Year 9 Science · Unit 3 · Lesson 10
Challenge Worksheet
Learning Goals
1. Most materials expand when heated. Describe how water behaves differently between 0 °C and 4 °C.
2. During severe heatwaves, some Australian trains run more slowly. Explain why, using particle theory and the term “constrained expansion”.
Plan an investigation
Question: does the type of metal (steel, copper or aluminium) affect how much a 1 m rod expands when it is heated by 50 °C? Plan a fair test.
Hypothesis
If the rod is made of ..., then it will expand the most, because ...
Variables
Method
Results table
| Metal | Trial 1 (mm) | Trial 2 (mm) | Average (mm) |
|---|---|---|---|
Safety
3. In the lesson, aluminium grows by 24 millionths of its length per °C, copper by 17 millionths and steel by 12 millionths. Use these values to predict the result for each 1 m rod. Name one reason the class’s measurements might not match your predictions exactly.
Aluminium mm
Copper mm
Steel mm
Data: an expansion joint in a steel roof beam
A shopping centre has a 100 m steel roof beam. At one end is an expansion joint. An engineer measured the width of the gap at the joint at different beam temperatures.
| Beam temperature (°C) | Gap width (mm) |
|---|---|
| 5 | 60 |
| 15 | 48 |
| 25 | 36 |
| 35 | 24 |
| 45 | 12 |
Source: sample values for this worksheet.
4. (a) By how much does the gap close for each 1 °C rise? Show that this matches the steel value from Question 3 for a 100 m beam. (b) At what beam temperature would the gap close completely?
(a) Gap closes by mm per °C
(b) Gap closes at °C
5. On a summer day the sun can heat the roof beam to 70 °C. How wide should the gap be at 5 °C so that it never closes? What would happen to the beam if the gap closed on a hotter day?
Gap needed at 5 °C mm
6. A student says: “Thermal expansion only matters for long structures like bridges. Small objects don’t expand enough to worry about.” Evaluate this claim. Use at least two small-object examples from the lesson.