CREATE A BOTTLED CLOUD
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) Safetygoggles
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.
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.