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Monday, November 28, 2011

The shrinking bottle

We already did several demonstrations here to prove that the air takes up space.
Today the demonstration is another way to play with the air.

What we need:
  • plastic bottle, with cap,
  • hot water,
  • funnel.
How to:
  1. Wash the bottle;
  2. Let it dry;
  3. Heat up the water, don’t let it boil, its not necessary;
  4. With the funnel pour the water in the bottle;
  5. Wait for 10 sec;
  6. Reject the water to the sink;
  7. Quickly cap the bottle again, you have to be fast.
What happen?
The bottle shrinks.
In other words, the bottle walls collapse.

Remember this? What happens to the bottle is exactly the same thing.
Before further explanations is very important to understand two things:
First: air exerts pressure on the bottle, like in everything around us, including ourselves.
Second: any forces system tends to look for equilibrium.

The hot water heats the air inside the bottle. Try to close the bottle immediately after pour the water inside, the bottle will swell, that’s because hot air can't escape to atmosphere. When you reject the water, the air inside the bottle rapidly cool. The cool air occupies less space then the hot air, and, theoretically there will be a lot of "empty space" inside the bottle, because of that the plastic walls collapse under the pressure of the air outside the bottle.

Et voilá!
Another fun way to spend some time


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