Concept : 1 Mark
Working : 2 Marks
Heat is transferred in air and water by convection in which the hotter part becomes lighter and rises up. This area is then filled with cooler objects from the top and sides. The hot-air balloon works on the same principle.
When air is heated, the air goes upwards. In the case of a hot-air balloon, this hot air is directed to inside the balloon where it gets trapped. Since the air is still hotter than the cooler air from outside, it pushes the balloon upwards. When sufficient hot air fills up the balloon, it starts to rise.