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Within each table, the units are listed alphabetically, ... Currently defined in US as 3 Statute miles, [3] but historically varied from 2 to 9 km ≈ 4828 m:
Earth radius R 🜨 ≈ 6,371 km [9] Lunar distance LD ≈ 384 402 km. [10] Average distance between the center of Earth and the center of the Moon. astronomical unit au. Defined as 149 597 870 700 m. [11] Approximately the distance between the Earth and Sun. light-year ly ≈ 9 460 730 472 580.8 km.
US spelling: meter per second: 1.0 m/s (3.3 ft/s) m/s ft/s (m/s foot/s) non-SI metric: kilometre per hour: km/h km/h US spelling: kilometer per hour: 1.0 km/h (0.62 mph) km/h mph; Imperial & US customary: mile per hour: mph mph 1.0 mph (1.6 km/h) mph km/h; mph kn; foot per second: ft/s (foot/s) ft/s long code "foot/s" outputs foot per second ...
For example, driving distances are normally given in kilometres (symbol km) rather than in metres. Here the metric prefix 'kilo-' (symbol 'k') stands for a factor of 1000; thus, 1 km = 1000 m. The SI provides twenty-four metric prefixes that signify decimal powers ranging from 10 −30 to 10 30, the most recent being adopted in 2022.
For example, 5 km is treated as 5000 m, which allows all quantities based on the same unit to be factored together even if they have different prefixes. A prefix symbol attached to a unit symbol is included when the unit is raised to a power. For example, 1 km 2 denotes 1 km × 1 km = 10 6 m 2, not 10 3 m 2.
Metric units are units based on the metre, gram or second and decimal (power of ten) multiples or sub-multiples of these. According to Schadow and McDonald, [ 1 ] metric units, in general, are those units "defined 'in the spirit' of the metric system, that emerged in late 18th century France and was rapidly adopted by scientists and engineers.
Conversion of units is the conversion of the unit of measurement in which a quantity is expressed, typically through a multiplicative conversion factor that changes the unit without changing the quantity.
Before and in addition to the SI, other metric systems include: the MKS system of units and the MKSA systems, which are the direct forerunners of the SI; the centimetre–gram–second (CGS) system and its subtypes, the CGS electrostatic (cgs-esu) system, the CGS electromagnetic (cgs-emu) system, and their still-popular blend, the Gaussian ...