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To develop a better understanding of the relationship between air density, air pressure, and air flow.
Because air is a fluid, it can move easily from place to place. Although several forces affect the direction in which air moves, differences in air pressure are what set the air in motion. Wind is the movement of air from an area of higher pressure to an area of lower pressure. Most differences in air pressure are caused by the unequal heating of the atmosphere. When air over an area of Earth's surface is heated, it expands and becomes less dense. As the air becomes less dense, its air pressure decreases. If a nearby surface is not heated as much, the air above it will be cooler and denser. The cooler, denser air exerts greater pressure, so it flows underneath the warmer, less dense air, forcing it to rise. In this way, equilibrium is achieved as high-pressure areas relieve their pressure into low-pressure areas, producing wind.
Students run a model that looks at how differences in the temperature, density, and pressure of two parcels of air influence their movement. They observe how air, cooled by ice water below it, contracts. They infer that it increases in density and creates an area of high pressure. At the same time, they observe how air, heated by warm water below it, expands. They infer that it decreases in density and creates an area of low pressure. Using smoke from an incense stick to monitor air flow, they see how the warmer, less dense air moves upward and the neighboring colder and more dense air moves in to take its place.
clear flexible tubing (about 10cm long), ruler, matches, 2 x 1-L plastic bottles, incense stick, ice, hot water, cold water