Underwater Exploration: What Happens with the Bends Science Experiment University of Wisconsin Sea Grant
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See What Happens when you get the Bends

1. You need: two bottles of carbonated drink and two glasses.

2. What to do: First, pour one drink into a glass very slowly, so that the bubbles can escape a few at a time.

When bottled up, gas is under pressure and remains dissolved in the liquid. When you open the cap and the pressure is released, the gas escapes in the form of bubbles. In carbonated drinks, the gas is carbon dioxide. The gas that is released in a diver's bloodstream is nitrogen, which makes up about 80 percent of ordinary air. If a diver rises slowly to the surface, the pressure changes slowly and the gas is released slowly and safely.

3. Now pour the other bottle of soda quickly into the other glass. See how it foams. Hear it hiss. A reaction similar to this takes place in a diver's bloodstream if he comes up to the surface of the water too quickly, causing a painful or even fatal reaction.