After Lunch Experiment: Make a Cloud
By Mark Steer
There’s an extraordinary amount of things you can do with a plastic bottle, but this has got to be one of the most inventive. Create your own mini weather systems without the hassle of getting cold or wet. It's the perfect Christmas experiment for getting you out of having to go on that after lunch walk.What to do
- Persuade a small child to drink two litres of fizzy pop.
- Send the child back to his mother, you won’t be needing him any longer. You will be needing, however, the empty plastic bottle.
- Add enough water to the bottle so as to cover the bottom. Put the cap back on and give it a good shake about.
- Light a match, let it burn about half way down before blowing it out and popping it straight into the bottle. Immediately replace the cap tightly.
- Squeeze the bottle hard four or five times. You should see a cloud form which disappears when you squeeze the bottle and reforms when you release it again.
- Point out that all this exertion has worn you out and settle down for a quiet nap whilst the rest of the family trudge off into the cold to 'walk off lunch'.
What’s happened
You’ve made clouds. Real life, bonsai clouds. Three elements have been crucial in the process – the water, the smoke from the match and the changing pressures inside the bottle (the small child bouncing off the walls is not crucial, just vaguely amusing).When you shake the bottle about with the water in it you disperse a lot of water molecules in the air – you’ve increased the humidity by creating water vapour. This is the basis of your cloud.
But clouds don’t just form spontaneously, they need something to form around; this is where the smoke comes in. Smoke is made of loads of tiny particles of ash, and it’s these particles that give the water vapour something to condense around, producing the cloud.
So what about the pressure? Increasing the pressure in the bottle by squeezing it raises the temperature, therefore the water in the air is more likely to stay as vapour and not condense out. When you release the pressure and the temperature drops again, the water will again start to condense into clouds again. If you leave it long enough the water will eventually all condense and run back down to the bottom of the bottle. If your bottle was big enough, the water might condense enough in the clouds to fall to the bottom as rain.
This kind of apparatus is a very crude version of a cloud chamber - machines which were used by physicists to study the behaviour of particles, such as electrons, at a time when scientists were only just beginning to understand what electrons were. Cloud chambers were invented by the Scottish physicist Charles Wilson who put the finishing touches to his first one in 1911.
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This experiment has been adapted from Mick O'Hare's excellent book How to Fossilise your Hamster see more at www.newscientist.com/hamster.
How about trying one of our other top tens:
This experiment has been adapted from Mick O'Hare's excellent book How to Fossilise your Hamster see more at www.newscientist.com/hamster.
How about trying one of our other top tens:
- Top Ten Crazy Xmas Gifts
- Top Ten Geek Holidays
- Top Ten Stupid Science Studies
- Top Ten Work-related Ills
- Top Ten Killer Vegetables
- Top Ten Weird Drinks
- Top Ten Grim Parasites
- Top Ten Things Science Hasn't Explained
Hub image: Paweł Jagielski
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