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Shake (unit)

physical science Maturity 11-13 Next article →

A shake is an informal metric unit of time. It represents a very brief interval of 10 nanoseconds. In scientific notation, this is written as 10⁻⁸ seconds. While it is not an official unit in formal science textbooks, it serves a specific purpose. It allows scientists to express extremely fast timing intervals more conveniently. This is especially helpful when working with very small numbers.

The unit originated within the field of nuclear physics. It was created to describe the timing of events during nuclear reactions. In these reactions, timing is measured in incredibly small increments. Using the term shake makes these measurements easier to communicate. It simplifies the way researchers discuss the speed of subatomic processes. This convenience was vital for the complex calculations required in physics.

To understand its use, one must look at the mechanism of a chain reaction. A chain reaction consists of a series of rapid, connected events. In one step, a single neutron causes a fission event. This fission event then releases more neutrons into the system. These new neutrons move on to cause further fission events. This cycle repeats many times in a very short period.

Nuclear physicists use the shake to measure these specific steps. The typical time required for just one step in a chain reaction is about 1 shake. This means one neutron causes a fission event every 10 nanoseconds. The entire chain reaction usually reaches completion very quickly. Most reactions are complete within a window of 50 to 100 shakes. This provides a clear scale for measuring the speed of the reaction.

The history of the shake is tied to the Manhattan Project. This was a top-secret operation conducted during World War II. Designers working on nuclear bombs needed a way to manage rapid timing. They found that many of their measurements rounded to 10 nanoseconds. They adopted the term shake to make their mathematical work more convenient. This informal naming helped them navigate the intense requirements of their secret research.

The name itself comes from an old English idiom. The phrase is "in two shakes of a lamb's tail." This expression has long been used to describe a very short time interval. Some believe the phrase was popularized by the 1840 book Ingoldsby Legends. However, the term was already part of common language long before that book was written. The scientists chose it because it captured the idea of extreme speed.

There are other informal units used by the same group of scientists. One notable companion unit is called a barn. While the shake measures time, the barn is used to measure cross-sectional area. It was created for the same general purposes during the same era. Scientists used the term barn because some measured values for nuclear-reaction cross sections were larger than expected. They jokingly described these areas as being "as big as a barn."

The shake belongs to a category of humorous or informal scientific units. These units help researchers bridge the gap between complex math and human language. They allow for quick communication during high-stakes work. Although they are not used in official formal papers, they remain a part of physics history. They show how scientists use language to make the invisible world more understandable.

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