7.3 Mass and Temperature 431 Example 3 demonstrates how convenient it is to convert from volume to mass in the metric system. Exercises 69 and 70 involve similar problems involving U.S. customary units of measure. Celsius Scale The metric system uses the Kelvin temperature scale. However, most sciences use the Celsius scale which is derived from the Kelvin scale. Figure 7.17 shows a thermometer with the Fahrenheit scale on the left and the Celsius scale on the right. On the Celsius scale, water freezes at 0 C° and boils at 100 C. ° In the past, the Celsius thermometer was called a “centigrade thermometer.” Recall that centi means , 1 100 and there are 100 degrees between the freezing point of water and the boiling point of water. Thus, 1 C° is 1 100 of this interval. Table 7.5 gives some common temperatures in both degrees Celsius ( C) ° and degrees Fahrenheit ( F). ° Example 2 Volume of a Fish Tank A fish tank is 1 m long, 50 cm high, and 250 mm wide (Fig. 7.15). 50 cm 250 mm 1 m Figure 7.15 a) Determine the volume of the tank in cubic meters. b) Determine the number of liters of water the tank holds. c) What is the mass of the water in kilograms? Solution a) We must convert all the measurements to the same units. Let’s convert them all to meters: 50 cm is 0.5 m, and 250 mm is 0.25 m. = × × = × × = V l w h 1 0.25 0.5 0.125 m3 Thus, the volume of the fish tank is 0.125 m .3 b) Since 1 m of water 1 k of water, 3 = 0.125 m 0.125 k , or 125 of water 3 = Thus the tank holds 125 of water. c) Since 1 of water has a mass of 1 kg, 125 of water has a mass of 125 kg. Thus the water in the fish tank has a mass of 125 kg. 7 Now try Exercise 63 210 10 20 30 40 50 60 70 80 90 100 0 qF qC –10 –20 200 190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0 –10 Figure 7.17
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