What it shows
Clouds form when moist air expands and cools, and water vapour condenses on tiny particles. Squeezing the bottle warms and clears the air; letting go expands and cools it so a cloud appears, but only when smoke particles are present to condense on.
The science
Warm water fills the bottle with vapour. Squeezing compresses the air and raises its temperature slightly; releasing lets it expand and its temperature drops, so some vapour must condense. Vapour cannot easily form droplets on its own; it needs tiny surfaces called condensation nuclei, which the smoke supplies. In the sky, dust, salt and pollution particles do the same job.
Materials
Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A clear 1 litre plastic bottle with cap
- A little warm water, not boiling
- An incense stick or a matchstick for a wisp of smoke
- A dark background to see the cloud
Safety
For this project: An adult must light and blow out the incense stick. The water should be warm to the touch only, never hot enough to soften the bottle.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Pour about three centimetres of warm water into the bottle and swirl it to make the air inside moist.
Squeeze the empty bottle hard and release it a few times with the cap on, watching against the dark background.
Note that nothing visible happens yet, even though the air is moist.
Ask an adult to light the incense stick, blow it out and hold the smoking tip at the bottle mouth for two seconds.
Cap the bottle at once, trapping a little smoke inside.
Squeeze hard, hold for three seconds, then let go suddenly and watch a cloud fill the bottle.
Squeeze again and watch the cloud vanish; release and it returns.
Try the same with cold water and compare how thick the cloud is.
What you should see
A visible white cloud appears every time the bottle is released and disappears when it is squeezed. Without the smoke no cloud forms, which shows that particles are needed.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1Why does the cloud appear when you release the bottle?
The air expands and cools, so vapour condenses into droplets.
2What is the job of the smoke?
It provides tiny particles for the water to condense on.
3Why does the cloud vanish when squeezed?
Compression warms the air and the droplets evaporate again.
4What are condensation nuclei in the real sky?
Dust, sea salt, pollen and pollution particles.
Take it further
Measure the temperature of the water each time and find the warmest water that still gives a clear cloud.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
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