99
Length. The centimetre
Textbook Part 3, pp. 52–53
GoalUnderstand why we measure length; meet the centimetre.
New words
length · uzunlikcentimetre (cm) · santimetr (cm)metre (m) · metr (m)ruler · chizg‘ich
Explanation
Long ago people measured length with elbows, hand-spans and steps. But everyone’s arm is different, so the results differed. That is why we need a unit that is the same for everyone. The distance between two long marks on a ruler is 1 centimetre (1 cm). In a notebook 1 cm = 2 squares. Short things are measured in centimetres, long things in metres.
Worked examples
Measure a desk in elbow-lengths: Aziz got 5, the teacher got 3. Why? Their arms are different lengths.
A pencil is 15 cm; a classroom is 8 m.
Class activity
Children measure a desk in hand-spans, then with a ruler. They compare: hand-span results differ, centimetre results agree.
Practice
1
A segment 6 notebook squares long is how many centimetres?
3 cm
2
What do we measure in cm and what in m: a pencil, a football pitch, a leaf?
Pencil and leaf — cm; football pitch — m
3
How many centimetres long is your ruler?
Usually 15 or 20 cm
4
4 cm + 5 cm = ?
9 cm