S3.5.2 For the adult
Evidence for particles
How can I smell food from across the room when I cannot see anything travel?
What this chapter teaches
We cannot see particles, so we look for evidence. A smell crossing a room and sugar vanishing in water both fit particles that move and mix. This spreading is called diffusion.
Three questions to ask
There is no one right wording. Listen for the idea.
- How do you know a smell is something that travels, when you cannot see it?
- Where do you think the sugar goes when you stir it into tea?
- Why might a smell reach you sooner when someone opens a door?
After the chapter, the learner can
- Explain how a smell spreads across a room
- Explain why a spoon of sugar seems to vanish in water
What they copy into their notebook
We cannot see particles, so we use evidence. A smell spreads because its particles fly about and mix with air. This is diffusion. Dissolved sugar is not gone. It is spread out.