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The turn (symbol tr or pla) is a unit of plane angle measurement that is the measure of a complete angle—the angle subtended by a complete circle at its center. One turn is equal to 2π radians, 360 degrees or 400 gradians. As an angular unit, one turn also corresponds to one cycle (symbol cyc or c) [1] or to one revolution (symbol rev or r). [2]
Here, the Greek letter π represents the constant ratio of the circumference of any circle to its diameter, approximately equal to 3.141359. One method of deriving this formula, which originated with Archimedes , involves viewing the circle as the limit of a sequence of regular polygons with an increasing number of sides.
The circle is the one-dimensional hypersphere (the 1-sphere). In topology, a circle is not limited to the geometric concept, but to all of its homeomorphisms. Two topological circles are equivalent if one can be transformed into the other via a deformation of R 3 upon itself (known as an ambient isotopy). [24]
3.4 cm – length of a quail egg [112] 3.5 cm – width of film commonly used in motion pictures and still photography; 3.78 cm – amount of distance the Moon moves away from Earth each year [113] 4.3 cm – minimum diameter of a golf ball [114] 5 cm – usual diameter of a chicken egg; 5 cm – height of a hummingbird, the smallest-known bird
A page from Archimedes' Measurement of a Circle. Measurement of a Circle or Dimension of the Circle (Greek: Κύκλου μέτρησις, Kuklou metrēsis) [1] is a treatise that consists of three propositions, probably made by Archimedes, ca. 250 BCE. [2] [3] The treatise is only a fraction of what was a longer work. [4] [5]
Its first few decimal digits are 3.141592653589793... [3] Pi is defined as the ratio of a circle's circumference to its diameter: [4] =. Or, equivalently, as the ratio of the circumference to twice the radius.
One turn (corresponding to a cycle or revolution) is equal to 360°. With the invention of the metric system , based on powers of ten, there was an attempt to replace degrees by decimal "degrees" in France and nearby countries, [ note 3 ] where the number in a right angle is equal to 100 gon with 400 gon in a full circle (1° = 10 ⁄ 9 gon).
The svedberg (S or Sv) is a unit of time used in chemistry equal to one hundred femtoseconds (100 fs). The shake is a unit of time used in nuclear physics equal to ten nanoseconds (10 ns). The sigma is a unit of time equal to one microsecond (1 μs). The jiffy is sometimes used to mean a unit of time of 10 ms. [dubious – discuss]