Introduction

This book has been prepared using the international systems of units (SI) that has been or is being adopted by all nations of the world. In SI practice, the approved units for energy and power are the joule and the watt:

When SI units are used for calculations, they are frequently preceded by a prefix that is a multiple of 10. Then the same basic unit can be used to measure a very large or a very small quantity. Thus, a millimeter is slightly more than 1/16 of an inch, while a kilometer is slightly more than ½ mile. The prefixes, symbols, and multipliers are:

The SI system of units has several important advantages: (i) it is universal, with a single unit for each quantity (e.g., m for length); (ii) it uses decimal arithmetic, facilitating changes, calculations, and conversions; and (iii) it is coherent, meaning that when two units are multiplied or divided, the product or quotient has the units of the resultant quantity (e.g., m and ha are coherent while ft and acre are not).

The common units of the SI system are the kilogram (mass), the meter (length), the second (time), the newton (force), the watt (power), and the joule (energy). Table B-1 lists common conversion factors for energy and power. Table B-2 includes other useful SI conversion factors.