Units and Measurement - Units and Measurement The...

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Units and Measurement The International System of Units Quantitative measurement is the cornerstone of modern science, but it has not always been so; the application of quantitative measurements to chemistry, for example, does not predate AD 1500. Quantitative measurement was developed for other purposes, as technology, and was only then adopted for scientific use. The system of weights and measures were developed on an ad hoc basis in different parts of the world. The most fundamental quantities measured were mass or weight, length or distance, and time. Systems of units for measuring these were developed from the very beginning of recorded history. Measurement of temperature was added in the sixteenth century, and measurement of electric current in the eighteenth century. More recently amount of substance and luminous intensity have been added in the International System of Units, or SI. The International System of Units or Systeme Internationale (SI) is an improved metric system adopted by the Eleventh General Conference of Weights and Measures in 1960. It is the universal measuring system used in all areas of science throughout the world. The entire SI system of measurement is constructed from seven base units, each of which represents a single physical quantity as shown in the table below. Table: Base Units of the International System Quantity Name of Unit Unit Symbol length meter (metre) m mass kilogram kg time second s temperature kelvin K amount of substance mole mol
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electric current ampere A luminous intensity candela cd Like earlier versions of the metric system, the SI units can be designated as decimal fractions or multiples by the use of appropriate prefixes. The acceptable SI prefixes are given in the table below. Table: Prefixes of the International System Factor Prefix Symbol Factor Prefix Symbol 10+24 yotta Y 10-24 yocto y 10+21 zetta Z 10-21 zepto z 10+18 exa E 10-18 atto a 10+15 peta P 10-15 femto f 10+12 tera T 10-12 pico p 10+9 giga G 10-9 nano n 10+6 mega M 10-6 micro GK mu 10+3 kilo k 10-3 milli m 10+2 hecto h 10-2 centi c 10+1 deca da 10-1 deci d
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