomas Ingoldsby of Tappington Manor, actually a pen-name of an English cl ...
'' (1840); however, the phrase was already part of vernacular language long before that.
Nuclear physics
For nuclear-bomb designers, the term was a convenient name for the short interval, rounded to 10 nanoseconds, which was frequently seen in their measurements and calculations: The typical time required for one step in a chain reaction (i.e. the typical time for each neutron to cause a fission event, which releases more neutrons) is of the order of 1 shake, and a chain reaction is typically complete by 50 to 100 shakes.See also
*Barn
A barn is an agricultural building usually on farms and used for various purposes. In North America, a barn refers to structures that house livestock, including cattle and horses, as well as equipment and fodder, and often grain.Allen G ...
, a companion unit of cross-sectional area created by the same people, for the same general purposes, at the same time (the measured value of nuclear-reaction cross section was larger than expected, hence deemed "''as big as a barn''").
* List of humorous units of measurement
Many people have made use of, or neologism, invented, units of measurement intended primarily for their humor value. This is a list of such units invented by sources that are notable for reasons other than having made the unit itself, and that ...
References
{{Time measurement and standards Units of time