7.2 Length, Area, and Volume 419 This section and the next section are designed to help you think metric , that is, to become acquainted with day-to-day usage of metric units. In this section, we consider length, area, and volume. Units of Length in the Metric System The basic unit of length in the metric system is the meter. Internationally, meter is spelled “metre.” Other commonly used units of length are the kilometer, centimeter, and millimeter. The meter, which is a little longer than 1 yard, is used to measure things that we normally measure in yards and feet. The length of a guitar is about one meter. A tractor trailer unit (an 18-wheeler) is about 18 meters long. A soccer field is about 105 meters long. The kilometer is used to measure what we normally measure in miles. For example, the distance from New York to Seattle is about 4600 kilometers. One kilometer is about 0.6 mile, and 1 mile is about 1.6 kilometers. Centimeters and millimeters are used to measure what we normally measure in inches. The centimeter is a little less than inch 1 2 (see Fig. 7.1), and the millimeter is a little less than inch. 1 20 A millimeter is about the thickness of a dime. A book may measure 20 cm by 25 cm with a thickness of about 3 cm. Millimeters are often used in scientific work and other areas in which small quantities must be measured. The length of a small insect may be measured in millimeters. 0 0 1 2 3 4 1 2 3 4 5 6 7 8 9 10 Centimeters (smaller markings are millimeters) Inches Figure 7.1 MATHEMATICS TODAY Tire Size Why This Is Important We see metric units used in many aspects of our lives today—from the medicines we take to tires on vehicles we drive. Having a knowledge of metric units allows us to be more informed consumers. On the side of every tire you will see a code that provides information about the tire. The P at the beginning of the code given below indicates that the tire is intended for a passenger vehicle. The three digits after the P, 205, represent the tire’s width in millimeters; see Fig. 7.2. The two-digit number after the slash, 65, represents the tire’s aspect ratio. This is the ratio of the tire’s height (from tread to rim) to its width. The height of this tire would be 65% of the tire’s width of 205 mm, or × = 0.65 205 133.25 mm. The R that follows the 65 indicates that the tire is a radial tire. The last two digits, 16, indicate that the tire is meant to be mounted on a wheel with a diameter of 16 inches. 16 in 133.25 mm 205 mm Figure 7.2 From Fig. 7.1 we can see that 1 inch is about 2.5 centimeters, or about 25 millimeters. Example 1 Choosing an Appropriate Unit of Length Determine which metric unit of length you would use to express the following. a) The diameter of a basketball b) The length of a bee c) The height of a five-story apartment building d) The distance between New Orleans and San Diego e) The height of a doorway in your home f) The distance of a running race Solution a) Centimeters b) Millimeters c) Meters d) Kilometers e) Meters or centimeters f) Meters or kilometers In some parts of this solution, more than one possible answer is listed. Measurements can often be made using more than one unit. 7 Now try Exercise 17 Why This Is Important Learning how metric units are used to measure items we encounter is important to understanding the world around us. Products leaving or coming into the U.S. are likely to have specifications given in metric units. Serezniy/123RF
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