Year 9 Science · Unit 2 · Lesson 1

Why Materials Matter

Foundation Worksheet

Name

Date

Class

Learning Goals

Recall the four steps engineers use to select a material.
Classify a property as physical or chemical.
Use the four steps of material selection to choose a material from data.

Warm Up

Fill the gap

Choose the correct word from the word bank. Each word is used once. Two words will not be used.

function recycling physical selection candidates properties solution density chemical trade-offs

Engineers follow a systematic material process. The first step is to identify the : what must the material do? Next, they list the required , such as hardness, conductivity or . They then compare the against those requirements, and finally consider cost and availability. Engineers must also accept : improving one property often makes another worse. A property can be measured without changing the substance, while a property describes how the substance reacts to form something new.

1. Give one physical property and one chemical property of candle wax.

Recall 2 marks

Your Turn

Sort it: physical or chemical?

Write each property in the correct box. Ask yourself: would measuring it turn the substance into something new?

copper conducts electricity iron rusts in moist air petrol is flammable diamond is very hard ice melts at 0 °C wood burns in air aluminium: density 2.7 g/cm³ gold does not react with seawater

Physical property

Chemical property

Go Deeper

Scenario: a drink bottle for bushwalkers

A company is designing a drink bottle for bushwalkers. It must be light to carry, it must not break if it is dropped on rocks, and it must not react with water or fruit juice.

Table 1. Candidate materials for the drink bottle

Material	Density (g/cm³)	Breaks if dropped on rock?	Reacts with water or juice?
Glass	2.5	Yes	No
Carbon steel	7.9	No	Yes, it rusts
Stainless steel	8.0	No	No
HDPE plastic	0.95	No	No

Source: typical values for each material at room temperature.

2. Step 3 of material selection is to compare the candidates with the requirements. Which two materials pass both the “breaks” and the “reacts” requirements? Which of those two is better for “light to carry”? Use the densities.

Apply 3 marks

3. Many bushwalkers still buy stainless steel bottles, even though they are heavier. Suggest one trade-off these buyers are accepting, and one reason they might think it is worth it.

Analyse 2 marks

Show What You Know

4. A council is choosing the material for a new playground slide in a sunny park. Use all four steps of the material selection process to explain how an engineer would decide between stainless steel and HDPE plastic.

Apply 4 marks