Fundamental units of measurement

Miles per transit Fundamental unit of measure for rail, truck, marine, and air enabling industry, company, or carrier accident rates to calculate a predicted number of accidents per transit. 

A standard is a material which allows a measurement to be made in such a way that there exists a pathway between the measurement and one of the fundamental imits of measmement. A Standard Reference Material (SRM), issued by the National Bureau of Standards, is such a material. Through the use of standards any two independent measurements may be compared providing each has a traceability pathway to the same fundamental unit of measurement. The pathway may be through the use of an absolute standard and a precise method of measurement or an absolute method of measurement alone. 

BECQUEREL. The fundamental unit of measurement for radioactivity in the International System for Measurement (SI). One becquerel, abbreviated Bqequals one disintegration per second. The unit honors French physicist Antoine-Henri Becquerel (1852-1908), who shared the 1903 Nobel Prize in Physics with Marie and Pierre Curie for fundamental discoveries related to radioactivity. See also CURIE RUTHERFORD. 

In the same way that mass, length, and time are fundamental units of measurement in physics, cost—as in the cost of goods and services— is a fundamental unit of measurement in economics. While the units of measurement may vary (based on currency, barter of goods, or exchange of assets), this concept of cost is ingrained in our economic systems. Most of our measurements involving money, or the accumulation of wealth, are predicated on the concept of the cost of goods and services. Even the term inflation is based on this concept. 

Unit of energy. The fundamental unit of energy in modern thermochemical measurements is the electrical joule, which is derived from standards of resistance and electromotive force maintained at the various national standardizing laboratories. 

In the section on Thermochemistry in the International Critical Tables (see Bichowsky1), the values were recorded in joules, in the hope that thermochemists might come to use this fundamental unit in their calculations and writings. But the attempt to break away from the calorie as a unit in thermochemical and thermodynamical calculations proved to be unpopular and apparently hopeless of accomplishment. In order to satisfy the popular demand for the calorie as a unit in calculations and tabulations, and at the same time depart as little as possible from the fundamental unit of energy, the joule, in terms of which all accurate thermochemical measurements are actually made, we have used in this book a defined calorie, that is, one which has no actual relation whatever, except incidentally and historically, to the heat capacity of water. 

SI units of measurement, used by scientists around the world, derive their name from the French Systeme International d Unites. Fundamental units (base units) from which all others are derived are defined in Table 1-1. Standards of length, mass, and time are the meter (m). kilogram (kg), and second (s), respectively. Temperature is measured in kelvins (K), amount of substance in moles (mol), and electric current in amperes (A). 

Table 1-2 lists some quantities that are defined in terms of the fundamental quantities. For example, force is measured in newtons (N), pressure is measured in pascals (Pa), and energy is measured in joules (J), each of which can be expressed in terms of the more fundamental units of length, time, and mass. 

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... 

Epoxy resins and curing agents must have a relatively low viscosity so that formulation compounding can be accomplished easily and without a great deal of energy or degradation of the components. Viscosity is defined as the resistance of a liquid material to flow. It is usually measured in fundamental units of poise (P) or centipoise (cP). Table 3.2 shows a relationship between various common fluids and their viscosity as measured in centipoise. 

The second, symbol s, is the SI unit of time, defined as the duration of 9,192,631,770 cycles of radiation associated with a specified transition of the cesium atom. The meter, symbol m, is the fundamental unit of length, defined as the distance light travels in a vacuum during 1/299,792,458 of a second. The kilogram, symbol kg, is the mass of a platinum/ iridium cylinder kept at the International Bureau of Weights and Measures at Sevres, France. The unit of temperature is the kelvin, symbol K, equal to 1/273.16 of the thermodynamic temperature of the triple point of water. A more detailed discussion of tern-perature, the characteristic dimension of thermodynamics, is given in Sec. 1.4. The measure of the amount of substance is the mole, symbol mol, defined as the amount of substance represented by as many elementary entities (e.g., molecules)... 

We have already dealt with a number of expressions in which frequency appears, and we shall encounter many more such expressions. In some instances it is preferable to use the more fundamental unit of radians/second, for which we employ the symbol co or ft, while in other cases it is more convenient to use the measured unit of cycles/second, or hertz, designated v (or occasionally F). Also,... 

Quantitative calculations and qualitative interpretations are fundamental to fully grasp the concepts of chemistry. Quantitative values must include a number and a unit. Two common units of measurement are the conventional (English) system and the metric system. The conventional set of units includes inches, feet, miles, gallons, and pounds. These units, although common in the United States, are not used in science or by most of the world. However, the metric system is becoming more common in the United States. The metric system s base-10 units are easier to use and essential for scientific calculations. However, because most readers of this book are more familiar with the conventional system, it will be necessary to convert to and from the metric system. 

Three fundamental dimensions of measurement, mass [M], length [L], and time [T], form the basis for most environmental quantities. A good understanding of these dimensions and of the way in which they are combined to form various units of measurement clarifies many problems of chemical fate and transport. 

In the next section, we introduce the standards for basic units of measurement. These standards were selected because they allow us to make precise measurements and because they are reproducible and unchanging. The values of fundamental units are arbitrary. In... 

Stars have two, and only two, fundamental observable properties brightness and color. Astronomers usually prefer the term luminosity rather than the term brightness. An even more precise term is absolute luminosity, which is defined as the brightness a star would have if it were placed at a distance of 10 parsecs from the Sun. The parsec is a unit of measure used in astronomy equal to 3.26 light-years. 

The mole is the fundamental unit of quantity of material. It provides a convenient way of scaling up molecular masses to those on a laboratory scale of measurement. A mole of substance is equal to as many molecules of that substance as there are atoms in exactly 12 g of the 12C isotope of carbon. This number, called Avogadro s constant, is 6.022 x 1023mor1. We can have moles not just of molecules but of ions, atoms, or any other particles. 

In this section we will examine briefly the effects of radiation on biological systems. Bnt first let us define quantitative measures of radiation. The fundamental unit of radioactivity is the curie (Ci) 1 Ci corresponds to exactly 3.70 X 10 ° nuclear disintegrations per second. This decay rate is equivalent to that of 1 g of radium. A millicurie (mCi) is one-thousandth of a curie. Thus, 10 mCi of a carbon-14 sample is the quantity that undergoes... 

Ampere The unit of measurement of current. 1 ampere = 1 coulomb/second. This is a fundamental SI unit from which many other electrical units are developed. If two infinitely long wires are placed parallel to each other, 1 meter apart, and an electrical current is passed through them such that 1 meter of length contains a magnetic force of 2 x 10 Newtons between the two wires, then 1 ampere of current is flowing in each wire. 

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