Movie courtesy of the Little Shop of Physics.

Air Pressure and Wind

What makes the wind blow? In a word: pressure. All other things being equal, air will flow from high pressure to low, a principle that is nicely demonstrated with two partially-inflated exercise balls connected by a tube containing tiny balls that show the flow of air. When Samantha or Cierra push on one side, they increase the pressure, so the air flows from the ball with higher pressure to the ball with lower pressure.

You can make higher pressure by applying a force, but you can also make higher pressure by collecting a gas with higher density. The mass of this denser air will be a bit heavier than the surrounding air, and so will have a higher pressure at the bottom. Where do you get a denser gas? Dry ice - frozen carbon dioxide. A jug, which has had its base removed, is set on the table and the dry ice goes inside. Several candles are set around the base. As the dry ice warms, the container fills up with carbon dioxide gas. When the jug is lifted, the higher pressure at the bottom of the jug pushes the carbon dioxide over the flames—with rapid and dramatic results!

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Last modified January 18, 2011 by Randy Russell.

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