Question

Why does air expands on heating ?​

Answer 1

Answer:

When the bottle is heated, the air molecules inside start moving faster. These molecules now collide into the balloon with more energy resulting in increased pressure. The increased pressure causes the balloon to expand. ... A given amount (mass) of air takes up more space when it is hot.

Answer 2

Answer:

So air ,like most other substances, expands heated and contracts when cooled. Because there is more space between the molecules ,the air is less dense than the surrounding matter and the hot air floats upward.