1. Fill the bottle 2/3 full of colored water
2. Insert the plastic straw through the stopper about 2/3 of the way up the straw.
3. Place the long end of the straw into the bottle (the end should be below the surface of the water in the bottle), and fit the stopper snugly into the bottle opening
4. Blow some air into the straw until water rises above the stopper
5. By attaching a card to the straw above the stopper, and recording the water level, observe how the varying air pressure causes the water level to rise and sink.
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