S3.5.6 For the adult
Expanding and shrinking
Why do railway lines have small gaps between them?
What this chapter teaches
Heating gives particles more energy, so they vibrate harder and sit a little further apart. The material expands. It contracts when it cools. The particles themselves do not get bigger.
Three questions to ask
There is no one right wording. Listen for the idea.
- Why do you think some railway lines and bridges have small gaps?
- What happens to a thermometer liquid when it gets warm, and why?
- If the particles do not get bigger, how can a rail get longer?
After the chapter, the learner can
- Explain why things expand when heated, using particles
- Explain why bridges and railway lines have small gaps
What they copy into their notebook
Heating gives particles energy. They move further apart, so the material expands. The particles stay the same size. Cooling makes it contract. Gaps give rails room to grow.