5.2. Converting units of density Density measures the mass of a body per unit volume. We usually need to use two conversion factors to convert its units. For example, the density of ketchup is 1.16 g/mL. We are going to write it in kg/m3. 48 In your notebook, order these units of time from smallest to largest. thousandth of a second second day year tenth of a second minute week hundredth of a second hour month 49 Calculate how many thousandths of a second there are in 47 seconds. 50 A film is 135 minutes long. How many hours does it last? 51 A song is 4.30 minutes long. How many tenths of a second does it last? 52 Mercury is a liquid metal with a high density. 1 L of mercury has a mass of 13.59 kg. Write its density in kg/m3. 53 The air we breathe has a density of approximately 1.29 kg/m3. Write it in g/L. 54 A car is travelling at a speed of 90 km/h. Write it in m/s. 55 The technical data for a hoverboard indicates that its maximum speed is 5 m/s. Write it in km/h. 56 A farmed snail moves at an average speed of 5.8 m/h. A common garden snail moves at an average speed of 13.9 mm/s. Which snail is faster? 57 Imagine you want to buy loose detergent to fill your 5 L container and the price is in €/kg. Can you calculate how much it will cost? How? A C T I V I T I E S 1 Density, d, is calculated as: density mass volume = 1. Find the equivalence between the initial unit and the final unit. 3. Simplify the units. Calculate and write the final result in the new unit. 1 kg = 1000 g = 103 g ® 1 kg = 103 g 1 m3 = 1 000 L = 1 000 000 mL ® 1 m3 = 106 mL 1.16 g/mL = 1.16 g mL × 1 103 kg g × 10 1 6 3 mL m = 1 160 kg/m3 2. Write the conversion factor for each of the units you want to convert, in order to simplify the units. 1.16 g mL × 1 103 kg g 1.16 g mL × 10 1 6 3 mL m 1st factor Convert: g ® kg. 2nd factor Convert: mL ® m3. 27
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