Pounds , English system

The English system of units is complicated compared to the metric system. In the English system, the units of mass are pounds-mass (Ibm) and the units of weight are pounds-force (Ibf). By definition, a weight (i.e., force) of one Ibf equals the force produced by one Ibm under the acceleration of gravity. Therefore, the constant, g, which has the same numerical value as g (32.17) and units of Ibm-ft/lbf-sec, is used in the definition of weight ... 

The constant of proportionality in the English system of units, g, which causes one pound of mass produces one pound of force under the acceleration of gravity, equal to 32.17 Ibm-ft/lbf-sec. ... 

In the cgs system, power has the units of ergs per second in the mks system, units of joules per second lor watts) and in the English system, units of foot-pounds per second. A common engineering unit is the horsepower, defined as 550 foot-pounds per second or 33.000 footpounds per minute. The SI unit of power is the wall. I watt = I joule per second. < I joule is the work done by I newton acting through a distance of I meler.l I joule = watt-second = I07 ergs= I07 dyne-centimeters. The SI unil of force is the newton. (I newton = 10s dynes). See also entry on Units and Standards. 

The example just given illustrates how. on a macroscopic scale, heat can he considered a form of energy. Regardless of the material involved, any amount of heat absorbed or released may be quantitatively expressed as an amount of energy. A grum-calorie or heal is equivalent to 4.19 joules, and in the English system, a British thermal unit (Btu) is equivalent to 778 foot-pounds. 

With the selection of water as the standard with cp = I. the left side of Equation (2) clearly becomes of unil value when m and (/ - t,) are each of unit value. In Ihe English system, we accordingly have the British thermal-unit (or Btu) as the heat required lo warm I pound of pure water through an interval of I E. In the metric system, the corresponding unit is the calorie. Ihe heat required to warm 1 gram of water l°C. A large unit or kilocalorie corresponding to 1.000 ordinary calorics is also frequently used in scientific work. 

The metric system is the system of choice for chemistry, as well as for other physical sciences such as physics and astronomy. You may not feel comfortable with this system, but two aspects of its usage should relieve your concerns. First, the most troublesome mathematical manipulation, changing back and forth between the metric system and the English system (pounds, miles, gallons, and so on), is rarely required and is not included here. Second, less frequently used metric units, such as decimeters, need not be part of what you need to learn. 

Napoleon s armies spread the system throughout continental Europe, but the British (and consequently the Americans) hung to the old English inch-pound-second system. From cgs the kilogram-meter-second (mks) system evolved, and finally SI (Systeme International d Unites) was bom from mks with the addition of units of current (ampere), temperature (kelvin), and brightness (candela). The International Temperature Scale is defined by 13.8033 K (triple point of equilibrium H2) 24.5561 K (triple point of Ne) and 1234.93 K (freezing temperature of Ag). 

In the SI system a typical set of units for the parameters would be p. in kilograms per second per meter, cp in kilojoules per kilogram per Celsius degree, and k in kilowatts per meter per Celsius degree. In the English system one would typically employ p. in pound mass per hour per foot, cp in Btu per pound mass per Fahrenheit degree, and k in Btu per hour per foot per Fahrenheit degree. 

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... 

FPS. The system of units based on the fundamental units of the English system foot, pound and second. 

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. 

Whenever we measure something, from the weight of a sack of potatoes to the distance to the moon, we must express the result as a number of specific units for example, pounds and miles in the English system of measurement (although even England no longer fully uses that system), or kilograms and kilometers in the metric system. As of 1994, every nation in the world had adopted some aspects of the metric system, with only four exceptions the United States, Brunei, Burma, and Yemen. 

