Texas Science Teacher Resource Hub

Warm air rises. Students often confuse "humid feels heavy" with "humid air is denser," but humid air is actually less dense than dry air at the same temperature because water vapor is lighter than the nitrogen and oxygen it displaces. What matters most for vertical movement is temperature: warm air expands, becomes less dense, and rises. Cool air contracts, becomes denser, and sinks.

This is a famous myth. The Coriolis effect is real, but it only produces noticeable deflection over large distances and long travel times, like hurricanes and jet streams. A bathtub, sink, or toilet is far too small for Earth's rotation to make any measurable difference. The direction water swirls down your drain is controlled by the shape of the basin and small currents already in the water.

Wind always has a cause, and that cause is almost always a pressure difference. Air flows from areas of higher pressure toward areas of lower pressure. The bigger the difference between the two regions, the stronger the wind. Pressure differences, in turn, come from uneven heating of Earth's surface, which comes back to solar energy.

Students often get this reversed from what meteorologists say. High pressure systems usually bring sinking air, clearing skies, and calm weather. Low pressure systems usually bring rising air, which cools and condenses, producing clouds and precipitation. A useful way to remember it: air sinks under a "high," and sinking air does not make clouds.