Metric System Derived units

SI units International System of units based on the metric system and units derived from the metric system. (A2.1)... 

Metric Units As previously noted, the metric system is a forenmner of SI. In the metric system, as in SI, units of the same quantity are related to each other by orders of magnitude. However, some derived quantities in the metric system have units that differ from those in SI. Because these units are familiar and equipment is often calibrated in these emits, they are still used today. Table A.3 lists several metric units that you might use. 

The metric system has long been preferred for most scientific work. In 1960 an infernafional agreement set up a comprehensive system of units called the International System (le Systeme Internationale in French), or SI. The SI units are based on the metric system and units derived from the metric system. The most important fundamental SI units are listed in Table 5.1. Later in this chapter we will discuss how to manipulate some of these units. 

SI units International System of units based on the metric system and units derived from the metric system. (A2.1) Side chain (of amino acid) the hydrocarbon group on an amino acid represented by H, CH3, or a more complex substituent. (21.6)... 

SI units (SI Systeme fnternational d Unites) The modern coherent rationalized internationally adopted metric system of units. It has seven BASE UNITS and two dimensionless units, formerly called supplementary units. DERIVED UNITS are formed by multiplication and/or division of base units. Standard prefixes are used for decimal multiples and submultiples of SI units, along with standard symbols for both units and prefixes. 

Base unit Derived unit Metric system SI units Section 3.2 Base... 

Metric system, SI units, derived unit, base unit... 

Systeme International d Unites Known more commonly as SI units, it is a system comprising sevenbase units of the international metric system. The units are metre (m) for length, kilogram (kg) for mass, ampere (A) for electrical current, second (s) for time, kelvin (K) for temperature, candela (cd) for luminosity, and mole (mol). Derived units are the newton, joule, pascal, and watt. 

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... 

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. 

Accurate measurement is crucial to scientific experimentation. The units used are those of the Systeme Internationale (SI units). There are seven fundamental SI units, together with other derived units Mass, the amount of matter an object contains, is measured in kilograms (kg) length is measured in meters (m) temperature is measured in kelvins (K) and volume is measured in cubic meters (m3). The more familiar metric liter (L) and milliliter (mL) are also still used for measuring volume, and the Celsius degree (°C) is still used for measuring temperature. Density is an intensive physical property that relates mass to volume. 

There are many derived units, each defined in terms of the base units for example, the newton (N)— unit of force—is defined by the formula kg x m/s2, and the joule (J), by the relationship Nxm. See metric system. 

The metric system consists of a base unit and (sometimes) a prefix multiplier. Most scientists and healthcare providers use the metric system, and you are probably familiar with the common base units and prefix multipliers. The base units describe the type of quantity measured length, mass, or time. The SI system is sometimes called the MKS (meter, kilogram, second) system, because these are the standard units of length, mass, and time upon which derived quantities, such as energy, pressure, and force, are based. An older system is called the CGS (centimeter, gram, second) system. The derived CGS units are becoming extinct. Therefore, we will focus on the MKS units. 

On the eve of the French Revolution, June 19, 1791, King Louis XVI of France gave his approval of the system. The next day, Louis tried to escape France but was arrested and jailed. A year later from his jail cell, Louis directed two engineers to make the measurements necessary to implement the metric system. Because of the French Revolution, it took six years to complete the required measurements. Finally, in June 1799 the Commission sur l unite de poids du Systeme Metrique decimal met and adopted the metric system. It was based on the gram as the unit of weight and the meter as the unit of length. All other measurements were to be derived from these units. The metric system was adopted For all people, for all time. ... 

The metric system is a decimal system, based on powers of 10. Table 2.5 is a list of the prefixes for the various powers of 10. Between scientific notation and the prefixes shown below, it is very simple to identify, name, read, and understand 36 decades of power of any given base or derived unit. 

The name SI is derived from Systbme International d Unites and has evolved from an original basis of a given length (meter) and mass (kilogram) established by members of the Paris Academy of Science in the late eighteenth century. The original system was known as the metric system, but there are differences in the modem SI system and the old metric system based primarily on new names being added for derived terms. 

According to Newton s second law of motion, force is proportional to the product of mass and acceleration (length/time ). Natural force units are, therefore, kg-m/s (SI), g-cm/s (CGS), and lbm-ft/s (American engineering). To avoid having to carry around these complex units in all calculations involving forces, derived force units have been defined in each system. In the metric systems, the derived force units (the newton in SI, the dyne in the CGS system) are defined to equal the natural units ... 

