Standard Units

Class 6 Science · Chapter 5: Measurement of Length and Motion · NCERT Curiosity section 5.2

Learn

Scientists around the world agreed on a common set of units called the International System of Units (SI). The SI unit of length is the metre (m).

For smaller lengths we divide the metre: 1 m = 100 centimetres (cm), and 1 cm = 10 millimetres (mm). For long distances we use the kilometre: 1 km = 1000 m.

1 km = 1000 m · 1 m = 100 cm · 1 cm = 10 mm

Choose a unit that suits the job: mm for the thickness of a coin, cm for a pencil, m for a room or a cricket pitch, km for the distance between two towns.

To change a bigger unit into a smaller one, multiply: 3 m = 3 × 100 = 300 cm. 4 cm 5 mm = 40 + 5 = 45 mm.

3 m = 300 cm · 4 cm 5 mm = 45 mm

Explore: pick the best unit.

1. Sort each into the best unit.

Remember

• The SI unit of length is the metre (m).
• 1 km = 1000 m, 1 m = 100 cm, 1 cm = 10 mm.

Quick check

How many centimetres are there in 2 metres?

1. 200 cm
2. 20 cm
3. 2000 cm
4. 100 cm

Think about it

Farhan's rope is 2 m 35 cm long. Write its length in centimetres and in millimetres.

Practice

Practise with fresh questions at three levels (easy, medium, hard), some answered hands-on, with hints and worked answers. Get 4 of your last 5 right to finish the topic.