Expansion Assignment

Why does the density of the hot air balloon decreases when it is heated?

When the air is heated, the particles move further apart and expands. The volume of the air increases but the mass remains the same. So the density decreases.

Why does the hot-air balloon rise when heated?

The density of the air in the balloon is lesser than the surrounding air. So the hot air balloon rises.

Explain what happens to the balloon when the hot air in the balloon cools?

When the hot air in the balloon cools, it contracts and becomes denser than the surrounding air. So it will descend and fall.