Jerk
From Academic Kids
- "Jerk" (as in "clean and jerk") is also a weightlifting term; also describes Jamaican jerk spice; "Jerk" is also the name of an Australian Music Band
In slang, the term "jerk" can be used to describe a foolish, rude, immature, stupid, or contemptible person. This word was originated with the "jerkwater" towns of mid 19th century America, the pit stops the old steam engine trains needed to make to "jerk" water to the train, to bring it from the river to the train. The term "jerkwater" came to represent any small, remote town. The term "jerk" was then derived from these towns to represent inferior, unimportant people. Also in slang, jerk is a euphemism for masturbation.
In physics, jerk (in British English, jolt), also called surge, is the derivative of acceleration with respect to time (or the third derivative of displacement). Yank is mass times jerk, or equivalently, the derivative of force with respect to time. Jerk is a vector, and there is no generally used term to describe its scalar value.
The units of jerk are metres per second cubed (m/s3). There is no universal agreement on the symbol for jerk, but j is commonly used.
Jerk is used at times in engineering, especially when building roller coasters. Some precision or fragile objects—such as passengers, who need time to sense stress changes and adjust their muscle tension, or suffer e.g. whiplash—can be safely subjected not only to a maximum acceleration, but also to a maximum jerk. Jerk may be considered when the excitation of vibrations is a concern.
Higher derivatives of displacement than jerk also exist, but they are rarely necessary, and hence lack agreed names. Many suggestions have been made, such as jilt, jouse and jolt. In development of the Hubble Space Telescope's pointing control system, the fourth derivative of position was considered and the engineers used the word jounce in their publications.
External links
- What is the term used for the third derivative of position? (http://math.ucr.edu/home/baez/physics/General/jerk.html), a very good (copyrighted) description of jerk in the Usenet Physics FAQ (http://math.ucr.edu/home/baez/physics/index.html).ja:躍度
