Answer: Hot air is less dense than cool air; the heated air causes the balloon to rise simply because it is lighter than an equal volume of cold air. Buoyancy is an upward force that the air exerts, and it helps hot-air balloons and blimps stay in the air. A hot air balloon uses a burner to heat up the air inside the balloon.
Explanation:
Because gas inside the balloon is less denser than the air outside(eg. helium). Due to this, the balloon rises until the air outside the balloon is as dense as the air inside.
