Length is the long dimension of any object. In mathematics the dimension of a Space is roughly defined as the minimum number of Coordinates needed to specify every point within it The length of a thing is the distance between its ends, its linear extent as measured from end to end. This may be distinguished from height, which is vertical extent, and width or breadth, which are the distance from side to side, measuring across the object at right angles to the length. Height is the measurement of vertical Distance, but has two meanings in common use In the physical sciences and engineering, the word "length" is typically used synonymously with "distance", with symbol l or L. Distance is a numerical description of how far apart objects are

Length is a measure of one dimension, whereas area is a measure of two dimensions (length squared) and volume is a measure of three dimensions (length cubed). Area is a Quantity expressing the two- Dimensional size of a defined part of a Surface, typically a region bounded by a closed Curve. The volume of any solid plasma vacuum or theoretical object is how much three- Dimensional space it occupies often quantified numerically In most systems of measurement, length is a fundamental unit, from which other units are derived. A set of fundamental units is a set of units for physical quantities from which every other unit can be generated

Units of length

In the physical sciences and engineering, when one speaks of "units of length", the word "length" is synonymous with "distance". Distance is a numerical description of how far apart objects are There are several units that are used to measure length. Measurement is the process of estimating the magnitude of some attribute of an object such as its length or weight relative to some standard ( unit of measurement) such as Units of length may be based on lengths of human body parts, the distance travelled in a number of paces, the distance between landmarks or places on the Earth, or arbitrarily on the length of some fixed object.

In the International System of Units (SI), the basic unit of length is the metre and is now defined in terms of the speed of light. The International System of Units (SI defines seven dimensionally independent SI base units. The metre or meter is a unit of Length. It is the basic unit of Length in the Metric system and in the International The centimetre and the kilometre, derived from the metre, are also commonly used units. A centimetre ( American spelling: centimeter, symbol cm) is a unit of Length in the Metric system, equal to one hundredth The kilometre ( American spelling: kilometer) symbol km is a unit of Length in the Metric system, equal to one thousand In U.S. customary units, English or Imperial system of units, commonly used units of length are the inch, the foot, the yard, and the mile. US customary units, also known in the United States as English units or Imperial units (in reference to the British Empire) (but see English Imperial units or the Imperial system is a collection of units first defined in the British Weights and Measures Act of 1824 Inches redirects here To see the Les Savy Fav album see Inches. A foot (plural feet or foot; symbol or abbreviation ft or sometimes &prime – the prime symbol) is a non-SI unit A yard (abbreviation yd) is a unit of Length in several different systems including English units Imperial units and United A mile is a unit of Length, usually used to measure Distance, in a number of different systems including Imperial units United States

Units used to denote distances in the vastness of space, as in astronomy, are much longer than those typically used on Earth and include the astronomical unit, the light-year, and the parsec. Astronomy (from the Greek words astron (ἄστρον "star" and nomos (νόμος "law" is the scientific study The astronomical unit ( AU or au or au or sometimes ua) is a unit of Length based on the distance from the Earth to the A light-year or light year (symbol ly) is a unit of Length, equal to just under ten trillion Kilometres As defined by History The first direct measurements of an object at interstellar distances were undertaken by German Astronomer Friedrich Wilhelm Bessel in 1838

Units used to denote microscopically small distances, as in chemistry, include the micron and the ångström. Chemistry (from Egyptian kēme (chem meaning "earth") is the Science concerned with the composition structure and properties An ångström or angstrom (symbol Å) (ˈɔːŋstrəm Swedish: ˈɔ̀ŋstrœm is an internationally recognized non- SI unit of length equal

Length of moving rods

While the length of a resting rod can be measured by direct comparison with a measuring rod, this comparison cannot be performed while the rod is moving. In this case we define its moving length as the distance between its two endpoints at a given instance.

If the world lines of the two endpoints of the rod expressed in the coordinates of an inertial reference frame are

and

,

then the length of the rod in this reference frame at the instance is

Since in special relativity the relation of simultaneity depends on the chosen frame of reference, the length of moving rods also depends. In physics the world line of an object is the unique path of that object as it travels through 4- Dimensional Spacetime. Special relativity (SR (also known as the special theory of relativity or STR) is the Physical theory of Measurement in Inertial The relativity of simultaneity is the concept that simultaneity is not absolute but dependent on the observer

See also

• Distance
• Dimension
• Orders of magnitude (length)
• How round is your circle? Contains a chapter giving the history of length and angle measurement. Distance is a numerical description of how far apart objects are In mathematics the dimension of a Space is roughly defined as the minimum number of Coordinates needed to specify every point within it To help compare different Orders of magnitude, the following list describes various Lengths between 1
• Smoot

The smoot is a nonstandard Unit of length created as part of an MIT fraternity prank.

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