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Q & A: Experiments on Air Pressure

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Most recent answer: 10/22/2007
Q:
do you have any experiments i can do on air pressure
- jay (age 10)
canada
A:
Here's a couple. Take a straw and suck some water into it. Then hold it over a sink or container with your finger firmly covering the top. The water will remain in the straw. Why? When your finger is not on the top of the straw. Air pressure pushes down and up the straw through both openings, and so is balanced. Gravity then makes the water fall. But if you block off the top of the straw, then air pressure can only push from the bottom, and it is stronger than Earth's gravity, so it keeps the water in the straw. Here's another one: hold a small piece of paper in both hands in front of your mouth, letting the other end of the paper droop down. Then blow across the top of the paper. What happened? The paper rises. This is because moving air has less pressure than still air. By blowing over the top you move the air above the paper and then the higher pressure below pushes the paper up. This is essentially how airplanes can stay up in the air, because the airflow is faster over the wing where it is smooth and not as fast below. As a result, air pushes the plane up, and gravity and air drag push down, keeping it in balance unless the pilot changes the orientation of the plane to change altitude.

(published on 10/22/2007)

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