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8.06 Measure and estimate mass


Are you ready?

Think about a feather and an elephant. Which one of those items do you think would be heavier?

Unit of mass

This video introduces the units of grams and kilograms and discusses the types of objects that would be measured by these units.

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Example 1

Which unit is best to measure the mass of this cup of flour?

This image shows a cup of flour.
Worked Solution
Create a strategy

Remember that 1 kilogram is equal to 1000 grams.

Think about these examples to help you.

ObjectBest unit
Bar of chocolateGrams
Apply the idea

A cup of flour is small and light like a bar of chocolate.

So the correct answer is B: Grams.

Idea summary

Grams are appropriate to measure small light objects like a pencil case or cup.

Kilograms are appropriate to measure heavy objects like people and bikes.

Measure mass with scales

This video looks at measuring the mass of objects using a scale. Key considerations are how to identify the scale used and how it is similar to a number line.

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Example 2

The scale below shows an object balanced evenly with a particular set of weights.

This image shows a scale that evenly balances an object and weights.

The following weights were on the scale:

This image shows 1 5 kilogram weight, 2 2 kilogram weights, and 3 1 kilogram weights.

What is the total mass of the object?

Worked Solution
Create a strategy

Find the total mass by adding all the values on the given weights.

Apply the idea

We can see there is one 5\text{ kg} weight, two 2\text{ kg} weights and three 1 \text{ kg} weights.

\displaystyle \text{Object}\displaystyle =\displaystyle 5+2+2+1+1+1Add the values
\displaystyle =\displaystyle 5 + 4 + 3Add the 2s and 1s
\displaystyle =\displaystyle 12 \text{ kg}Add the values
Idea summary

When two items are balanced on a scale then their weights are equal.

Estimate the mass of an object

We may not always need to know the exact mass of an object, especially if we can compare our object to other objects. This video looks at objects using grams (g) and kilograms (kg).

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Example 3

Choose the best estimate for the mass of baby.

45 \text{ kg}
95 \text{ kg}
25 \text{ kg}
2 \text{ kg}
Worked Solution
Create a strategy

Use the following examples of objects with approximately these weights:

ObjectWeight (kg)
16\, \text{year old}45
\text{adult male}95
Apply the idea

A cat, which is 2\text{ kg,} is likely to have roughly the same weight as a baby.

The best estimate is in Option D.

Idea summary

A gram has a mass similar to a piece of paper, or a feather.

A kilogram has a mass similar to a 1 litre bottle of milk or juice.



Use scaled instruments to measure and compare lengths, masses, capacities and temperatures

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