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Measurement Systems Help

By — McGraw-Hill Professional
Updated on Oct 25, 2011

Introduction to Measurement Systems

Numbers by themselves are abstract. Units make numbers concrete. We can say that a quantity is this wide, is that heavy, lasts this long, or is that hot; it extends for this many millimeters, weighs that many pounds, lasts this many hours, or is heated to that many degrees Celsius. Some of the material in this chapter might at first seem too scientific to be considered “everyday math.” But when it comes to math, it’s always important to know precisely what you mean when you say something. After you’ve gone through this material, nobody will be able to legitimately say that you don’t know what you’re talking about when you quote units of measurement.

Systems of Units

There are various systems of physical units. The meter/kilogram/second ( mks ) system , also called the metric system and which is essentially the same as the International System , is favored in most of the developed world. The centimeter/gram/second ( cgs ) system is less often used. The foot/pound/second ( fps ) system , also called the English system , is popular among nonscientists in the United States. Each system has several fundamental, or base , units from which all the others are derived.

The International System (SI)

The International System is abbreviated SI (for the words Système International in French). This scheme in its earlier form, mks, has existed since the 1800s, but was more recently defined by the General Conference on Weights and Measures.

The base units in SI quantify displacement, mass, time, temperature, electric current, brightness of light , and amount of matter . Respectively, the units in SI are known as the meter , the kilogram , the second , the Kelvin (or degree Kelvin ), the ampere , the candela , and the mole .

The CGS System

In the centimeter/gram/second (cgs) system, the base units are the centimeter (exactly 0.01 meter), the gram (exactly 0.001 kilogram), the second (identical to the SI second), the degree Celsius (approximately the number of Kelvins minus 273.15), the ampere (identical to the SI ampere), the candela (identical to the SI candela), and the mole (identical to the SI mole).

The English System

In the English or fps system, the base units are the foot (approximately 30.5 centimeters), the pound (equivalent to about 2.2 kilograms in the gravitational field at the earth’s surface), and the second (identical to the SI second). Other units include the degree Fahrenheit (where water freezes at 32 degrees and boils at 212 degrees at standard sea-level atmospheric pressure), the ampere (identical to the SI ampere), the candela (identical to the SI candela), and the mole (identical to the SI mole).

Find practice problems and solutions for these concepts at: Units of Measurement Practice Test.

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