Systeme Internationale d Unites

For historic reasons a number of different units of measurement have evolved to express quantity of the same thing. In the 1960s, many international scientific bodies recommended the standardisation of names and symbols and the adoption universally of a coherent set of units—the SI units (Systeme Internationale d Unites)— based on the definition of five basic units metre (m) kilogram (kg) second (s) ampere (A) mole (mol) and candela (cd). 

Under an international agreement concluded in 1960, scientists throughout the world now use the International System of Units for measurement, abbreviated SI for the French Systeme Internationale d Unites. Based on the metric system, which is used in all industrialized countries of the world except the United States, the SI system has seven fundamental units (Table 1.3). These seven fundamental units, along with others derived from them, suffice for all scientific measurements. We ll look at three of the most common units in this chapter—those for mass, length, and temperature—and will discuss others as the need arises in later chapters. 

The most widely sanctioned set of units, the Systeme Internationale d Unites or SI set, is summarized here. In this book (as elsewhere, and for good reason ) this system has been only partially adopted. Thus, we use joules (instead of calories) but retain other earlier units, most importantly, Angstroms, atmospheres, and degrees Celsius. 

The Systeme Internationale d Unites, or SI for short, has gained widespread acceptance in the scientific and engineering community. Two of the base SI units—the ampere for electrical current and the candela for luminous intensity—will not concern us in this book. A third, the kelvin for temperature, will be discussed later. The others are the meter (m) for length, the kilogram (kg) for mass, and the second (s) for time. 

Since 1960, scientists worldwide have used a set of units called the Systeme Internationale d Unites or SI. The system is built on the seven base units listed in Tabie 1. The last two find little use in chemistry, but the first five provide the foundation of all chemical measurements. 

For centuries, units of measurement were fairly inexact. A person might mark off the boundaries of a property by walking and counting the number of steps. The passage of time could be estimated with a sundial or an hourglass filled with sand. Such estimates worked for ordinary tasks. Scientists, however, need to report data that can be reproduced by other scientists. They need standard units of measurement. In 1795, French scientists adopted a system of standard units called the metric system. In 1960, an international committee of scientists met to update the metric system. The revised system is called the Systeme Internationale d Unites, which is abbreviated SI. 

Recall from Chapter 2 that the universal unit system used by scientists is called Le Systeme Internationale d Unites, or SI. It is a metric system based on seven base units—meter, second, kilogram, kelvin, mole, ampere, and candela—from which all other units are derived. The size of a unit in the metric system is indicated by a prefix related to the difference between that unit and the base unit. For example, the base unit for length in the metric system is the meter. One-tenth of a meter is a decimeter, where the prefix deci- means one-tenth. One thousand meters is a kilometer, where the prefix kilo- means one thousand. 

Systeme Internationale d Unites Donble-ended, linear arc tnbe. 

International System of Units (abbreviated SI from Systeme Internationale d Unites, die French version of the name). The conversion factors are reported only to four significant figures. 

The adoption of the international system of units, Systeme Internationale d Unites, or S.I. units for short, as the legal system in Great Britain and other countries is now complete, the system receiving official recognition at the Conference Generale des Poids et Mesures (C.G.P.M.) held in Paris attended by representatives from the National Physical Laboratory(N.P.L.) and the Bureau of Standards (U.SA.). Six basic units are involved metre (length), kilogramme (mass), second (time), ampere (electric current), kelvin (thermodynamic temperature) and candela (luminous intensity) from which other units are derived. 

The International System of Units (Systeme Internationale d Unites, SI) establishes the standards of comparison used by all countries when the measured values of physical and chemical properties are reported. There are seven SI base quantities (dimensions), for which the defined units of measurement can be combined appropriately to give the SI units for aU other measurable quantities (i.e., the SI system is a coherent system of units). 

Throughout this book, physical quantities have been expressed in customary units in accordance with dominant commercial practice. However, it is recognized that the International System of Units (Systeme Internationale d Unites or SI) is finding increasing use. In this appendix some common SI units are listed and the customary units used in the book may be changed into these units by multiplication by the conversion factors shown. 

The revised metric system is called the International System of Units (abbreviated SI, from the French Systeme Internationale d Unites). Table 1.2 lists the seven SI base units. All other units of measurement can be derived from these base units. The SI unit for volume, for instance, is derived by cubing the SI base unit for length. The prefixes listed in Table 1.3 are used to denote deeimal fractions and multiples of SI units. This enables scientists to tailor the magnitude of a unit to a particular application. For example, the meter (m) is appropriate for describing the dimensions of a classroom, bnt the kilometer (km), 1000 m, is more appropriate for describing the distance between two cities. Units that yon will encounter frequently in the study of chemistry include those for mass, temperature, volume, and density. 

Bureau internationale de poids et mesures, Le Systeme international d unites (SI), Organisation Intergouvernemental de la Convention du Metres, Sevres, 1998. 

The modern metric system uses SI (Sysfrme Internationale d Unites) units that have seven base units (see ... 

Several systems of measurement are used in chemistry and environmental chemistry. The most systematic of these is the International System of Units (Syst me Internationale d Unit ), abbreviated SI, a self-consistent set of units based upon the metric system recommended in 1960 by the General Conference on Weights and Measures to simplify and make more logical the many units used in the scientific and engineering community. Table 1.4 gives the seven base SI units in terms of which aU other units are derived. 

The scientific system of measurement is called the Systkme Internationale d Unites (International System of Units) and is abbreviated SI. It is a modern version of the metric system, a system based on the unit of length called a meter (m). The meter was originally defined as 1/10,000,000 of the distance from the equator to the North Pole and translated into the length of a metal bar kept in Paris. Unfortunately, the length of the bar is subject to change with temperature, and it cannot be exactly reproduced. The SI system substitutes for the... 

You probably know your height in feet and inches. Most people outside the United States, however, measure height in meters and centimeters. The system of standard units that includes the meter is called the metric system. Scientists today use a revised form of the metric system called the SystSme Internationale d Unit6s, or SI. 

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