Units of Scientific Measurements

Scientific measurements range from fantastically large to incredibly small numbers, and units that are appropriate for one measurement may be entirely inappropriate for another. To avoid the creation of many different sets of units, it is common practice to vary the size of a fundamental unit by attaching a suitable prefix to it. Table 4-1 shows common metric prefixes and the multiples they indicate for any given unit of measurement. Thus a l g gs ater is 1000 meters, a microgram is 10-6 ram ana a nanosecond is Q-9 

Except for temperature and time, nearly all scientific measurements are based on the metric system. In recent years, there has been a concerted international effort to persuade scientists to express all metric measurements in terms ofjust seven basic units, called SI units (for Systeme International). In addition to the seven basic SI units, there are seventeen other common units derived from them that have special names. However, despite the logical arguments that have been put forth for undeviating adherence to SI units, there has not been a strong popular move in this direction. For one thing, each scientist must cope 

Prefix Factor Symbol Prefix Factor Symbol 

Dimension measured Metric unit English unit Conversion factor F 

There is one metric unit with a special name that scientists frequently use because it permits the use of simple numbers when talking about the sizes of atoms and molecules. It is called an angstrom (A) 1 A = 10 8 cm- 

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Calorie A unit of scientific measure for heat and energy. One calorie is the amount of energy needed to raise the temperature of one gram of water by one degree Celsius. 

The problem of changing over a highly industrialized nation such as the United States to a new system of measurements is a substantial one. Once the metric system is in general use in the United States, its simplicity and convenience will be enjoyed, but the transition period, when both systems are in use, can be difficult. Nevertheless, it will be easier than it seems. While the complete SI is intimidating because it covers every conceivable kind of scientific measurement over an enormous range of magnitudes, there are only a small number of units and prefixes that are used in everyday life. 

We recognize that the International System of Units (SI) has become the fundamental basis of scientific measurement worldwide and is used for everyday commerce in virtually every country except the United States. As painM as it may be for those of us who have learned and practiced the British or US Customary system of units, we feel that it is time to put aside the units of the industrial revolution and adopt the SI system of measurement in all aspects of modern engineering and science. For this reason, SI units have been adopted as the primary system of units throughout this book. However, it is recognized that US customary or British units are stiU widely used in the United States and some use of them is provided herein for the benefit of those who still relate closely to them. Dimensional constants specific to the British system, such as gc, have been left out of the formulae. 

In the metric system, pressure has a unit of newtons per square meter, which is called a pascal (Pa). Although the pascal is the scientific unit and is preferred, pounds per square inch (Ibs/iif) is comnion in the United States. For example, in most of Europe, tire pressure is recorded in pascals (typically 220,000 Pa), whereas tire pressure in American cars is measured in pounds per square inch (typically 32 Ibs/in ). As a point of reference, the pressure that the earth s... 

Scientific measurements are expressed in the metric system. As you know, this is a decimal-based system in which all of the units of a particular quantity are related to one another by factors of 10. The more common prefixes used to express these factors are listed in Table 1.2 (page 7). 

For scientific work the fundamental standard of mass is the international prototype kilogram, which is a mass of platinum-iridium alloy made in 1887 and deposited in the International Bureau of Weights and Measures near Paris. Authentic copies of the standard are kept by the appropriate responsible authorities in the various countries of the world these copies are employed for the comparison of secondary standards, which are used in the calibration of weights for scientific work. The unit of mass that is almost universally employed in laboratory work, however, is the gram, which may be defined as the one-thousandth part of the mass of the international prototype kilogram. 

A unit of measurement is an agreed-upon standard with which other values are compared. Scientists use the meter as the standard unit of length. The meter was originally chosen to be 10 times the length of a line from the North Pole to the equator. Volume can be measured in pints, quarts, and gallons, but the scientific units are the cubic meter and the liter. Temperature can be measured in degrees Fahrenheit (°F), degrees Celsius (°C), or kelvins (K). 

The international scientific community prefers to work exclusively with a single set of units, the Systeme International (SI), which expresses each fundamental physical quantity in decimally (power of 10) related units. The seven base units of the SI are listed in Table 1-3. The SI unit for volume is obtained from the base unit for length A cube that measures 1 meter on a side has a volume of 1 cubic meter. 

