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In general English usage, length (symbol: l) is but one particular instance of distance – an object's length is how long the object is – but in the physical sciences and engineering, the word length is in some contexts used synonymously with " distance". Height is vertical distance; width (or breadth) is a lateral distance; an object's width is less than its length. No one speaks of "the length from here to Alpha Centauri", but rather of "the distance from here to Alpha Centauri," but when one speaks of distance more abstractly, one says "A kilometre or a mile, is a unit of length" or "...of distance", and the two statements are synonymous. Likewise, a mountain might be a mile in height. Length is the metric of one dimension of space. The metric of space itself is volume, or (length)3. Length is commonly considered to be one of the fundamental units, meaning that it cannot be defined in terms of other dimensions. However, a set of units can be constructed where units of length can be derived from fundamental physical constants - see Planck units and Planck length. Colloquially length sometimes refers to duration, especially when used in context of music.
The SI unit of Length is the metreFor other uses of "metre" and "meter", see Metre (disambiguation). The metre is the basic unit of length in the International System of Units (SI: Systeme International d'Unites). It is defined as the length of the path travelled by light in absolute vacu, from which can be derived:
- centimetrecm redirects here, alternate uses: cm (disambiguation A centimetre (symbol cm American spelling: centimeter is an SI unit of length. One centimetre is: one-hundredth of one metre one-tenth of a decimetre ten millimetres. millimetre << centimetre << decime
- kilometre
2 Other units of length
- inchAn inch is an Imperial unit of length. Sweden also briefly had a "decimal inch" based on the metric system: see below for more. According to some sources, the inch was originally defined informally as the distance between the tip of the thumb and the firs
- footA foot is a non- SI unit of distance or length. The popular belief is that original standard was the length of a man's foot. The average foot length is about 240 mm (9. 4 in) for current Europeans. About 996 of 1000 British men have a foot that is less th
- yard
- mile
2.2 Units are used in astronomy
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