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Clouds in a Fizzy Drink
You will need:
- A large glass of fizzy drink, freshly poured
- Some Salt
What to do:
Add the salt to the drink. Although the drink is super-saturated with carbon dioxide, all of the gas does not escape spontaneously when you open the can or bottle and pour the drink into a glass.If you look closely, you can see that bubbles can only form at places where there are imperfections or dirt on the surface of the glass.Points where the CO2 changes phase and escapes from the drink are called nucleation sites.Try adding salt to the drink. This increases the number of nucleation sites and allows more bubbles to form.In effect, this creates a “reverse cloud”, with a cloud of CO2 gas in the liquid drink.
How does this relate to the weather?
Clouds should form where the temperature is low enough for water to condense faster than it evaporates. However, in practice, it is very hard for very small water droplets to exist. In practice, most raindrops or ice crystals form where there are small particles or Cloud Condensation Nuclei (typically salt crystals, dust, soot, phytoplankton or sulphate) for the water to condense on to. These nuclei are usually 0.0001mm in diameter. In this way, pollutants in the atmosphere are incorporated into clouds and can subsequently be rained out of the atmosphere.
More Information
Condensation:
http://www.ace.mmu.ac.uk/eae/english.html and select 'atmosphere' and 'clouds'
Encyclopaedia of the Environment
Cloud condensation nuclei:
http://en.wikipedia.org/wiki/Condensation_nuclei
Cloud seeding experiments:
http://en.wikipedia.org/wiki/Cloud_seeding
http://www.sciencemuseum.org.uk/antenna/climatechange/Cip5/231.asp
http://www.usatoday.com/news/world/2006-06-29-china-rain_x.htm