430 CHAPTER 7 The Metric System The milligram is used extensively in the medical and scientific fields as well as in the pharmaceutical industry. Nearly all bottles of tablets are now labeled in either milligrams or grams. The metric tonne (t) is used to express the mass of heavy items. One metric tonne equals 1000 kg. A metric tonne is a little larger than our customary ton of 2000 lb. The mass of a large truck may be expressed in metric tonnes. Example 1 Choosing the Appropriate Unit Determine which metric unit you would use to express the mass of the following. a) An 8-year-old child b) A locomotive c) A dinner plate d) A box of cereal e) A laptop computer f) A vitamin tablet g) A pat of butter h) A refrigerator Solution a) Kilograms b) Metric tonnes c) Grams d) Grams e) Grams or kilograms f) Milligrams g) Grams h) Kilograms 7 Now try Exercise 15 Cubic measure or 1000 cm3 or 1000 m, or 1000 g Water Liquid measure Mass of water = = 1 dm3 1 , 1 kg Figure 7.14 One cubic decimeter of water has the volume of one liter and the mass of one kilogram. The kilogram was originally defined as the mass of one liter of water. While this is no longer the official definition, it is accurate enough for us to use. Recall from Section 7.2 that a cubic decimeter has the same volume as a liter of water. A liter of water has the mass of one kilogram. Figure 7.14 shows these remarkable connections that make converting between volume and mass very convenient in the metric system. Since 1 dm 1000 cm , 3 3 = 1 1000 m , = and 1 kg 1000 g, = we can reason that for water 1cm 1m 1g 3 = = Table 7.4 gives some important information regarding measurements involving water. Table 7.4 Volume and Mass of Water Volume in Cubic Units Volume in Liters Mass of Water 1 cm3 = 1 m = 1 g 1 dm3 = 1 = 1 kg 1 m3 = 1 k = 1 t (1000 kg) MATHEMATICS TODAY It’s a Metric World Why This Is Important The European Union (EU) adopted a directive that requires all exporters to EU nations to indicate the dimensions of their products in metric units. To trade goods in many parts of the world, U.S. manufacturers must use metric measurements. United States Liberia Myanmar Figure 7.16 The United States is the only westernized country not currently using the metric system as its primary system of measurement. The only countries in the world besides the United States not committed to using the metric system are Liberia and Myanmar (although Liberia and Myanmar use it in practice); see Fig. 7.16.
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