Why do hot air balloons float?

The video explains how hot air balloons work. Initially, the balloon is a flat bag on the ground. The pilot uses burners to heat the air inside, causing the molecules to move more and the air to expand, making it less dense than the surrounding cold air. This density difference allows the balloon to rise. To land, the pilot lets the air cool, making it denser and causing the balloon to descend.

What happens to the air inside the balloon when it cools?

Describe the process that allows hot air balloons to float.