Recall from Chapter 2 that the universal unit system used hy scientists is called Le Systeme Internationale d Unit6s 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 a 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. And, one thousand meters is a kilometer. The prefix kilo- means one thousand. 

With the current trend toward metrication, the question of using a consistent system of units has been a problem. Wherever possible, the authors of this Handbook of Environmental Engineering series have used the British system (fps) along with the metric equivalent (mks, cgs, or SIU) or vice versa. For the convenience of the readers around the world, this book provides a 55-page detailed Conversion Factors for Environmental Engineers. In addition, the basic and supplementary units, the derived units and quantities, important physical constants, the properties of water, and the Periodic Table of the Elements, are also presented in this document. 

The International System of Measurement (SI for Systeme International d Unith), a modern elaboration of the original metric system, was set up in I960. It was developed to provide a very organized, precise, and practical system of measurement that everyone in the world could use. The SI system is constructed using seven base units, from which all other units are derived (Table 1.1). The chemist is not usually interested in electric currents or luminous intensity, so only the first five of the base units on Table 1.1 will appear in this text. The meaning of mole, the base unit for amount of substance, is explained in Chapter 9. Until then, we will use the first four base units meter (m), kilogram (kg), second (s), and kelvin (K). 

As you saw in Chapter 1, one of the convenient features of the metric system is that the relationships between metric units can be derived from the metric prefixes. These relationships can easily be translated into conversion factors. For example, milli- means 10 (or 0.001 or 1/1000), so a milliliter (mL) is 10 liters (L). Thus there are 1000 or 10 milliliters in a liter. (A complete list of the prefixes that you need to know to solve the problems in this text is in Table 1.2.) Two possible sets of conversion factors for relating milliliters to liters can be obtained from these relationships. 

The metric system is a system of measurement using units based on the decimal system. Today, in English, it is formally called the International System, abbreviated SI from the original French, Systtme International. The base units of the modern metric system used in general chemistry are given in the following table. From these, you can derive all other units of measure. 

For many years scientists recorded measurements in metric units, which are related decimally, that is, by powers of 10. In 1960, however, the General Conference of Weights and Measures, the international authority on units, proposed a revised metric system called the International System of Units (abbreviated SI, from the French 5ysteme /ntemationale d Unites). Table 1.2 shows the seven SI base units. All other units of measurement can be derived from these base units. Like metric units, SI units are modified in decimal fashion by a series of prefixes, as shown in Table 1.3. We will use both metric and SI units in this book. 

Many people and many ASTM procedures use SI system, which is not the same as the metric system. The SI units are derived from the metric system units. However, for example, the SI system does not allow the use of the centimeter as a unit. It uses meters. 

The metric system was modified as Systeme International (SI) units (Table 1.6) to prevent some confusion. The SI is based on seven fundamental units—including the mole, meter, kilogram, and second—from which the others are derived. The significant changes for soil chemistry are mole of ion charge for equivalent, siemens for mho, joule for calorie, and pascal for pressure. Table 1.4 summarizes the SI units most frequently encountered in sod chemistry. SI allows easier conversion and communication between disciplines, but unfortunately discards some useful and familiar units, such as angstrom and equivalent,... 

The SI base units are summarized in Table 1.12. The SI units comprise a rigorously coherent form of the metric system, i.e., all remaining units may be derived from the base units using formulas that do not involve any numerical factors. For example, the unit of force is the newton (N) a 1-N force will accelerate a 1-kg mass at 1 m/s2. Hence 1 N = 1 kgm/s2. The unit of pressure is the N/m2, often referred to as the pascal. In the SI system there is one unit of energy (thermal, mechanical, or electrical), the joule (J) 1 J = 1 N-m. The unit for energy rate, or power, is joules per second (J/s), where one J/s is equivalent to one watt (1 J/s = 1 W). 

The standardized measurement units used in science and technology today are known as the metric system. It was originally established in 1790 by the French National Academy, and has undergone changes since then. The fundamental or base units of the modem metric system (SI for Systeme International d Unit6s) are found in Table 1-1. In chemistry, for the most part, you will encounter the first five of these. All other units are derived from these fundamental units. For example ... 

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