Q1.
How can we demonstrate the movement of gas particles that cannot be seen with the naked eye?
Answer
Indirectly — by watching something we can detect being carried about by the gas particles we cannot.
The chapter uses three such stand-ins:
| Method | What we can detect | What it shows about the invisible particles |
|---|---|---|
| Smoke in gas jars (Activity 7.5) | The grey smoke spreading from Jar A into Jar B | The tiny smoke particles suspended in the air are constantly hit by the invisible particles of the gases, and their movement lets us observe the motion of gas particles |
| Iodine vapour in a closed gas jar (Fig. 7.8) | The violet vapour filling the whole jar | Gas particles move in all directions and occupy the entire available space |
| A burning incense stick (Activity 7.9) | The fragrance, reaching the far side of the room | Air particles are moving constantly and knock the fragrance particles right across the room |
Why this counts as evidence: smoke does not swim and fragrance does not walk. Something must be pushing them, and it must be everywhere in the room, and it must never stop. Constantly moving air particles are the explanation that fits.