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Length
Length
In general English usage, length 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 the term for vertical length, width
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 mile, or a kilometer, 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 length is
dimensionless – see
Planck units.
Length is not an intrinsic property of anything, however, in
that two observers can measure the same "thing" (i.e. distance between events,
length of a board) and come up with a different answer. This strange property of
space is explained by
Albert Einstein's
special theory of relativity.
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