At the end of the book you will find for reference lists of commonly used scientific symbols and values, units of measurement and also a periodic table. 

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). 

It is a pleasure to thank Rudolph Black of the United States Advanced Research Projects Agency, who, in May 1971, funded our proposal that "temperature variations in past climates may be evaluated by measuring stable isotope ratios in natural data banks such as tree ring and varve sequences". We thank William Best of the U.S. Air Force Office of Scientific Research who monitored our study and Frank Eden of the U.S. National Science Foundation who subsequently provided further funds. 

A physical unit system is implicitly defined by the choice of three underlying base units, which suffice to determine dimensionally consistent units for other measurable physical quantities. (Why three such base units are required is as yet an unanswered physical question.) Although the choice of units may superficially appear arbitrary, it was recognized by Gibbs (in his first scientific communication)1 that one can rationally address the question of the conditions which it is most necessary for these units to fulfil for the convenience both of men of science and of the multitude. ... 

While feet and yards are still used in Britain and other countries, the usual length is now the metre. At the time of the French Revolution in the 18th century and soon after, the French Academy of Sciences sought to systemize the measurement of all scientific quantities. This work led eventually to the concept of the Systeme Internationale, or SI for short. Within this system, all units and definitions are self-consistent. The SI unit of length is the metre. 

When working with measurements, you often have to convert units before performing other calculations. There are two methods of converting measurements. One is using proportions and the other is using a scientific method called dimensional analysis. 

Acknowledgements Authors thank to the Scientific Research Projects Unit of Akdeniz University for the support of this work through the project 2003.01.0300.009, to the Spectra Corp. (MA., USA) for providing the ACC and to METU for carrying out measurements to determine the surface properties of the ACC. 

Chemists routinely measure quantities that run the gamut from very small (the size of an atom, for example) to extremely large (such as the number of particles in one mole). Nobody, not even chemists, likes dealing with scientific notation (which we cover in Chapter 1) if they don t have to. For these reasons, chemists often use a metric system prefix (a word part that goes in front of the base unit to indicate a numerical value) in lieu of scientific notation. For example, the size of the nucleus of an atom is roughly 1 nanometer across, which is a nicer way of saying 1x10- meters across. The most useful of these prefixes are in Table 2-2. 

This Report is one of the series developed under the auspices of Scientific Committee 46, a scientific program area committee of the National Council on Radiation Protection and Measurements (NCRP) concerned with operational radiation safety. The Report provides practical recommendations on the use of personal monitors to estimate effective dose equivalent (Hg) and effective dose (E) for occupationally-exposed individuals. The Report is limited to external exposures to low-LET radiation. Recent additions to the radiation protection literature have made the recommendations possible. In order to avoid delay in utilizing the recommendations in the United States, the quantity as well as E, has been included until such time as the federal radiation protection guidance and associated implementing regulations are revised to express dose limits in E as recommended by the NCRP. 

Either directly or indirectly, the concept of density plays an important role in a myriad of scientific operations construction of equipment, preparation of solutions, determination of volumes, accurate weighings, measuring buoyancy of objects, studying properties of gases, and so on. Density is defined as the mass per unit volume, or... 

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. 

Dimensional calculations are greatly simplified if a consistent set of units is employed. The three major reference dimensions for mechanics are length, mass, and time, but length can be measured in units of inches, feet, centimeters, meters, etc. Which should be used The scientific community has made considerable progress toward a common system of reference units. This system is known as SI from the French name Systeme International d Unites. In SI, the reference units for length, mass, and time are the meter, kilogram, and second, with symbols m, kg, and s, respectively. 

Here we propose the additional concepts under which analysts can formally substantiate and record their traceability link. A chain of such links should lead from the value of a quantity in a sample or reference material (RM) up to the value of a relevant unit in the International System of Units (SI) [5] or - where this is not possible - up to internationally agreed measurement scales. A protocol records specific details of scientifically reliable measurement procedures for the benefit of equity in trade and commerce, as well as for legal interpretations of scientific realities. Some ideas in this article go beyond established international understandings these are presented for debate and possible refinement. 

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