If air is heated at constant pressure, what happens to its density compared to surrounding air?

• A. More dense, sink
• B. Less dense, rise
• C. Equal dense, remain
• D. Less dense, sink

Answer: (B)

When air is heated at constant pressure, its density decreases compared to the surrounding air. This phenomenon occurs because as air temperature rises, the molecules gain kinetic energy and move more rapidly, leading to an expansion of the air volume. Since density is defined as mass per unit volume, as the volume increases while the mass remains the same, the density of the heated air decreases.

Consequently, this less dense, warmer air will rise because it is buoyant relative to the cooler, denser surrounding air. The principle of buoyancy dictates that less dense substances will rise in denser mediums. Therefore, when you heat air at constant pressure, it becomes less dense and rises, creating upward vertical movement in the atmosphere, which can also contribute to weather phenomena such as convection currents.