Metric system pressure measurement

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... 

At the core of any science is measurement. Being able to measure volumes, pressures, masses, and temperatures as well as the ability to count atoms and molecules allows chemists to understand nature more precisely. Modern science uses the International System of Units (SI) that was adopted worldwide in 1960. The metric system of measurement, which is consistent with the International System, is widely used in chemistry and is the principal system used in this book. 

Scientists measure many different quantities—length, volume, mass (weight), electric current, temperature, pressure, force, magnetic field intensity, radioactivity, and many others. The metric system and its recent extension, Systeme International d Unites (SI), were devised to make measurements and calculations as simple as possible. In this chapter, length, area, volume, and mass will be introduced. Temperature will be introduced in Sec. 2.7 and used extensively in Chap. 11. The quantities to be discussed here are presented in Table 2-1. Their units, abbreviations of the quantities and units, and the legal standards for the quantities are also included. 

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. 

A variety of pressure units are in use. These units are related to the column of mercury shown in Figure 6.2. The height of the mercury column in the tube is commonly measured in inches or in millimeters. As you listen to the weather report on the evening news, notice that the atmospheric pressure is given in inches. Where the metric system is in use, millimeters are favored. Millimeters are synonymous with torr, a unit named for the Italian scientist Evangalista Torricelli. Less frequently used units are atmospheres and pascals. The following equation shows the relationship among these various units of pressure. 

The common unit of measurement for natural gas is the standard cubic foot in the English system and the standard cubic meter in the metric system. Each of these standards is expressed at pressures and temperatures commonly used as standard to the system in the geographical area of concern. In the United States, where standards frequently vary from state to state, the cubic foot is frequently expressed in the English system at standard conditions of 14.73 pounds per square inch absolute (psia) and 60 degrees Fahrenheit (60°F), although there are a number... 

You definitely must not confuse the standard atmosphere with atmospheric pressure. The standard atmosphere is defined as the pressure (in a standard gravitational field) equivalent to 1 atm or 760 mm Hg at 0 C or other equivalent value, whereas atmospheric pressure is a variable and must be obtained from a barometer each time you need it. The standard atmosphere may not equal the bara-metric pressure in any part of the world except perhaps at sea level on certain days, but it is extremely useful in converting from one system of pressure measurement to another (as well as being useful in several other ways to be considered later). Expressed in various units, the standard atmosphere is equal to... 

In the above relationship, the back pressure is measured in bars. This is just one of a number of systems of units used in HPLC to measure pressure. The SI unit of pressure is the Pascal (Pa), although this is not used very often in this context, probably because of the large and unwieldy numbers needed to describe typical HPLC pressures. Other units that may be encountered include pounds per square inch (psi), which tends to be the favoured unit in the United States, and its metric equivalent kg/cm. ... 

Polyacrylonitrile was ground under a constant pressure of 1 atm with vinyl chloride and with butadiene to give graft and block copolymers as well as minor amounts of homopolymer in the first system [33]. The products were characterized by chemical and infrared analysis, viscometric and turbidi-metric measurements, and solubility. The results are reported in Table 5.4. 

A simple serviceability metric that can be applied to all infrastructure systems is to compare capacity or supply to customer demand as a simple ratio. Another type of metric is to determine whether an infrastructure system is able to provide service at some threshold condition, e.g., potable water at sufficient pressure and quality or electric power at sufficient voltage. Table 2 lists some examples ot metrics that may be used to measure serviceability tor different infrastructure systems, although this list is not exhaustive. 

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