4.1. Measuring surface area If it is a regular body, we can measure its sides and angles and use a mathematical formula . If it is an irregular body, we can use a graph paper template or weigh it. 1 Measure surface area by weight Calculate the surface area Measured surface area: SM = 1 dm2 MM = 20.8 g Surface area you need to find: SF = 8 3 1 20 8 2 . . g g dm × ® SF = 0.39 dm2 1. Cut out the irregular surface area. 1 dm2 1 dm2 3. Weigh the measured surface area, SM. Its mass is MM. 4. Weigh the irregular surface area. The surface area you need to find is SF. 36 Sometimes, you need to be inventive to measure a quantity indirectly. Use the pictures to help you design a method that allows you to: a) Measure the thickness of a sheet of paper. b) Find out how many screws are in a drawer without counting them. 37 The owner of a fabric shop wants to know how many square metres of fabric are left on a roll that is 2 m wide. Can you think of a way of measuring this without having to unroll all the fabric? Clue: you can use scales. A C T I V I T I E S 2. Cut out a measured surface area from the same material (for example, a square with side 1 dm). 23
RkJQdWJsaXNoZXIy