# Stage 2 – mass

## Strategy

Students can:

• compare masses by hefting
• measure mass using a variety of scales
• measure mass to the nearest 10 grams

## Activities to support the strategy

### Activity 1 – ordering cupfuls

1. Students make a list of objects that they would measure in kilograms which are found:

2. Students will investigate the mass of different objects that are less than one kilogram and discover if cupful’s of different materials have the same mass.

Materials:

• kitchen scales
• plastic bags for measuring
• measuring cups
• a variety of different materials

Ask students to collect six different materials from around the home and bring to school in different containers. They place the materials in piles on their desk. Suggested materials include flour, rice, and beads, sand, small pebbles, cotton wool, leaves, dirt, bark chips.

• Have students fill a cup with the first material, then place the cupful into a plastic bag and tie the bag. Repeat for the other five materials until the students have six bags.
• Students compare two bags at a time by hefting. To do this, choose two bags and hold one in each hand. They decide which bag is the lighter and which bag is the heavier. Then choose another two bags and compare.
• Continue hefting pairs of bags until the students have ordered all the bags from the lightest to the heaviest and recorded the order.

Discuss:

• What was the order of the materials from the lightest to the heaviest?
• How do you know which was the heaviest or the lightest material?
• Did any bags seem to be about the same mass when you hefted? Which ones?
• Students check their estimates by measuring the bags on the kitchen scales. They calculate the mass to the nearest 50 grams and record the results in a table.

For example:

• Was there any difference in the order of materials when you hefted and when you measured? Give details.
• Each bag contained a cupful. Why did the masses differ if the materials all took up the same space?

Discuss:

• Which would weigh more - one kilogram of feathers or one kilogram of bricks? Give reasons.

### Activity 2 – using balance scales

Discuss what measuring instruments we can use to measure the mass of objects.

Measuring devices may include bathroom scales, kitchen scales and balance scales. Discuss that when using any measuring instrument students must:

• know how to read the scale
• check that the scale is set at zero

If you only wanted to find out how heavy an object is you could use bathroom scales, kitchen scales, a spring scale or balance scales.

If you wanted to compare two objects to find out which is the heavier you could use balance scales.

On a flat, level surface, such as a table, the teacher places balance scales which are out of balance.

• Do the two masses on these balance scales weigh the same?
• Which is the heavier mass? How do you know?

### Activity 3 – making 100 grams

Students collect a variety of small objects and estimate how many of each object is needed to equal a mass of 100 grams.

Materials:

• balance scales, if you have them, if not, use kitchen scales
• weights to balance the scales
• objects to weigh e.g. pencils, lego blocks, teaspoons, lollies, erasers, coloured textas, blackboard duster

1. Students select one object and compare the mass of the object with a kilogram weight by hefting. They:

• estimate how many of this object would be needed to equal 100 grams and record their estimate in the table (below).
• measure and record the actual number of objects using balance scales

Ensure that students are measuring accurately using the balance scales by following these steps:

Object Estimated number Actual no of objects to balance 100 grams Students use this table to estimate, measure and record the number of objects needed to balance 100 grams.

2. Students choose three different objects from their collection and measure the mass of each object to the nearest 10 grams. They draw or write the objects and record the masses.

3. Students could repeat these steps to measure 50 grams.

### Activity 4 – "Mass-ive" Model

#### Materials:

• Unifix cubes (or any other interlocking blocks e.g. Lego, centicubes)
• Kitchen scales or balance scales

1. Students build a model using 20 unifix cubes, they estimate the mass of their model and record their estimate. Then measure the mass in grams and record in a table.

Number of cubes Estimate Measure
20 ..........g ..........g

#### Discuss:

Was your estimate close to the actual mass?

Students add more cubes to their model until there are 40 altogether. They estimate the mass, then measure and record the mass in grams. Repeat with 60 cubes and 50 cubes.

Number of cubes Estimate Measure
40 ..........g ..........g
60 ..........g ..........g
50 ..........g ..........g

View/print Measure and record the mass template (PDF 103.04KB)

Using these results students estimate what would be the mass of

• 100 cubes
• 200 cubes
• 400 cubes
• 1000 cubes

2. Students decide on the number of cubes to use and build three more models. They estimate and record the mass of the models in a table.

Number of cubes Estimate Measure
enter here ..........g ..........g
enter here ..........g ..........g
enter here ..........g ..........g

#### Discuss:

• Were your estimates reasonably accurate?
• Did you use other measurements from this activity to help you estimate? Give details.

### Activity 5 – reflecting

Students reflect on the activities they have completed.

#### Discuss:

• Are you close to the correct measure when you estimate mass in kilograms or grams?
• Can you accurately measure masses to the nearest 10 grams using balance scales and kitchen scales?
• When would you use grams to weigh an object?
• Students complete this paragraph to explain what a gram is.

If you wanted to find the mass of an object (lighter/heavier) than a kilogram, you would use a unit of measurement (less/greater) than 1 kilogram. You would use grams.

## References

### Australian curriculum

ACMMG084: Use scaled instruments to measure and compare lengths, masses, capacities and; temperatures.