Mass
2.0 Measurement · 2.4 Mass
Syllabus tag: Kenya CBC | Grade 6 Mathematics | Strand 2.0 Measurement | Sub-Strand 2.4 Mass (14 Lessons)
Lesson objectives
By the end of this topic, you will be able to:
- Identify the tonne as a unit for measuring mass
- Identify the relationship between the kilogramme and the tonne
- Estimate mass in tonnes
- Convert, add, subtract, multiply, and divide tonnes and kilogrammes
- Appreciate the use of the kilogramme and tonne in measuring mass
Mass
Mass is how heavy something is. You already know the gramme and the kilogramme. Grade 6 adds the tonne, for very heavy things.
a) The tonne
A tonne is 1 000 kilogrammes.
It is used for lorry loads, harvests, and building materials. A small car weighs about one tonne.
The short way to write it is t. So 3 t means three tonnes.
b) Converting
To change tonnes to kilogrammes, multiply by 1 000.
To change kilogrammes to tonnes, divide by 1 000.
A check: kilogrammes are smaller, so there are more of them. Tonnes give the smaller number.
c) Estimating in tonnes
| Thing | About |
|---|---|
| A bag of cement | 50 kg |
| Twenty bags of cement | 1 tonne |
| A small car | 1 tonne |
| A loaded lorry | 10 tonnes |
| A full water tank of 5 000 litres | 5 tonnes |
Before calculating, guess. If you expect about 3 tonnes and get 300, something is wrong.
d) Adding and subtracting
Add the kilogrammes first, then the tonnes.
The kilogrammes may come to 1 000 or more. Change each 1 000 into a tonne and carry it across.
In subtraction there may not be enough kilogrammes. Borrow one tonne and turn it into 1 000 kg.
e) Multiplying and dividing
Multiply or divide each part, then tidy up.
Three loads of 2 t 400 kg come to 6 t 1 200 kg. Change the 1 200 kg, giving 7 t 200 kg.
f) Where this is used
A farmer weighs a maize harvest in tonnes. A lorry has a load limit. A builder orders sand by the tonne. A shopkeeper weighs sugar in kilogrammes.
Words to know
- Tonne (t) — a unit of mass; 1,000 kg = 1 tonne.
- Kilogramme (kg) — the standard unit of mass, used for everyday-scale objects.
:::checkpoint Check yourself
- How many kilogrammes make one tonne?
- Change 7 tonnes into kilogrammes.
- Change 3 200 kg into tonnes.
- Add 1 t 700 kg and 2 t 500 kg. :::
Bridge to practice
Try the exercises below — converting, adding, subtracting, multiplying, and dividing masses given in tonnes and kilogrammes.