Question

When you heat the air inside a hot air balloon, it rises. Why does this occur??

Answer 1

This occurs because as molecules heat up they start moving around more causing expansion an example of this you may be familiar with is the water to ice the molecules cool down there so the ice takes up less volume than the water it took to make the ice but then when water turns to steam it turns to a gas taking up a greater volume than before

Answer 2

The hot air inside the balloon becomes less dense than the air outside the balloon.