The units for K will depend on the units prescribed for the other terms. Thus, in the English system of units, if the pressure change is in psf (pounds per square foot), the distance is in feet, and the viscosity value is in Bvu s (British viscosity units of pounds/ft-sec), with the velocity in ft/sec, then the dimensions of K will be ft /sec. (It may be noted that the viscosity in poises has the dimensions of grams/cm-sec, and the viscosity in centipoises has the dimensions of centigrams/cm-sec. Accordingly, to convert a viscosity value in centipoises, multiply the value by 6.72 x 10 to yield the viscosity value in Bvu s.)... 

In a chemistry laboratory, the metric system of measurement is used rather than the more familiar English system. The most common measurement unit for mass is the gram, not the pound. The most common measurement unit for volume is the milliliter, not the cup. One milliliter of water is a little more than half a tablespoon of water. One milliliter (abbreviated mL ) of water weighs approximately one gram (abbreviated g ). 

The same prefixes are used with mass as with distance, and they have the same meanings. That is one facet that makes the metric system so easy. In the English system, the subdivisions of a yard are a foot—one-third of a yard—and an inch—one-thirty-sixth of a yard. The subdivision of an Avoirdupois pound is an ounce, one-sixteenth of a pound. The subdivision of a Troy pound is an ounce, one-twelfth of that pound. (Gold and silver are measured in Troy ounces.) Each type of measurement has a different subdivision, and none is a multiple of 10. The metric system uses the same prefixes for all types of measurements, they are all multiples of 10, and they always mean the same thing. The symbols for the units and prefixes are easier to learn than those for the English system units. For example, pound is abbreviated lb and ounce is oz, whereas the metric prefixes are almost always closely related to their names. It is easier to convert metric measurements because the prefixes mean some multiple of 10 times the fundamental unit. 

The English system is a collection of functionally unrelated units. In the English system of measurement the standard pound (lb) is the basic unit of weight. The fundamental unit of length is the standard yard (yd), and the basic unit of volume is the standard gallon (gal). The English system is used in the United States in business and industry. However, it is not used in scientific work, primarily because it is difficult to convert from one unit to another. Eor example. 

The unit of heat in the English system is the British thermal unit (Btu). When the unit of mechanical energy is the pound-force-foot (lbf ft), then... 

Engineering is about real physical things, which can be measured and described in terms of the units of measure. Most engineering calculations involve these units of measure. It would be simple if there were only one set of such units that the whole world agreed on and used, but that is not the case today. In the United States, most measurements use the English system of units, based on the foot, pound, and degree Fahrenheit, but most of the world uses the metric... 

In the English system, 1 pound-force = 1 pound-mass thus, (gc reconciles the mass and... 

Conversion factors for some of the English system units commonly used in the United States for nonscientific measurements (for example, pounds and inches) are provided inside the back cover of this book. 

The two most common unit systems are the English system, used in the United States, and the metric system, used in most of the rest of the world. The English system uses imits such as inches, yards, and pounds, while the metric system uses centimeters, meters, and kilograms. The most convenient system for science measmements is based on the metric system and is called the International System of units or SI units. SI units are a set of standard units agreed on by scientists throughout the world. 

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). 

The two systems of units with which you are probably most familiar are the English system (foot, gallon, pound, etc.) and the metric system (meter, liter, kilogram, etc.). Although there has been an increase in the use of metric units in the United States in recent years, English units still are used commonly. For many years scientists recorded measurements in metric units, but in 1960, the General Conference on Weights and Measures, the international authority on units, proposed a revised metric system for universal use by scientists. We wiU use both metric and revised metric (SI) units in this book. 

The measurement system that uses such familiar units as feet, yards, ounces, pounds, and gallons is known as the English system. Another system of measurement, the metric system, will be en5>hasized in this chapter and subsequent chapters. The metric system of measurement is used almost exclusively in all... 

In one English system of units, lengths are measured in feet, masses are measured in pounds, abbreviated lb (1 lb = 0.4536 kg), and time is measured in seconds. The absolute temperature scale is the Rankine scale, such that 1.8° R corresponds to 1°C and to 1K. 

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