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A second of arc, arcsecond (abbreviated as arcsec), or arc second, denoted by the symbol ″, [2] is a unit of angular measurement equal to 1 / 60 of a minute of arc, 1 / 3600 of a degree, [1] 1 / 1 296 000 of a turn, and π / 648 000 (about 1 / 206 264.8 ) of a radian.
The foot per second (plural feet per second) is a unit of both speed (scalar) and velocity (vector quantity, which includes direction). [1] It expresses the distance in feet (ft) traveled or displaced, divided by the time in seconds (s). [2] The corresponding unit in the International System of Units (SI) is the meter per second.
One barn is equal to 1.0 × 10 −28 m 2. The name derives from the folk expressions "As big as a barn," and "Couldn't hit the broad side of a barn", used by particle accelerator physicists to refer to the probability of achieving a collision between particles. For nuclear purposes, 1.0 × 10 −28 m 2 is actually rather large. [25]
These include the equivalence of mass and energy (E = mc 2), length contraction (moving objects shorten), [Note 8] and time dilation (moving clocks run more slowly). The factor γ by which lengths contract and times dilate is known as the Lorentz factor and is given by γ = (1 − v 2 /c 2) −1/2, where v is the speed of the object.
More simply, the speed of sound is how fast vibrations travel. At 20 °C (68 °F), the speed of sound in air, is about 343 m/s (1,125 ft/s; 1,235 km/h; 767 mph; 667 kn), or 1 km in 2.91 s or one mile in 4.69 s. It depends strongly on temperature as well as the medium through which a sound wave is propagating.
World leaders in 2015 agreed to limit warming to well below 2 degrees C and also to aim for 1.5 degrees. But many countries are struggling to cut fossil fuels from their economies, and efforts ...
A nautical mile is a unit of length used in air, marine, and space navigation, and for the definition of territorial waters. [2] [3] [4] Historically, it was defined as the meridian arc length corresponding to one minute ( 1 / 60 of a degree) of latitude at the equator, so that Earth's polar circumference is very near to 21,600 nautical miles (that is 60 minutes × 360 degrees).
In the mid-1960s, to defeat the advantage of the recently introduced computers for the then popular rally racing in the Midwest, competition lag times in a few events were given in centids (1 ⁄ 100 day, 864 seconds, 14.4 minutes), millids (1 ⁄ 1,000 day, 86.4 seconds), and centims (1 ⁄ 100 minute, 0.6 seconds) the latter two looking and ...