In this topic you will

• Measure mass using grams ($\text{g}$) and kilograms ($\text{kg}$).
• Read scales that show grams ($\text{g}$), kilograms ($\text{kg}$), and temperature.
• Estimate the mass of familiar objects.

The mass of a light object such as a pencil is measured in grams. A heavier object such as a bag of flour is measured in kilograms. Light things are not always small. Big things are not always heavy.

This balloon is big and light.

We can measure temperature using a thermometer. The hotter something is, the higher up the scale the colour inside it goes.

EXERCISES

$1$. The recipe for $12$ chocolate chip cookies is

How much of each would you need if you wanted to make $6$ biscuits?

__________ flour    __________ butter    __________ sugar

__________ chocolate chips

Tell your partner how you worked out your answers.

👀 Show answer

$6$ is half of $12$, so halve each amount: flour $50$ grams, butter $20$ grams, sugar $15$ grams, chocolate chips $10$ grams.

$2$. Estimate and record the mass of four objects in your classroom.

Use weighing scales and record in the table below.

👀 Show answer

Answers will vary depending on the objects you choose. Example entries:

• Pencil: estimate $10$ g, mass $8$ g, less than $100$ g.
• Rubber/eraser: estimate $25$ g, mass $22$ g, less than $100$ g.
• Small book: estimate $300$ g, mass $280$ g, more than $100$ g.
• Water bottle (empty): estimate $60$ g, mass $55$ g, less than $100$ g.

$3$. Work with a partner.

You will need balance scales.

Use the weights on your table.

Estimate and then find $2$ weights that equal $1$ kilogram ______ + ______

Find $3$ weights that equal $20$ grams ______ + ______ + ______

Find $4$ weights that equal $20$ grams ______ + ______ + ______ + ______

👀 Show answer

Answers depend on which weights you have. Example solutions (using common classroom weights):

• $1$ kilogram: $500$ g + $500$ g.
• $20$ grams using $3$ weights: $10$ g + $5$ g + $5$ g.
• $20$ grams using $4$ weights: $5$ g + $5$ g + $5$ g + $5$ g.

$4$. Find the mass of an object using different non-standard units.

Keep the object you are weighing the same but change the non-standard unit each time. A non-standard unit could be counters, cubes, wooden blocks or something else.

Record your findings.

What do you notice?

Which non-standard unit was the best to use? Explain why.

Which non-standard unit was not good to use? Explain why.

👀 Show answer

• What do you notice? The number of units changes depending on the unit you choose. Smaller units usually need more pieces; larger units need fewer pieces.
• Best non-standard unit: A unit that is the same size and weight each time (for example, identical cubes) because it gives a fair, consistent result and is easy to count.
• Not good to use: Units that are different sizes or are awkward to balance (for example, mixed blocks) because the result is less reliable and harder to compare.

Think like a Mathematician

Play this game on your own. You will need some mass cards. The aim of the game is to get as close to $100$ grams as you can.

Method:

1. Place the cards face down in a pile.
2. Take a card. Place it on one of the spaces by your scales.
3. Draw an arrow on the scales to match your card.
4. Take a second card. Add this to the first card and draw an arrow showing the combined mass of both cards.
5. You can pick up to $4$ cards, in turn.
6. The player whose scales show a mass closest to $100$ grams is the winner.

Follow-up Questions: