Conversions, unit metric-English

In this chapter, I offer suggestions on how to choose the unit or units and then how to work with the unit or units you ve chosen. This chapter also covers the tricky conversions of square feet to square inches or cubic yards to cubic feet. And, of course, no discussion of units is complete without introducing meters and kilograms, so you get conversions involving metric and English measures. 

In the literature, information is found using different systems of units metric, SI, and the English system. Quotations from the literature are presented in their original form. It would be difficult to change all these units in the book to one system. To assist the reader in converting these units, an appendix is provided with conversion factors for all units found in the text. 

Conversions between the English and SI (metric) systems are conveniently made by the unit factor method. Several conversion factors are listed in Table 1-7. It may be helpful to remember one each for... 

The conversion of a quantity expressed in units of one system to an equivalent quantity in the other system (English to metric or metric to English) requires a bridging conversion unit. Examples are shown in Table 1.3. 

English units may need conversion to metric units or vice versa. 

Metric units have been generally used and conversion from the English system has been followed except for special cases particularly involving complex units. Where appropriate, we have cited the units used in the original papers, which has generally precluded use of the more recent and more appropriate S.I. system. 

Conversions between English and metric units can be made using Table 1.3. 

Beginning students often regard the metric system as difficult because it is new to them and because they think they must learn all the English-metric conversion factors (Table 2-3). Engineers do have to work in both systems in the United States, but scientists generally do not work in the English system at all. Once you familiarize yourself with the metric system, it is much easier to work with than the English system is. 

Instructors often require English-metric conversions for two purposes to familiarize the student with the relative sizes of the metric units in terms of the more familiar English units, and for practice in conversions (see Sec. 2.4). Once you really get into the general chemistry course, the number of English-metric conversions that you do is very small. 

Still other units encountered in the literature and workplace come from various other systems (absolute and otherwise). These include metric systems (c.g.s. and MKS), some of whose units overlap with SI units, and those (FPS) based on English units. The Fahrenheit and Rankine temperature scales correspond to the Celsius and Kelvin, respectively. We do not use these other units, but some conversion factors are given in Appendix A. Regardless of the units specified initially, our approach is to convert the input to SI units where necessary, to do the calculations in SI units, and to convert the output to whatever units are desired. 

Chemistry is full of calculations. Our basic goal is to help you develop the knowledge and strategies you need to solve these problems. In this chapter, you will review the Metric system and basic problem solving techniques, such as the Unit Conversion Method. Your textbook or instructor may call this problem solving method by a different name, such as the Factor-Label Method and Dimensional Analysis. Check with your instructor or textbook as to for which SI (Metric) prefixes and SI-English relationships will you be responsible. Finally, be familiar with the operation of your calculator. (A scientific calculator will be the best for chemistry purposes.) Be sure that you can correctly enter a number in scientific notation. It would also help if you set your calculator to display in scientific notation. Refer to your calculator s manual for information about your specific brand and model. Chemistry is not a spectator sport, so you will need to Practice, Practice, Practice. 

The system of units used in chemistry is the SI system (Systeme International), which is related to the metric system. There are base units for length, mass, etc. and decimal prefixes that modify the base unit. Since most of us do not tend to think in these units, it is important to be able to convert back and forth from the English system to the SI system. These three conversions are useful ones, although knowing the others might allow you to simplify your calculations ... 

You ve decided to go to Europe and you want to be sure that you order the right size beverage, know how far you ll be traveling by car, and dress appropriately for the weather on any particular day. All these functions relate to changing from English units of measure to metric measure. Here are some of the more useful conversion equivalences you ll need for your travels. For help with the temperatures, refer to Chapter 10 for conversions from Celsius to Fahrenheit and back again. 

Table 4-2 shows how some of the basic metric units are related to units commonly used in English-speaking countries for nonscientitle measurements. Although the United States, Great Britain, and Canada have officially resolved to convert to the metric system, it will be many years before the conversion is complete. In the meantime, you must learn to convert from one system to the other. The three conversion factors given in Table 4-2 (rounded off to 2.54... 

Dimension measured Metric unit English unit Conversion factor F... 

It is important to know that all the questions are based on real numbers. In terms of measurement, units of measure are used from both the English and metric systems. Although conversion will be given between English and metric systems when needed, simple conversions will not be given. (Examples of simple conversions are minutes to hours or centimeters to millimeters.)... 

Convert 3.50 yards to (a) millimeters, (b) meters. According to Table 1-2, the conversion factor used to move between the English and metric system (SI) units is 1 in/2.54cm (2.54 x 10-2 m). 

The SI (metric) system of units is the primary one for the text. Because the Btu-ft-pound system is still in wide use, answers and intermediate steps to examples are occasionally stated in these units. A few examples and problems are completely in English units. Some figures have dual coordinates that show both systems of units. These displays will enable the student to develop a bilingual capability during the period before full metric conversion is achieved. 

A conversion factor (see below) is used when working with English engineering units no factor is necessary for SI metric units. For a given impeller geometry, the power number is a constant for conditions of turbulent agitation. Values of turbulent power numbers for some agitator impellers are shown in Fig. 12.1. 

Some conversions between mettic and English system units are presented in Table 2.4. Engineers must know how to do such conversions because they still use some English system units. However, scientists rarely use English system units, and therefore, these conversions are less important for them. (The use of a metric unit that is slowly becoming familiar to the general public is shown in Figure 2.5. Note that 80 km/h is about 50 mph.)... 

English-metric conversions are most often presented, if at all, to give an idea of the size of the metric unit. They are not used very much in this course. 

How important are conversions from one unit to another If you ask the National Aeronautics and Space Administration (NASA), very important In 1999 NASA lost a 125 million Mars Climate Or-biter because of a failure to convert from English to metric units. 

The graphs are arranged by carbon number and chemical formula to provide ease of use. English units are used for the property values. For those involved in SI and metric usage, each graph displays a conversion factor to provide the SI and metric units. 

English units are still common in some countries, while people in other countries (and the scientific community everywhere), use metric units almost exclusively. Unit analysis provides a convenient method for converting between English and metric units. Several of the most commonly needed English-metric conversion factors are listed in Table 8.1 on the next page. Because the English inch is defined as 2.54 cm, the number 2.54 in this value is exact. The numbers in the other conversion factors in Table 8.1 are not exact. 

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