What's the difference between cold moving air and hot moving air? For instance, suppose you put two fans, of the same type, each in one room. One room is cold because the walls are covered in ice and one room is hot because due to the effect of heaters. Turn both fans on and the air flow, the pushing of the air particles in one direction, are both blown towards one direction with the same (almost?) velocity. What makes one moving air hot and the other cold? The moving air are both moving at the same velocity (about) aren't they? Isn't temperature based on how fast the particles are moving.