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The Mach number (M or Ma), often only Mach, (/ m ɑː k /; German:) is a dimensionless quantity in fluid dynamics representing the ratio of flow velocity past a boundary to the local speed of sound. [1] [2] It is named after the Austrian physicist and philosopher Ernst Mach. =, where: M is the local Mach number,
Dimensionless numbers (or characteristic numbers) have an important role in analyzing the behavior of fluids and their flow as well as in other transport phenomena. [1] They include the Reynolds and the Mach numbers, which describe as ratios the relative magnitude of fluid and physical system characteristics, such as density, viscosity, speed of sound, and flow speed.
Earth's rate of rotation must be integrated to obtain time, which is Earth's angular position (specifically, the orientation of the meridian of Greenwich relative to the fictitious mean sun). Integrating +1.7 ms/d/cy and centering the resulting parabola on the year 1820 yields (to a first approximation) 32 × ( year − 1820 / 100 ) 2
1837 – George Green find the minimal number of elastic moduli. [12] 1838-40 – Gotthilf Hagen and Jean Léonard Marie Poiseuille study laminar flow, independently establishing Hagen–Poiseuille equation. [1] 1841 – George Biddell Airy publishes the first correct formulation of Airy wave theory of water waves. [27]
More than 99 percent of all species, amounting to over five billion species, [7] that ever lived on Earth are estimated to be extinct. [8] [9] Estimates on the number of Earth's current species range from 10 million to 14 million, [10] of which about 1.2 million have been documented and over 86 percent have not yet been described. [11]
The Jiffy is the amount of time light takes to travel one femtometre (about the diameter of a nucleon). The Planck time is the time that light takes to travel one Planck length. The TU (for time unit) is a unit of time defined as 1024 μs for use in engineering. The svedberg is a time unit used for sedimentation rates (usually
SET assumes that the animal has a clock, a working memory, a reference memory, and a decision process. The clock contains a discrete pacemaker that generates pulses like the ticks a mechanical clock. A stimulus that signals the start of a timed interval closes a switch, allowing pulses to enter an accumulator.
Terrestrial Time (TT) is a modern astronomical time standard defined by the International Astronomical Union, primarily for time-measurements of astronomical observations made from the surface of Earth. [1] For example, the Astronomical Almanac uses TT for its tables of positions (ephemerides) of the Sun, Moon and planets as seen from Earth.