What happens to the density of air as it is heated?

When air is heated, its density decreases. This phenomenon occurs because as the temperature of air rises, the molecules within it gain kinetic energy and begin to move more rapidly and spread apart. The increase in molecular motion leads to a greater volume occupied by the same amount of air, resulting in a lower density.

In the context of HVAC systems, understanding how air density changes with temperature is crucial. For instance, when warm air rises, it creates convection currents that can impact the efficiency and effectiveness of heating and cooling systems. The behavior of air in response to temperature changes directly affects how it can be circulated and conditioned within a space.

Generally, the other options are less applicable. An increase in density (as suggested in the first option) contradicts the principles of thermodynamics related to gases. The idea that density remains constant (the second option) fails to account for changes in temperature directly affecting molecular behavior. Lastly, the notion that density fluctuates does not accurately describe the predictable response of air density to temperature changes as described by the ideal gas law.