Lesson 6 - Understanding Air Movement

Wind

The movement of air has fascinated every culture in the human race, for wind holds both power and mystery. To early man, wind was an unpredictable god, able to punish with frightening force, or reward with gentle kindness. As the ages passed, many societies learned to harness the wind, relying on the wind's strength to draw water from wells, drive ships across the sea, generate electricity to light cities. Yet wind has never been tamed or controlled, and humankind is still at its mercy, sometimes cowering from freezing blasts cold enough to cause frostbite, sometimes running from storms that rip apart houses and forests, always aware of wind's destructive nature while at the same time frequently delighting in its softer side. Wind is air in the act of moving. Wind is air tumbling and swirling and clashing. But why does air move?

The rise and fall of air

Temperature is the secret of all air movement. As already discussed, warmer air possesses more kinetic energy than cold air. As this kinetic energy increases, the air molecules expand, becoming less dense and therefore rising above more compact, cooler air. The more warm air rises, the more space it leaves for cooler air to fill. When the warm air begins to lose its heat, it gradually contracts, growing more and more dense until once again, it sinks. And this perpetual cycle of motion is constantly interacting with dozens of other fluctuating forces: the spinning of the earth, the currents of the oceans, and the position of the sun. With such incredible variables always at work, it is not surprising that wind can suddenly whip itself into a frenzy, unleashing storms of such enormous violence that they are sometimes referred to as "furies."

Cool Air Drops

Warm Air Rises