Year 9 Science · Unit 3 · Lesson 10

Thermal Expansion and Contraction

Challenge Worksheet

Name

Date

Class

Learning Goals

Sequence the steps of a bimetallic strip thermostat through a full heating cycle.
Design a controlled investigation comparing thermal expansion of different metals.
Identify and control variables in an experimental investigation.

Warm Up

Order the steps

Number the events from 1 to 10 to show the correct sequence. This describes one complete heating-and-cooling cycle of a bimetallic strip thermostat in a home heating system.

Order	Event
	The circuit closes again and the heater turns back on.
	The two bonded metals expand at different rates, causing the strip to bend.
	The bimetallic strip straightens as it returns to room temperature.
	The room reaches the set temperature and the strip has bent enough to break the circuit.
	The heater turns on; thermal energy flows into the room.
	The bimetallic strip is at room temperature and the circuit is closed.
	The heater turns off.
	The room cools below the set temperature as heat is lost through walls and windows.
	The strip heats up as the room warms and begins to bend toward the metal with the lower expansion rate.
	The thermostat detects that the room is cold and the heater is switched on automatically.

Go Deeper

Design a mini-experiment

A scientist wants to test: "Which of steel, copper, and aluminium expands the most when heated by 50 °C?" Plan the investigation below. Be specific, name the materials, measurements, and controls.

What I will change (independent variable)
What I will keep the same (controlled variables, list at least 3)
What I will measure (dependent variable)
Equipment needed
Method (step by step, at least 3 steps)
Safety precaution
Predicted result (which metal expands most, and why?)
One limitation of this experiment

Show What You Know

1. Explain why Australia's train operators reduce train speeds during severe heatwaves. Use particle theory and the term "constrained expansion" in your answer.

Challenge 3 marks

2. A student says: "Thermal expansion only matters for very long structures like bridges, tiny objects don't expand enough to worry about." Evaluate this claim with a specific counterexample from the lesson.

Challenge 3 marks

Wrap Up

In one sentence, what was the main idea of this lesson?