Flying Teabag Experiment
Why does the teabag fly?
Lighting the top of the teabag cylinder heats the air inside the cylinder. The air molecules start to move more quickly and spread out to take up more space. As the air molecules spread out, the air inside the cylinder becomes less dense. Warm, less dense air rises above cool, dense air. The ash of the teabag is light and doesn't require much force to lift it. As the warm, less dense air rises, it has enough force to lift the ash of the teabag.
Hot air balloons use a similar principle.The burner beneath the balloon heats the air inside the balloon. The less dense, heated air in the balloon rises above the denser, cooler air around the balloon and the balloon flies.