# Stage 3 – mass

## Strategy

Students can:

• measure mass accurately
• record mass in grams and kilograms to 3 decimal places
• convert between kilograms and grams

## Activities to support the strategy

1. Students discuss different ways of recording mass. Complete the table to show equivalence between kilograms and grams.

### Ways we write units of mass

One kilogram One half of a kilogram One quarter of a kilogram Three quarters of a kilogram 1 kilogram 1 kg 1000 grams 1000 g ½ kilogram ½ kg 500 grams 500 g enter answer enter answer enter answer enter answer enter answer enter answer enter answer enter answer

#### Discuss:

Why is it harder to find examples of the number of grams written in word form? (i.e. too long and unnecessary)

When are kilograms more likely to be used and when are grams more likely to be used?

2. Introduce the key vocabulary used in recording metric mass by discussing these prefixes:

• milli - thousandth of
• centi - hundredth of
• kilo - 1000 wholes

These prefixes are used with measurements. They tell us how much of something we have. The prefixes milli and centi tell us there is less than one whole.

Milli means a thousandth of; centi means a hundredth of; kilo means 1000 wholes. A kilometre means 1000 metres and kilogram means 1000 grams.

Use concrete examples of equivalence in mass to illustrate each unit.

Discuss how to convert between kilograms and grams. Students practise converting from grams to kilograms and kilograms to grams.

convert grams to kilograms convert kilograms to grams
0.03 kg 78 g
1.65 kg 3 kg
0.02 kg 36 g
1.2 kg 0.75 kg
946 g 2132 g
2.8 kg 5034 g
0.9 kg 600 g

In pairs, students play 'Top Heavy'.

Prepare a set of kilograms and grams cards (PDF 71.92KB), each card has a mass written on it in either grams or kilograms. Cards are shuffled and dealt face down to each player. Players each turn over a card; the player who turned over the card with the heavier mass, scores one point.

• Play continues until all cards have been played.
• The player with the highest score wins the game.

3. Students determine the average mass of the lunch eaten by students in the class. Introduce the task by discussing:

• the strategies the students can use to find the average mass
• the importance of accuracy when measuring
• how to convert between kilograms and grams

Students complete the task by following these steps.

• Measure and record (in grams) the mass of each item in their lunch box. Find the total number of grams and compare to other students.
• Divide the class into manageable groups. Group members record the total mass of each student's lunch both in kilograms (recorded to 3 decimal places) and in grams.

Name Mass (kg) Mass (g)
enter name 1.215 kg 1215 g

View/print Measure and record the total mass (PDF 42.78KB)

Discuss:

• Which group had the lightest average mass?
• Which group had the heaviest average mass?
• What is the difference between the lightest and heaviest mass?
• How many 5 kg crates would be needed to carry all the class lunches to the lunch area? How could you work this out?
• What other questions could we ask to discover more information about our investigation?

Students write a report to explain the strategies they used and the information they discovered.

Present students with other problems which involve converting between kilograms and grams. See Teaching Measurement Stage 2 and Stage 3 (PDF 850MB).

## References

### Australian curriculum

ACMMG108: Choose appropriate units of measurement for length, area, volume, capacity and mass

### NSW syllabus

MA3-12MG: Selects and uses the appropriate unit and device to measure the masses of objects and converts between units of mass.