Hot air goes up
Heated air expands, gets lighter and rises.
Smoke from an incense stick
When an agarbatti burns, its smoke goes straight up. Pema also sees the smoke rising from the burning firewood.
Why does smoke rise?
What this lesson covers
The idea
Air expands on heating, occupies more space, becomes lighter and rises; smoke, a mixture of hot gases and tiny solid particles released on burning, rises because it is warmer than the surrounding air.
Smoke from an incense stick
When an agarbatti burns, its smoke goes straight up. Pema also sees the smoke rising from the burning firewood.
Why does smoke rise?
- It is warmer than the air around it
- It is heavier than air
- The floor pushes it up
Balloon in the Sun
Slide the Sun heat up and watch the air in the balloon. Then tap Smoke.
More space, so lighter
The air in the balloon took up more space when it was heated. The same air in more space is lighter, so it rises. Smoke is warmer than the air around it, so it rises too.
Air expands on heating, occupies more space, becomes lighter and rises. Smoke, a mixture of hot gases and tiny solid particles released on burning, rises because it is warmer than the surrounding air.
Notes
Air expands on heating, occupies more space, becomes lighter and rises. Smoke, a mixture of hot gases and tiny solid particles released on burning, rises because it is warmer than the surrounding air.
Check yourself
What happens to air when it is heated?
Heated air becomes …
A partly inflated balloon is kept in the Sun. After some time it becomes …
Smoke is a mixture of …
- It shrinks into a smaller space. Heated air expands. It does not shrink.
- It expands and occupies more space — correct. Yes!
- It stays exactly the same size. Heated air takes up more space, as the balloon showed.
- heavier, so it sinks. Heated air spreads out and becomes lighter, so it goes up.
- heavier, so it rises. Heavier air does not rise. Heated air is lighter.
- lighter, so it rises — correct. Yes!
- larger, because the air inside has expanded — correct. Yes!
- smaller, because the air has gone away. No air has gone away. The air inside has expanded.
- the same size, because air cannot change. Air changes. When it is heated it expands.
- only cold water. Smoke is not water. It is hot gases and tiny solid particles.
- hot gases and tiny solid particles — correct. Yes!
- only air from the sky. Smoke is made when something burns. It has hot gases and tiny solid particles.