What happens to air as it gets warmer?

As air gets warmer, it expands due to the increase in kinetic energy of the molecules. When the temperature rises, the air molecules move more vigorously and spread apart, causing the volume of the air to increase. This principle of thermal expansion explains why hot air balloons rise; the warm air inside the balloon is less dense than the cooler air outside, allowing the balloon to float.

The other options do not accurately describe the behavior of air when it is heated. For instance, air does not shrink in volume as it warms; rather, it expands. It does not become heavier because, in fact, warmer air is lighter and less dense compared to cooler air. Additionally, the air does not cool down when it is warm; the question is specifically about the effects of warming on air. Thus, the expansion of air as it warms up is a fundamental concept in understanding both meteorology and physics.