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Measuring Length Accurately

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Measuring Length Accurately

Help a community workshop check lengths before cutting materials. Use millimetres (mm), centimetres (cm) and metres (m) as appropriate. Show working for calculations. Remember: 10 mm = 1 cm and 100 cm = 1 m.

Read the scale

A careful start makes an accurate measurement.

1.A pencil is 8.6 cm long. What is its length in millimetres? Explain how you converted the measurement.

2.A ruler has a chipped end, so Maia places a screw at the 1.4 cm mark. The other end is at 7.9 cm. What is the screw's length?

3.Which method is most reliable for measuring the curved edge of a large planter?

Hold a rigid ruler across the curve and estimate.
Lay a flexible tape along the curve, then read its length.
Measure the planter's height and use that as the curve length.
Use a ruler but leave a gap between it and the edge.

Convert and compare

Choose units that suit the job, and keep conversions precise.

4.Convert each length: (a) 245 mm to cm; (b) 3.08 m to cm; (c) 0.6 cm to mm.

5.A builder needs to measure the thickness of a plywood sheet, the length of a garden bed and the distance between two towns. Choose a suitable unit (mm, cm, m or km) for each, in that order.

6.Two people measure the same timber board. One records 1.274 m and the other 1.27 m. Are these measurements necessarily different? Explain.

Workshop challenge

Use the supplied measurements to plan a cut and spot possible errors.

Strip A: 84.6 cm

Strip B: 0.92 m

Strip C: 875 mm

Strip D: 0.81 m

7.Convert strips B, C and D to centimetres, then order all four strips from shortest to longest.

8.The workshop needs a piece exactly 2.35 m long. It has one 1.28 m length and one 96 cm length. Can these be joined to make the required length? Show the calculation and state the difference, if any.

9.A student measures a board with a ruler but starts at the ruler's worn edge instead of the zero line. Name one likely effect on the reading and one way to prevent this error.

10.Hana measures a curved garden border by laying a piece of string along it, marking the endpoints, then straightening the string beside a ruler. Give one reason this method works and one way Hana could improve its accuracy.