What happens to air as it is heated in a fire?

When air is heated in a fire, it becomes less dense due to the increase in temperature. As the molecules within the air gain energy, they move apart, causing the air to expand. This decrease in density causes the heated air to rise, demonstrating the principle of convection. As warm air rises, it also creates a vacuum effect that pulls in cooler, denser air from surrounding areas, which can also become heated and rise in turn.

This upward movement plays a crucial role in how fire behaves, as it can affect the spread of flames and the overall dynamics of heat in a burning environment. Understanding this principle is important for fire safety and management, as it affects how firefighters approach a fire scene and how they plan their extinguishing strategy. The other choices suggest contrary behaviors, which do not align with the fundamental physical principles governing air movement in the presence of heat.