Warm air rises primarily due to its lower density compared to cooler air, a phenomenon explained by buoyancy. As air is heated, its molecules move faster and spread apart, decreasing its density. This decrease in density allows the warm air to rise through the cooler, denser air surrounding it. The discussion emphasizes understanding the relationship between temperature and the physical properties of gases. Overall, the principles of buoyancy and density are crucial for explaining why warm air ascends.