Length is a physical measurement of distance that is fundamentally measured in the SI unit of a meter

LEARNING OBJECTIVE

· Distinguish SI and customary units of length

KEY POINTS

· The SI unit for length is the meter.

· One meter is defined as the distance that light travels in a vacuum in 1299,792,458 of a second.

· Derivatives of measurement units related to the meter are devised around the convenience of the number 10.

TERM

How far apart objects are physically.

FULL TEXT

Length can be defined as a measurement of the physical quantity of distance. Many qualitative observations fundamental to physics are commonly described using the measurement of length. The distance between objects, the rate at which objects are traveling, and how much force an object exerts are all dependent on length as a variable. In order to describe length in a standardized and quantitative manner, an accepted unit of measurement must be utilized.

Many different units of length are used around the world. In the United States, the U.S. customary units operationally describe length in terms of the basic unit of an inch. Varying lengths are thus described in relation to the inch, such as a foot equaling 12 inches, a yard equaling three feet, and a mile equaling 1,760 yards.

Though regional use of different measurement units is not generally problematic, it can raise issues of compatibility and understanding when working abroad or collaboratively with international partners. As such, a standard unit of measurement that is internationally accepted is needed. The basic unit of length as identified by the International System of Units (SI) is the meter. The meter is expressed more specifically in terms of speed of light.

One meter is defined as the distance that light travels in a vacuum in 1299,792,458 of a second. All lengths are measured in terms related to the meter, where its multiples are devised around the convenience of the number 10. For example, a centimeter is equal to 1100 of a meter (or 10−2 meters), and a kilometer is equal to 1,000 meters (or 103 meters).

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