L2 · Measuring lengths of straight lines and curves (described readings)

Learning goal

“I can measure a straight line with a ruler - start at the 0 mark and read the end mark, and count the spaces when a line does not start at 0 - and I can measure a curve by laying a string along it and then measuring the string.”

Ruler — a measuring tool marked with units. The marks are the same space apart all the way along.

Zero mark — the mark where measuring starts. A line is lined up with the 0 mark first.

Curve — a line that bends, like a wavy path.

String method — a way to measure a curve: lay a string along the curve, pinch the end, straighten the string, and measure it with a ruler.

Worked example

A line starts at the 0 mark on a ruler. It ends at the 14 mark. Step 1: The start is at 0, so the end mark tells the length directly. Step 2: The line is 14 cm long. Now a harder one: a line starts at the 2 mark and ends at the 9 mark. Step 1: The end mark (9) is NOT the length, because the line did not start at 0. Step 2: Count the spaces from 2 to 9: 9 - 2 = 7. Step 3: The line is 7 cm long. Say it plainly: starting at 0 - read the end mark. Starting anywhere else - count the spaces (end mark minus start mark).

Check yourself — explain it

When a line does not start at the 0 mark, we find its length by...

Paired problem — example still visible

A line starts at the 0 mark and ends at the 11 mark. How long is it? -> 11 cm

Faded completion — last step is yours

"A line runs from the 3 mark to the 10 mark: 10 - 3 = ___ cm" -> 7

Ready to practise?

10 scored questions with a 3-rung hint ladder. Mastery needs 8/10 plus both gate questions.

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