143
The kilometre
Textbook: Part 4, lesson 133, pp. 38–39
GoalThe kilometre as a unit of length; 1 km = 1000 m; converting between units of length.
New words
kilometre (km) · kilometrmetre (m) · metrdecimetre (dm) · detsimetrmillimetre (mm) · millimetr
Explanation
Long distances are measured in kilometres: 1 km = 1000 m. Also: 1 m = 10 dm, 1 dm = 10 cm, 1 m = 100 cm, 1 cm = 10 mm, 1 dm = 100 mm. Going from a bigger unit to a smaller one we multiply: 2 km = 2000 m, 97 cm = 970 mm. 2 m 30 cm = 200 cm + 30 cm = 230 cm.
Worked examples
1 km − 900 m = 1000 m − 900 m = 100 m.
150 m + 350 m = 500 m, which is half a kilometre.
Class activity
“Length staircase”: on the board a staircase: km – m – dm – cm – mm. Children take a card (for example 3 m), step down the staircase and say “3 m = 300 cm”, naming the multiplier (10 or 100) at each step.
Practice
1
How many metres is 2 km?
2000
2
1 km − 540 m = how many metres?
460
3
2 m 30 cm is how many centimetres?
230
4
97 cm is how many millimetres?
970
5
345 m + 144 m = how many metres?
489