There is nothing mystical about clouds. In fact, it is perfectly possible to make your own cloud in a used drinks bottle. It might not be as massive as a 500,000kg white cumulus cloud, but at least you won’t have to go paragliding to get up close and personal.
You will need:
- A bike valve (we cut one out of an old inner tube)
- A bike pump (ideally a foot pump with pressure gauge)
- Surgical spirit or 90% isopropyl alcohol (rubbing alcohol)
- Hand drill (needs a drill bit with a similar diameter to the valve)
- Hot glue gun
- Empty plastic drinks bottle (minimum two-litre volume)
- Safety goggles
- Adults MUST carry out the cloud experiment. Children can watch.
- Be careful with the drill and glue gun.
- The bottle lid will undo with a lot of force. Hold tightly when unscrewing and point away from eyes.
- Do not pressurise bottle to more than 10psi.
- Wear safety goggles.
- Do not consume chemicals. Wash hands after use.
DIY Science – create a bottled cloud (YouTube/BBC Focus Magazine – science and technology)
1. Carefully drill a hole in the lid of the plastic bottle that is just wide enough so that the valve will fit through.
2. Push the valve through the hole from the inside. It should be a tight fit. Fix valve in place with glue gun to make strong seal.
3. Pour a little rubbing alcohol/surgical spirit into the bottle. Now it’s time to take this experiment outside!
4. Swirl the alcohol to coat the sides. Tightly screw on the lid. Attach bike pump to valve and put on your safety goggles.
5. Start pumping. Make sure bottle is not leaking air – if it is, add more glue. Pump to about 10psi. Do not overinflate.
6. Holding the bottle firmly, unscrew the lid, which may come off with a bang. And poof! A white cloud instantly appears!
What’s going on?
As the Sun heats the ground, it warms the air above it, causing it to expand and rise. When rising moist air reaches an altitude of 600 to 900 metres, the water vapour in the air starts to cool and condense into tiny droplets. Each droplet then serves as a site where another droplet can easily form. Amalgamating into clusters that we know as clouds, these droplets scatter all frequencies of light to give them a white colour.
In our experiment, we coat the inside of a bottle with alcohol. We use alcohol because it evaporates faster than water, making it easier to get impressive results. When the bottle is sealed, it is quickly saturated with invisible alcohol vapour. Pumping air into the bottle increases both pressure and temperature. When the lid is opened, there is a sudden drop in pressure and temperature, which triggers airborne alcohol and water molecules to come together into liquid droplets – almost as if it had ascended by over 300m in a fraction of a second.