Metric system pressure unit

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... 

Temperature scale, Celsius (°C) A temperature scale used in the metric system of units. For water, the freezing point is taken as 0°C and the boding point, under standard pressure conditions, is taken as 100 C. The term is more correct in modem usage than is centigrade. 

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. 

Many units are used to express pressure. Because pressure is defined as force per unit area, a common unit used in the United States is pounds per square inch. This unit is commonly used for tire inflation pressure. The atmospheric pressure at sea level is about 14.7 pounds per square inch. In the metric system, the basic unit for force is the newton, abbreviated N, and area is mea-... 

When solving gas law problems using the combined gas law, the pressure and volume units do not have to be as indicated by the authors of the laws and by the ideal gas law they don t even have to be in the metric system. However, temperature must be in the Kelvin scale. Explain. 

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... 

The physical properties of water are used to define many physical constants and units. The freezing point of water (saturated with aii at 1 atm pressure) is taken as 0° C, and the boiling point of water at 1 atm is taken as 100° C. The unit of volume in the metric system is chosen so that 1 ml of water at 3.98° C (the temperature of its maximum density) weighs 1.00000 gram. A similar relation holds in the... 

For gases the standard reference material is dry air and its density is taken at the same temperature and pressure for which the density of the gas is given. The distinction between specific gravity and density must he kept clearly in mind. In the metric system, the density of water is essentially equal to one. Consequently, specific gravities and densities have substantially the same numerical values in this system of units. However, this is not generally true. 

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. ... 

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. 

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 first careful experiments on gases were performed by the Irish scientist Robert Boyle (1627-1691). Using a J-shaped tube closed at one end (see Figure 13.3), which he reportedly set up in the multistory entryway of his house, Boyle studied the relationship between the pressure of the trapped gas and its volume. Representative values from Boyle s experiments are given in Table 13.1. The units given for the volume (cubic inches) and pressure (inches of mercury) are the ones Boyle used. Keep in mind that the metric system was not in use at this time. 

A couple of preliminary items should be done first. In the middle of the window, there are two boxes in which we can specify the units to be used in the simulation. Figme 3.15 shows the standard three alternatives ENG (English engineering), MET (metric), and SI (Systeme International). We will use SI units in most of the examples in this book because of the increasing importance of our global economy. However, we will make one departure from regular SI units. In the SI system, pressures are in pascals (N/m ), which are quite inconvenient for most chemical processes because typical pressme are very large numbers in pascals (1 atm = 101,325 Pa). Therefore, we will use pressmes in atmosphere in most of the examples. However, make sure that you select the correct units when you enter data. 

In countries that use the metric system, such as Canada, atmospheric pressure in weather reports is given in units of kPa. Convert a pressure of 745 torr to kPa. 

The units of pressure are those of force per unit area. In the English system, these are pounds per square inch (Ib/in. ), often abbreviated as psi and in the metric system, these are newtons per square meter (N/m ), also called a pascal (Pa). Several other units of pressure are also in common use (Table 11-1). 

When you are using the metric SI system of units, it is wise to remember that many units are named in terms of a magnitude of 10, e.g., kilo or mega as a prefix. When you are performing computations, it is advised to reduce these terms to their most basic set of units. For example, if you have a cylinder that is 609.6mm (24") ID that contains 1000KPa of pressure that is 24mm thick, the hoop stress is... 

Table 12.1. The units given for the volume (cubic inches) and pressure (inches of mercury) are the ones Boyle used. Keep in mind that the metric system was not in use at this time.

This section will try to assist the reader in sizing SRVs. In the first part, sizing data are given in English units (United States Customary System, USCS) consistent with the requirements of ASME Section VIII, API Recommended Practice 520, for pressures above 1.03 barg (15psig). Metric units are given only for the most common sizes. 

The pressnre P exerted by a flnid on a snrface is defined as the normal force exerted by tlie finid per nnit area of the snrface. If force is measnred in N and area in m, the unit is tlie newton per sqnare meter or N m , called the pascal, symbol Pa, the basic SI nnit of pressure. In tlie metric engineering system a common nnit is the kilogram force per sqnare centimeter (kgf cm ). 

P to point 2 witli volume Vj pressure P2- This path relates the pressure at any point of the process to tlie volume. Tlie work required is given by Eq. (1.3) and is proportional to the area under tlie curve of Fig. 1.3. The SI unit of work is the newton-meter or joule, symbol J. In the metric engineering system the nnit often used is the meter-kilogram force (m kgl). 

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... 

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